POST DEPOSITION HEAT TREATMENT OF COATING ON SUBSTRATE

TECHNICAL FIELD

The disclosure relates to techniques for forming coating systems for high-temperature mechanical systems, such as gas turbine engines.

BACKGROUND

The components of gas turbine engines operate in severe environments. For example, the high-pressure turbine airfoils exposed to hot gases in commercial aeronautical engines typically experience surface temperatures of about 1000 degrees Celsius (° C.). Components of high-temperature mechanical systems may include a superalloy substrate, a ceramic substrate, or a ceramic matrix composite (CMC) substrate. In many examples, the substrates may be coated with one or more coatings to modify properties of the surface of the substrate. For example, superalloy, ceramic, or CMC substrates may be coated with a thermal barrier coating to reduce heat transfer from the external environment to the substrate, an environmental barrier coating to reduce exposure of the substrate to environmental species, such as oxygen, water vapor, or Calcium-Magnesium-Alumino-Silicate (CMAS) containing materials, an abradable coating to improve a seal between the substrate and an adjacent component, or combinations thereof.

SUMMARY

In some examples, the disclosure describes a method that comprises depositing a coating on a substrate to form an as-deposited coating, wherein the coating includes at least one of a thermal barrier coating (TBC) layer, an environmental barrier coating (EBC) layer, or an abradable coating layer; and heat treating the as-deposited coating at or above a first temperature for a first period of time following the deposition of the as-deposited coating on the substrate, wherein heat treating the as-deposited coating includes heating the as-deposited coating to or above the first temperature at a controlled heating rate, and wherein the controlled heating rate is selected such that the heat treated coating exhibits a compressive residual stress state upon cooling.

In some examples, the disclosure describes a system comprising a deposition device configured to deposit a coating on a substrate to form an as-deposited coating, wherein the coating includes at least one of a thermal barrier coating (TBC) layer, an environmental barrier coating (EBC) layer, or an abradable coating layer; a furnace configured to heat the as-deposited coating following deposition of the as-deposited coating by the deposition device; and a controller device configured to control the heat treatment of the as-deposited coating at or above a first temperature for a first period of time following the deposition of the as-deposited coating on the substrate, wherein heat treating the as-deposited coating includes heating the as-deposited coating to or above the first temperature at a controlled heating rate, and wherein the controlled heating rate is selected such that the heat treated coating exhibits a compressive residual stress state upon cooling.

The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual and schematic diagram illustrating an example system for forming a coating on a substrate in accordance with an example of the disclosure.

FIG. 2 is a conceptual block diagram illustrating an example article including an EBC layer and a bond layer on a substrate.

FIG. 3 is a conceptual block diagram illustrating an example article including an abradable layer, an EBC layer and a bond layer on a substrate.

FIG. 4 is a flow diagram illustrating an example technique for forming an article in accordance with an example of the disclosure.

FIGS. 5A-5D are plots showing four example post deposition heat treatments on a time versus temperature basis.

FIG. 6 is a flow diagram illustrating an example technique for evaluating heat treatment processes in accordance with an example of the disclosure.

FIGS. 7A and 7B are plots showing an example coated sample before and after heat treatment, respectively.

FIGS. 8-10 are images related to example experiments evaluating various aspects of the present disclosure.

DETAILED DESCRIPTION

The disclosure describes systems and techniques for forming and heat treating coating systems such as ceramic coatings employed for components in high temperature mechanical systems. Example coating systems may include abradable coatings, environmental barrier coatings (EBCs) and/or thermal barrier coatings. The coatings may be deposited on substrates such as, e.g., ceramic substrates, CMC substrates and/or superalloy substrates. The coating may be deposited using, e.g., thermal spray deposition, such as air plasma spraying, slurry deposition, or other suitable technique. The coating may be deposited on the substrate that function as components of gas turbine engines, e.g., jet engines or other aircraft engines, or other high temperature systems. As described herein, following deposition, the as-deposited coating system may undergo heat treatment on the substrate so that the heat treated coating exhibits a compressive residual stress state.

While examples of the present disclosure are predominantly described in the context of heat treatment of coating systems including abradable and/or EBC layers, examples of the present disclosure may include the heat treatment of coating system alternatively or additionally including one or more other layers such as thermal barrier coating layers.

EBC systems may be an important contributor to the success of CMCs in a high temperature system. For example, the EBCs may be configured to protect against oxidation, water vapor recession, and other deleterious reactions from damaging the structural CMC, e.g., during operation of the high temperature system. In some examples, EBCs may be employed for components of high temperature mechanical systems such as gas turbine engines to protect Si containing substrates such as silicon carbide (SiC)/SiC ceramic matrix composites (CMC) from water vapor attack. Rare earth silicates such as ytterbium di-silicate (YbDS) and mono-silicate (YbMS) are example EBC compositions for SiC based CMCs. When these rare silicates are thermally sprayed on a substrate, e.g., via the air plasma spray process, the material forming the deposited layer may be mostly in an amorphous state due to the rapid quenching from molten state to solid state of the particles upon impact with a substrate. This may be particularly true when the plasma entropy is high and most of the rare earth powder particles are melted going through the plasma.

Since the deposited EBC layer(s) may reach relatively high temperatures during operation in gas turbine engine systems, such as above 1200 degrees Celsius in an advanced engine high pressure turbine environment, the amorphous EBC material may crystallize over engine operating time, depending mostly on the coating temperature and hot time, among others. Put another way, the resulting amorphous structure may change to a crystalline structure over time when subjected to higher temperatures, e.g., during operation of a high temperature system. An uncontrolled transition from amorphous to crystalline structure over time may also result in volumetric changes and, thus, internal stresses in the EBC layer(s) (e.g., a rare-earth disilicate layer). In particular, in some examples, as the EBC structure changes from amorphous to crystalline, there may be shrinkage in the overall area. This may cause a build-up in stress on the EBC as well as the silicon bond coat. Eventually, the build-up in stress may reach a threshold and causes a crack to propagate to relieve the stress state.

To provide for a more consistent EBC before an engine including the EBC coated component enters into service, such components may go through a heat treatment process following deposition to crystallize the EBC. In some examples, the heat treatment process also has the additional advantages of healing micro defects in the EBC and, thus, increasing the hermeticity, stiffness and/or strength of the EBC.

As will be described in further detail below, the heat treatment of ceramic coatings, such as EBC, TBC, and/or abradable coating layers, during the manufacturing process may be used to influence and otherwise tailor the residual stress of the ceramic coating before the coated component is used in high temperature operation, e.g., similar to that used in metal components to control their surface residual stresses from processing to enhance their operational life. Ceramic coatings such as EBCs may be relatively brittle in their residual state, e.g., following thermal spraying or other deposition. Such brittle coatings may be relatively susceptible to cracking under residual stress or in combination with tensile stresses that may occur during operation in a high temperature environment. Thus, it may be beneficial to manufacture ceramic coatings in a manner in which the coating is in a compressive residual stress state, e.g., by compressing the coating relative to the residual state of the coating following deposition on a substrate. For example, for a ceramic coating that is in a compressive residual stress state, even when the coating experiences additional tensional or other stresses during operation, the coating may remain in a compressive state (e.g., a slightly less compressive state than the residual state) or in a relatively low tension state (e.g., below a threshold tension that may cause cracking of the coating).

In accordance with examples of the disclosure, systems and techniques are described that include controlling the heating rate (e.g., the rate at which the temperature is increased to the target heat treatment temperature) of a post deposition treatment process in a manner that causes the coating to be in a compressive residual stress state following the heat treatment (e.g., upon cooling from the heat treatment temperature). For example, the post deposition heat treatment of a EBC may be conducted where the rate of heating to an elevated heat treatment temperature (e.g., from room temperature or other lower ambient temperature following deposition) is selected so that the heat treated coating exhibits a target compressive residual stress upon cooling, e.g., as compared to a coating exhibiting tension in its residual state.

As will be described below, it has been found that the particular rate of heating during a heat treatment may influence whether or not the heat treated coating exhibits compression stress in its residual state. For example, heating the coating at a first heating rate to an elevated heat treatment temperature for may cause the coating to exhibit a compressive residual stress state following the heat treatment while heating the same coating at a second heating rate different from the first heating rate to the same elevated temperature and for the same time at the elevated temperature may cause the coating to not exhibit a compressive residual stress state following the heat treatment. Additionally, in some examples, different heating rates for heat treatments at the same elevated temperature and time may result in both coatings exhibiting a compressive residual stress state but of different magnitudes (e.g., with one of the coatings exhibiting greater compressive stress in the residual state than the other coating).

In this manner, by controlling the heating rate for a heat treatment process, such techniques may allow compressive stresses to be introduced into a coating during manufacturing of a coated component that is employed in a high temperature mechanical system, e.g., to provide for a coating that is less brittle or susceptible to cracking during operation in a high temperature environment. In addition to providing for a coating with a compressive residual stress state (e.g., as compared to non-compressive residual stress state), the magnitude of the compressive stress of a coating in its residual state may be tailored by selecting a specific heating rate for a heat treatment, e.g., a specific heating rate known to cause a compressive residual stress with the targeted magnitude.

In some examples, the disclosure relates to example techniques for controlling an EBC (or other coating such as an abradable coating and/or TBC) residual stress state by controlling the heating rates during its heat treatment. For example, example techniques may provide an avenue for tailoring the residual stress in EBC or other coating such that the residual stress is compressive with different magnitudes. A compressive EBC residual stress state may be preferred in some instances, e.g., as when the EBC coated components are employed in aircraft engines and subject to varying thermal mechanical loadings during engine operations, such as start-up, take-off, climb, cruise and landing. These different engine operating conditions, such as rapid engine power decrease, create temperatures distributions, can put the EBC coating into high tensile state. In addition, bond coat and/or topcoat creep in a coating system can also generate high tensile stresses in an EBC or other overlying layer. By using heat treatment so that an EBC or other overlying layer has a compressive residual stress state following the heat treatment, the compressive coating stress may also slow down the oxidant transport through the EBC (or other layer) (e.g., to reduce the oxidation rate of an underlying Si bond coat; and reduce CMAS infiltration into the EBC or other layer.

FIG. 1 is a conceptual and schematic diagram illustrating an example system 10 for depositing a coating on a substrate and subsequently heat treating the as-deposited coating. The heat treatment may be configured to control the residual stress of the heat treated coating (e.g., by causing the heat treated coating to exhibit a compressive residual stress state). As shown, system 10 includes deposition device 12, heat treatment furnace 14, and transfer device 16.

Deposition device 12 may be configured to deposit one or more layers of a coating system on a substrate to form a coated article, such as article 20 in FIG. 2, which includes coating 24 on substrate 22, or article 30 in FIG. 3, which includes coating 34 on substrate 22. In some examples, deposition device 12 may be configured to deposited coating 24 using a thermal spray process, a slurry deposition process, and/or other process suitable for depositing a coating, such as, an EBC and/or abradable coating. Example thermal spray processes may include suspension plasma spray, low pressure plasma spraying, plasma spray physical vapor deposition, and air plasma spraying. In one example, deposition device 12 may be configured to deposit the one or more layers of a coating system using a plasma spray process, such as an air plasma spray process. Coating 24 may be deposited via deposition device 12 in an atmosphere including, for example, air, an inert atmosphere, a vacuum, or the like. In some examples, the deposition of coating 24 by deposition device 12 may take place in a heated environment or may take place at room temperature. For ease of description, the operation of system 10 will primarily be described herein with regard to article 20 of FIG. 2 although other articles formed using system 10 are contemplated including article 30 of FIG. 3.

Furnace 14 may be configured to heat and maintain article 20 at a relatively high temperature following the deposition of layer(s) of a coating system using deposition device 12, e.g., to perform a post-deposition heat treatment on the coated substrate. Furnace 14 may include an internal cavity sized and otherwise configured to contain article 20 after the deposition of coating 24 on substrate 22. Any suitable type of furnace 14 may be used that is capable of functioning as described in this disclosure. Furnace 14 may be an air furnace or a box furnace. In one example, a box furnace may be used with a controllable heat source. In some examples, furnace 14 may include one or more suitable heat sources such as moly-disilicide and/or silicon carbide heating elements, although other types of heat sources are contemplated. In one example, a conveyor-belt furnace may be employed. In one examples, an induction system may be used to directly heat article 20 to deliver high heating rates. In some examples, article 20 may be heated for heat treatment using an oxy-fuel burner rather than a furnace.

Transfer device 16 may be configured to robotically transfer article 20 between furnace 14 and thermal spray device 12, as desired before and/or after the deposition of coating 24 via deposition device 12. In other examples, article 20 may be manually transferred from deposition device 12 to furnace 14 following the deposition of coating 24.

Controller device 18 may be configured as a control device that controls deposition device 12, furnace 14, and/or transfer device 16 to operate in the manner described herein. For example, controller device 18 may be configured to control the temperature, including heating rate and temperature of furnace 14, e.g., during the post-deposition heat treatment of article 20. Controller device 18 may be configured to control transfer device 16 to control the transfer of article 20 from deposition device 12 to furnace 14. Controller device 18 may be communicatively coupled to at least one of deposition device 12, furnace 14, and/or transfer device 16 using respective communication connections. Such connections may be wireless and/or wired connections. While controller device 18 is shown as a single device, in other examples, controller device 18 may be more than one controller device, such as, e.g., where each of furnace 14, deposition device 12 and transfer device 16 are controlled by different controller devices.

Controller device 18 may include, for example, a desktop computer, a laptop computer, a workstation, a server, a mainframe, a cloud computing system, or the like. Controller device 18 may include or may be one or more processors or processing circuitry, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Accordingly, the term “processor” and “processing circuitry” as used herein may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein. In addition, in some examples, the functionality of controller device 18 may be provided within dedicated hardware and/or software modules.

In one example, system 10 may be configured to form an article such as article 20 shown in FIG. 2, which includes coating 24 deposited on substrate 22. For example, system 10 may be configured to deposit one or more layers of coating 24 on substrate 24 using deposition device 12, e.g., by slurry deposition, air plasma spraying or other thermal spray deposition process. Following the deposition of coating 24 on substrate 22 by deposition device 12, article 20 may be moved to furnace 14 (e.g., via transfer device 16) for a post deposition heat treatment. As will be described further below, the post-deposition heat treatment in furnace 14 may be controlled by controller device 18 so that article 66 is at an elevated temperature (e.g., a temperature at or above the crystallization temperature of one or more layers of coating 24) for a desired duration of time. Controller device 18 may control the specific rate that the temperature is increased to reach the elevated heat treatment temperature. In some examples, the post-deposition heat treatment in furnace 14 may provide for a heat treated coating that exhibits compressive residual stress state upon cooling, e.g., based at least in part on the rate of temperature increase selected for the heat treatment.

FIG. 2 is a conceptual diagram illustrating an example article 20 including a substrate 22 and coating system 24 (also referred to as coating 24). Coating 24 includes an optional bond coat 26 and EBC layer 28. In some examples, article 20 may include a component of a gas turbine engine. For example, article 20 may include a part that forms a portion of a flow path structure, a seal segment, a blade track, an airfoil, a blade, a vane, a combustion chamber liner, or another portion of a gas turbine engine. Although not shown in FIG. 2, EBC layer 28 may exhibit a compressive residual stress state. As described herein, heat treatment of coating 24 may provide for the compressive residual stress state (e.g., based at least in part on the heating rate during the heat treatment).

Substrate 22 may include a material suitable for use in a high-temperature environment. In some examples, substrate 22 may include a ceramic or a ceramic matrix composite (CMC). Suitable ceramic materials, may include, for example, a silicon-containing ceramic, such as silica (SiO₂) and/or silicon carbide (SIC); silicon nitride (Si₃N₄); alumina (Al₂O₃); an aluminosilicate; a transition metal carbide (e.g., WC, Mo₂C, TiC); a silicide (e.g., MoSi₂, NbSi₂, TiSi₂); combinations thereof; or the like. In some examples in which substrate 22 includes a ceramic, the ceramic may be substantially homogeneous.

In examples in which substrate 22 includes a CMC, substrate 22 may include a matrix material and a reinforcement material. The matrix material may include, for example, silicon metal or a ceramic material, such as silicon carbide (SiC), silicon nitride (Si₃N₄), an aluminosilicate, silica (SiO₂), a transition metal carbide or silicide (e.g., WC, Mo₂C, TIC, MoSi₂, NbSi₂, TiSi₂), or another ceramic material. The CMC may further include a continuous or discontinuous reinforcement material. For example, the reinforcement material may include discontinuous whiskers, platelets, fibers, or particulates. Additionally, or alternatively, the reinforcement material may include a continuous monofilament or multifilament two-dimensional or three-dimensional weave, braid, fabric, or the like. In some examples, the reinforcement material may include carbon (C), silicon carbide (SIC), silicon nitride (Si₃N₄), an aluminosilicate, silica (SiO₂), a transition metal carbide or silicide (e.g., WC, Mo₂C, TiC, MoSi₂, NbSi₂, TiSi₂), or the like.

Substrate 22 may be manufactured using one or more techniques including, for example, chemical vapor deposition (CVD), chemical vapor infiltration (CVI), polymer impregnation and pyrolysis (PIP), slurry infiltration, melt infiltration (MI), combinations thereof, or other techniques.

Coating 24 may help protect underlying substrate 22 from chemical species present in the environment in which article 20 is used, such as, e.g., water vapor, calcia-magnesia-alumina-silicate (CMAS; a contaminant that may be present in intake gases of gas turbine engines), or the like. Additionally, in some examples, coating 24 may also protect substrate 22 and provide for other functions besides that of an EBC, e.g., by functioning as a thermal barrier coating (TBC), abradable coating, erosion resistant coating, and/or the like.

As illustrated in FIG. 2, optional bond coat 26 of coating 24 is on substrate 22. As used herein, “formed on” and “on” mean a layer or coating that is formed on top of another layer or coating, and encompasses both a first layer or coating formed immediately adjacent a second layer or coating and a first layer or coating formed on top of a second layer or coating with one or more intermediate layers or coatings present between the first and second layers or coatings. In contrast, “formed directly on” and “directly on” denote a layer or coating that is formed immediately adjacent another layer or coating, e.g., there are no intermediate layers or coatings. In some examples, as shown in FIG. 2, bond coat 26 of coating system 24 may be directly on substrate 22. In other examples, one or more coatings or layers of coatings may be between bond coat 26 of coating 24 and substrate 22.

Bond coat 26 may be between EBC layer 28 and substrate 22 and may increase the adhesion of EBC layer 28 to substrate 22. In some examples, bond coat 26 may include silicon and take the form of a silicon bond layer. In some examples, bond coat 16 may include silicon, a metal silicide, RE monosilicate, RE disilicate, hafnium silicate, mullite, SiC, a metal oxide or a mixture thereof. Bond coat 16 may be in direct contact with substrate 22 and EBC layer 28. In some examples, bond coat 26 has a thickness of approximately 25 microns to approximately 250 microns, although other thicknesses are contemplated.

In examples in which substrate 22 includes a ceramic or CMC, bond coat 26 may include a ceramic or another material that is compatible with the material from which substrate 22 is formed. For example, bond coat 26 may include mullite (aluminum silicate, Al₆Si₂O₁₃), silicon metal or alloy, silica, a silicide, or the like. Bond coat 26 may further include other elements, such as a rare earth silicate including a silicate of lutetium (Lu), ytterbium (Yb), thulium (Tm), erbium (Er), holmium (Ho), dysprosium (Dy), gadolinium (Gd), terbium (Tb), europium (Eu), samarium (Sm), promethium (Pm), neodymium (Nd), praseodymium (Pr), cerium (Ce), lanthanum (La), yttrium (Y), and/or scandium (Sc).

The composition of bond coat 26 may be selected based on the chemical composition and/or phase constitution of substrate 22 and the overlying layer (e.g., EBC layer 28 of FIG. 2). For example, if substrate 22 includes a ceramic or a CMC, bond coat 26 may include silicon metal or alloy or a ceramic, such as, for example, mullite.

In some cases, bond coat 26 may include multiple layers. For example, in some examples in which substrate 22 includes a CMC including silicon carbide, bond coat 26 may include a layer of silicon on substrate 22 and a layer of mullite, a rare earth silicate, or a mullite/rare earth silicate dual layer on the layer of silicon. In some examples, a bond coat 26 including multiple layers may provide multiple functions of bond coat 26, such as, for example, adhesion of substrate 22 to an overlying layer (e.g., EBC layer 28 of FIG. 2), chemical compatibility of bond coat 26 with each of substrate 22 and the overlying layer, a better coefficient of thermal expansion match of adjacent layers, or the like.

Bond coat 26 may be applied on substrate 22 using, for example, thermal spraying, e.g., air plasma spraying, high velocity oxy-fuel (HVOF) spraying, low vapor plasma spraying, suspension plasma spraying; physical vapor deposition (PVD), e.g., electron beam physical vapor deposition (EB-PVD), directed vapor deposition (DVD), cathodic arc deposition; chemical vapor deposition (CVD); slurry process deposition; sol-gel process deposition; electrophoretic deposition; or the like.

Coating 24 includes EBC layer 28, which may be configured to help protect substrate 22 against deleterious environmental species, such as CMAS and/or water vapor. EBC layer 28 may include at least one of a rare-earth oxide, a rare-earth silicate, an aluminosilicate, or an alkaline earth aluminosilicate. For example, EBC 28 may include mullite, barium strontium aluminosilicate (BSAS), barium aluminosilicate (BAS), or strontium aluminosilicate (SAS). In some examples, EBC 28 may include at least one rare-earth oxide, at least one rare-earth monosilicate (RE₂SiO₅, where RE is a rare-earth element), at least one rare-earth disilicate (RE₂Si₂O₇, where RE is a rare-earth element), or combinations thereof. The rare-earth element in the at least one rare-earth oxide, the at least one rare-earth monosilicate, or the at least one rare-earth disilicate may include at least one of lutetium (Lu), ytterbium (Yb), thulium (Tm), erbium (Er), holmium (Ho), dysprosium (Dy), gadolinium (Gd), terbium (Tb), curopium (Eu), samarium (Sm), promethium (Pm), neodymium (Nd), prascodymium (Pr), cerium (Ce), lanthanum (La), yttrium (Y), or scandium (Sc).

EBC layer 28 may be any suitable thickness. For example, EBC layer 28 may be about 0.005 inches (about 127 micrometers) to about 0.100 inches (about 2540 micrometers). In examples in which layer 28 is a non-abradable layer, layer 28 may have a thickness of about 0.001 inches (about 25.4 micrometers) to about 0.005 inches (about 127 micrometers). In other examples, layer 28 may have a different thickness.

FIG. 3 is a conceptual diagram illustrating another example article 30 including a substrate 22 and coating 34. Coating 34 and substrate 22 may be the same or substantially similar to that of coating 24 and substrate 22 of FIG. 2 and are similarly numbered. However, unlike that of article 20 shown in FIG. 2, coating 34 includes abradable layer 32 on EBC layer 28. In such a configuration, coating 34 may be configured such that abradable layer 32 has a greater porosity than EBC layer 28, and the porosity of abradable layer 32 may be provided such that the outer surface of abradable layer 32 is abraded, e.g., when brought into contact with an opposing surface such as a blade tip. Abradable layer 32 may be on EBC layer 28, which may provide for better adhesion of abradable layer 32 to optional bond layer 26 or substrate 22. In some examples, abradable layer 32 may be about 0.005 inches (about 127 micrometers) to about 0.100 inches (about 2540 micrometers) thick. In other examples, layer 32 may have a different thickness. Although abradable layer 32 is shown as being formed on EBC layer 28, in other examples, coating 24 of article 30 may not include EBC layer 28.

The composition of abradable layer 32 may be the same or substantially similar to that of the composition described above for EBC layer 28. Regardless of the composition or the thickness of EBC layer 28 or abradable layer 32 of FIGS. 2 and 3, EBC layer 28 and abradable layer 32 may include a plurality of voids. For example, EBC layer 28 and abradable layer 32 may have a porous microstructure or a columnar microstructure. A porous microstructure may include a plurality of pores (e.g., voids) within the layer material, and a columnar microstructure may include columns of the layer material extending from the surface of a substrate (or another coating layer) with elongated intercolumnar voids. A porous or a columnar microstructure may improve the in-plane strain tolerance and/or the thermal cycle resistance of layers 28 and 32. In some examples, an average minimum dimension of the voids, such as, for example, an average minimum diameter of a pore of a porous microstructure, may be about 0.1 micrometers (μm) to about 20 μm.

In some examples, layer 28 or layer 32 may include a porosity of more than about 10 vol. %, such as more than about 20 vol. %, more than 30 vol. %, or more than about 40 vol. %, where porosity is measured as a percentage of pore volume divided by total volume of the respective layer. When configured as a non-abradable layer, EBC layer 28 may include a porosity of more than about 1 vol. %, such as more than about 2 vol. %, more than 3 vol. %, or about 5 vol. % to about 10 vol. %, where porosity is measured as a percentage of pore volume divided by total volume of EBC layer 28. In some examples, EBC 28 may include a porosity of less than about 10%, such as about 1% to about 5%, where porosity is measured as a percentage of pore volume divided by total volume of EBC 28. The porosity of EBC 28 may be the porosity following the EBC heat treatment described herein. When configured as an abradable layer, abradable layer 32 may include a porosity of more than about 15 vol. %, such as more than about 25 vol. %, more than 35 vol. %, or about 25 vol. % to about 45 vol. %, where porosity is measured as a percentage of pore volume divided by total volume of layer 32. In some examples, abradable layer 32 may include a porosity of more than about 5%, such as about 7% to about 20% where porosity is measured as a percentage of pore volume divided by total volume of layer 32. The porosity of abradable layer 32 may be the porosity following the abradable coating heat treatment described herein. The porosity of abradable layer 32 may be greater than the porosity of EBC layer 28. In each case, the porosity of layers 28 and 32 may be measured using mercury porosimetry, optical microscopy or Archimedean method.

In some examples, substrate 22 includes a superalloy including, for example, an alloy based on Ni, Co, Ni/Fe, or the like. In examples in which substrate 22 includes a superalloy material, substrate 22 may also include one or more additives such as titanium (Ti), cobalt (Co), or aluminum (Al), which may improve the mechanical properties of substrate 22 including, for example, toughness, hardness, temperature stability, corrosion resistance, oxidation resistance, or the like.

In some examples, coatings 24 or 34 may additionally or alternatively include one or more thermal barrier coating (TBC) layers, e.g., that thermal protection and/or CMAS resistance to substrate 22. For example, in FIGS. 2 and 3, layer 28 may function as a TBC layer that provide thermal cycling resistance, a low thermal conductivity, erosion resistance, combinations thereof, or the like. In such examples, layer 28 may include zirconia or hafnia stabilized with one or more metal oxides, such as one or more rare earth oxides, alumina, silica, titania, alkali metal oxides, alkali earth metal oxides, or the like. For example, layer 28 may include yttria-stabilized zirconia (ZrO₂) or yttria-stabilized hafnia, or zirconia or hafnia mixed with an oxide of one or more of lutetium (Lu), ytterbium (Yb), thulium (Tm), erbium (Er), holmium (Ho), dysprosium (Dy), gadolinium (Gd), terbium (Tb), europium (Eu), samarium (Sm), promethium (Pm), neodymium (Nd), praseodymium (Pr), cerium (Ce), lanthanum (La), yttrium (Y), or scandium (Sc).

As one example, layer 28 may include a rare earth oxide-stabilized zirconia or hafnia layer including a base oxide of zirconia or hafnia and at least one rare-earth oxide, such as, for example, at least one oxide of lutetium (Lu), ytterbium (Yb), thulium (Tm), erbium (Er), holmium (Ho), dysprosium (Dy), gadolinium (Gd), terbium (Tb), curopium (Eu), samarium (Sm), promethium (Pm), neodymium (Nd), praseodymium (Pr), cerium (Ce), lanthanum (La), yttrium (Y), or scandium (Sc). In some such examples, TBC layer 28 may include predominately (e.g., the main component or a majority) the base oxide including zirconia or hafnia mixed with a minority amount of the at least one rare-earth oxide.

While layer 28 is shown at a single layer, in other examples, coating 24 or coating 34 may include multiple layers having the same or different compositions.

In cases in which layer 28 is a TBC layer, bond coat 26 may include any suitable material configured to improve adhesion between substrate 22 and layer 28. In some examples, bond coat 26 may include an alloy, such as an MCrAlY alloy (where M is Ni, Co, or NiCo), a β-NiAl nickel aluminide alloy (either unmodified or modified by Pt, Cr, Hf, Zr, Y, Si, and combinations thereof), a γ-Ni+γ′-Ni₃Al nickel aluminide alloy (either unmodified or modified by Pt, Cr, Hf, Zr, Y, Si, and combination thereof), or the like. The composition of bond coat 26 may be selected based on the chemical composition and/or phase constitution of substrate 22 and the overlying layer (e.g., layer 28 of FIG. 2). For example, if substrate 22 includes a superalloy with a γ-Ni+γ′-Ni₃Al phase constitution, bond coat 26 may include a γ-Ni+γ′-Ni₃Al phase constitution to better match the coefficient of thermal expansion of the superalloy substrate 22. In turn, the mechanical stability (e.g., adhesion) of bond coat 26 to substrate 22 may be increased.

Coating 24 and coating 34 may be deposited using a wide variety of coating techniques, including, for example, a thermal spraying technique such as plasma spraying or suspension plasma spraying, physical vapor deposition (PVD) such as EB-PVD (electron beam physical vapor deposition) or DVD (directed vapor deposition), cathodic arc deposition, slurry process deposition, sol-gel process deposition, or combinations thereof.

In some examples in which EBC layer 28 or abradable layer 32 has a columnar microstructure, layer 28 or layer 32 may be deposited on substrate 32 using a suspension plasma spray technique, an EB-PVD technique, a plasma spray physical vapor deposition (PSPVD) technique, or a directed vapor deposition (DVD) technique. In some examples, layer 28 or layer 32 including a columnar microstructure may include a dense vertically cracked (DVC) coating, which in some cases, may be deposited on substrate 22 using an air plasma spray technique.

As described herein, layers 26, 28, and/or 32 of coatings 24 and 34 in articles 20 and 30 may exhibit a compressive residual stress state, e.g., following a post-deposition heat treatment. In a compressive residual stress state, layers 26, 28, and/or 32 may be more resilient against tensional or other stresses during subsequent operation of articles 20 and 30 in a high temperature environment, e.g., to prevent cracking of coating 24/34 or other damage. In a compressive residual stress state, layers 26, 28, and/or 32 of coatings 24 and 34 may be more resistant to thermal mechanical stresses generated from engine operations and therefore lower propensity for cracking and coating loss. The compressive residual stress state of layers 26, 28, and/or 32 following the heat treatment may also slow down the oxidant transport through the respective layers (e.g., to reduce the oxidation rate of an underlying Si bond coat), and/or reduce CMAS infiltration into the respective layers and/or underlying layers.

The presence and/or magnitude of the compressive residual stress state for layers 26, 28, and/or 32 of coatings 24 and 34 may be observed and characterized using any suitable technique. As will be described with regard to FIGS. 7A and 7B, coating 60 may be formed on substrate 62, where the as-deposited coating 60 and substrate are substantially flat prior to heat treatment. Following a post-deposition heat treatment, the compressive residual stress state of coating 60 may cause substrate 62 to bend upwardly as shown in FIG. 7B (also shown in FIG. 8). Thus, such a property has been found to be indicative of a coating in a compressive residual stress state, e.g., following a post-deposition heat treatment of coating 60.

By applying a post-deposition heat treatment to the coating, the compression stress state of all or part of coatings 24 and 34 (e.g., layers 26, 28, and/or 32) may be increased. In some examples, the as-deposited coatings 24 and 34 may have a compression residual stress state but the post-deposition heat treatment may increase the magnitude of the compressive residual stress state. In other examples, the as-deposited coatings 24 and 34 may have a non-compression (e.g., tension) residual stress state but the post-deposition heat treatment may cause all or portions of coatings 24 and 34 to exhibit a compressive residual stress state.

The post-deposition heat treatment may heat the layer(s) and substrate 22 to an elevated temperature, e.g., within an oven or other suited environment. The layer(s) and substrate 22 be maintained at or above the heat treatment temperature for a specified amount of time, after which the layer(s) and substrate 22 are cooled, e.g., back to room temperature. During the heat treatment, the rate of heating to the elevated heat treatment temperature may be controlled to achieve a target compressive residual stress state. Some heating rates may result in heat treated layer(s) with compressive residual stress state while other heating rates may result in heat treated layer(s) with a non-compressive residual stress state (e.g., where the curvature of a sample such as that shown in FIG. 7A may be curved inwardly (opposite of that shown in FIG. 7B)). In some examples, different heating rates may result in different relative magnitudes of compressive residual stress state for layers 26, 28, and/or 32.

FIG. 4 is a flow diagram illustrating an example technique for forming a coating that on a substrate followed by a post deposition heat treatment, where the heat treatment is such that the heat treated layer(s) exhibited a compressive residual stress state, e.g., as compared to the as-deposited state of the coating prior to heat treatment. The technique of FIG. 4 will be described with respect to system 10 of FIG. 1 and article 20 of FIG. 2 for case of description only. A person having ordinary skill in the art will recognize and appreciate that the technique of FIG. 4 may be implemented using systems other than system 10 of FIG. 1, may be used to form articles other than article 20 of FIG. 2, or both. In some examples, the technique of FIG. 4 may be used to form article 30 of FIG. 3.

As shown in FIG. 4, substrate 22 may be positioned within deposition device 12 and controller device 18 may control deposition device 12 to deposit one or more layers of coating 24 on substrate 22 (40). For example, deposition device 12 may deposit bond layer 26 and EBC layer 28 by thermal spraying (e.g., air plasma spraying) or slurry deposition under the control of controller device 18 (40). In some examples, a tape casting process may be used to deposit one or more of layers 26 and 28. The temperature within deposition device 12 may be approximately room temperature or elevated above room temperature.

When coating 24 is deposited, EBC layer 28 and/or bond layer 26 may have a relatively high amorphous phase concentration, e.g., due to the high cooling rates/quenching of the particles upon impact with substrate 24. For example, the layer(s) of EBC system 68 may have an amorphous phase of at least about 70%, such as, at least about 85 wt %. Conversely, the layer(s) of EBC system 68 may have a crystalline phase of less than about 30%, such as less than about 15 wt %. As noted above, without a post-deposition heat treatment, the amorphous phase may change to a crystalline structure over time when subjected to higher temperatures, e.g., during operation of a jet engine. An uncontrolled transition from amorphous to crystalline structure with time may also result in volumetric changes and, thus, internal stresses in the layer(s).

Following deposition of coating 24 on substrate 22, article 20 may be transferred to furnace 14 by transfer device 16 for a post-deposition heat treatment (42). Once article 20 is within furnace 14, controller device 18 may control the temperature of furnace to heat treat article 20 by heating coating 24 to or above a selected temperature for a selected period of time (44). In some examples, the post-deposition heat treatment may take place before or after article 20 cools to room temperature following deposition. The post-deposition heat treatment temperature and duration within furnace 14 may be controlled by controller device 18 and may be selected to increase the crystalline phase concentration of EBC system 68 on substrate 24. For example, furnace 14 may be at a treatment temperature of at or above the crystalline temperature of the layer(s) of EBC system 68.

In accordance with some examples of the disclosure, the post-deposition heat treatment of coating 24 may be configured to cause coating 24 to exhibit a compressive residual stress state upon cooling. In some examples, the heat treatment may include increasing the temperature of coating 24 to or above the heat treatment temperature at a rate that has been determined to cause coating 24 to exhibit a compressive residual stress state upon cooling. The heating rate employed to achieve a target compressive residual stress state for coating 24 may be determined empirically, e.g., by testing the heat treatment conditions on samples of the same or similar coating like described with regard to FIG. 6. In some examples, the heating rate may be greater than 0.5° C./min, such as, greater than 5° C./min, greater than 10° C./min, greater than 15° C./min, about 0.5° C./min to about 20° C./min or about 1° C./min to about 15° C./min). In some examples, the heating rate may be less than about 20° C./min, such as less than 15° C./min, less than 10° C./min or as less than 5° C./min). In some examples, heating rates greater than 20° C./min may be difficult to achieve, e.g., for components with large volume/thermal mass to heat up uniformly. In some examples, coating 24 may be at approximately room temperature (e.g., about 23° C.) at the beginning of the heat treatment. The temperature of coating 24 may be increased (e.g., by heating in furnace 14) at the specified rate to the desired elevated heat treatment temperature. In some examples, the heat treatment temperature may be at or above about 500° C. to about 1500° C. Coating 24 may be held at or above the heat treatment temperature for a desired period of time (e.g., about 1 hour to about 100 hours). Controller device 18 may control furnace 14 to hold a substantially constant heat treatment temperature within furnace or a heat treatment temperature that varies within a prescribed range over a selected period of time.

In some examples, article 20 may be held within furnace 14 at the heat treatment temperature such that coating 24 reaches a temperature at or above the crystalline phase temperature of the one or more layers of coating 24. Article 20 may be held within furnace 14 at the heat treatment temperature such that EBC layer 28 and/or bond layer 26 reaches a temperature at or above the temperature at which the amorphous phase transitions to a crystalline phase. In the case of a rare earth disilicate material, the transition during the heat treatment may proceed from amorphous to alpha phase to beta phase (e.g., with the material be substantially all beta at the end of the heat treatment). In the case of a rare earth monosilicate material, the transition during the heat treatment may proceed from amorphous to X1 phase to X2 phase (e.g., with the material be substantially all X2 at the end of the heat treatment). Article 66 may be held within furnace 14 for heat treatment for a suitable amount of time to provide for a desired amount of crystalline phase in EBC system 68. In some examples, coating 24 in the as-deposited state prior to heat treatment includes at least about 40 volume percent amorphous prior to heat treatment. Following heat treatment, coating 24 may include less than about 10 volume percent of amorphous phase, such as less than about 5 volume percent amorphous phase or substantially free of amorphous phase, and/or greater than about 90 volume percent of crystalline phase, such as approximately 100 percent crystalline phase.

Following the post-deposition heat treatment, article 20 may be cooled within furnace 14 or outside furnace from that of the heat treatment temperature. In some examples, controller device 18 may control the rate of cooling of furnace 14 over a particle period of time such that article 20 cools at a controlled rate over the period of time, as compared to simply removing article 20 from furnace 14 and or simply turning off furnace 14 while article 20 is inside. In other example, controller device 18 may simply turn off the heating of furnace 14 or article 20 may be removed from furnace 14 into a cooler environment.

In some examples, in order to achieve and control desired temperature(s), system 10 may be configured to monitor the temperature of coating 24, substrate 22, and/or furnace 14 using one or more suitable temperature sensors (e.g., thermocouples) located to accurately measure temperature (e.g., in substantially real-time) during the described techniques. In some examples, such components may be thermocoupled during process development trials to confirm that the desired heating/cooling rates are as expected, with the measured temperatures in that particular furnace zone used for control afterwards.

As described herein, by employing a particular heating rate during heat treatment, coating 24 may exhibit a compressive residual stress state following the heat treatment (e.g., by increasing the compressive stress within coating 24 as compared to the as-deposited coating 24). Although not being bound by theory, it is thought that the heating rate (in combination with other heat treatment parameter such as heat treatment temperature, duration, and cooling rate) may influence the crystallization rates and/or phase transformation rates of coating 24. For example, different heat treatment conditions may lead to different crystallization rates and phase transformation rates, which can result in difference in compressive stress states for coating following heat treatment. Thus, different heating rates may cause different magnitudes of compressive residual stress states for a heat treated coating (or in some case no compressive stress at all). In one example a rare earth silicate coating may contract upon crystallization around 1050 degrees Celsius (the particular temperature may vary slightly depending on the composition), which may result in tensile stress in the coating at this stage. But as the heat treatment of the coating is continued, there is phase transformation from metastable ytterbium disilicate and monosilicate phases to their stable phases. This transformation may be the primary reason for volumetric expansion, which produce compressive stress in the coating upon completion of heat treatment. As noted above, different heat treatment conditions can lead to different crystallization and phase transformation rates can result in difference in compressive stress. In some examples, the compressive residual stress of coating 24 following the heat treatment using the selected heating rate may be measured using a synchrotron or other suitable instrument. The compressive stress state may be for induvial layers or for the layers of coating 24 in combination. For multiple layer coatings, stress levels for two layer system may be backed out. For three or four layer systems, the stresses may be estimated by in combination with each other, e.g., by lumping Si bond coating, EBC layer(s) with an abradable layer.

FIGS. 5A and 5B are plots showing two example post deposition heat treatments of article 20 in terms of temperature of coating 24 versus time during the heat treatment of article 20. Similar example heat treatment protocols may be conducted on other coatings, such as, coating 34 of article 30 shown in FIG. 3.

With reference to FIG. 5A, prior to the post deposition heat treatment, coating 24 may be at a relatively low temperature T (RT), e.g., room temperature or approximately 25° C. The heat treatment of coating 24 may begin at time t1 when coating 24 is heated, e.g., by placing article 20 in already heated furnace 14 and/or turning on furnace 14 while article 20 is within furnace 14 to heat up furnace 14 with article 20. Regardless, coating 24 is heated to increase the temperature of coating 24 at a relatively fast rate from temperature T (RT) to temperature T (HT) from time t1 to time t2. Although the ramp up of the temperature is shown to be approximately linear, it is understood that the rate of change may be non-linear. In some examples, the rate of temperature changes may be defined as the overall change in temperature (ΔTemp) divided by the difference in time between t1 and t2. In some examples, the rate of temperature change of coating 24 from time t1 to time t2 may be greater than 0.5° C./min, such as, about 1° C./min to about 15° C./min or about 1° C./min to about 20° C./min. As described herein, the rate of temperature change may cause one or more layers of coating 24 to exhibit a compressive residual stress state, e.g., as compared to the as-deposited layers.

Once coating 24 reaches the desired heat treatment temperature T (HT), coating 24 may be held at (or above) temperature T (HT) for the time period from time t2 to time t3. In some examples, T (HT) may be about 500° C. to about 1500° C., such as, about 900° C. to about 1300° C. or about 1000° C. to about 1300° C. In some examples, the duration from time t2 to time t3 (referred to as “hold time”) may be about 1 hour to about 100 hours. The duration of the heat treatment may be selected by observation of the changes in microstructure, phase equilibra via XRD, density measurements, permeability measurements, and the like. Using one or more of these techniques, a duration may be selected based on when the changes appear to stop or become more stable. In some examples, a higher heat treatment temperature may result in a shorter duration of the heat treatment. The heat treatment duration may be selected to allow enough time for the effects from the phase transformation described herein to provide for a desired compressive residual stress state following the heat treatment.

At time t3, the heat treatment may end and article 20 may be cooled, e.g., within furnace 14 or by removing article 20 from furnace, back to temperature T (RT) at time t4. The rate of cooling may be controlled or may be uncontrolled following the heat treatment.

In the example heat treatment of FIG. 5B, the heat treatment has the same initial temperature T (RT) and elevated heat treatment temperature T (HT) as the heat treatment of FIG. 5A. The heat treatment of coating 24 may begin at time t1 like in FIG. 5A when coating 24 is heated, e.g., by placing article 20 in already heated furnace 14 and/or turning on furnace 14 while article 20 is within furnace 14 to heat up furnace 14 with article 20. Regardless, coating 24 is heated to increase the temperature of coating 24 at a relatively slower rate from temperature T (RT) to temperature T (HT) from time t1 to time t5. The rate of change may define the rate of temperature change for the first segment of the heat treatment. Coating 24 may be held at temperature T (HT) for a selected duration of time of the first segment from time t5 to time t3, which is less that the duration in FIG. 5A. However, in other examples, the duration at T (HT) may be the same between the two heat treatment protocols. Like that of FIG. 5A, at time t3, the heat treatment ends, at which time coating 24 may be cooled as described above with regard to FIG. 5A until coating 24 reaches temperature T (RT) at time t4.

Despite the similarities between the heat treatments of FIGS. 5A and 5B, the residual stress state of coating 24 may be different after each heat treatment at least in part due to the different heating rates used to heat coating 24 to the elevated heat treatment temperature T(HT). For example, after the heat treatment of FIG. 5A, coating 24 may exhibit a compressive residual stress state of a first magnitude. Conversely, same coating 24 instead being heat treated as shown in FIG. 5B may exhibit a non-compressive residual stress state or a compressive residual stress state of a second magnitude different from the first. Such differences may be employed to generate a heat treated coating have a target compressive residual stress state. For example, during a manufacturing process, controller device 18 may be configured to control the heating rate of coating 24 following deposition so that the heat treated coating 24 exhibits a target compressive residual stress state. Although not being bound by theory, the different heating rates between the example of FIG. 5A and the example of FIG. 5B may cause different crystallization rates and/or phase transformation rates for the material of coating 24, and there are volume changes in both crystallization and phase transformation. For example, in some instances, faster heating rate can delay the onset of crystallization temperature and, in some examples, transformation temperature as well.

FIGS. 5C and 5D are plots showing two example post deposition heat treatments of article 20 in terms of temperature of coating 24 versus time during the heat treatment of article 20. Similar example heat treatment protocols may be conducted on other coatings, such as, coating 34 of article 30 shown in FIG. 3. The example heat treatment protocol of FIG. 5C may be similar to that of FIG. 5A. However, the heat treatment temperature T (HT′) for the example of FIG. 5C is less than the heat treatment temperature T (HT) example of FIG. 5A. Similarly, the example heat treatment protocol of FIG. 5D may be similar to that of FIG. 5A. However, the hold time (time from the end of ramp up (t5) to the start of the ramp down t6) for the example of FIG. 5D is longer the example of FIG. 5A. Additionally, the rate of cooling in the example of FIG. 5D is greater than the rate of cooling in the example of FIG. 5A.

Any suitable technique may be employed to identify which heating rates (e.g., in addition to other heat treatment parameters such as heat treatment temperature, duration, cooling rate, and/or the like) result in one or more target compressive stress states for a coating. FIG. 6 is a flow diagram illustrating an example technique for estimating or otherwise determining the influence of a heat treatment on a coating using a given heating rate with respective to the residual stress state of the heat treated coating. The technique will be described with regard to FIGS. 7A and 7B, which illustrate an example coating 60 on substrate 62 prior to heat treatment and following heat treatment, respectively. Coating 60 may be an example of coating 24 in articles 20 and 30 described above. The material of substrate 62 may be an example of substrate materials described for substrate 22 with respect to FIGS. 2 and 3.

As will be described further below, the technique of FIG. 6 includes heat treating a coating on a substrate, where the substrate only partially constrains the coating. The partial constraint may result from the properties of substrate 62. For example, the dimensions (e.g., thickness) and Young's modulus of substrate 62 may determine the degree that substrate 62 constrains coating 60. As shown in FIG. 7A, substrate 62 is substantially planar when coating 60 is initially deposited. The partial constraint of substrate 62 is such that coating 60 under compressive residual stress state will cause substrate 62 to curve in the manner shown in FIG. 7B, e.g., following a heat treatment that imparts a compressive residual stress state on coating 60.

As shown in FIG. 6, sample for evaluation may be formed by depositing coating 60 on substrate 62 (40), e.g., as described with regard to FIG. 4. The sample may be heat treated for a selected duration like described herein, wherein the heat treatment includes heating coating 60 at a selected heating rate to the elevated heat treatment temperature. Following the cooling of the sample, the curvature of the sample will be measured (54). If the curvature of the sample displays a positive curvature (e.g., where the ends of the substrate are directed downward in the position shown in FIG. 7B), the selected heating rate is associated with a compressive residual stress state (56). When associated with a compressive residual stress state, the heating rate may be identified (along with the other heat treatment parameters) as a heating rate that produces a compressive residual stress state in coating 60. Conversely, if the curvature of the sample does not display a positive curvature (e.g., where the ends of the substrate are directed upward or substrate does not display any curvature from the initial state), the selected heating rate is associated with a non-compressive residual stress state (58). When associated with a non-compressive residual stress state, the heating rate may be identified (along with the other heat treatment parameters) as a heating rate that does not produce a compressive residual stress state in coating 60. This information may be stored by controller device 18 for later retrieval, e.g., in a data look-up table.

The process of FIG. 6 may be repeated with numerous samples to heat treated coatings with the same composition using different specified heating rates (e.g., with the same heat treatment temperature and duration) to evaluate the different heating rates. Such a process may be used to identify different heating rates that result in coating 60 exhibiting a compressive residual stress state following heat treatment. Additionally, for the heating rates that result in positive curvature (compressive residual stress state), the height 64 of the curvature for each sample may be measured to quantify the curvature. This value may be used to determine the relative magnitude of the compressive stress between the different samples. For example, the greater the height 64 of a heat treated sample, the greater the compressive residual stress state. The magnitude of the compressive residual stress state imparted on a coating may be important. For example, if the compressive stress is too high, then coating interfacial shear failure mode may become dominant. If the compressive stress is too low, then there may not be much to negate/offset the tensile stresses generated from engine operations. The heights 64 for each respective heating rate (or other indicator of the relative magnitude of the compressive residual stress state measured during the process of FIG. 6) may be stored by controller device 18 for later retrieval.

Another indicator of relative magnitude of the compressive residual stress state for multiple sample may be the overall change of curvature before and after heat treatment. This value may be different that the height 64 shown in FIG. 7B, e.g., when the initial state of the sample is not planar. In other examples, the compressive stress magnitude may be determined using, e.g., the formulae described in Y. C. Tsui, T. W. Clyne, An analytical model for predicting residual stresses in progressively deposited coatings Part 1” Planar geometry, Thin Solid Films 306 (1997) 23-33; or A. Brenner, S. Senderoff, Calculation of Stress in Electrodeposits from the Curvature of a Plated Strip, J. Res. Natl. Bur. Stand. 42 (1949) 105-123.

In some examples, the heating rate (and other heat treatment parameters) that provide for a desirable or optimal compressive residual stress state for a coating following heat treatment may be identified by a direct residual stress measurement (e.g., for example coatings each undergoing a heat treatment with different parameter values such as different heating rates). In cases in which direct residual stress measurement is not available or practical, one may rely on other tests such as interlaminar tensile and thermal gradient tests to find the desirable/optimal residual stress state.

EXAMPLES

Various experiments and investigations were conducted to evaluate aspects of one or more examples of the disclosure. However, the disclosure is not limited by the experiments, investigation, or the corresponding description.

As a way to demonstrate different EBC residual stress states, two coated substrate samples were prepared. Each sample included a silicon bond coat, a rare earth silicate EBC layer, and rare earth silicate abradable layer (e.g., with a porosity of about 5% to about 35%) that were each thermally sprayed onto a CMC substrates. The substrates had a thickness of approximately 0.2 inches. The coating on the substrate had an overall thickness of approximately 0.05 inches. These two coated CMC substrates were then heat treated, with one sample being heated from room temperature at a rate of 1 degree Celsius per minute to 1200 degrees Celsius and the other being heated at a rate of 15 degrees Celsius per minute to 1200 degrees Celsius. Each sample was held at 1200 degrees Celsius for 2 hours before cooling down to room temperature at a rate of 15 degrees Celsius per minute.

The curvature before and after heat treatment for each sample was measured to determine the coating stress states of the samples. FIG. 8 is a photograph of the two samples from a side view following the heat treatment. The samples each displayed a positive curvature, indicating each coating was in a compressive residual stress state. Additionally, the larger curvature of the sample heated at a rate of 15 degrees Celsius per minute indicates higher coating stresses in the sample compared to the other sample. As noted above, the exact stress magnitudes can be calculated using the formulae noted above. Table 1 below shows the curvature change values for the two heating rates tested:

TABLE 1

Curvature Changes at Two Heating Rates during Heat Treatment

Heating
Curvature

Rate
Change

C/min
1/m

1
1.39

15
2.84

As indicated in Table 1, for the sample heated with the 15 degrees Celsius per minute heating rate, the curvature change was more than double that of the 1 degree Celsius per minute heating rate, which is visually apparent in FIG. 8. It was estimated that such a difference implies the coating compressive stress was more than doubled (approximately) in the sample with the 15 degrees Celsius per minute heating rate compared to the 1 degree Celsius per minute heating rate.

In another experiment, the thermal expansion and contraction of two free standing EBCs was also measured for heat treatments including a 15 degrees Celsius per minute heating rate and a 1 degrees Celsius per minute heating rate. The EBC samples were free standing in the sense that the coating was not attached to a substrate. Each sample “bar” was about 3 millimeter (mm) by about 4 mm by about 50 mm (length). The “length change” with respect to the 50 mm length of each sample bar was monitored during the heat treatments and plotted with regard to temperature in FIGS. 9 and 10. The 1 degree Celsius per minute heating rate heating rate sample (FIG. 10) showed less overall expansion than the 15 degrees Celsius per minute heating rate heating rate sample (FIG. 9). The 15 degrees Celsius per minute heating rate heating rate induced more than twice the thermal expansion from the 1 degree Celsius per minute heating rate heating rate. This was thought to agree with the findings on the two EBC coated CMC substrates described above as higher thermal expansion would put the EBC more in compression.

In addition to the two heating rates evaluated above, it was thought that other heating rates could produce different results with regard to residual stress states in a coating following heat treatment. Similarly, other parameters of a heat treatment such as the elevated heat treatment temperature, heat treatment duration, and/or the cooling rates may also be explored with regard to their influence on the residual stress states of a heat treated coating.

Although the data shown are from air plasma sprayed EBC, it was believed that the same method can be extended to EBCs, as well as TBCs and abradable coatings, produced using other deposition techniques such as EB PVD and other thermal spray techniques, e.g., as long as the as-deposited coatings are substantially amorphous (or have a relatively high amorphous content) prior to heat treatment. A relatively high amorphous content may refer to an amorphous content of at least about 30 volume percent, such as at least about 40 volume percent.

The techniques described in this disclosure may be implemented, at least in part, in hardware, software, firmware, or any combination thereof. For example, various aspects of the described techniques may be implemented within one or more processors, including one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or any other equivalent integrated or discrete logic circuitry, as well as any combinations of such components. The term “processor” or “processing circuitry” may generally refer to any of the foregoing logic circuitry, alone or in combination with other logic circuitry, or any other equivalent circuitry. A control unit including hardware may also perform one or more of the techniques of this disclosure.

Such hardware, software, and firmware may be implemented within the same device or within separate devices to support the various techniques described in this disclosure. In addition, any of the described units, modules or components may be implemented together or separately as discrete but interoperable logic devices. Depiction of different features as modules or units is intended to highlight different functional aspects and does not necessarily imply that such modules or units must be realized by separate hardware, firmware, or software components. Rather, functionality associated with one or more modules or units may be performed by separate hardware, firmware, or software components, or integrated within common or separate hardware, firmware, or software components.

The techniques described in this disclosure may also be embodied or encoded in a computer system-readable medium, such as a computer system-readable storage medium, containing instructions. Instructions embedded or encoded in a computer system-readable medium, including a computer system-readable storage medium, may cause one or more programmable processors, or other processors, to implement one or more of the techniques described herein, such as when instructions included or encoded in the computer system-readable medium are executed by the one or more processors. Computer system readable storage media may include random access memory (RAM), read only memory (ROM), programmable read only memory (PROM), erasable programmable read only memory (EPROM), electronically erasable programmable read only memory (EEPROM), flash memory, a hard disk, a compact disc ROM (CD-ROM), a floppy disk, a cassette, magnetic media, optical media, or other computer system readable media. In some examples, an article of manufacture may comprise one or more computer system-readable storage media.

Various examples have been described. These and other examples are within the scope of the following clauses and claims.

Clause 1. A method comprising: depositing a coating on a substrate to form an as-deposited coating, wherein the coating includes at least one of a thermal barrier coating (TBC) layer, an environmental barrier coating (EBC) layer, or an abradable coating layer; and heat treating the as-deposited coating at or above a first temperature for a first period of time following the deposition of the as-deposited coating on the substrate, wherein heat treating the as-deposited coating includes heating the as-deposited coating to or above the first temperature at a controlled heating rate, and wherein the controlled heating rate is selected such that the heat treated coating exhibits a compressive residual stress state upon cooling.

Clause 2. The method of clause 1, wherein the as-deposited coating includes at least about 30 volume percent amorphous phase, and wherein the heat treated coating includes at least about 90 volume percent crystalline phase.

Clause 3. The method of any one of clauses 1 or 2, wherein the controlled rate is greater than or equal to 0.5 degrees Celsius per minute (° C./min).

Clause 4. The method of any one of clauses 1 or 2, wherein the controlled rate is about 1° C./min to about 15° C./min.

Clause 5. The method of any one of clauses 1-4, further comprising, prior to heat treating the as-deposited coating: heat treating a first sample coating using a first heating rate; determining a change in curvature for the heat treated first sample coating; and selecting the first heating rate as the controlled heating rate based on the change in the curvature for the heat treated first sample coating.

Clause 6. The method of clause 5, further comprising: heat treating a second sample coating using a second heating rate, wherein the first sample coating is substantially the same as the second sample coating prior to heat treatment; and determining a change in curvature for the heat treated second sample coating, wherein selecting the first heating rate as the controlled heating rate based on the change in the curvature for the heat treated first sample coating comprises selecting the first heating rate as the controlled heating rate based on a comparison of the change in curvature for the heat treated first sample coating and the change in curvature for the heat treated second sample coating.

Clause 7. The method of any one of clauses 1-6, wherein depositing the coating on the substrate to form the as-deposited coating comprises depositing the coating on the substrate via at least one of thermal spray deposition or slurry deposition.

Clause 8. The method of any one of clauses 1-7, wherein the coating includes at least one of rare earth (RE) monosilicate or RE disilicate.

Clause 9. The method of any one of clauses 1-8, wherein the heat-treated coating includes the EBC on the substrate and the abradable layer on the EBC.

Clause 10. The method of any one of clauses 1-9, wherein the controlled heating rate is selected such that the heat treated coating exhibits a target compressive residual stress state upon cooling.

Clause 11. The method of any one of clauses 1-10, wherein the controlled heating rate is selected such that the heat treated coating exhibits an increased compressive residual stress state upon cooling compared to the as-deposited coating.

Clause 12. A system comprising: a deposition device configured to deposit a coating on a substrate to form an as-deposited coating, wherein the coating includes at least one of a thermal barrier coating (TBC) layer, an environmental barrier coating (EBC) layer, or an abradable coating layer; a furnace configured to heat the as-deposited coating following deposition of the as-deposited coating by the deposition device; and a controller device configured to control the heat treatment of the as-deposited coating at or above a first temperature for a first period of time following the deposition of the as-deposited coating on the substrate, wherein heat treating the as-deposited coating includes heating the as-deposited coating to or above the first temperature at a controlled heating rate, and wherein the controlled heating rate is selected such that the heat treated coating exhibits a compressive residual stress state upon cooling.

Clause 13. The system of clause 12, wherein the as-deposited coating includes at least about 30 volume percent amorphous phase, and wherein the heat treated coating includes at least about 90 volume percent crystalline phase.

Clause 14. The system of any one of clauses 12 or 13, wherein the controlled rate is greater than or equal to 0.5 degrees Celsius per minute (° C./min).

Clause 15. The system of any one of clauses 12 or 13, wherein the controlled rate is about 1° C./min to about 15° C./min.

Clause 16. The system of any one of clauses 12-15, further comprising, prior to heat treating the as-deposited coating: heat treating a first sample coating using a first heating rate; determining a change in curvature for the heat treated first sample coating; and selecting the first heating rate as the controlled heating rate based on the change in the curvature for the heat treated first sample coating.

Clause 17. The system of clause 16, further comprising: heat treating a second sample coating using a second heating rate, wherein the first sample coating is substantially the same as the second sample coating prior to heat treatment; and determining a change in curvature for the heat treated second sample coating, wherein selecting the first heating rate as the controlled heating rate based on the change in the curvature for the heat treated first sample coating comprises selecting the first heating rate as the controlled heating rate based on a comparison of the change in curvature for the heat treated first sample coating and the change in curvature for the heat treated second sample coating.

Clause 18. The system of any one of clauses 12-17, wherein depositing the coating on the substrate to form the as-deposited coating comprises depositing the coating on the substrate via at least one of thermal spray deposition or slurry deposition.

Clause 19. The system of any one of clauses 12-18, wherein the coating includes at least one of rare earth (RE) monosilicate or RE disilicate.

Clause 20. The system of any one of clauses 12-19, wherein the heat-treated coating includes the EBC on the substrate and the abradable layer on the EBC.

Clause 21. The system of any one of clauses 12-20, wherein the controlled heating rate is selected such that the heat treated coating exhibits a target compressive residual stress state upon cooling.

Clause 22. The system of any one of clauses 12-21, wherein the controlled heating rate is selected such that the heat treated coating exhibits an increased compressive residual stress state upon cooling compared to the as-deposited coating.

Clause 23. An article comprising: a substrate; and a coating on the substrate, wherein the coating is heat treated according any one of clauses 1-11.

POST DEPOSITION HEAT TREATMENT OF COATING ON SUBSTRATE

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