Patent Description:
Inkjet printing has also been used to print liquid functional agents in some three-dimensional (3D) printing techniques. 3D printing may be an additive printing process used to make three-dimensional solid parts from a digital model. 3D printing is often used in rapid product prototyping, mold generation, mold master generation, and short run manufacturing. Some 3D printing techniques are considered additive processes because they involve the application of successive layers of material. This is unlike traditional machining processes, which often rely upon the removal of material to create the final part. Some 3D printing methods use chemical binders or adhesives to bind build materials together. Other 3D printing methods involve at least partial curing, thermal merging/fusing, melting, sintering, etc. of the build material to build the material together. For some materials, at least partial melting may be accomplished using heat-assisted extrusion, and for some other materials (e.g., polymerizable materials), curing or fusing may be accomplished using, for example, ultra-violet light or infrared light.

<CIT> concerns a metallurgical powder composition comprising a major amount of an iron based metal powder and a minor amount of a particulate inorganic oxide having an average particle size below <NUM>. <CIT> relates to a molding powder used in a powder bed melt bonding method. <NPL>) concerns the effect of bimodal powder mixture on powder packing density and sintered density in binder jetting of metals. <CIT> relates to a metal magnetic powder and a method of manufacturing the same, and more particularly to a ferromagnetic metal powder used in a coated magnetic recording medium and a method of manufacturing the same. <CIT> describes flowability-improving particles adhered to surfaces of iron powder through a binder to provide an iron-based powder for powder metallurgy. <CIT> describes iron-based metallurgical powder compositions that contain nanoparticle metal or metal oxide flow agents.

Some examples of the composition of the present disclosure may be used in a process to create a final metal object. For example, the process to create the final metal object may be a 3D printing process. In some examples, the 3D printing process may include subsequent patterning of uniformly spread layers of the composition (which includes a flow additive) with liquid binder applied by means of an inkjet printhead. Each patterned layer of the composition forms an individual cross-section of the final metal object. Stacking of the binder-patterned layers produces an intermediate structure which can be extracted from the powderbed after the patterning has been finished. The extracted intermediate structure may be subjected to post-printing processing (e.g., heating via sintering), leading to consolidation of the particles of the composition into a mechanically stronger final metal object.

In other examples, the 3D printing process may include Selective Laser Melting (SLM). In these examples, uniformly spread layers of the composition are individually exposed to a laser beam of high energy density. The laser spot scans the spread metal powder surface, heats the metal particles, melts the metal particles and fuses the molten metal into continuous layers. During a SLM printing process, stacked fused layers (each layer representing a portion of the printed part) produce the final metal object (i.e., each subsequent laser-patterned layer is fused on top of the previous one). With SLM, the final metal object is produced without printing an intermediate structure and without sintering the intermediate structure. Therefore the sintering-related advantages of smaller particles size are not applicable to SLM; however, the flow additives disclosed herein enable non-classified, lower cost metal powders with wide particle size distribution to be used with SLM. The flow additives disclosed herein may also enable the recovery of metal particles that have been excessively used in SLM. The SLM process produces metal vapor that condenses into very fine micro to nanoscale particles. Over time, these particulates accumulate in the powder, and can effectively shift the particle size distribution to a point where a once flowable powder becomes non-flowable. Without being bound to any theory, it is believed that the flow additives disclosed herein may enable the recovery of a heavily used SLM powder.

Examples of the composition disclosed herein may be referred to as a build material composition, which may be used to form a 3D printing composition. While some of the examples provided herein relate to 3D printing, it is to be understood that the composition may also be used in other methods and applications.

The composition disclosed herein comprises a host metal present in an amount ranging from about <NUM> weight percent to about <NUM> weight percent, based on a total weight of the composition; a flow additive present in an amount ranging from about <NUM> weight percent to about <NUM> weight percent, based on the total weight of the composition, wherein the flow additive consists of a metal containing compound that is reducible to an elemental metal in a reducing environment at a reducing temperature less than or equal to a sintering temperature of the host metal, wherein the elemental metal is capable of being incorporated into a bulk metal phase of the host metal in a final metal object; and wherein the composition is spreadable, having a Hausner Ratio less than <NUM>.

As used herein, the term "elemental metal" means one or more metals obtained from the reduction, decomposition, or decomposition and reduction of a metal containing compound. The number of elemental metals obtained will depend upon the metal containing compound and the reaction(s) it undergoes. Unlike the elemental metal, the metal containing compound contains a non-metal component, such as oxygen, hydroxide, etc. in accordance with the examples disclosed herein.

As such, in examples of the present disclosure, the composition is mainly the host metal. The host metal may be in powder form, i.e., particles. Sintering of the host metal particles usually happens below a melting temperature of the host metal. The sintering temperature of the host metal particles may be dependent, in part, on the size of the host metal particles. A host metal with a smaller average particle size will experience a faster sintering rate than a host metal having a larger average particle size. The rate of sintering of solid crystalline powders obeys Herring's scaling law and is inversely proportional to the particle size by a power of between <NUM> and <NUM>. Therefore, reducing a metal particle size may allow faster sintering at a lower sintering temperature. Both the speed of sintering and the sintering temperature may beneficially alter a structure of the sintered part. For example, a fast sintering rate at a lower temperature may prevent large grain growth. The prevention of large grain growth may improve ultimate tensile strength, yield strength, and other mechanical properties of the final metal objects.

Thus, it may be desirable to use metal powders with the smallest particle size in 3D printing processes involving sintering. However, spreading of a powder into uniform thin layers of well-controlled thickness becomes increasingly difficult with decreased particle size. Without being held bound to any theory, it is believed that the reduced spreadability with decreasing particle size is due to inter-particle forces (i.e., van der Waals, electrostatic attraction, etc.) becoming significantly stronger than gravitational pull. Therefore, in general, powders become increasingly cohesive when a particle size of the powder is well below <NUM>. Smaller particles agglomerate together and the powders lose flowability. In the case of metals, even powders with spherical particles become non-spreadable into thin layers when the average particle size of the metal particles is within or below the range of about <NUM> to about <NUM>; especially when a fraction of particles present in the powder is within or smaller than the range of about <NUM> to about <NUM>. It is possible to remove the small particles from a metal powder by classification; however, classification is an additional process that adds to cost and removes the beneficial effects of small particles discussed above. It is also possible to use gas atomization to produce a spreadable metal powder without classification, however, the cost of such a spreadable metal powder may be disadvantageous compared to the cost of the composition disclosed herein.

As mentioned above, examples of the composition disclosed herein include a flow additive in addition to the host metal. The flow additive disclosed herein is a metal containing compound that is reducible to an elemental metal in a reducing environment at a reducing temperature less than or equal to a sintering temperature of the host metal. The elemental metal is capable of being incorporated into a bulk metal phase of the host metal in a final metal object. Thus, examples of the flow additive disclosed herein are unlike comparative flow additives that have been added to improve the flowability of difficult-to-spread cohesive metal powders with small particle sizes.

In examples of the present disclosure, the reducing environment may be an atmosphere of hydrogen gas, carbon monoxide gas, or mixtures consisting of an inert gas (e.g., argon gas, helium gas, etc.) with hydrogen gas or carbon monoxide gas. Forming gas is an example of a mixture consisting of an inert gas with hydrogen gas or carbon monoxide gas. Forming gas is a mixture of hydrogen gas and nitrogen gas.

Examples of comparative flow additives include fumed oxide powders, which have been used to decrease the inter-particle cohesive forces in difficult-to-flow powders. It is believed that many, if not all, current commercially available comparative flow additives are based on different grades of fumed silica and, in some cases, fumed aluminum oxides. In some cases, precipitated colloidal silica powders have been used as comparative flow additives after surface modification.

These comparative flow additives are very low density powders made of loosely aggregated nano-particles. A typical particle size for the comparative flow additives ranges from about <NUM> to about <NUM> orders of magnitude smaller than the particle size of the cohesive powders to which the comparative flow additives are added. When added and mixed with cohesive host powders, these comparative flow additive nano-particles or their small aggregates stick to surfaces of the host particles. The host particle surfaces are coated with flow additive nano-spacers, thereby preventing agglomeration of the cohesive powder particles. Thus, formerly cohesive powders treated with an effective amount of the comparative flow additive (about <NUM> weight percent to <NUM> weight percent of the host powder) may be made flowable, with the potential of being spread in thin uniform layers. As used herein, better flowability of a composition means that the composition has better spreadability.

<FIG> depicts a graph of Hausner Ratio as a function of weight percentage for a mixture of a fumed silica comparative flow aid in <NUM> stainless steel powder. The <NUM> stainless steel powder had an "as is" Hausner Ratio of about <NUM>. Hausner Ratio (H[n]) is a powder flowability metric that can be measured by a tap density test. More specifically, the Hausner Ratio is a ratio of powder densities after and before compaction by tapping. A lower H[n] correlates to better flowability. Generally metal powders with spherical particle shape are suitable for 3D printing applications with a Hausner Ratio less than or equal to about <NUM>. In some cases suitable flowability may be found with a Hausner Ratio up to about <NUM>. The function depicted in <FIG> was determined from laboratory test results. The stainless steel powder was SAE <NUM>, grade -<NUM> (<NUM>%) powder from "Sandvik", (average particle diameter is approximately <NUM>). The fumed silica flow aid was Aerosil R812, available from Evonik.

It has been found that the comparative flow additives based on fumed oxides of silicon and aluminum discussed above cannot be used to improve flowability of metal powders used in certain additive manufacturing processes (e.g., those involving sintering) without negatively affecting structural properties of the final metal objects produced during the sintering process. Silica and alumina are not reduced during sintering processes with or without a reducing atmosphere. As such, both silica and alumina flow additive nano-particles become part of the structure of the final metal object. More particularly, the silica and alumina flow additive nano-particles get incorporated into grain boundary space of the final metal object structure. The presence of silica and/or alumina inclusions in a metal object structure diminishes the mechanical strength, ductility and toughness of the metal object. Thus, although comparative flow additives may improve flowability of certain metal powders, the comparative flow additives deleteriously affect mechanical properties of 3D objects formed therefrom.

In the examples disclosed herein, the flow additive is a metal containing compound that is reducible to an elemental metal in a reducing environment at a reducing temperature less than or equal to a sintering temperature of the host metal. The elemental metal is capable of being incorporated into a bulk metal phase of the host metal in a final metal object. It is to be understood that incorporation into a bulk metal phase may include dissolution into the bulk metal phase, and/or alloying with a bulk metal phase. Further, incorporation into a grain boundary space, as occurs with comparative silica and alumina flow additive nano-particles, is not a form of incorporation into a bulk metal phase. Thus, unlike the build compositions that have the comparative flow additives discussed above, the build composition of the present disclosure has better spreadability/flowability and is able to be incorporated into the bulk metal phase. Further, final metal objects made from the build composition of the present disclosure have comparable strength properties to parts made from sintered powdered metal without flow additives. Therefore, the flow additives disclosed herein include metallurgy-friendly flow additives based on reducible metal oxide nano-powders that enable using small particle metal powder with low inherent flowability in additive manufacturing processes to yield final metal objects with comparable strength properties to parts made from sintered powdered metal without flow additives.

<FIG> is a diagram depicting the composition (also referred to herein as a build material composition <NUM>) of the present disclosure going through certain steps of an example of an additive manufacturing process. <FIG> begins with a portion of an intermediate structure <NUM>, which includes the build material composition <NUM> (host metal <NUM> and flow additive <NUM>) patterned with a binder agent (not shown). After patterning, the example flow additive <NUM> is decomposed/reduced to one or more elemental metals <NUM> and a gaseous byproduct <NUM> in a thermal decomposition reaction and/or a reduction reaction. The cloud <NUM> shown in <FIG> represents the gaseous byproduct <NUM> being removed from the build material composition <NUM>. The remaining intermediate structure <NUM>', including the elemental metal(s) <NUM>, is then sintered to form the final metal object or part <NUM>.

<FIG> is a block diagram depicting an example of the composition and processing shown in <FIG>. <FIG> begins with a portion of an intermediate structure <NUM>, which includes the build material composition <NUM> (host metal <NUM> and flow additive <NUM>) patterned with a binder agent (not shown). After patterning, the example flow additive <NUM> is decomposed/reduced with the introduction of heat from an energy source <NUM> in a reducing environment <NUM>. A thermal decomposition reaction and optionally a reduction reaction yields elemental metal(s) <NUM> in the intermediate structure <NUM>' and a gaseous byproduct <NUM>. The gaseous byproduct <NUM> is removed from the build material composition <NUM>. It is to be understood that the elemental metal <NUM> depicted in <FIG> is not separated from the host metal <NUM>; rather, the elemental metal <NUM> is dispersed throughout the intermediate structure <NUM>'. The elemental metal(s) <NUM> is/are capable of being incorporated into a bulk metal phase of the host metal <NUM> in the final metal object <NUM>. Therefore, the elemental metal(s) <NUM> remains/remain dispersed throughout the final metal object <NUM>. The remaining intermediate structure <NUM>', including the elemental metal(s) <NUM>, is then sintered by the addition of heat from the energy source <NUM> to form the final metal object or part <NUM>.

Some examples of the composition/build material composition <NUM> disclosed herein include the host metal <NUM> and the flow additive <NUM>. In some examples, the build material composition <NUM> includes particles of the host metal <NUM> and particles of the flow additive <NUM>. In the present disclosure, the term "particles" means discrete solid pieces of components of the build material composition <NUM>. As used herein, the term "particles" does not convey a limitation on the shape of the particles. As examples, particles may be spherical beads or irregularly shaped beads of lower aspect ratio.

In some examples, the particles of the host metal <NUM> may have an average host metal particle size less than <NUM> micrometers. In some examples, at least <NUM> percent of the host metal particles have a host metal particle size smaller than <NUM>. In some examples, some host metal particles in a mixture of host metal particles may be as small as about <NUM>. The particles of the flow additive may have an average flow additive primary particle size ranging from about <NUM> to about <NUM> orders of magnitude smaller than an average host metal particle size. In some examples, the average flow additive primary particle size may range from about <NUM> nanometers to about <NUM> nanometers.

As disclosed herein, flow additives for dry powders may be highly structured agglomerates of particulate materials with a relatively low density (e.g., <NUM>% to <NUM>% of a bulk density of the particulate material forming the flow additive). For example, the highly structured agglomerates of particulate materials may have an agglomerate size ranging from a few µm to about <NUM>. The agglomerates of particulate materials are composed from primary particles having a primary particle size in a nano-range. In a container of the flow additive, primary particles of the particulate may be encountered in low density, often fractal structures. When the flow additive agglomerates of particulates are mixed with a carrier powder (e.g. the host metal <NUM>), the flow additive agglomerates of particulates break down into either individual primary particles or small fragments containing a few primary particles. The small fragments and individual primary particles stick to a surface of the carrier powder particles and improve flowability of the carrier powder.

In examples, the host metal <NUM> is present (in the build material composition <NUM>) in an amount ranging from about <NUM> weight percent to about <NUM> weight percent, based on a total weight of the build material composition <NUM>. In other examples, the host metal <NUM> may be present in an amount ranging from about <NUM> weight percent to about <NUM> weight percent, based on a total weight of the build material composition <NUM>. In still other examples, the host metal <NUM> may be present in an amount ranging from about <NUM> weight percent to about <NUM> weight percent, based on a total weight of the build material composition <NUM>.

The flow additive <NUM> substantially makes up the remaining portion of the build material composition <NUM>. "Substantially makes up the remaining portion" means that trace amounts of other materials may be present in the build material composition <NUM>, whether intentionally or unintentionally. For example, dust or microbes may be found in the build material composition <NUM> in amounts that are too small to significantly alter the material properties of the build material composition <NUM>. Therefore, the weight percent of the host metal <NUM>, and the weight percent of the flow additive <NUM> add to yield about <NUM> weight percent of the build material composition <NUM>.

In examples, the flow additive <NUM> is present in an amount ranging from about <NUM> weight percent to about <NUM> weight percent, based on the total weight of the build material composition <NUM>. In other examples, the flow additive <NUM> may be present in an amount ranging from about <NUM> weight percent to about <NUM> weight percent, based on the total weight of the build material composition <NUM>. In still other examples, the flow additive <NUM> may be present in an amount ranging from about <NUM> weight percent to about <NUM> weight percent, based on the total weight of the build material composition <NUM>.

In an example, the host metal <NUM> may be a single phase metallic material composed of one element. In this example, the sintering temperature of the build material composition <NUM> may be below the melting point of the single element.

In another example, the host metal <NUM> is composed of two or more elements, which may be in the form of a single phase metallic alloy or a multiple phase metallic alloy. In these other examples, sintering generally occurs over a range of temperatures.

The host metal <NUM> may be composed of a single element or alloys. Some examples of the host metal <NUM> include steels, stainless steel, bronzes, titanium (Ti) and alloys thereof, aluminum (Al) and alloys thereof, nickel (Ni) and alloys thereof, cobalt (Co) and alloys thereof, iron (Fe) and alloys thereof, nickel cobalt (NiCo) alloys, gold (Au) and alloys thereof, silver (Ag) and alloys thereof, platinum (Pt) and alloys thereof, tungsten (W) and alloys thereof, and copper (Cu) and alloys thereof. Some specific examples include AlSi10Mg, 2xxx series aluminum, 4xxx series aluminum, CoCr MP1, CoCr SP2, MaragingSteel MS1, Hastelloy C, Hastelloy X, NickelAlloy HX, Inconel IN625, Inconel IN718, SS GP1, SS <NUM>-4PH, SS <NUM>, SS <NUM>, Ti6Al4V, and Ti-6Al-4V ELI7. While several example alloys have been provided, it is to be understood that other alloys may be used.

Referring now to <FIG>, in examples of the present disclosure, the flow additive <NUM> may include a thermally decomposing precursor <NUM> selected from the group consisting of a transition metal hydroxide and a transition metal oxo-hydroxide. For example, the flow additive may include Goethite (FeO(OH)) or ferric hydroxide (Fe(OH)<NUM>).

In examples of the present disclosure, the elemental metal <NUM> may be obtainable from the thermally decomposing precursor <NUM> by: thermally decomposing the thermally decomposing precursor <NUM> to form a thermal decomposition product <NUM>; and reducing the thermal decomposition product <NUM> in the reducing environment <NUM>. As used herein, obtainable means producible. In other words, the elemental metal <NUM> can be produced from the thermally decomposing precursor <NUM> by following the procedure above. In examples, the thermally decomposing precursor <NUM> may be selected from the group consisting of ferric hydroxide (Fe(OH)<NUM>), Goethite (FeO(OH)), chromic hydroxide (Cr(OH)<NUM>), nickel(II) hydroxide (Ni(OH)<NUM>), and nickel(III) hydroxide (Ni(OH)<NUM>).

When the elemental metal(s) <NUM> is/are to be obtained from the flow additive <NUM>, the reaction(s) (e.g., a thermal decomposition reaction and optionally a reduction reaction) may generate/produce the elemental metal(s) <NUM> and a gaseous byproduct <NUM>. It is to be understood that the elemental metal <NUM> depicted in <FIG> is not separated from the host metal <NUM>; rather, the elemental metal <NUM> is dispersed throughout the intermediate structure <NUM>'. The elemental metal <NUM> is capable of being incorporated into a bulk metal phase of the host metal <NUM> in the final metal object <NUM>. Therefore, the elemental metal <NUM> remains dispersed throughout the final metal object <NUM>. Gaseous byproduct(s) <NUM> may be removed from the system <NUM> (<FIG>) using a flowing purge gas or some other suitable gas removal mechanism. The elemental metal(s) <NUM> may be obtained from the flow additive <NUM> by thermally decomposing the flow additive <NUM>, or by thermally decomposing a thermally decomposing precursor <NUM> to produce a thermal decomposition product <NUM> and then reducing the thermal decomposition product <NUM>.

When the elemental metal <NUM> is obtained from the flow additive <NUM> by thermally decomposing the flow additive <NUM> (see, e.g., <FIG>) or by thermally decomposing the flow additive <NUM> to produce a thermal decomposition product <NUM> and then reducing the thermal decomposition product <NUM> (see, e.g., <FIG>), the flow additive <NUM> includes a thermally decomposing precursor <NUM>. Examples of thermally decomposing precursors <NUM> include organic substances, such as metal salts that are capable of producing a metal oxide upon thermal decomposition. Examples of suitable metal salts include Ni(NO<NUM>)<NUM>, NiSO<NUM>, Ni(SCN)<NUM>, Nd(NO<NUM>)<NUM>, Co(NO<NUM>)<NUM>, CoSO<NUM>, Co(SCN)<NUM>, Cr(NO<NUM>)<NUM>, CrSO<NUM>, Bi(NO<NUM>)<NUM>, VSO<NUM>, VOSO<NUM>, Pb(NO<NUM>)<NUM>, CuSO<NUM>, Cu(NO<NUM>)<NUM>, ZnSO<NUM>, Zn(NO<NUM>)<NUM>, Ag(NO<NUM>)<NUM>, Y(NO<NUM>)<NUM>, NiC<NUM>O<NUM>, FeC<NUM>O<NUM>, etc. Some metal salts may be hygroscopic (and thus attract moisture) and may be suitable as flow aids in non-ambient environments (e.g., in inert environments).

The thermally decomposing precursor <NUM> may be thermally decomposed by heating. The heat may be directly applied by an energy source <NUM>, or it may be heat transferred from the build material composition <NUM> which absorbs the energy applied by the energy source <NUM>. It is to be understood that in some examples, the thermal decomposition reaction takes place in an inert or reducing environment <NUM> so that the thermally decomposing precursor <NUM> thermally decomposes, rather than undergoing an alternate reaction which would fail to liberate the elemental metal <NUM> or the thermal decomposition product <NUM> (which can then be reduced to liberate the elemental metal <NUM>).

In some examples, the thermally decomposing precursor <NUM> decomposes directly to the elemental metal <NUM>. In these examples, reduction is not required and the elemental metal <NUM> is incorporated directly into a bulk metal phase of the host metal <NUM>. For example, there may be an alloying interaction involving the elemental metal <NUM> and the host metal <NUM> to form an alloy. The alloying interaction involving the elemental metal <NUM> and the host metal <NUM> may be spontaneous or may be initiated by energy applied by the energy source <NUM>. As such, in some examples, upon exposure to the energy, the thermally decomposing precursor <NUM> may thermally decompose to produce the elemental metal <NUM>, and the elemental metal <NUM> may react with the host metal <NUM> to form the alloy.

In other examples, the thermally decomposing precursor <NUM> decomposes to a thermal decomposition product <NUM>. The thermal decomposition product <NUM> may be reduced to produce the elemental metal <NUM>. Examples of thermally decomposing precursors <NUM> that produce the thermal decomposition product <NUM>, which yields the elemental metal <NUM> by further reduction, include the previously listed metal salts, including, Ni(NO<NUM>)<NUM>, NiSO<NUM>, Ni(SCN)<NUM>, Nd(NO<NUM>)<NUM>, Co(NO<NUM>)<NUM>, CoSO<NUM>, Co(SCN)<NUM>, Cr(NO<NUM>)<NUM>, CrSO<NUM>, Bi(NO<NUM>)<NUM>, VSO<NUM>, VOSO<NUM>, Pb(NO<NUM>)<NUM>, CuSO<NUM>, Cu(NO<NUM>)<NUM>, ZnSO<NUM>, Zn(NO<NUM>)<NUM>, Ag(NO<NUM>)<NUM>, NiC<NUM>O<NUM>, and FeC<NUM>O<NUM>. As mentioned herein, those metal salts that are hygroscopic may be suitable as flow aids in non-ambient environments.

When reduction is able to obtain the elemental metal <NUM> from the thermal decomposition product <NUM> (which is the decomposition product of the thermally decomposing precursor <NUM>), reduction can be accomplished by several mechanisms. As one example, reduction can be accomplished by heating the flow additive <NUM> or thermal decomposition product <NUM> in an environment containing a reducing gas. The heat may be directly applied by the energy source <NUM>, or it may be heat transferred from the build material composition <NUM> which absorbs the energy applied by the energy source <NUM>.

Once the elemental metal(s) <NUM> has/have been obtained from the flow agent <NUM> or thermal decomposition product <NUM>, the elemental metal(s) <NUM> may interact with the build material <NUM> to form the alloy. The alloying interaction may be initiated by energy applied by the energy source <NUM>.

In examples, the build material composition <NUM> is spreadable, having a Hausner Ratio less than <NUM>. In other examples, the Hausner Ratio may be less than or equal to <NUM>. The Hausner Ratio is determined at a spread temperature of the build material composition <NUM>. As mentioned above and used herein, the spread temperature for the build material composition <NUM> is the temperature to which the build material composition <NUM> is exposed when it is to be spread as a layer. For example, the build material composition <NUM> may be spread at <NUM>, <NUM>, or at any other suitable spread temperature (including those temperatures between <NUM> and <NUM>). The relevant Hausner Ratio for the build material composition <NUM> of the present disclosure is the Hausner Ratio at the spread temperature of the composition/build material composition <NUM>. As stated above, better flowability of the build material composition <NUM> means that the build material composition <NUM> has better spreadability.

Referring now to <FIG>, a flow diagram <NUM> depicts an example of a method for making the build material composition <NUM> according to the present disclosure. As depicted at box <NUM>, the method includes, "combining a host metal and a flow additive to form a build material mixture, the host metal being present in an amount ranging from about <NUM> weight percent to about <NUM> weight percent based on a total weight of the build material mixture and the flow additive being present in an amount ranging from about <NUM> weight percent to about <NUM> weight percent based on the total weight of the build material mixture, wherein the flow additive consists of a metal containing compound that is reducible to an elemental metal in a reducing environment at a reducing temperature less than a sintering temperature of the host metal, wherein the elemental metal is capable of being incorporated into a bulk metal phase of the host metal in a final metal object". As shown at box <NUM>, the method further includes "mixing the build material mixture until a build material composition having a Hausner Ratio less than <NUM> is formed.

In examples of the method <NUM>, the host metal <NUM> may be present in any of the amounts described herein, e.g., ranging from about <NUM> weight percent to about <NUM> weight percent, or from about <NUM> weight percent to about <NUM> weight percent, based on a total weight of the build material composition <NUM>. Also in the examples of the method <NUM>, the flow additive <NUM> may be present in any of the amounts described herein, e.g., ranging from about <NUM> weight percent to about <NUM> weight percent, or from about <NUM> weight percent to about <NUM> weight percent, based on the total weight of the build material composition <NUM>.

Any suitable conditions may be used to mix the host metal <NUM> with the flow additive <NUM>. The Hausner Ratio may be tested periodically throughout the mixing process to determine when the desirable Hausner ratio has been obtained. In an example, simple mixing of the host metal <NUM> with the flow additive <NUM> in a rotating container for about <NUM> hour to about <NUM> hours may be sufficient mixing to obtain a uniform Hausner Ratio throughout the mixture. Very long mixing, (e.g., <NUM> days or more) may result in flowability degradation (i.e., an increase in the Hausner Ratio over the Hausner Ratio that is achieved by an amount of mixing that has a duration at a threshold of sufficiency to be effective).

Some processes that use the composition/build material composition <NUM> of the present disclosure to make metal objects may include spreading a thin layer of the build material composition <NUM> for subsequent processing. For example, in a 3D printing process, the build material composition <NUM> may be spread one layer upon another layer, with each layer patterned by a functional agent prior to the addition of the next layer. (See <FIG>. ) The functional agent may be a binder agent <NUM>. Together, the build material composition <NUM> and the binder agent <NUM> to be selectively applied thereto may be referred to as a three-dimensional (3D) printing composition, which will be described more in reference to <FIG>.

The build material composition <NUM> described herein may also be part of a 3D printing kit. In an example, the kit for three-dimensional (3D) printing, comprises: a host metal present in an amount ranging from about <NUM> weight percent to about <NUM> weight percent, based on a total weight of the composition; a flow additive present in an amount ranging from about <NUM> weight percent to about <NUM> weight percent, based on the total weight of the composition, wherein the flow additive consists of a metal containing compound that is reducible to an elemental metal in a reducing environment at a reducing temperature less than or equal to a sintering temperature of the host metal, wherein the elemental metal is capable of being incorporated into a bulk metal phase of the host metal in a final metal object; and wherein the composition is spreadable, having a Hausner Ratio less than <NUM>; and a binder agent to be applied to at least a portion of a layer of the build material composition via an inkjet printhead to pattern a cross-section of an intermediate part. The kit may consist of the build material composition and the binder agent with no other components. The components of the kit may be maintained separately until used together in examples of the 3D printing method disclosed herein.

As used herein, "material set" or "kit" is understood to be synonymous with "composition. " Further, "material set" and "kit" are understood to be compositions comprising one or more components where the different components in the compositions are each contained in one or more containers, separately or in any combination, prior to and during printing but these components can be combined together during printing. The containers can be any type of a vessel, box, or receptacle made of any material.

<FIG> is a block diagram that shows components of the build material composition <NUM> and the 3D printing composition <NUM> as disclosed herein. In examples, the build material composition <NUM> and the binder agent <NUM> to be applied thereto yield the 3D printing composition <NUM>. As such, examples of the 3D printing composition <NUM> disclosed herein include a build material composition <NUM>, and the binder agent <NUM>. More specifically, examples of the 3D printing composition <NUM> include the build material composition <NUM>, which includes the host metal <NUM> present in an amount ranging from about <NUM> weight percent to about <NUM> weight percent, based on a total weight of the build material composition, and the flow additive <NUM> present in an amount ranging from about <NUM> weight percent to about <NUM> weight percent, based on the total weight of the build material composition <NUM>, wherein the flow additive <NUM> consists of a metal containing compound that is reducible to an elemental metal <NUM> in a reducing environment at a reducing temperature less than or equal to a sintering temperature of the host metal <NUM>. The elemental metal(s) <NUM> is/are capable of being incorporated into a bulk metal phase of the host metal <NUM> in a final metal object <NUM>. The build material composition <NUM> is spreadable, having a Hausner Ratio less than <NUM>. The binder agent <NUM> is to be applied to at least a portion of a layer of the build material composition <NUM> via an inkjet printhead to pattern a cross-section of an intermediate structure.

Any example of the host metal <NUM> and the flow additive <NUM> described herein may be used in any of the amounts described herein to form the build material composition <NUM> that is used to form the 3D printing composition <NUM>.

The binder agent <NUM> may include a binder and a liquid vehicle. Examples of suitable binders include latexes (i.e., an aqueous dispersion of polymer particles), polyvinyl alcohol, polyvinylpyrrolidone, and combinations thereof.

Examples of polyvinyl alcohol include low weight average molecular weight polyvinyl alcohols (e.g., from about <NUM>,<NUM> to about <NUM>,<NUM>), such as SELVOL™ PVOH <NUM> from Sekisui. Examples of polyvinylpyrrolidones include low weight average molecular weight polyvinylpyrrolidones (e.g., from about <NUM>,<NUM> to about <NUM>,<NUM>), such as LUVITEC™ K <NUM> from BASF Corp.

The polymer particles may be any latex polymer (i.e., polymer that is capable of being dispersed in an aqueous medium) that is jettable via inkjet printing (e.g., thermal inkjet printing or piezoelectric inkjet printing). In some examples disclosed herein, the polymer particles are heteropolymers or co-polymers. The heteropolymers may include a more hydrophobic component and a more hydrophilic component. In these examples, the hydrophilic component renders the particles dispersible in the binder agent <NUM>, while the hydrophobic component is capable of coalescing upon exposure to heat in order to temporarily bind the host metal particles <NUM>.

The polymer particles of the latex may have several different morphologies. The polymer particles may include two different copolymer compositions, which may be fully separated core-shell polymers, partially occluded mixtures, or intimately comingled as a polymer solution. In an example, the polymer particles may be individual spherical particles containing polymer compositions of hydrophilic (hard) component(s) and/or hydrophobic (soft) component(s) that may be interdispersed according to IPN (interpenetrating networks), although it is contemplated that the hydrophilic and hydrophobic components may be interdispersed in other ways. For another example, the polymer particles may be made of a hydrophobic core surrounded by a continuous or discontinuous hydrophilic shell. This may lead to good water dispersibility and jetting reliability. For another example, the polymer particle morphology may resemble a raspberry, in which a hydrophobic core is surrounded by several smaller hydrophilic particles that are attached to the core. For still another example, the polymer particles may include <NUM>, <NUM>, or <NUM> or more relatively large particles (i.e., lobes) that are at least partially attached to one another or that surround a smaller polymer core. The latex polymer particles may have a single phase morphology, may be partially occluded, may be multiple-lobed, or may include any combination of the morphologies disclosed herein.

The latex polymer particles may have a weight average molecular weight ranging from about <NUM>,<NUM> to about <NUM>,<NUM>. As examples, the weight average molecular weight of the latex particles may range from about <NUM>,<NUM> to about <NUM>,<NUM>, from about <NUM>,<NUM> to about <NUM>,<NUM>, or from about <NUM>,<NUM> to about <NUM>,<NUM>.

Latex particles may include a heteropolymer including a hydrophobic component that makes up from about <NUM>% to about <NUM>% (by weight) of the heteropolymer, and a hydrophilic component that makes up from about <NUM>% to about <NUM>% (by weight) of the heteropolymer, where the hydrophobic component may have a lower glass transition temperature than the hydrophilic component. In general, a lower content of the hydrophilic component is associated with easier use of the latex particles under typical ambient conditions. The glass transition temperature of the latex particles may range from about -<NUM> to about <NUM>, or in a specific example, from about <NUM> to about <NUM>. The particle size of the latex particles may range from about <NUM> to about <NUM>.

Examples of monomers that may be used to form the hydrophobic component include low Tg monomers. Some examples include C4 to C8 alkyl acrylates or methacrylates, styrene, substituted methyl styrenes, polyol acrylates or methacrylates, vinyl monomers, vinyl esters, ethylene, maleate esters, fumarate esters, itaconate esters, or the like. Some specific examples include methyl methacrylate, butyl acrylate, butyl methacrylate, hexyl acrylate, hexyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, <NUM>-ethylhexyl acrylate, <NUM>-ethylhexy methacrylate, hydroxyethyl acrylate, lauryl acrylate, lauryl methacrylate, octadecyl acrylate, octadecyl methacrylate, isobornyl acrylate, isobornyl methacrylate, stearyl methacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetrahydrofurfuryl acrylate, alkoxylated tetrahydrofurfuryl acrylate, <NUM>-phenoxyethyl methacrylate, benzyl acrylate, ethoxylated nonyl phenol methacrylate, cyclohexyl methacrylate, trimethyl cyclohexyl methacrylate, t-butyl methacrylate, n-octyl methacrylate, tridecyl methacrylate, isodecyl acrylate, dimethyl maleate, dioctyl maleate, acetoacetoxyethyl methacrylate, diacetone acrylamide, pentaerythritol tri-acrylate, pentaerythritol tetra-acrylate, pentaerythritol tri-methacrylate, pentaerythritol tetra-methacrylate, divinylbenzene, styrene, methylstyrenes (e.g., α-methyl styrene, p-methyl styrene), <NUM>,<NUM>-butadiene, vinyl chloride, vinylidene chloride, vinylbenzyl chloride, acrylonitrile, methacrylonitrile, N-vinyl imidazole, N-vinylcarbazole, N-vinyl-caprolactam, combinations thereof, derivatives thereof, or mixtures thereof.

The heteropolymer may be formed of at least two of the previously listed monomers, or at least one of the previously listed monomers and a higher glass transition temperature (Tg) hydrophilic monomer, such as an acidic monomer. Examples of acidic monomers that can be polymerized in forming the latex polymer particles include acrylic acid, methacrylic acid, ethacrylic acid, dimethylacrylic acid, maleic anhydride, maleic acid, vinylsulfonate, cyanoacrylic acid, vinylacetic acid, allylacetic acid, ethylidineacetic acid, propylidineacetic acid, crotonoic acid, fumaric acid, itaconic acid, sorbic acid, angelic acid, cinnamic acid, styrylacrylic acid, citraconic acid, glutaconic acid, aconitic acid, phenylacrylic acid, acryloxypropionic acid, aconitic acid, phenylacrylic acid, acryloxypropionic acid, vinylbenzoic acid, N-vinylsuccinamidic acid, mesaconic acid, methacroylalanine, acryloylhydroxyglycine, sulfoethyl methacrylic acid, sulfopropyl acrylic acid, styrene sulfonic acid, sulfoethylacrylic acid, <NUM>-methacryloyloxymethane-<NUM>-sulfonic acid, <NUM>-methacryoyloxypropane-<NUM> -sulfonic acid, <NUM>-(vinyloxy)propane-<NUM>-sulfonic acid, ethylenesulfonic acid, vinyl sulfuric acid, <NUM>-vinylphenyl sulfuric acid, ethylene phosphonic acid, vinyl phosphoric acid, vinyl benzoic acid, <NUM> acrylamido-<NUM>-methyl-<NUM>-propanesulfonic acid, combinations thereof, derivatives thereof, or mixtures thereof. Other examples of high Tg hydrophilic monomers include acrylamide, methacrylamide, monohydroxylated monomers, monoethoxylated monomers, polyhydroxylated monomers, or polyethoxylated monomers.

In an example, the selected monomer(s) is/are polymerized to form a polymer, heteropolymer, or copolymer. In some examples, the monomer(s) are polymerized with a co-polymerizable surfactant. In some examples, the co-polymerizable surfactant can be a polyoxyethylene compound. In some examples, the co-polymerizable surfactant can be a HITENOL® compound e.g., polyoxyethylene alkylphenyl ether ammonium sulfate, sodium polyoxyethylene alkylether sulfuric ester, polyoxyethylene styrenated phenyl ether ammonium sulfate, or mixtures thereof.

The polymer particles may have a particle size that can be jetted via thermal inkjet printing or piezoelectric printing or continuous inkjet printing. In an example, the particle size of the polymer particles ranges from about <NUM> to about <NUM>.

Any suitable polymerization process may be used. In examples, the aqueous dispersion of polymer particles (latexes) may be produced by emulsion polymerization or co-polymerization of any of the previously listed monomers.

In an example, the polymer particles may be prepared by polymerizing high Tg hydrophilic monomers to form the high Tg hydrophilic component and attaching the high Tg hydrophilic component onto the surface of the low Tg hydrophobic component.

In another example, each of the polymer particles may be prepared by polymerizing the low Tg hydrophobic monomers and the high Tg hydrophilic monomers at a ratio of the low Tg hydrophobic monomers to the high Tg hydrophilic monomers that ranges from <NUM>:<NUM> to <NUM>:<NUM>. In this example, the soft low Tg hydrophobic monomers may dissolve in the hard high Tg hydrophilic monomers.

In still another example, each of the polymer particles may be prepared by starting the polymerization process with the low Tg hydrophobic monomers, then adding the high Tg hydrophilic monomers, and then finishing the polymerization process. In this example, the polymerization process may cause a higher concentration of the high Tg hydrophilic monomers to polymerize at or near the surface of the low Tg hydrophobic component.

In still another example, each of the polymer particles may be prepared by starting a copolymerization process with the low Tg hydrophobic monomers and the high Tg hydrophilic monomers, then adding additional high Tg hydrophilic monomers, and then finishing the copolymerization process. In this example, the copolymerization process may cause a higher concentration of the high Tg hydrophilic monomers to copolymerize at or near the surface of the low Tg hydrophobic component.

Other suitable techniques, specifically for generating a core-shell structure, may be used, such as : i) grafting a hydrophilic shell onto the surface of a hydrophobic core, ii) copolymerizing hydrophobic and hydrophilic monomers using ratios that lead to a more hydrophilic shell, iii) adding hydrophilic monomer (or excess hydrophilic monomer) toward the end of the copolymerization process so there is a higher concentration of hydrophilic monomer copolymerized at or near the surface, or iv) any other method known in the art to generate a more hydrophilic shell relative to the core.

The low Tg hydrophobic monomers and/or the high Tg hydrophilic monomers used in any of these example methods may be any of the low Tg hydrophobic monomers and/or the high Tg hydrophilic monomers (respectively) listed above. In an example, the low Tg hydrophobic monomers are selected from the group consisting of C4 to C8 alkyl acrylate monomers, C4 to C8 alkyl methacrylate monomers, styrene monomers, substituted methyl styrene monomers, vinyl monomers, vinyl ester monomers, and combinations thereof; and the high Tg hydrophilic monomers are selected from the group consisting of acidic monomers, unsubstituted amide monomers, alcoholic acrylate monomers, alcoholic methacrylate monomers, C1 to C2 alkyl acrylate monomers, C1 to C2 alkyl methacrylate monomers, and combinations thereof.

The resulting polymer particles may exhibit a core-shell structure, a mixed or intermingled polymeric structure, or some other morphology.

In some examples, the polymer particles have a MFFT or a glass transition temperature (Tg) that is greater (e.g., >) than ambient temperature. In other examples, the polymer particles have a MFFT or Tg that is much greater (e.g., >>) than ambient temperature (i.e., at least <NUM>° higher than ambient). As mentioned herein, "ambient temperature" may refer to room temperature (e.g., ranging about <NUM> to about <NUM>), or to the temperature of the environment in which the 3D printing method is performed. Examples of the 3D printing environment ambient temperature may range from about <NUM> to about <NUM>. The MFFT or the Tg of the bulk material (e.g., the more hydrophobic portion) of the polymer particles may range from <NUM> to about <NUM>. In an example, the MFFT or the Tg of the bulk material (e.g., the more hydrophobic portion) of the polymer particles is about <NUM> or higher. The MFFT or the Tg of the bulk material may be any temperature that enables the polymer particles to be inkjet printed without becoming too soft at the printer operating temperatures.

The polymer particles may have a MFFT or Tg ranging from about <NUM> to about <NUM>. In an example, the polymer particles may have a MFFT or Tg of about <NUM>.

In an example, the binder is present in the binder agent <NUM> in an amount ranging from about <NUM> wt% to about <NUM> wt% based on a total weight of the binder agent. In another example, the binder is present in the binder agent <NUM> in an amount ranging from about <NUM> wt% to about <NUM> wt% based on the total weight of binder agent <NUM>.

In addition to the binder, the binder agent <NUM> may also include water, co-solvent(s), surfactant(s) and/or dispersing aid(s), antimicrobial agent(s), and/or anti-kogation agent(s).

The co-solvent may be an organic co-solvent present in an amount ranging from about <NUM> wt% to about <NUM> wt% (based on the total weight of the binder agent <NUM>). It is to be understood that other amounts outside of this range may also be used depending, at least in part, on the jetting architecture used to dispense the binder agent <NUM>. The organic co-solvent may be any water miscible, high-boiling point solvent, which has a boiling point of at least <NUM>. Classes of organic co-solvents that may be used include aliphatic alcohols, aromatic alcohols, diols, glycol ethers, polyglycol ethers, <NUM>-pyrrolidones/pyrrolidinones, caprolactams, formamides, acetamides, glycols, and long chain alcohols. Examples of these co-solvents include primary aliphatic alcohols, secondary aliphatic alcohols, <NUM>,<NUM>-alcohols, <NUM>,<NUM>-alcohols, <NUM>,<NUM>-alcohols, ethylene glycol alkyl ethers, propylene glycol alkyl ethers, higher homologs (C<NUM>-C<NUM>) of polyethylene glycol alkyl ethers, N-alkyl caprolactams, unsubstituted caprolactams, both substituted and unsubstituted formamides, both substituted and unsubstituted acetamides, and the like. In some examples, the gas generating liquid functional agent may include <NUM>-pyrrolidone, <NUM>-methyl-<NUM>,<NUM>-propanediol, <NUM>-(<NUM>-hydroxyethyl)-<NUM>-pyrrolidone, <NUM>,<NUM>-butanediol, or combinations thereof.

The binder agent <NUM> may also include surfactant(s) and/or dispersing aid(s). Surfactant(s) and/or dispersing aid(s) may be used to improve the wetting properties and the jettability of the binder agent <NUM>. Examples of suitable surfactants and dispersing aids include those that are non-ionic, cationic, or anionic. Examples of suitable surfactants/wetting agents include a self-emulsifiable, non-ionic wetting agent based on acetylenic diol chemistry (e.g., SURFYNOL® SEF from Air Products and Chemicals, Inc. ), a non-ionic fluorosurfactant (e.g., CAPSTONE® fluorosurfactants from DuPont, previously known as ZONYL FSO), and combinations thereof. In a specific example, the surfactant is a non-ionic, ethoxylated acetylenic diol (e.g., SURFYNOL® <NUM> from Air Products and Chemical Inc. In other examples, the surfactant is an ethoxylated low-foam wetting agent (e.g., SURFYNOL® <NUM> or SURFYNOL® CT-<NUM> from Air Products and Chemical Inc. ) or an ethoxylated wetting agent and molecular defoamer (e.g., SURFYNOL® <NUM> from Air Products and Chemical Inc. Still other suitable surfactants include non-ionic wetting agents and molecular defoamers (e.g., SURFYNOL® 104E from Air Products and Chemical Inc. ) or secondary alcohol ethoxylates (commercially available as TERGITOL® TMN-<NUM>, TERGITOL® <NUM>-S-<NUM>, TERGITOL® <NUM>-S-<NUM>, etc. from The Dow Chemical Co. In some examples, it may be desirable to utilize a surfactant having a hydrophilic-lipophilic balance (HLB) less than <NUM>. Examples of suitable dispersing aid(s) include those of the SILQUEST™ series from Momentive, including SILQUEST™ A-<NUM>. Whether a single surfactant or dispersing aid is used or a combination of surfactants and/or dispersing aids is used, the total amount of surfactant(s) and/or dispersing aid(s) may range from about <NUM> wt% to about <NUM> wt% based on the total weight of the binder agent <NUM>.

The binder agent <NUM> may also include antimicrobial agent(s). Suitable antimicrobial agents include biocides and fungicides. Example antimicrobial agents may include the NUOSEPT® (Ashland Inc. ), UCARCIDE™ or KORDEK™ or ROCIMA™ (Dow Chemical Co. ), PROXEL® (Arch Chemicals) series, ACTICIDE® B20 and ACTICIDE® M20 and ACTICIDE® MBL (blends of <NUM>-methyl-<NUM>-isothiazolin-<NUM>-one (MIT), <NUM>,<NUM>-benzisothiazolin-<NUM>-one (BIT), and Bronopol) (Thor Chemicals), AXIDE™ (Planet Chemical), NIPACIDE™ (Clariant), blends of <NUM>-chloro-<NUM>-methyl-<NUM>-isothiazolin-<NUM>-one (CIT or CMIT) and MIT under the tradename KATHON™ (Dow Chemical Co. ), and combinations thereof. In an example, the binder agent <NUM> may include a total amount of antimicrobial agents that ranges from about <NUM> wt% to about <NUM> wt% of the binder agent <NUM>.

An anti-kogation agent may also be included in the binder agent <NUM>. Kogation refers to the deposit of dried solids on a heating element of a thermal inkjet printhead. Anti-kogation agent(s) is/are included to assist in preventing the buildup of kogation, and thus may be included when the binder agent <NUM> is to be dispensed using a thermal inkjet printhead. Examples of suitable anti-kogation agents include oleth-<NUM>-phosphate (commercially available as CRODAFOS™ O3A or CRODAFOS™ N-<NUM> acid) or dextran <NUM>. Other suitable examples of the anti-kogation agents include CRODAFOS™ HCE (phosphate-ester from Croda Int. ), CRODAFOS® N10 (oleth-<NUM>-phosphate from Croda Int. ), or DISPERSOGEN® LFH (polymeric dispersing agent with aromatic anchoring groups, acid form, anionic, from Clariant), etc. The anti-kogation agent may be present in the binder agent <NUM> in an amount ranging from about <NUM> wt% to about <NUM> wt% of the total weight of the binder agent <NUM>.

The balance of the binder agent <NUM> is water (e.g., deionized water). As such, the amount of water may vary depending upon the weight percent of the other binder agent <NUM> components.

Examples of a printing method <NUM>, which include the build material composition <NUM> and the binder agent <NUM> are shown in <FIG>. As depicted in <FIG> at reference numeral <NUM>, a 3D printing system <NUM> may include an inkjet applicator <NUM>, a supply bed <NUM> (including a supply of build material composition <NUM>), a delivery piston <NUM>, a spreader <NUM>, a fabrication bed <NUM>, and a fabrication piston <NUM>. The delivery piston <NUM> and the fabrication piston <NUM> may be the same type of piston, but are programmed to move in opposite directions. In an example, when a layer of the intermediate structure <NUM> is to be formed, the delivery piston <NUM> may be programmed to push a predetermined amount of the build material composition <NUM> out of the opening in the supply bed <NUM> and the fabrication piston <NUM> may be programmed to move in the opposite direction of the delivery piston <NUM> in order to increase the depth of the fabrication bed <NUM>. The delivery piston <NUM> will advance enough so that when the spreader <NUM> pushes the build material composition <NUM> into the fabrication bed <NUM> and onto the build surface <NUM> or the previously formed layer, the depth of the fabrication bed <NUM> is sufficient so that a layer <NUM> of the build material composition <NUM> and the binder agent <NUM> may be formed in the fabrication bed <NUM>. The spreader <NUM> is capable of spreading the build material composition <NUM> into the fabrication bed <NUM> to form the build material layer <NUM>, which is relatively uniform in thickness.

In an example, the build material composition <NUM> may be spreadable in a layer <NUM> having a layer thickness less than <NUM>. In another example, the build material composition <NUM> may be spreadable in a layer <NUM> having a layer thickness less than <NUM>. In an example, the thickness of the build material layer <NUM> ranges from about <NUM> to about <NUM>, although thinner or thicker layers may also be used. For example, the thickness of the layer may range from about <NUM> to about <NUM>. Depending upon the desired thickness for the layer <NUM> and the particle size(s) within the build material composition <NUM>, the layer <NUM> that is formed in a single build material application may be made up of a single row of the build material composition <NUM> or several rows of build material composition <NUM>.

While the system <NUM> is depicted, it is to be understood that other printing systems <NUM> may also be used. For example, another support member, such as a build area platform, a platen, a glass plate, or another build surface may be used instead of the fabrication bed <NUM>. The build material composition <NUM> may be delivered from another source, such as a hopper, an auger conveyer, or the like. It is to be understood that the spreader <NUM> may be a rigid or flexible blade, which is a more common spreader for metal/metal alloy build materials. However, the spreader may also be replaced by other tools, such as a roller, or a combination of a roller and a blade.

Each of these physical elements of the 3D printing system <NUM> may be operatively connected to a central processing unit <NUM> (see <FIG>) of the 3D printing system <NUM>. The central processing unit <NUM> (e.g., running computer readable instructions <NUM> stored on a non-transitory, tangible computer readable storage medium) manipulates and transforms data represented as physical (electronic) quantities within the printer's registers and memories <NUM> in order to control the physical elements to create the final metal object <NUM>. The data for the selective delivery of the binder agent <NUM>, the build material composition <NUM>, etc. may be derived from a 3D model of the final metal object <NUM> to be formed. For example, the instructions <NUM> may cause the controller to utilize an applicator (e.g., an inkjet applicator <NUM>) to selectively dispense the binder agent <NUM>, and to utilize a build material distributor (spreader <NUM>) to dispense the build material composition <NUM>. The central processing unit <NUM> controls the selective delivery (i.e. dispensing) of the binder agent <NUM> in accordance with delivery control data <NUM>.

The binder agent <NUM> may be dispensed from any suitable applicator. As illustrated in <FIG> at reference number <NUM>, the binder agent <NUM> may be dispensed from an inkjet applicator, such as a thermal inkjet printhead or a piezoelectric inkjet printhead. The printhead may be a drop-on-demand printhead or a continuous drop printhead. The inkjet applicator <NUM> may be selected to deliver drops of binder agent <NUM> at a resolution ranging from about <NUM> dots per inch (DPI) to about <NUM> DPI. In other examples, the inkjet applicator <NUM> may be selected to be able to deliver drops of the binder agent <NUM> at a higher or lower resolution. The drop velocity may range from about <NUM>/s to about <NUM>/s and the firing frequency may range from about <NUM> to about <NUM>. The inkjet applicator <NUM> may include an array of nozzles through which it is able to selectively eject drops of fluid. In one example, each drop may be in the order of about <NUM> ng per drop, although it is contemplated that a higher (e.g., <NUM> ng) or lower (e.g., <NUM> ng) drop size may be used. In some examples, inkjet applicator <NUM> is able to deliver variable size drops of the binder agent <NUM>.

The inkjet applicator(s) <NUM> may be attached to a moving XY stage or a translational carriage (neither of which is shown) that moves the inkjet applicator(s) <NUM> adjacent to the build surface <NUM> in order to deposit the binder agent <NUM> in desirable area(s) <NUM>. In other examples, the applicator(s) <NUM> may be fixed while a support member (supporting the build surface <NUM>) is configured to move relative thereto.

The inkjet applicator(s) <NUM> may be programmed to receive commands from the central processing unit <NUM> and to deposit the binder agent <NUM> according to a pattern of the layer <NUM> to be achieved. In an example, a computer model of the final metal object <NUM> to be printed is generated using a computer aided design (CAD) program. The computer model of the final metal object <NUM> is sliced into N layers, which are then divided into voxels. The printing parameters for each voxel are computed based on the desired composition and physical properties of the final metal object <NUM> to be printed. The printing parameters for each voxel may include the X, Y, and Z coordinates that define its location and the amount of the binder agent <NUM> (if any) that is to be received. The central processing unit <NUM> may then use this information to instruct the inkjet applicator(s) <NUM> as to how much (if any) of the binder agent <NUM> should be jetted into each voxel.

The inkjet applicator <NUM> selectively applies the binder agent <NUM> on those portions <NUM> of the layer <NUM> of the build material composition <NUM> that is to form the intermediate structure <NUM>, and ultimately the final metal object <NUM>, which may be a 3D part. The binder agent <NUM> may not be applied on the entire layer <NUM>, as shown at the portions <NUM>.

After the binder agent <NUM> is selectively applied in a pattern on the desired portion(s) <NUM> of the layer <NUM> of build material composition <NUM>, another layer of the build material composition <NUM> is applied, as shown at reference numeral <NUM> in <FIG>, and patterned with the binder agent <NUM>, as shown at reference numeral <NUM>. The formation and patterning of additional layers may be repeated in order to form the intermediate structure <NUM>.

During and/or after formation of the intermediate structure <NUM>, liquid components of the binder agent <NUM> may be evaporated. At least substantially evaporation (with or without the application of heat) activates the binder, and the activated binder provides enough adhesive strength to hold the intermediate structure <NUM> together with enough mechanical stability to survive removal from any non-patterned build material composition <NUM>.

The intermediate structure <NUM> may be extracted or separated from the non-patterned build material composition <NUM> (e.g., in portion(s) <NUM>) by any suitable means. In an example, the intermediate structure <NUM> may be extracted by lifting the intermediate structure <NUM> from the non-patterned build material composition <NUM>. Any suitable extraction tool may be used. In some examples, the intermediate structure <NUM> may be cleaned to remove non-patterned build material composition <NUM> from a surface of the intermediate structure <NUM>. In an example, the intermediate structure <NUM> may be cleaned with a brush and/or an air jet, may be exposed to mechanical shaking, or may be exposed to other techniques that can remove the non-patterned build material composition <NUM>.

The intermediate structure <NUM> may then be placed in a heating mechanism (not shown). Examples of the heating mechanism include a conventional furnace or oven, a microwave oven, or devices capable of hybrid heating (i.e., conventional heating and microwave heating).

The heating mechanism may be used to perform a heating sequence, which involves exposing the intermediate structure <NUM> to a reducing temperature that causes a thermal decomposition reaction and/or a reduction reaction to obtain the elemental metal(s) <NUM> from the flow additive <NUM>. The heating sequence may form the final metal object <NUM> (see, e.g., <FIG>). In some examples, heating involves exposure to a series of temperatures.

The series of temperatures may involve heating the intermediate structure <NUM> to a decomposing/reducing temperature, a de-binding temperature, and then to the sintering temperature. The reducing temperature decomposes/reduces the flow additive <NUM> to the elemental metal(s) <NUM>, and the de-binding temperature removes the binder, from the intermediate structure <NUM> to produce an at least substantially binder-free intermediate structure <NUM>' with the elemental metal(s) <NUM> dispersed throughout the intermediate structure <NUM>'. The structure <NUM>' may be sintered to incorporate the elemental metal(s) <NUM> into a bulk metal phase of the host metal <NUM> and to form the final metal object <NUM>. Heating to decompose/reduce, de-bind, and sinter may take place at several different temperatures, where the temperatures for decomposing/reducing and de-binding are lower than the temperature(s) for sintering. In some instances, heating to de-bind and heating to decompose/reduce may take place at the same temperature or within the same temperature range (e.g., from about <NUM> to about <NUM>). In other cases, heating to de-bind will occur in a lower temperature range than heating to decompose/reduce the flow additive <NUM>, and heating to decompose/reduce the flow additive <NUM> will occur in a lower temperature range than heating to sinter the host metal <NUM>. In some examples, (e.g., with alloys that sinter at the low end of the sintering temperature range), heating to de-bind and heating to decompose/reduce may take place at temperature(s) that are near, but below, the sintering temperature.

Heating to decompose/reduce is accomplished at a reducing temperature that is sufficient to thermally decompose/reduce the flow additive <NUM>. As such, the reducing temperature depends upon the flow additive <NUM> used. In an example, the reducing temperature ranges from about <NUM> to about <NUM>. In another example, the reducing temperature ranges from about <NUM> to about <NUM>. In another example the reducing temperature greater than <NUM>. In any of these examples, it is to be understood that the flow additive <NUM> is paired with a metal host <NUM> that sinters at a higher temperature than the decomposition/reduction temperature of the flow additive <NUM>.

Heating to de-bind is accomplished at a thermal decomposition temperature that is sufficient to thermally decompose the binder. As such, the temperature for de-binding depends upon the binder in the binder agent <NUM>. In an example, the thermal decomposition temperature ranges from about <NUM> to about <NUM>. In another example, the thermal decomposition temperature ranges from about <NUM> to about <NUM>. The binder may have a clean thermal decomposition mechanism (e.g., leaves non-volatile residue in an amount <<NUM> wt% of the initial binder, and in some instances non-volatile residue in an amount <<<NUM> wt% of the initial binder). The smaller residue percentage (e.g., close to <NUM>%) is more desirable.

While not being bound to any theory, it is believed that the at least substantially binder-free intermediate structure <NUM>' may maintain its shape due, for example, to one or more of: i) the low amount of stress experience by the part <NUM>' due to it not being physically handled, and/or ii) low level necking occurring between the host metal particles <NUM> at the reducing temperature and at the thermal decomposition temperature of the binder. The at least substantially binder-free intermediate structure <NUM>' may maintain its shape although the binder is at least substantially removed and the host metal particles <NUM> are not yet sintered.

The temperature may be raised to sinter the substantially binder-free intermediate structure <NUM>', which can result in the formation of weak bonds that are strengthened throughout sintering. During sintering, the host metal particles <NUM> coalesce to form the final metal object <NUM>, and so that a desired density of the final metal object <NUM> is achieved. The sintering temperature is a temperature that is sufficient to sinter the remaining host metal particles <NUM>. The sintering temperature is highly depending upon the composition of the host metal particles <NUM>. During sintering, the at least substantially binder-free intermediate structure <NUM>' may be heated to a temperature ranging from about <NUM>% to about <NUM>% of the melting point of the host metal particles <NUM>. In another example, the at least substantially binder-free intermediate structure <NUM>' may be heated to a temperature ranging from about <NUM>% to about <NUM>% of the melting point of the host metal particles <NUM>. In still another example, the at least substantially binder-free intermediate structure <NUM>' may be heated to a temperature ranging from about <NUM>% to about <NUM>% of the melting point of the host metal particles <NUM>. In still another example, the sintering temperature may range from about <NUM> below the melting temperature of host metal particles <NUM> to about <NUM> below the melting temperature of the host metal particles <NUM>. The sintering temperature may also depend upon the particle size and time for sintering (i.e., high temperature exposure time). As an example, the sintering temperature may range from about <NUM> to about <NUM>. In another example, the sintering temperature is at least <NUM>. An example of a sintering temperature for bronze is about <NUM>, and an example of a sintering temperature for stainless steel is between about <NUM> and about <NUM>. While these temperatures are provided as sintering temperature examples, it is to be understood that the sintering temperature depends upon the host metal particles <NUM> that are utilized, and may be higher or lower than the provided examples. Heating at a suitable sintering temperature sinters and coalesces the host metal particles <NUM> to form a completed final metal object <NUM>. As a result of final sintering, the density may be <NUM>% to over <NUM>% of the theoretical density. In some cases the density of the final metal object <NUM> may be very close to <NUM>% of the theoretical density.

The length of time at which the heat (for each of decomposing/reducing, de-binding, and sintering) is applied and the rate at which the intermediate structure <NUM>, <NUM>' is heated may be dependent, for example, on one or more of: characteristics of the heating mechanism, characteristics of the flow additive <NUM> and binder, characteristics of the host metal particles <NUM> (e.g., metal type, particle size, etc.), and/or the characteristics of the final metal object/part <NUM> (e.g., wall thickness).

Heating, respectively, at the reducing and de-binding temperature may occur for a time period ranging from about <NUM> minutes to about <NUM> hours. When the intermediate structure <NUM> has open porosity to vent out binder and/or gaseous byproducts from the flow aid <NUM> decomposition/reduction, and/or the amount of the binder and/or flow aid byproducts is low, and/or the wall thickness of the intermediate structure <NUM> is relatively thin, the time period for de-binding and reduction may be <NUM> hours (<NUM> minutes) or less. Longer times may be used if the structure <NUM> has less open porosity, if the structure <NUM> has thicker walls, and/or if the structure <NUM> has a higher concentration of binder. In an example, the reduction and de-binding time period is about <NUM> minutes. In another example, the reduction and de-binding time period is about <NUM> minutes. The intermediate structure <NUM> may be heated to the reducing and/or de-binding temperatures at a heating rate ranging from about <NUM>/minute to about <NUM>/minute. The heating rate (i.e. temperature rise rate) may depend, in part, on one or more of: the amount of the flow additive and/or binder and/or the porosity of the intermediate structure <NUM>.

The at least substantially binder-free intermediate structure <NUM>' may be heated at the sintering temperature for a time period ranging from about <NUM> minutes to about <NUM> hours. In an example, the sintering time period is <NUM> minutes. In another example, the sintering time period is <NUM> minutes. In still another example, the sintering time period is less than or equal to <NUM> hours. The at least substantially binder-free intermediate structure <NUM>' may be heated to the sintering temperature at a heating rate ranging from about <NUM>/minute to about <NUM>/minute.

While <FIG> illustrates one example 3D printing process, it is to be understood that the build material composition <NUM> may be used in other additive manufacturing processes. An example of another additive manufacturing process is direct metal laser sintering (DMLS). During DMLS, an energy beam is aimed at a selected region (in some instances less than the entire layer) of a layer of the build material composition <NUM>. The energy beam may first be applied to cause the flow additive <NUM> in the build material composition <NUM> to decompose/reduce, and then the intensity may be increased to raise the temperature so that the remaining host metal particles <NUM>, which are exposed to the energy beam, sinter to form the layer of the final metal object <NUM> (3D part). The application of additional build material composition <NUM> layers and the selective energy beam exposure may be repeated to build up the final part layer by layer. In examples that use DMLS, a binder agent <NUM> may be omitted from the process.

To further illustrate the present disclosure, an example and a prophetic example are given herein. It is to be understood that this example and prophetic example are provided for illustrative purposes and are not to be construed as limiting the scope of the present disclosure.

Build material compositions were tested. The host metal was stainless steel, <NUM>, grade -<NUM> (<NUM>%) powder from "Sandvik", (average particle diameter was about <NUM>). As shown in <FIG>, the baseline build material composition (the host metal powder without any flow additive) demonstrated poor flowability, with a Hausner ratio of about <NUM>. The result for the baseline build material composition corresponds to <NUM>% FeOx Flow Additive in <FIG>. When the host metal powder was blended with iron oxide (FeOx) flow additives, the flowability improved as detailed below. Iron oxide (FeOx) flow additive candidates were prepared as follows:.

Ferric Oxide (Fe<NUM>O<NUM>) Nano-Powder having an average primary particle size of about <NUM> to <NUM> was procured from Inframat Corporation. It is to be understood that individual nano-particles may agglomerate into low density µm to multi-pm size agglomerates, with a typical agglomerate size ranging from about <NUM> to about <NUM>. However, these agglomerates quickly break apart into the primary particles during mixing of the flow aid with the host metal.

Magnetite (Fe<NUM>O<NUM>) Nano-Powder having an average primary particle size of about <NUM> to <NUM> was procured from Nanum Nanotecnologia. As stated above, individual nano-particles may agglomerate into low density µm to multi-pm size agglomerates. However, these agglomerates quickly break apart into the primary particles during mixing of the flow aid with the host metal.

Build material composition sample <NUM> was made by mixing the Ferric Oxide Nano-Powder Flow Additive at <NUM> weight percent with the <NUM> host metal powder for <NUM> hours. Build material composition sample <NUM> was made by mixing the Magnetite Nano-Powder Flow Additive at <NUM> weight percent with the <NUM> host metal powder for <NUM> hours. Build material composition sample <NUM> was made by mixing the Ferric Oxide Nano-Powder Flow Additive at <NUM> weight percent with the <NUM> host metal powder for <NUM> hours. Build material composition sample <NUM> was made by mixing the Magnetite Nano-Powder Flow Additive blended at <NUM> weight percent with the <NUM> host metal powder for <NUM> hours.

A Granupack density tester tap (available from Granutools, www. granutools. com) was used to evaluate the powder flowability of the build material composition samples. As shown in <FIG>, the build material composition sample <NUM> had a Hausner Ratio of about <NUM>. The build material composition sample <NUM> had a lower Hausner Ratio than the baseline build material composition, but build material composition sample <NUM> was still considered non-spreadable. As shown in <FIG>, build material composition sample <NUM> had a Hausner Ratio of about <NUM>. Build material composition sample <NUM> had a slightly higher Hausner Ratio than build material composition sample <NUM>; and build material composition sample <NUM> was considered non-spreadable. As shown in <FIG>, build material composition sample <NUM> had a Hausner Ratio of about <NUM>. Build material composition sample <NUM> had a lower Hausner Ratio than build material composition samples <NUM> and <NUM>; and build material composition sample <NUM> was considered spreadable. As shown in <FIG>, build material composition sample <NUM> had a Hausner Ratio of about <NUM>. Build material composition sample <NUM> had a lower Hausner Ratio than build material composition samples <NUM> and <NUM>. Build material composition sample <NUM> had a slightly higher Hausner Ratio than build material composition sample <NUM>; however, build material composition sample <NUM> was considered spreadable.

As shown in <FIG>, the <NUM> weight percent addition of the iron oxide (FeOx) flow additives lowered the Hausner Ratio of build material composition sample <NUM> and build material composition sample <NUM> compared to the host metal powder without any flow additive; but the flowability improvement was not enough to make the powder reliably spreadable, for example for a 3D printing process. However, the addition of the iron oxide (FeOx) flow additives at <NUM> weight percent lowered the Hausner Ratio below <NUM>, and made it feasible to spread build material composition sample <NUM> and build material composition sample <NUM> in uniform thin layers for reliably successful usage in a 3D printing process.

A 3D printing process, including layer patterning with a binder agent and heating, was used to make blanks for hardness testing. The blanks were tested with a Vickers Hardness tester. Vickers Hardness is a measure of the hardness of a material, calculated from the size of an impression produced under a load by a pyramid-shaped diamond indenter. Vickers Hardness is normally reported without units, however the units of Vickers Hardness number is kilograms-force per square millimeter (kgf/mm<NUM>). Hardness is a resistance to plastic deformation. Ultimate tensile strength is a measure of the maximum stress that a material can withstand while being stretched before breaking. Hardness has a strong correlation with ultimate tensile strength.

The baseline build material composition described above was not used to make the SS316L control blank because the host metal powder (alone) had insufficient spreadability for the 3D printing process. The SS316L powder used to make the SS316L control blank was a grade -<NUM> gas atomized powder from "Additive Metal Alloys Ltd. ", (average particle Diameter was <NUM>-<NUM>). A round particle shape and narrow particle size range gave the desired flowability without being classified, and without a flow additive. As used herein, "classified" means fine particles were removed from the SS316L powder. A Vickers Hardness test result from the SS316L control blank is labeled "SS316L" in <FIG>.

Build material composition sample <NUM> was used in the same 3D printing process (with a binder agent and heating) to make blanks. The intermediate structure for the control blank was placed in the oven together with the intermediate structure for the SS316L+FA blank. The 3D printing process included a debinding hold at <NUM> and <NUM>; a sinter hold at <NUM> with hydrogen gas to reduce oxides and carbon; and a final sinter at <NUM>. The Vickers Hardness test result for the blank made from the SS316L+FA blank is labeled "SS316L+FA" in <FIG>.

<FIG> is a column graph depicting the Vickers Hardness test results for the SS316L and SS316L+FA blanks. As shown in <FIG>, the Vickers Hardness for SS316L was about <NUM> kgf/mm<NUM>; and the Vickers Hardness for SS316L+FA was about <NUM> kgf/mm<NUM>. Thus, the Vickers Hardness for the blank made from the build material composition sample <NUM> (SS316L+FA) was within <NUM>% of the Vickers Hardness for the control specimen with no flow additive. The error bars in <FIG> were constructed using <NUM> standard deviation from the mean. As stated above, hardness has a strong correlation with ultimate tensile strength. The SS316L and SS316L+FA blanks have similar Vickers hardness test results. The similarity of ultimate tensile strengths of test specimens machined from the SS316L and SS316L+FA blanks is confirmed by the tests results disclosed below. The results shown in <FIG> indicate that the flow additive improves the flowability of the baseline build material composition, but does not deleteriously affect the hardness of the part formed.

The blanks from the Vickers Hardness tests were machined into tensile test specimens according to DIN <NUM> - B <NUM> x <NUM>. The test specimens were tested according to ASTM E8 / E8M-16a, Standard Test Methods for Tension Testing of Metallic Materials, ASTM International, West Conshohocken, PA, <NUM>, www. Test results from the SS316L control specimens are labeled "SS316L" in <FIG>, and <FIG>. Test results from the SS316L+FA specimens are labeled "SS316L+FA" in <FIG>, and <FIG>.

<FIG> is a column graph depicting the Ultimate Tensile Strength (UTS) test results for the SS316L and SS316L+FA test specimens. As shown in <FIG>, the mean UTS for SS316L was about <NUM> MegaPascals (MPa); and the mean UTS for SS316L+FA was about <NUM> MPa. The ASTM A240 standard for UTS (<NUM> MPa) is shown as a dashed horizontal line in <FIG>. Thus, the mean UTS for the specimen with the flow additive was within <NUM>% of the mean UTS for the control specimen with no flow additive, and well above the ASTM A240 standard. The error bars in <FIG> were constructed using <NUM> standard deviation from the mean.

<FIG> is a column graph depicting the Yield Strength test results for the SS316L and SS316L+FA test specimens. As shown in <FIG>, the mean Yield Strength for SS316L was about <NUM> MegaPascals (MPa); and the mean Yield Strength for SS316L+FA was about <NUM> MPa. The ASTM A240 standard for Yield Strength (<NUM> MPa) is shown as a dashed horizontal line in <FIG>. Thus, the mean Yield Strength for the specimen with the flow additive was within <NUM>% of the mean Yield Strength for the control specimen with no flow additive, and well above the ASTM A240 standard. Similarly to the error bars in <FIG>, the error bars in <FIG> were constructed using <NUM> standard deviation from the mean.

<FIG> is a column graph depicting the Percent Elongation test results for the SS316L and SS316L+FA test specimens. As shown in <FIG>, the mean Percent Elongation for SS316L was about <NUM>%; and the mean Percent Elongation for SS316L+FA was about <NUM>%. The ASTM A240 standard for Percent Elongation (<NUM>%) is shown as a dashed horizontal line in <FIG>. Thus, the mean Percent Elongation for the specimen with the flow additive was within <NUM>% of the mean Percent Elongation for the control specimen with no flow additive, and well above the ASTM A240 standard. Similarly to the error bars in <FIG>, the error bars in <FIG> were constructed using <NUM> standard deviation from the mean.

These results indicate that the flow additive improves the flowability of the baseline build material composition, while producing final objects with comparable strength properties which meet standard specifications (ASTM, MPIF, etc.).

To form other examples of the build material composition (referred to as "BMC" in Table <NUM>), the metal oxide flow additives shown in Table <NUM> can be mixed with the respective host metals shown in Table <NUM>. The amount of the metal oxide flow additive in these prophetic examples can range from about <NUM> wt% to about <NUM> wt%, with the remainder of the BMC being the host metal. Table <NUM> also shows the sintering temperature of the particular host metal and the environment that can be used in a furnace for reducing the particular metal oxide flow additive during heating. It is believed that these prophetic examples are compatible with the binder agent that can be used in 3D printing and are also stable at room temperature.

It is to be understood that the ranges provided herein include the stated range and any value or sub-range within the stated range, as if the value(s) or sub-range(s) within the stated range were explicitly recited. For example, a range from <NUM> weight percent to about <NUM> weight percent should be interpreted to include the explicitly recited limits of <NUM> weight percent to about <NUM> weight percent, as well as individual values, such as <NUM> weight percent, <NUM> weight percent, <NUM> weight percent, etc., and sub-ranges, such as from about <NUM> weight percent to about <NUM> weight percent, from about <NUM> weight percent to about <NUM> weight percent, etc. Furthermore, when "about" is utilized to describe a value, this is meant to encompass minor variations (up to +/- <NUM>%) from the stated value. As used herein, the term "few" means about three.

In describing and claiming the examples disclosed herein, the singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise.

Claim 1:
A build material composition, comprising:
a host metal (<NUM>) present in an amount ranging from about <NUM> weight percent to about <NUM> weight percent, based on a total weight of the build material composition;
a flow additive (<NUM>) present in an amount ranging from about <NUM> weight percent to about <NUM> weight percent, based on the total weight of the build material composition, wherein the flow additive (<NUM>) consists of a metal containing compound that is reducible to an elemental metal (<NUM>) in a reducing environment (<NUM>) at a reducing temperature less than or equal to a sintering temperature of the host metal (<NUM>), wherein the elemental metal (<NUM>) is capable of being incorporated into a bulk metal phase of the host metal (<NUM>) in a final metal object (<NUM>), wherein the flow additive includes a thermally decomposing precursor (<NUM>); wherein the thermally decomposing precursor (<NUM>) selected from the group consisting of a transition metal hydroxide, and a transition metal oxo-hydroxide, or a metal salt that is capable of producing a metal oxide upon thermal decomposition, the metal salt selected from Ni(NO<NUM>)<NUM>, NiSO<NUM>, Ni(SCN)<NUM>, Nd(NO<NUM>)<NUM>, Co(NO<NUM>)<NUM>, CoSO<NUM>, Co(SCN)<NUM>, Cr(NO<NUM>)<NUM>, CrSO<NUM>, Bi(NO<NUM>)<NUM>, VSO<NUM>, VOSO<NUM>, Pb(NO<NUM>)<NUM>, CuSO<NUM>, Cu(NO<NUM>)<NUM>, ZnSO<NUM>, Zn(NO<NUM>)<NUM>, Ag(NO<NUM>)<NUM>, Y(NO<NUM>)<NUM>, NiC<NUM>O<NUM>, FeC<NUM>O<NUM>; and
wherein the build material composition is spreadable, having a Hausner Ratio less than <NUM>.