Patent Description:
Combustion engines including internal combustion engines and gas turbine engines such as turbofans, turboshafts, and turboprops provide motive power in a wide variety of industries and applications. Ground-based combustion engines such as internal combustion engines and gas or steam turbines are also used for generating electrical and/or mechanical power. Advances in material compositions and processing have led to the use of more exotic materials in an effort to improve engine efficiency. A more refractory (e.g., more thermally resistant) material could be used to insulate a less refractory material. Thermal-resistance properties generally relate to resistance of a substrate to thermally induced phase changes.

Since a more refractory material is typically heavier, more expensive, and/or lacking in a key property (e.g., ductility) than less thermally resistant materials, it would be helpful to use a less refractory material where there is less risk of exposure of that material to extreme conditions. However, there have historically been at least two issues with this approach. First, there is often a mismatch in the coefficient of thermal expansion (CTE) between materials. If the mismatch is too large, it increases thermally induced strains and the risk of premature failure at the material interface. Second, a suitable, more refractory material may still have a relatively high thermal conductivity, and does not adequately insulate the otherwise suitable less refractory material.

The issues of differential CTE and high thermal conductivity arise, among other places, in the hot section of turbine engines. For example, combustor and turbine components are exposed to hot working gases and thus are often manufactured from combinations of specialized superalloys, ceramics, and/or composites. Turbine blades and combustor parts often require vapor or thin film deposition of a metallic bond layer to form a suitable interface between a less refractory superalloy substrate and a more refractory ceramic coating. The metallic bond layer mediates the different CTEs of the superalloy substrate and ceramic coating, while also controlling conduction of heat into the superalloy substrate. Despite a mediating metallic layer, substantial practical limitations remain on usable combinations of superalloy and/or refractory ceramic substrates in other applications.

To reduce weight and improve efficiency, it would be helpful to be able to utilize the best and most cost-effective materials in all parts of the engine. This would require a number of dissimilar materials to be in close proximity to each other. However, each material is likely to have different thermal and mechanical responses. Thus designers must be extremely careful about which materials can be used together, and particularly about combinations of materials which are to be physically joined or fastened together.

The article of <NPL>) discloses TLP for dissimilar materials, including ceramic and CMCs and mentions gas turbine engines, but does not disclose protrusions integrally formed, nor a thermal protection space.

A method for joining engine components according to claim <NUM> is provided.

<FIG>, <FIG>, <FIG>, <FIG> are according to the invention.

<FIG>, <FIG>, <FIG>, <FIG> are illustrative but are outside of the scope of the invention.

<FIG> shows a chart with method <NUM> for joining engine components with dissimilar materials. Embodiments of method <NUM> allow for joining of numerous combinations of components throughout internal combustion engines, gas and steam turbine engines, among others. By providing a joining method which minimizes different thermal and mechanical responses of each material, it becomes more likely that each component material can be better optimized. With careful design and selection of thermal protection structures and transient liquid phase (TLP) or partial transient liquid phase (PTLP) bonds, numerous combinations of metallic, ceramic, and composite components can be joined in a turbine or other combustion engines, which allows increased flexibility in structural material selection, reduced cooling demands, and increased efficiency. The combination of thermal protection structures and TLP or PTLP bonds can also reduce the number of fasteners, interference fits, or the like, in certain applications as they can provide robust bonds at relatively low temperatures.

Method <NUM> is a process for quickly and economically joining a variety of dissimilar materials in components for combustion engines including gas turbine engine components. Method <NUM> begins with steps <NUM> and <NUM> which respectively include providing first and second engine components. Each of the first and second engine components has respective first and second thermal protection surfaces formed from different first and second surface materials. The first surface material can have a higher melting point than the second surface material, making the first material "more refractory". The use of materials with different melting points or other thermally resistant properties can be done in the interest of reducing weight and/or cost.

Example classes of materials suitable for the first and second surfaces include ceramic materials, metallic materials, ceramic matrix composite (CMC) materials, and metal matrix composite (MMC) materials. Non-limiting examples of suitable ceramic and ceramic matrix materials can include aluminum oxide (Al<NUM>O<NUM>), silicon nitride (Si<NUM>N<NUM>), silicon carbide (SiC), tungsten carbide (WC), zirconium oxide (ZrO<NUM>), and combinations thereof. Examples of fibers for the CMC and/or MMC materials can include but are not limited to silicon carbide (SiC), titanium carbide (TiC), aluminum oxide (Al<NUM>O<NUM>), carbon (C), and combinations thereof. Other example fibers for MMC materials can include boron (B), boron carbide (B<NUM>C), graphite, steel, tungsten (W), and titanium boride (TiB<NUM>), and combinations thereof. Non-limiting examples of suitable metals for the metallic materials and/or the metallic matrix materials can include aluminum, nickel, iron, titanium, and alloys thereof. As is known in the case of composites, the fibers can be coated to prevent reaction with the surrounding matrix or to provide additional contact area. A number of these materials have favorable thermal and mechanical properties for turbine engine applications.

At step <NUM>, the first and second thermal protection surfaces are arranged in such a way as to have at least one thermal protection space therebetween. The thermal protection space can serve a number of simultaneous purposes, depending on the relative composition and properties of the two surface materials. First, a space between the surfaces may exist where one would not be feasible using other joining techniques, thereby reducing weight. In other applications, the thermal protection space can provide convective and/or impingement cooling to one or both materials. In one example of an engine case, holes could be formed through a less refractory surface, and which direct cooling air through the space toward the underside of a more refractory surface. In other examples, the arrangement could serve as a portion of a path for secondary air flow or leakage flow.

Step <NUM> of method <NUM> includes positioning a plurality of first thermal protection structures across the thermal protection space between the first thermal protection surface and the second thermal protection surface. The plurality of first thermal protection structures generally include one or more geometric shapes which, alone or together, bridge the space between the first and second thermal protection surfaces.

As part of step <NUM> the first component segment and the second component segment can be locally joined by forming a plurality of first TLP or PTLP bonds along corresponding ones of the plurality of first thermal protection structures between the first thermal protection surface and the second thermal protection surface. Depending on the degree of similarity or dissimilarity, the thermal protection structures may have one or more thermal protection elements which are integral to one, both, or neither of the first and second thermal protection surfaces. The thermal protection elements can additionally or alternatively be joined via one or more of the first TLP or PTLP bonds. Example configurations of TLP or PTLP bonds disposed along a thermal protection element are shown in <FIG>.

It will be recognized that, when referring to TLP bonding, the process can encompass one or both of a standard TLP bonding process and a partial transient liquid phase (PTLP) bonding process. PTLP bonding generally performs better than standard TLP bonding when joining two ceramic materials. References to TLP and/or PTLP bonding, when joining a metallic surface to a non-metallic surface, also include bonds with are technically termed active TLP bonds.

A combination of TLP or PTLP bonds along corresponding ones of the thermal protection structures minimize heat transfer by optimizing the conduction paths and empty thermal protection space between the first and second thermal protection surfaces. This permits the optimization of different combinations of materials, particularly in previously impractical areas of turbine engines, due to the compliance of the thermal protection structures and design flexibility of the TLP and PTLP bonding processes. Unlike other bonding processes such as sintering, diffusion bonding, etc., TLP and PTLP bonds can be used at or above the bonding temperature. This can prevent damage to the bonding/thermal protection surfaces and the components being joined.

Optional step <NUM> includes positioning a plurality of second thermal protection structures across the thermal protection space between the first thermal protection surface and the second thermal protection surface. In conjunction with step <NUM>, optional step <NUM> describes locally joining the first component segment and the second component segment by forming a plurality of second TLP or PTLP bonds along corresponding ones of the plurality of second thermal protection structures.

Using different geometries of thermal protection structures allows organization of different (e.g. first and second) thermal protection structures according to localized thermal gradients, hot spots, or the like. First and second geometries can be combined and used to reinforce high stress areas or to avoid high strain areas of one or both materials being joined. Thus the different thermal protection structures can be graded, arranged transversely to one another, or may be placed in discrete or localized regions of the thermal protection surfaces. Example geometries are shown and described with respect to <FIG>.

<FIG> show various configurations of first engine component <NUM> being joined to second engine component <NUM>. First engine component <NUM> has first thermal protection surface <NUM> formed from a first surface material, and second engine component <NUM> has second thermal protection surface <NUM> formed from a second surface material different from the first surface material. Thermal protection space <NUM> is disposed between first and second thermal protection surfaces <NUM>, <NUM>. These configurations are representative of method <NUM> in which thermal protection structures and TLP or PTLP bonds are formed between thermal protection surfaces. It should be noted that in <FIG>, the dimensions of bonds 214A, 214B are exaggerated for clarity.

Typically, the first surface material can have a higher melting point than the second surface material, making first thermal protection surface <NUM> "more refractory" than second thermal protection surface <NUM>. As a result there is substantial risk of mismatched thermal growth and/or thermal conduction when joining first surface <NUM> directly to second surface <NUM>. Thus in <FIG>, first and second surfaces <NUM>, <NUM> are spaced apart and space <NUM> is bridged with thermal protection structures 210A. Each structure 210A includes a single (e.g., first) thermal protection element 212A projecting from first thermal protection surface <NUM> into thermal protection space <NUM>. TLP or PTLP bond 214A is then formed along distal edge 216A of each thermal protection structure 210A and second surface <NUM> to locally join surfaces <NUM> and <NUM> across thermal protection space <NUM>.

<FIG>, outside of the scope of the invention, shows a similar configuration to <FIG>. The difference in <FIG> is that second thermal protection element 212B projects from second thermal protection surface <NUM> into thermal protection space <NUM> to form thermal protection structures 210B. In this instance a TLP or PTLP bond 214B is then formed along each distal edge 216B of thermal protection structures 210B and first surface <NUM>, thereby locally joining first and second thermal protection surfaces <NUM> and <NUM> across thermal protection space <NUM>.

In <FIG>, thermal protection structures 210C are defined by a combination of first thermal protection elements 212A and second thermal protection elements 212B. First and second thermal protection elements 212A, 212B each project from respective first and second thermal protection surfaces <NUM>, <NUM> partially into thermal protection space <NUM>. A TLP or PTLP bond 214A can then be added at each interface of distal edges 216A, 216B so that when second thermal protection elements 212B are properly aligned with first elements 212A, the bonded pair of opposed thermal protection elements define thermal protection structure 210C across space <NUM>.

In certain embodiments, such as in the examples of <FIG>, one or both thermal protection elements 212A, 212B can be integrally formed with corresponding first and second thermal protection surfaces <NUM>, <NUM>. This can be done, for example, when thermal conductivity between engine component(s) <NUM>, <NUM> is less of a concern and/or when materials of surfaces <NUM>, <NUM> have compatible CTE values. In these embodiments, integration of first and/or second thermal protection elements 212A, 212B can be readily incorporated into the production of engine component(s) <NUM>, <NUM>, such as by casting or additive manufacturing.

<FIG> shows an alternative arrangement, not claimed, in which thermal protection structures 210D are joined to first and second thermal protection surface <NUM>, <NUM> by TLP or PTLP bonds 214A and 214B. In other words, thermal protection structures 210D include separately formed thermal protection elements 212C which have respective TLP or PTLP bonds 214A, 214B joining first and second thermal protection surfaces <NUM>, <NUM> to edges 218A, 218B of thermal protection elements 212C.

In certain embodiments, thermal protection structures 210A-210D can be made from the same material as one of the first and second thermal protection surfaces <NUM>, <NUM>. Examples are described with reference to <FIG> above. In certain alternative embodiments, such as those shown in <FIG>, thermal protection structures 210D can be made from a third material which has different composition from the materials of first and second thermal protection surfaces <NUM>, <NUM>. The third material can be less refractory than the first material and more refractory than the second material. It can additionally or alternatively have a lower thermal conductivity (i.e., be thermally insulating) relative to one or both of the first and second materials.

The third material of thermal protection structures 210D can, for example, be a compliant bridging material. In an example of joining two different ceramic surfaces (either monolithic ceramics or matrix binders of CMC materials), the compliant bridging material can be a third ceramic which is compatible with the TLP or PTLP bonding process, examples of which is shown in <FIG>.

One or more of the configurations shown in <FIG> can be combined in the same joining region. For example, first engine component <NUM> can be joined to second engine component <NUM> using alternating instances or rows of two or more thermal protection structures 210A-210D so as to potentially enhance the overall bonding strength, and/or simplify the formation of the total number of TLP and/or PTLP bonds.

<FIG> respectively show a TLP bond and a PTLP bond joining a thermal protection element to an adjacent surface, such as is described in steps <NUM>/<NUM> of method <NUM>. In these embodiments, standard TLP bonds typically work best for joining metallic materials (the metal-to-metal joining being outside of the scope of the invention) while PTLP bonds typically work best for joining non-metallic materials (e.g., monolithic ceramic or ceramic matrix composite).

<FIG> depicts a standard TLP bond setup before joining thermal protection element <NUM> to adjacent bonding structure <NUM>. Adjacent bonding structure <NUM> can include, for example, one of thermal protection surfaces <NUM>, <NUM> shown in <FIG>. Alternatively, adjacent bonding structure <NUM> can include a surface of a second thermal protection element such as element 212B depicted in <FIG>.

Standard TLP bonds include interlayer <NUM> which is diffused into the two bonding surfaces (surfaces <NUM> and <NUM> in <FIG>). TLP interlayer <NUM> begins as a foil, powder, braze paste, or other suitable format for applying the metallic material (e.g., electroplating or PVD). Pressure can be applied to the TLP bond setup along with heat to raise the temperature of the TLP bond assembly. The bonding temperature is above the original melting point of interlayer <NUM> before formation of the TLP bond.

When performing the TLP process, solid TLP interlayer <NUM> begins to diffuse into the substrate materials <NUM>, <NUM> and then melts on reaching a suitable temperature. This temperature is either the direct melting point of interlayer <NUM> or, for each interface, it is the eutectic melting point of interlayer <NUM> and the respective substrate (e.g., <NUM> or <NUM>). This causes a degree of meltback into substrates <NUM>, <NUM> as equilibrium is attained. To control excessive meltback, TLP interlayer <NUM> can be provided with a similar composition to one of the substrates and/or can have a eutectic composition. After a sufficient bonding time, the liquefied interlayer <NUM> isothermally solidifies at the bonding temperature to form a standard TLP bond (e.g., bonds 214A, 214B shown in <FIG>). Optional homogenization of the TLP bond serves to further diffuse material into substrates <NUM>, <NUM>, and can increase the melting temperature of the resulting TLP bond.

<FIG> is an alternate bonding arrangement for thermal protection element <NUM> joined to adjacent bonding structure <NUM>. To bond non-metallic substrates, <FIG> shows a PTLP bond setup with interlayer <NUM> which can include first layer <NUM>, second layer <NUM>, and refractory layer <NUM>. Layers <NUM>, <NUM> are shown as individual layers, but one or both layers <NUM>, <NUM> can alternatively comprise multiple layers. Refractory layer <NUM> can be, for example, nickel or an alloy thereof. Alternative examples of suitable metals for refractory layer <NUM> include gold, cobalt, copper, niobium, palladium, platinum, silicon, tantalum, titanium, vanadium, and alloys thereof. Layers <NUM>, <NUM> are selected so as to wet the ceramic substrates (here, surfaces <NUM>, <NUM> when the bond assembly is heated to the bonding temperature. As layers <NUM>, <NUM> are heated, they cause a controlled degree of meltback to refractory layer <NUM> while also wetting the adjacent ceramic surfaces <NUM>, <NUM>. This wetting can be caused directly by layers <NUM>, <NUM> or by alloys formed on each side of the bond between layer <NUM> or <NUM> and refractory layer <NUM>, respectively. The bond assembly can then be maintained at a bonding temperature for a suitable time so as to isothermally solidify and optionally homogenize the bonding materials into the interlayer.

In addition to joining two different components, a hybrid component made of dissimilar materials can also be produced via TLP bonding of one or more thermal protection structures. A space is left between the materials to minimize thermal conduction and/or provide cooling of the more refractory component. The combination of a hybrid design and thermal protection structures allow for complex geometries at a reasonable cost.

The remaining figures show various suitable geometries for thermal protection structures and hybrid components formed according to the preceding description.

<FIG> show an array of first thermal protection structures <NUM> extending through thermal protection space <NUM> between first engine component <NUM> and second engine component <NUM>. In <FIG>, an irregular array of thermal protection elements <NUM> having a polygonal cross-section are integrally formed with first thermal protection surface <NUM>, in accordance with the invention. In a comparative example, <FIG> shows rectangular thermal protection elements <NUM> while TLP or PTLP bonds 414A, 414B join edges 418A, 418B of thermal protection elements <NUM> to respective thermal protection surfaces <NUM>, <NUM>.

<FIG> show an array of first thermal protection structures <NUM> extending through thermal protection space <NUM> between first engine component <NUM> and second engine component <NUM>. In <FIG>, a regular array of thermal protection elements <NUM> having a round or curved cross-section are integrally formed with first thermal protection surface <NUM> of first engine component <NUM>, in accordance wot the invention. In a comparative example, <FIG> shows circular thermal protection elements <NUM> with TLP or PTLP bonds 514A, 514B joining edges 518A, 518B of thermal protection elements <NUM> to respective thermal protection surfaces <NUM>, <NUM>.

<FIG> show similar arrays of first thermal protection structures having a rounded (circular, oval, etc.) cross-section. The array of protrusions can be of any cross-sectional shape, and can either be arranged in a regular grid (<FIG>) or an offset grid (<FIG>). The plurality of individual protrusions can extend generally normal to at least one of the first thermal protection surface and the second thermal protection surface. It will be appreciated that any regular, irregular, or random pattern of protrusions can be used, for example, to address hot spots, areas of potential fatigue or weakness or the like.

In certain embodiments, a second plurality of thermal protection structures is also positioned across the thermal protection space between the first and second thermal protection surfaces.

A first example, outside of the scope of the invention, of an assembly with multiple thermal protection structures is shown in <FIG> in which a plurality of corrugated ribs 612A serve as first thermal protection structures 610A across thermal protection space <NUM> between first engine component <NUM> and second engine component <NUM>. First TLP or PTLP bonds 614A, 614B are disposed along first thermal protection structures 610A to locally join first thermal protection surface <NUM> and second thermal protection surface <NUM>.

<FIG> also show a set of second, longitudinal ribs 612B arranged transversely to corrugated ribs 612A. A corresponding group of TLP or PTLP bonds 642A, 642B also locally join thermal protection surfaces <NUM>, <NUM>. In the absence of longitudinal ribs 612B, corrugated ribs 612A can define longitudinal passages along space <NUM>.

In <FIG> (outside of the scope of the invention), first thermal protection structures 710A, 710B also have a plurality of corrugated ribs 712A, 712B serving as first thermal protection structures 710A across thermal protection space <NUM> between first engine component <NUM> and second engine component <NUM>. As in <FIG>, first TLP or PTLP bonds 714A, 714B are disposed along first thermal protection structures 710A to locally join first thermal protection surface <NUM> and second thermal protection surface <NUM>.

In place of the longitudinal transverse ribs, <FIG> shows a set of second corrugated ribs 712B arranged transversely to first corrugated ribs 712A. <FIG> illustrates how both sets of ribs 712A, 712B can be disposed across thermal protection space <NUM> between first engine component <NUM> and second engine component <NUM>. Second TLP or PTLP bonds 742A, 742B are formed along respective corresponding ones of the first and second thermal protection structures 710A, 710B to locally join thermal protection surfaces <NUM>, <NUM>.

It will be appreciated that, with respect to <FIG> not all of the thermal protection structures are required to be ribs. For example, some or all of the ribs can be replaced by isolated projections as shown in <FIG>. Two final comparative examples are shown in <FIG>. In <FIG>, a plurality of first thermal protection structures <NUM> include an interconnected grid of repeating polygonal shapes extending across space <NUM>, between first and second thermal protection surfaces <NUM>, <NUM> of respective first and second engine components <NUM>, <NUM>. In <FIG>, a grid of ribs <NUM> are arranged into interlocking hexagonal shapes. Alternatively, ribs <NUM> can be arranged so that the hexagons are replaced with a rectangular grid or a triangular isogrid. TLP or PTLP bonds 814A, 814B complete connection of first and second components <NUM>, <NUM>.

Claim 1:
A method (<NUM>) for joining engine components, the method comprising:
providing a first engine component (<NUM>) including a first thermal protection surface (<NUM>) formed from a first surface materia (step <NUM>) ;
providing a second engine component (<NUM>) including a second thermal protection surface (<NUM>) formed from a second surface material different from, and less refractory than, the first surface materia (step <NUM>);
arranging the first and second thermal protection surfaces to have at least one thermal protection space (<NUM>) therebetween (<NUM>);
providing a plurality of first thermal protection structures (<NUM> A,C) across the thermal protection space between the first thermal protection surface (<NUM>) and the second thermal protection surface (<NUM>) step <NUM>), the first thermal protection structures each comprising a first thermal protection element (212A) projecting from the first thermal protection surface (<NUM>) into the thermal protection space (<NUM>); wherein each of the first thermal protection elements is integrally formed with the first engine component; and
locally joining the first engine component and the second engine component by forming a plurality of first transient liquid phase (TLP) or partial transient liquid phase (PTLP) bonds (214A) between the first thermal protection surface (<NUM>) and the second thermal protection surface (<NUM>) step <NUM>);
wherein at least one of the first surface material and the second surface material is selected from one of: a ceramic material and a ceramic matrix composite (CMC) material.