Patent Description:
The following discussion of the background to the invention is intended to facilitate an understanding of the invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge as at the priority date of the application.

Metal powders having a specific particle size and morphology are required for direct (additive) manufacturing processes such as cold spray, electron (laser) beam melting or continuous direct powder rolling processes. For example, titanium / titanium alloy powder used in electron (laser) beam melting preferably has a particle size of less than <NUM> with a narrow particle size distribution range. The particles are also required to have a regular morphology, such as spherically or cylindrically shaped powder particles, in order to provide high flowability.

Existing commercial titanium / titanium alloy powder production processes include hydride-de-hydride (HDH), gas atomization (GA), plasma-rotating electrode and plasma atomization (PREP) processes. Each of these processes requires the production of a solid Ti or Ti alloy feedstock product, such as a wire, bar, rod or billet, which is subsequently processed using brittle fracture, atomization, arcing or the like to produce the powder.

In the hydride-de-hydride process, solid Ti or Ti alloy feedstock are processed to remove contaminants, hydrogenated to produce brittle material and then ground under argon in a vibratory ball mill. The resulting particles are angular and measure between <NUM> and <NUM>. This process is time consuming, can introduce contamination, and produces particles having a sharp angular shaped morphology which are not favourable for additive manufacturing processes. In contrast, fine powders produced by plasma-rotating electrode and plasma atomization or gas atomisation methods are spherically shaped, but are extremely expensive to produce compared to hydride-de-hydride processed metal or metal alloy powders due to the high temperatures used to atomize the metal in these processes. Significant metal loss can also result from such process conditions.

It would therefore be desirable to provide an alternate method of producing a powder, preferably a powder having a desired morphology and size, suitable for additive manufacturing applications. <CIT> relates to a tantalum metal powder with controlled size distribution. The tantalum powder used has a polydispersed substantially bimodal basic lot agglomerate size distribution. The agglomerate powder was mixed by a Ross High-Shear Mixer and subsequently heat treated at thermal agglomeration temperature. The tantalum powder was subsequently sintered to form a porous body for use as a capacitor electrode. <CIT> relates to a hydrogen permeable membrane made of a metal composite material. <CIT> discloses a method of producing a spherical titanium powder by melting and resolidifying a comminuted precursor particulate.

The present invention provides a method of producing an additive manufacturing powder from a Ti or Ti alloy precursor particulate material comprising irregularly shaped Ti or Ti alloy particulate material according to independent claim <NUM>.

The present invention provides a novel powder manipulation method for producing a Ti or Ti alloy additive manufacturing powder from a precursor Ti or Ti alloy particulate material. The Ti or Ti alloy precursor particulate material is subjected to a high shear milling process to produce a powder having selected properties. The method produces a Ti or Ti alloy powder with a desirable powder morphology, particle size and particle size distribution (PSD) without the need for plasma-rotating electrode and plasma atomization, gas atomisation or hydride-de-hydride routes. The Ti or Ti alloy powder product is preferably processed to a suitable morphology and particle size for use as raw materials for the additive manufacturing (AM) processes, such as (but not limited to) Arcam & cold spray, or for other consolidation processes such as powder metallurgy (PM).

The method of the present invention has been developed for titanium / titanium alloys powders.

The powder product is processed by the method of the present invention to preferably produce a powder product that has at least one of: high flowability; high apparent/tap density; and low contamination, and preferably each of these properties.

With respect to flowability, it is preferred that the flowability of the powder product, and in particular Ti /Ti alloy powders, is improved from non-flowable to at most <NUM> seconds / <NUM><NUM>, preferably at most <NUM> seconds / <NUM><NUM>, more preferably at most <NUM> seconds / <NUM><NUM>, yet more preferably between <NUM> seconds / <NUM><NUM> and <NUM> seconds / <NUM><NUM>. Similarly, in some embodiments the apparent / tap density of the powder product is improved at least by <NUM>%, preferably by > <NUM>%.

With respect to contamination, it is preferred that the powder product is not contaminated with compounds or elements distinct/different from the desired metal or metal alloy (or combination thereof). In some embodiments, the powder product to be at least <NUM>% pure, more preferably at least <NUM> % pure.

In an exemplary application, the process is used to produce a powder product having a suitable morphology and particle size for use as raw materials for additive manufacturing (AM) processes or for other consolidation processes such as powder metallurgy (PM). In such applications, the process of the present invention mills the precursor particulate material to a powder to optimise the following powder characteristics: a high production yield of desired particle size in the produced powder; having high flowability; and having high apparent / tap density. It is also preferred for the powder product to have a low contamination. It should be appreciated that the ranges for these factors preferably fall within the values defined above.

The morphology and physical properties of precursor particulate material including that material's porosity and hardness affects the morphology, reduction of particle size and yield of the powder with desired particle size product. Fine powder production yields by high shear milling of harder and denser particulates are lower than that of softer and more porous particulates. Thus, where precursor particulate material are dense and hard, the milling yield may be significantly reduced compared to porous or soft particulate material.

Notwithstanding the above, the precursor particulate material can comprise any suitable starting material. In some embodiments, the precursor particulate material comprises a coarse particulate material. In some instances, the precursor material comprises, irregularly shaped particulates, which may be porous. The precursor material is preferably a metal, metal alloy or mixture thereof. Examples of precursor materials include Ti particulates produced from a Ti manufacturing process, such as Ti sponge or particulates produced from the Kroll process, or the Armstrong process. Another suitable precursor particulate material is the particulate or powder product produced from the TIRO process as detailed in international patent publication No. <CIT> and international patent publication No. <CIT>, of which the contents of each should be taken as being incorporated into the present specification by the above references.

In some embodiments, the precursor particulate material comprises a porous or soft particulate material. For example, CP grade titanium is softer than most titanium alloys (for example TiAl<NUM>V<NUM>). Therefore, high shear milling of CP grade titanium sponge will typically produce more fine and spherical shaped powder than high shear milling of most titanium alloys.

The precursor particulate material typically has a particle size distribution which is unsuitable for additive manufacturing processes or for powder metallurgy applications. The process of the present invention is therefore used to reduce the average particle size of the precursor particulate material. In some embodiments, the reduced particle has a particle size distribution in which at least <NUM>%, preferably <NUM>% of the particles have an average particle size <<NUM>. In some embodiments, the precursor particulate material has a particle size distribution in which at least <NUM>%, preferably <NUM>% of the particles have an average particle size <<NUM>. In some embodiments, at least <NUM>%, preferably at least <NUM>%, more preferably at least <NUM>% of the particles have an average particle size <<NUM>, preferably <<NUM>, and more preferably <<NUM>. In some embodiments, the above average particle size results for application of the process of the present invention to <NUM> precursor particulates.

It should be appreciated that the size of precursor particulate material which can be subjected to a high shear milling process is dependent a number of factors. The maximum size of particulates is related to the size of rotor used in the high shear mill process and also the morphology and the physical properties of particulates, including porosity, hardness and ductility. For example, the maximum particle size processable in a high shear milling process having a high shear milling device with a <NUM> diameter rotor would be about <NUM> diameter, where that precursor particulate material was a relatively porous particulate material. However, where that material has a suitably high porosity, it may be possible to process ><NUM> particulates. Exemplary porosities of the precursor particulate which assist high shear milling would be preferably > <NUM>%.

If the size of particulates is too large for high shear milling, then the particulates can be broken into smaller pieces by another comminution process prior to the high shear milling process. In such embodiments, the precursor particulate material may be subject to one or more pre-processing stage prior to undergoing the high shear milling process. These pre-processing stages include one or more comminution processes including crushing, grinding, milling or the like. In some embodiments, the pre-processing stages include the use of at least one of jaw crusher, cone crusher, hammer crusher, ball mill, vertical ring mill, roller mill, hammer mill, roller press, vibration mill, jet mill, press, or the like.

The high shear milling process of the present invention modifies the particle morphology of the precursor particulate material from an irregular shape to powder product having a substantially spherical shaped particles. The particle morphology of the powder product comprises a substantially) spherical shaped particles.

It should be appreciated that the morphology of the powder product is dependent on and can be controlled by changing the shear milling process conditions including at least one of shear milling rotor speed; shear milling time; or amount of precursor powder. For example, a precursor particulate material which is subject to a high shear milling process with higher milling speeds and/or longer milling times compared to another high shear mill process would typically include a higher proportion of spherical shape morphology.

Furthermore, the critical mass of powder also contributes to a change of powder morphology to spherical shape during high shear milling, because the collisions between powder particles and/or between powder particles and stator during the milling process contribute to morphology change of the processed powder.

The reduced average particle size of the powder product is a result of comminution of the precursor particulate material by the high shear milling. The particle size range which is produced by the high shear milling depends on milling conditions and the properties of particulates. The fine powder produced by the high shear milling process preferably has a particle size range in which at least <NUM>%, preferably at least <NUM>%, more preferably at least <NUM>% of the particles have an average particle size <<NUM>. In some embodiments, the fine powder produced by the high shear milling process has a particle size range in which at least <NUM>%, preferably at least <NUM>%, more preferably at least <NUM>% of the particles have an average particle size <<NUM>, and preferably <<NUM>. In some embodiments, the particle size range of <<NUM> is preferably ><NUM>%, and more preferably ><NUM>%. In some embodiments, the particle size ranges between <NUM> and <NUM> would be ><NUM>%, and preferably ><NUM>%. Milling yield of metal powder depends on physical property of the precursor particulates. For example, high shear milling of a highly porous titanium sponge produced from the Kroll, Armstrong and TIRO processes can in some embodiments result in a ><NUM> % production yield of sub-<NUM> micron powder.

The high shear milling process of the present invention includes at least one high shear milling device. A high shear milling device typically includes milling head which includes a rotatable rotor or impeller housed within a stator. The stator comprises a stationary cover or cage, preferably having a series of diagonal slots, which surrounds and encloses the rotor. The slots are preferably angled between <NUM> and <NUM> degrees to/ from the central longitudinal axis of the stator, more preferably between <NUM> and <NUM> degrees, yet more preferably between <NUM> and <NUM> degrees, and in some embodiments about <NUM> degrees to the central longitudinal axis of the stator. The slots can have any suitable dimension. In one embodiment, the slots have are <NUM> wide and <NUM> long. In operation, the milling head is brought into contact with the precursor particulates and the rotor (in combination with the stator) contacts and comminutes the precursor particulate material through shear and other mechanical forces. In some embodiments, the precursor particulate material is immersed in a liquid during the high shear milling process. This reduces the dust produced during the high shear milling process, improves the safety and reduces the risk of dust related explosion. The liquid preferably comprises at least one of water, alcohol, kerosene or other liquids.

Many high shear milling conditions were examined by the inventors to optimise the desired powder characteristics. Whilst not wishing to be limited to any one parameter, it was found that some important parameters affecting high shear milling processes include:.

In a second aspect not forming part of the present invention, there is provided a method of producing a powder for additive manufacturing and/or powder metallurgy applications from a precursor particulate material comprising:.

It is to be understood that this second aspect can include the above defined features of the first aspect.

In a third aspect not forming part of the present invention, there is provided a powder of particulate material produced from a method according to the first aspect.

The present invention will now be described with reference to the figures of the accompanying drawings, which illustrate particular preferred embodiments of the present invention, wherein:.

The present invention relates to powder manipulation method for producing an additive manufacturing powder from a Ti or Ti alloy precursor particulate material. The present invention is preferably used to produce cost effective, fine and highly flowable Ti or Ti alloy powders with minimum contamination by manipulating a coarse particulate precursor material which has a large particle size and irregularly shaped particles.

In the process of the present invention, a Ti or Ti alloy precursor particulate material is subjected to a high shear milling process to produce a powder having selected properties. In one exemplary application, the powder product is processed to a suitable morphology and particle size for use as raw materials for the additive manufacturing (AM) processes or for other consolidation processes such as powder metallurgy (PM).

It should be appreciated that the inventors of the present invention considered a large number of comminution processes for comminuting a coarse particular precursor material into a powder product having the desired particle size and morphology suitable for additive manufacture and other powder metallurgy application. The properties of high shear milled titanium powder were:.

A number of crushing, grinding and pressing processes were considered by the inventors to provide the above desired powder properties from a precursor particulate material. None of these processes were found to provide the required powder product properties. Despite the shortcomings of these and other similar comminuting processes, the inventors found that the application of a high shear milling process to the same precursor particulate material provided a powder product having the desired properties. High shear milling processes and conditions were then investigated in order to optimise the process to produce the powder product and morphology and average particle size characteristics required for additive manufacturing (AM) processes and other powder consolidation processes such as powder metallurgy (PM).

One type of high shear milling device used in the process of the present invention is shown in <FIG>. Three different sized shear milling devices are illustrated in <FIG> comprising (A) <NUM> diameter rotor and <NUM> diameter stator (or milling shaft); (B) <NUM> diameter rotor and <NUM> diameter stator and (C) <NUM> diameter rotor and <NUM> diameter stator. The high shear milling device used in the present invention can be sourced from a variety of manufacturers. However, in the particular illustrated embodiments, three devises are shown in <FIG>, namely (A) Small device (<NUM> diameter stator) and (B) medium device (<NUM> diameter stator) High Shear Mill are high shear mixing/milling devices from Ystral GmbH, <NUM> type (220V, <NUM>. 25A, <NUM>, 260W, Max: <NUM> rpm). Furthermore, (C) the large device (<NUM> diameter) is a high shear mixing/milling device from Ystral GmBH, comprising <NUM>/38E3 type (230V, <NUM>. 2A, <NUM>-60W, 1800W, Max: <NUM> rpm).

The illustrated high-shear mill devices <NUM> comprise a milling shaft 100A and a milling head <NUM> having a stator <NUM> and a rotatably driven rotor or impeller <NUM> enclosed within the stator <NUM>. As best illustrated in <FIG>, each stator <NUM> comprises a cage with a series of diagonal thin slots which is seated around the rotating rotor, through which material is drawn and engages through contact and rotation forces of the rotor <NUM>. For the illustrated embodiment shown in <FIG> and 1B(C), the stator <NUM> has a diameter of <NUM>, internal diameter of about <NUM> and includes <NUM> equispaced slots <NUM> which are <NUM> wide and <NUM> long comprising apertures which penetrate through the wall of the stator <NUM>. Each slot <NUM> is angled about <NUM> degrees from the axial axis running through the length of the stator <NUM>. The <NUM> internal diameter of the stator <NUM> provides around <NUM> gap between the outer edge of the rotor <NUM> and inner wall of the stator <NUM>. The stator <NUM> is preferably constructed from high tensile steel, for example <NUM> high tensile steel. The rotor <NUM> is driven by a motor <NUM>, in the illustrated case the motor is an electric motor, though it should be appreciated that any suitable driver or motor could be used. The high-shear mill device <NUM> is typically immersed in a tank or other receptacle <NUM> containing the material to be milled, as shown in <FIG>.

The rotor <NUM> can have a large variety of suitable configurations. <FIG> and <FIG> shows the rotor <NUM> configuration in detail. In this Figure, each of these rotors <NUM> has two or four spaced apart rotor blades 102A set on a drive disc 102B. With reference to the high shear milling devices shown in <FIG>, the rotor <NUM> has two blades 102A for each of these embodiments (rotor <NUM> having diameters <NUM>, <NUM>, <NUM>). A four blade rotor <NUM> is preferably used on larger diameter rotors, for example a rotor having a <NUM> diameter, such as shown in <FIG>. It should be appreciated that the rotor blades 102A rotate through rotation of drive disc 102B, impacting material which is drawn into the stator <NUM>.

Two alternate configurations used in the milling heads <NUM> of the high shear milling device shown in <FIG> are shown in <FIG> and <FIG>. Each of these rotors <NUM> has four spaced apart rotor blades 102A set on a drive disc 102B. Again, it should be appreciated that the rotor blades 102A rotate through rotation of drive disc 102B, impacting material which is drawn into the stator <NUM>. It should be appreciated that other rotor configurations can be used having a different number of rotor blades, blade configurations and the like.

<FIG> provides a cross-sectional view of two embodiments of the shear milling devices used in the shear milling process according to an embodiment of the present invention. As shown in <FIG> these embodiments have (A) <NUM> diameter rotor <NUM> and <NUM> diameter stator <NUM>, and B) <NUM> diameter rotor <NUM> and <NUM> diameter stator <NUM>. The particular rotors <NUM> of these devices are illustrated in <FIG>. As described above, the rotor <NUM> comprises two or four spaced apart rotor blades 102A set on a drive disc 102B. The rotor <NUM> in <FIG> comprises a two blade rotor <NUM> where the blades 102A are position <NUM> degrees apart. Each blade 102A extends relative to the central axis between R8 mm and R17. <NUM> (i.e. the out radius of the rotor <NUM>). Each blade 102A is <NUM> wide and <NUM> long (measured from the base side of drive disc 102B). However, it should be appreciated that any suitable dimensions could be used for a specific application, and the invention should not be restricted to this particular exemplified configuration. The rotor <NUM> in <FIG> comprises a four blade rotor <NUM> where the blades 102A are position <NUM> degrees apart. Each blade 102A extends relative to the central axis between R26 mm and R47. <NUM> (i.e. the out radius of the rotor <NUM>). Each blade 102A is <NUM> wide and <NUM> long (measured from the base side of drive disc 102B). However, it should be appreciated that any suitable dimensions could be used for a specific application, and the invention should not be restricted to this particular exemplified configuration. Each rotor <NUM> is operatively connected to drive shaft <NUM>, which in turn is connected to shaft coupler <NUM>, which (whilst not illustrated) is operatively connected to a motor. Operation of the motor drives rotation of drive shaft <NUM>, which in turn rotates the rotor <NUM> within the stator <NUM>.

Moreover, as shown in <FIG>, the stators <NUM> of each of these embodiments comprise cylindrical cages have the following configurations:.

Again, each stator <NUM> is preferably constructed from high tensile steel, for example <NUM> high tensile steel.

Without wishing to be limited to any one theory, a fluid (in this case with the precursor particles) flows into the bottom opening of the stator <NUM> and flows out through the slots <NUM> and undergo shear when one area of that fluid travels with a different velocity relative to an adjacent area. A high-shear mill device <NUM> therefore uses the high-speed rotor <NUM> to create flow and shear, resulting in comminution and deformation of the particles flowing through and around the rotor <NUM> and stator <NUM>. The tip velocity, or speed of the fluid at the outside diameter of the rotor <NUM> is higher than the velocity at the center of the rotor <NUM>, and it is this velocity difference that creates shear. The stator <NUM> creates a close-clearance gap between the rotor <NUM> and itself and forms an extremely high-shear zone for the material as it exits the rotor <NUM>.

As shown in <FIG>, a high shear milling apparatus <NUM> (in this case an experimental, laboratory apparatus) comprises the high shear mill device <NUM> installed and clamped in place on a stable stand <NUM> with the milling head <NUM> inserted into a mixing container, in the illustrated case, jar <NUM>. The jar <NUM> includes a cover <NUM> to seal the precursor particulates and powder product within the jar <NUM>. As the process of the present invention concerns milling a particulate material into a powder, the precursor particulates are immersed in a fluid, typically one of water, an alcohol, or kerosene, when milled within the jar <NUM>, to reduce the production of fine dust during milling. This reduces the dust produced during the high shear milling process, improves the safety and reduces the risk of dust related explosion.

In operation, the milling head <NUM> is brought into contact with the precursor particulates and the rotor <NUM> in combination with the stator <NUM> of the milling head <NUM> contacts and comminutes the precursor particulate material through shear and other mechanical forces as described above.

It should be appreciated that persons skilled in the art would understand that the laboratory scale device <NUM> and apparatus <NUM> shown in <FIG> and <FIG> could be scaled up to an industrial scale using for example larger high shear milling devices, and a number of parallel or series arranged devices.

As can be appreciated, a number of design factors can affect the high shear milling process include the diameter of the rotor and its rotational speed, the distance between the rotor and the stator, the duration of milling, and the number of high shear milling devices used. These factors and other properties of the process of the present invention will be demonstrated in the following examples:.

The method of the present invention has been developed primarily for titanium / titanium alloys powders, and as such the following examples demonstrate that particular application.

High shear milling yields were examined as a function of mixing speed (mixer rpm) to determine the effect of mixing speed on particle size reduction and particle size distribution.

A laboratory scale, bench top high shear milling apparatus <NUM> (as shown in <FIG>) was used to mill <NUM> batches of Ti particulates. The details of the specimens for the Ti-<NUM> titanium powder experimental runs are provided in Table <NUM>.

As shown in <FIG>, the high shear mill <NUM> apparatus contains high shear milling device <NUM>, having a milling head <NUM> comprising a stator <NUM> and enclosed rotor <NUM>. Rotation of the rotor is driven by an electric motor <NUM> via a drive shaft (not shown in <FIG>). The high shear milling device <NUM> is installed on a stable stand <NUM>. The milling head is designed to be received within a container, in this case milling jar <NUM>. The jar <NUM> includes a cover <NUM> to seal the precursor particulates and powder product within the jar <NUM>. In use, a specified amount of a milling liquid (as specified in the respective example run), and the precursor particulates to be milled are placed in a jar. The total amount of the mixture is ideally less than half of the jar height to prevent over spilling during milling. The milling head <NUM> of the high shear mill device <NUM> is lowered to the milling jar <NUM>, with the end of the rotor <NUM> being spaced <NUM> apart from the bottom of the milling jar <NUM>. The high shear milling device <NUM> is then operated for a designated period, after which the device <NUM> is turned off and the the resulting slurry of milled particulates and milling liquid is removed from the jar <NUM> and dried for at least <NUM> hours in a vacuum oven at <NUM>.

After being dried, the resulting powder is placed in a stack of sizing sieves (of a particle sizing sieve arrangement) which was mounted and vibrated on a vibrating table for <NUM> hour to separate the powder into the respective size fractions.

The resulting particle size distribution of high shear milled powder is shown in Table <NUM>.

A comparison of the above resultant particle size distributions indicates that more fine powder is produced using higher milling speeds.

High shear milling yields were examined as a function of milling time to determine the effect of mixing speed on particle size reduction and particle size distribution.

A laboratory scale, bench top high shear milling apparatus <NUM> (as shown in <FIG>) was used to mill <NUM> batches of Ti particulates. The high shear milling conditions for the Ti-<NUM> titanium powder experimental runs are provided below:.

The same high shear milling device was used as described and operated in Example <NUM>. After high shear milling, the resulting slurry of particles and milling liquid was dried for at least <NUM> hours in a vacuum oven at <NUM>.

The particle size distributions of Ti-2a, Ti-2b and Ti-2c experimental runs are shown in Table <NUM>.

It was identified from analysis of the particle size distribution of Ti-<NUM> after high shear milling that the longer period of high shear milling was, the higher portion of fine particles was produced.

After <NUM> minutes of high shear milling, ~<NUM> wt% of <NUM> to <NUM> and ~<NUM> wt% of <<NUM> powder were produced (total ~<NUM> wt% of <<NUM>).

High shear milling of titanium particulates was undertake at two different circumferential speeds (<NUM> and <NUM> diameter rotors, <NUM> and <NUM> diameter stators respectively at <NUM>,<NUM> rpm, see <FIG> and corresponding description above) to determine the effect of rotor and stator size on particle size reduction and particle size distribution.

The same high shear milling device was used as described and operated in Example <NUM>. In this case, the mixture of Ti powder and isopropanol was placed in a plastic milling jar. Milling was undertaken in a fume cupboard with compress air blown over the top of the container to disperse the alcohol fume. The mixer was also earthed.

After operating the high shear mill for the designated time (<NUM> and <NUM> hours), the resulting slurry of particles and milling liquid was dried in a vacuum oven at <NUM> for at least <NUM> hours. The resulting dried powder was then placed in a sieve sizing apparatus, which was placed in a vibrating table for <NUM> hour to separate the powder into the respective size fractions.

The results after sieving are shown in Table <NUM>:.

The yield of the production of < <NUM> Ti powder from coarse titanium particulates after high shear milling with a <NUM> diameter rotor was a half of that with <NUM> diameter rotor. This indicated that the high shear milling experimental run with higher circumferential speed produced more fine powder.

High shear milling yields were examined as a function of batch amount to determine the effect of mixing speed on particle size reduction and particle size distribution.

A laboratory scale, bench top high shear milling apparatus <NUM> (as shown in <FIG>) was used to mill two different batch sizes of Ti particulates. The milling conditions for the Ti-<NUM> titanium powder experimental runs are provided below:.

The milling process was same described in Example <NUM>.

The production yield of <<NUM> Ti powder from milling a larger amount of Ti powder (<NUM>, Ti-4b) under the same milling conditions was significantly lower than that of Ti-4a. This indicates that milling batch size can affect the particle size distribution, and in particular smaller batches are preferred to larger batches for a desired production yield of specified particle size powder.

High shear milling yields were examined as a function of the gap distance between rotor and inside wall of the stator to determine the effect of the gap distance on particle size reduction and particle size distribution.

It was identified from various high shear milling of titanium particulates that the gap distance between the rotor and a stator is an important parameter to obtain high yields of fine powder. Therefore two different gap distances were examined, L1 and L2 (detailed below) where L1 <L2.

A laboratory scale, bench top high shear milling apparatus <NUM> (as shown in <FIG>) was used to mill <NUM> batches of Ti particulates. The milling conditions the Ti-<NUM> titanium powder experimental runs are provided below:.

The same high shear milling device was used as described and operated in Example <NUM>. After milling, the resulting slurry of particles and milling liquid was dried and sieved as described in Example <NUM>.

The result is shown in Table <NUM> and <FIG> which shows the particle size distribution of high shear milled Ti-<NUM> titanium powder as a function of gap distance between rotor and casing.

As seen in Table <NUM> and <FIG>, a small gap (Ti-5a) produced a lot more fine powder.

The particle morphology of the powder product from the high shear milling process was examined to determine the effect of the high shear milling process on particle morphology.

The morphology of the particulate before (T-6a) and after (T-6b) high shear milling was investigated using an optical microscope. The flowability, apparent density and tap density of the powder before and after high shear milling were also investigated using ASTM B8555-<NUM>, ASTM B703 and ASTM B527.

<FIG> show a comparison of the particle morphology before (T-6a) and after (T-6b) the high shear milling. As can be observed, the high shear milling process modified the morphology of the powder from an irregular shape to a spherical shape.

Powder morphology changes from irregular to spherical shapes after high shear milling are noticed in up to <NUM> micron size powder. Smaller than <NUM> micron powder which was high shear milled had angular shape morphology. This indicated that the critical mass of powder (to have enough impact energy to modify the surface of the particles) would an important factor to change their morphology to spherical shape during high shear milling in liquid, because morphology change of the powder would be caused by the collisions between powder particles, and the collisions between particle and rotor / stator during the milling process. Titanium powder which was high shear milled with higher milling speeds and longer milling times contain a higher proportion of spherical shape morphology.

Flowability measurements of two similar particle size range of titanium powders (before (as received) and after high shear milling) found that the flowability of the high shear milled titanium powder was increased from not flowable (as-received powders) to up to <NUM> seconds / <NUM><NUM>. As a comparison, the flowability of commercial spherical shape Ti /Ti alloy powders (produced by gas atomisation method) for EBM was <NUM> seconds / <NUM><NUM>. The apparent density and also tap density after high shear milling were also improved by more than <NUM>% (e.g. apparent density: from <NUM>/cm<NUM> to ><NUM>/cm<NUM>, tap density : from <NUM>/cm<NUM> to ><NUM>/cm<NUM>).

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described.

Claim 1:
A method of producing an additive manufacturing powder from a Ti or Ti alloy precursor particulate material comprising irregularly shaped Ti or Ti alloy particulate material , said method comprising:
subjecting the Ti or Ti alloy precursor particulate material to at least one high shear milling process comprising milling the material with at least one high shear milling device which includes a rotor configured to contact and comminute the Ti or Ti alloy precursor particulate material and a stator which extends substantially around the rotor,
thereby producing a Ti or Ti alloy powder product having a reduced average particle size and a particle morphology consisting essentially of spherically shaped particles.