Patent Description:
Ceramic or ceramic matrix composite (CMC) materials may be useful in a variety of contexts where mechanical and thermal properties are important. For example, components of high temperature mechanical systems, such as gas turbine engines, may be made from ceramic or CMC materials. Ceramic or CMC materials may be resistant to high temperatures, but some ceramic or CMC materials may react with some elements and compounds present in the operating environment of high temperature mechanical systems, such as water vapor. Reaction with water vapor may result in the recession of the ceramic or CMC material. These reactions may damage the ceramic or CMC material and reduce mechanical properties of the ceramic or CMC material, which may reduce the useful lifetime of the component. Thus, in some examples, a ceramic or CMC material may be coated with an environmental barrier coating (EBC), which may reduce exposure of the substrate to elements and compounds present in the operating environment of high temperature mechanical systems. The ceramic or CMC material may also be coated with an abradable coating on the EBC, e.g., to provide a seal between an adjacent component such as a blade tip or rotating knife during operation of the high temperature mechanical system.

<CIT> relates to a method of depositing abradable coating on an engine component is provided wherein the engine component is formed of ceramic matrix composite (CMC) and one or more layers, including at least one environmental barrier coating, may be disposed on the outer layer of the CMC. An outermost layer of the structure may further comprise a porous abradable layer that is disposed on the environmental barrier coating and provides a breakable structure which inhibits blade damage. The abradable layer may be gelcast on the component and sintered or may be direct written by extrusion process and subsequently sintered.

The invention relates to coating systems including abradable coatings and environmental barrier coatings (EBCs) on a substrate, e.g., for use in high-temperature mechanical systems, and techniques for forming the coating systems, as set out in the appended claims.

The invention describes a method that comprises depositing an environmental barrier coating (EBC) on a ceramic or ceramic matrix composite (CMC) substrate to form an as-deposited EBC; heat treating the as-deposited EBC following the deposition of the as-deposited EBC on the substrate to form a heat treated EBC having a first porosity; subsequently depositing an abradable coating on the heat treated EBC to form an as-deposited abradable coating; and subsequently heat treating the as-deposited abradable coating following deposition of the abradable coating on the EBC to form a heat treated abradable coating having a second porosity that is greater than the first porosity of the heat treated EBC, wherein heat treating the as-deposited EBC includes heating the as-deposited EBC at a first controlled rate, wherein heat treating the as-deposited abradable coating includes heating the as-deposited abradable coating at a second controlled rate that is less than the first controlled rate, and wherein the EBC and abradable coating each includes at least one of rare earth (RE) monosilicate or RE disilicate.

In some examples, heat treating the as-deposited EBC comprises heat treating of the as-deposited EBC to decrease a porosity of the heat treated EBC as compared to the as-deposited EBC.

In some examples, heat treating the as-deposited EBC comprises heating the as-deposited EBC at a first controlled rate, wherein the controlled rate is selected to decrease at least one of an open porosity or microcracks of the heat-treated EBC compared to the as-deposited EBC.

In some examples, decreasing the at least one of the open porosity or the microcracks of the heat-treated coating compared to the as-deposited coating comprises decreasing a percentage of interconnected pores and crack networks of the heat-treated coating compared to the as-deposited coating; and/or decreasing the at least one of the open porosity or the microcracks of the heat-treated coating compared to the as-deposited coating comprises closing at least a portion of the interconnected pores and microcrack networks of the as-deposited coating.

In some examples, the first controlled rate is greater than about <NUM> degrees Celsius per minute; and/or the second controlled rate is less than <NUM> degrees Celsius per minute.

In some examples, heat treating the as-deposited EBC includes heating the as-deposited EBC to or above a first temperature, and heat treating the as-deposited abradable coating includes heating the as-deposited EBC to or above a second temperature, wherein the first temperature and the second temperature are approximately equal.

In some examples, the heat treated EBC has a porosity of less than about <NUM> %; and/or the as-deposited abradable coating has a porosity of greater than <NUM>%; and/or the heat treated abradable coating has a porosity of greater than <NUM> %.

In some examples, the as-deposited abradable coating includes a fugitive material, the method further comprising removing the fugitive material of the as-deposited abradable coating to create open pores in the abradable coating.

In some examples, depositing the EBC on the substrate to form the as-deposited EBC comprises depositing the EBC on the substrate via at least one of thermal spray deposition or slurry deposition; and/or the heat treated EBC is a substantially hermetic EBC.

In some examples, the heat treatment of the as-deposited EBC including heating at the first controlled rate increases a density of the heat treated EBC as compared to the as-deposited EBC such that an amorphous phase of the as-deposited EBC flows to fill pores and/or microcracks of the as-deposited EBC before transitioning to crystalline phase during the heat treatment.

In some examples, the heat treatment of the as-deposited abradable including heating at the second controlled rate maintains a porosity of the heat treated abradable coating as compared to the as-deposited abradable coating such that an amorphous phase of the as-deposited abradable coating transitions to crystalline phase without flow of the amorphous phase to fill pores and/or microcracks of the as-deposited abradable coating during the heat treatment.

The disclosure describes systems and techniques for forming and heating treating a coating system including an abradable coating and an environmental barrier coating (EBC) on a ceramic or CMC substrate. The coating system may be deposited using, e.g., thermal spray deposition, such as air plasma spraying, slurry deposition, or other suitable technique. The coating system may be deposited on the substrate that serves as components of gas turbine engines or other high temperature mechanical systems.

A component of a high temperature mechanical system may include a coating system having both an EBC and an abradable coating on substrate, where the EBC is formed on the substrate and the abradable coating is formed on the EBC. The EBC may reduce exposure of an underlying substrate and/or bond layer to elements and compounds present in the operating environment of high temperature mechanical systems, such as water vapor or oxygen. The abradable coating may be configured to be abraded during the operation of a component in a high temperature mechanical system, e.g., to reduce clearance between a rotating component, such as a gas turbine blade, and a surrounding stationary component, such as blade track or blade shroud. For example, the abradable coating may be formed on a blade track or blade shroud and may be abraded as results of contact by the tip of a rotating turbine blade. As another example, the abradable coating may be formed on a runner of a knife seal and may be abraded as results of contact by the tip of a rotating knife of a knife seal. As the rotating component rotates, the tip of the rotating component contacts the abradable coating and wears away a portion of the abradable coating to form a groove in the abradable coating corresponding to the path of the rotating component tip. The intimate fit between the tip of the rotating component and abradable coating provides a seal that can reduce the clearance gap between the rotating component and an inner wall of the stationary component, which can reduce leakage around a tip of the rotating part to enhance the power and efficiency of the gas turbine engine.

In some examples, an EBC and abradable coating may be formed on a substrate by a thermal spray process. Due to the rapid quenching of sprayed EBC and abradable coatings, the as-sprayed EBC and abradable coatings may be primarily in an amorphous state. Following the thermal spray deposition of the EBC and abradable coatings, the combined coating system may undergo a heat treatment process to crystalize the coatings to achieve a consistent and more stable material state before entering into service.

In some examples, a single heat treatment step for the combined coating system (EBC plus abradable coating) following thermal spray deposition may present one or more issues. For example, a heat treatment with a relatively high heating rate may be desirable for the EBC to decrease the porosity of the heat treated EBC as compared to the as-deposited EBC. However, a heat treatment that decreases the porosity of the EBC may not be desirable for the abradable layer. Instead, a relatively slow heating rate may be desirable for an abradable coating, as the abradable coating may retain relatively high porosity and, thus, abradability. In other examples, it may be desirable to not heat treat the abradable coating following deposition of the coating. In some examples, if an abradable coating is heat treated at a slow heating/cooling rate such as about <NUM>/min, the coating may retain a certain amount of porosity and abradability. However, if the coating is heat treated at a very high heating/cooling rate such as, e.g., about <NUM>/min, for example by putting the coatings inside a preheated furnace, the coating densifies substantially and makes the abradable coating difficult to cut and more susceptible to unintended damage.

As another example, for water vapor attack, it may be desirable to have a dense EBC to slow down water vapor diffusion. For abradability, it is desirable to have a porous abradable coating to facilitate blade cut. Thus, to maintain the desired coating microstructures, the EBC and abradable coatings may therefore not be able to be heat treated together.

As described herein, an example process employed to form the coating system may include heat treating an as-deposited EBC prior to the deposition of the abradable coating on the EBC. The heat treatment of the EBC coating may be tailored to reduce the porosity of the as-deposited EBC, which may be desirable for an EBC but undesirable for an abradable coating formed on the EBC. In some examples, a relatively high heating rate and/or cooling rate (e.g., greater than <NUM>/min or greater, such as about <NUM>/min) may be employed for the EBC heat treatment, e.g., by placing the EBC and underlying substrate in a preheated furnace. The heat treatment of the EBC may convert an amorphous phase of the EBC to crystalline phase while reducing porosity of the as-deposited EBC.

The abradable coating may then be formed on the EBC following the heat treatment of the EBC rather than prior to the heat treatment of the EBC. In some examples, a separate heat treatment following deposition of the abradable coating on the heat treated EBC may be performed, which may be tailored to maintain or not significantly reduce the porosity of the heat treated abradable coating compared to the as-deposited abradable coating. In some examples, the abradable coating heat treatment may employ a relatively low heating rate (e.g., less than <NUM>/min, such as, about <NUM>/min) and/or a heating rate that is less than the heating rate of the EBC heat treatment. As noted above, if an abradable coating is heat treated at a slow heating/cooling rate such as about <NUM>/min, the coating may retain a certain amount of porosity and abradability. In some examples, the porosity of the abradable coating may be increased by the heat treatment. In some examples, the heat treatment of the abradable coating may convert an amorphous phase of the abradable coating to crystalline phase while maintaining the porosity of the abradable coating, while the separate heat treatment of the EBC may convert an amorphous phase of the EBC to crystalline phase while maintaining the porosity of the EBC. In this manner, the porosity of the EBC coating may be reduced by a heat treatment without undesirably reducing the porosity of the abradable coating during the heat treatment of the EBC. Instead, separate heat treatments may be performed with the conditions of the first heat treatment being tailored for the as-deposited EBC and the conditions of the second heat treatment being tailored for the as-deposited abradable coating. In some examples, the heating rate, heat treatment temperature, duration, and/or cooling rate of the EBC heat treatment may be different than the heating rate, heat treatment temperature, duration, and/or cooling rate of the abradable coating heat treatment, e.g., to reduce the porosity of the as-deposited EBC while not reducing or reducing the porosity of the abradable coating to a lesser degree.

As described above, the heat treatment of the as-deposited EBC coating on a substrate, prior to the deposition of the abradable coating, may be configured to reduce the porosity of the as-deposited EBC and/or provide for one or more other changes to the as-deposited EBC (e.g., by using a relatively high heating rate). For example, the as-deposited EBC may undergo a heat treatment on the substrate to decrease the open porosity and/or microcracks of the heat treated EBC as compared to the as-deposited EBC porosity, control the crystalline phase grain size of the EBC, and/or control the microstructure of the EBC (e.g., control the size and distribution of secondary phases such as ytterbium monosilicate in the coating).

In some examples, the decrease in open porosity and/or microcracks of the heat-treated EBC may include a decrease in the percentage of open porosity and/or microcrack networks of the heat treated EBC compared to the as-deposited EBC (e.g., by filling or otherwise closing at least some of the interconnected pores and/or microcrack networks in the as-deposited EBC). The decrease in the open porosity and/or microcracks of the heat-treated EBC may decrease the viscous gas permeability of the heat treated EBC compared to the as-deposited EBC. In some examples, the heat treatment may increase the density of the heat treated EBC compared to the as-deposited EBC.

EBCs may be an important contributor to the success of ceramics or CMCs in a high temperature system. For example, the EBCs may be configured to protect against oxidation, water vapor recession, and other deleterious reactions damaging the structure of a ceramic or CMC, e.g., during operation of the high temperature system. In some examples, an EBC may contain a multilayered structure including a silicon bond layer and a rare-earth silicate (e.g., rare earth monosilicate and/or rare earth disilicate) layer. The layers of the EBC may be deposited, e.g., using a thermal spraying process, such as, air plasma spraying, which may produce an amorphous structure within the coating, e.g., due to the high cooling rates/quenching of the particles upon impact with a substrate. 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 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 in the EBC as well as the silicon bond coat. Eventually, the build-up in stress reaches a threshold and causes a crack to initiate and propagate to relieve the stress state.

In some examples, an EBC may undergo a post deposition heat treatment to convert the amorphous phase of the EBC to crystalline phase. Depending on the parameters of the heat treatment, the heat treated EBC may still exhibit relatively high porosity (e.g., open porosity) and/or microcracks. The relatively high porosity and/or microcracks may reduce the ability of the coating to protect the underlying CMC substrate from oxidation and volatilization, as well as CMAS infiltration. Furthermore, the number of grains and/or the relatively small size of the grains of the crystalline phase within the heat treated EBC may result in an undesired concentration of grain boundaries within the heat treated EBC. The grain boundaries may provide pathways for penetration of water vapor through the EBC, resulting in oxidation of the underlying CMC substrate.

As one example, a CMC plus EBC system may include a SiC/SiC CMC that is coated with a Si bond coat and a multilayered rare-earth silicate-based EBC. A thermally sprayed or otherwise deposited EBC may encompasses a certain level of open porosity and microcracks that act as open pathways for oxygen and water vapor to transport through the coating and oxidize the underlying bond coat and CMC. In addition, grain boundaries have been shown to be fast transport pathways for oxidants in rare-earth silicates. Reducing open porosity, healing microcracks and/or controlling grain size may be crucial to maximize the EBC's performance as a barrier to protect the SiC-based CMCs from oxidation.

The as-deposited EBC may contain a significant volume percentage of amorphous material and thus devitrification (crystallization) will occur at elevated temperatures. Various densification mechanisms of the EBC may apply depending upon the coatings amorphous content, chemistry and heat treatment procedure. As will be described further below, some heat treatment procedures may actually cause a coating to become more porous, e.g., as a result of a relatively low rate of temperature increase to the heat treatment temperature.

In accordance with examples of the disclosure, systems and techniques are described that include heat treating an EBC following deposition on a ceramic or CMC substrate but prior to the deposition of an abradable layer. The deposited EBC may include one or more EBC layers. The heat treatment of the as-deposited coating may be configured to at least one of decrease the porosity (e.g., open porosity and/or microcracks) of the heat treated EBC as compared to the as-deposited EBC, control, e.g., increase, the grain size of the crystalline phase of the heat treated EBC, and/or control the microstructure and distribution of the heat treated EBC (e.g., control the size and distribution of secondary phases such as ytterbium monosilicate in the coating).

In some examples, the heat treatment of the EBC may include heating the as-deposited EBC at a relatively high rate to the elevated heat treatment temperature (e.g., from room temperature). For example, the heat treatment may include raising the temperature of the as-deposited EBC at a rate of greater than <NUM> degrees Celsius (°C/min), such as about <NUM>/min to about <NUM>/min to the elevated heat treatment temperature. In some examples, the elevated heat treatment temperature may be set at about <NUM> to about <NUM>. The EBC may be maintained at the elevated heat treatment temperature for a selected period of time.

As will be described below, in some examples, the relatively high rate of temperature change to reach the elevated heat treatment temperature may allow the amorphous phase of the as-deposited coating to flow, e.g., to fill the pores and/or microcracks of the coating, before transitioning to crystalline phase. In some examples, the flow of the amorphous material may close at least some of the interconnected pores of the open porosity and/or close at least some of the microcrack networks present in the as-deposited EBC. In this manner, the porosity and/or microcracks of the EBC may be decreased, which may increase the hermeticity of the EBC for protection of the underlying substrate from water vapor and oxygen. In some examples, the density of the heat treated EBC may be increased compared to the as-deposited EBC.

Conversely, it has been found that is some cases, increasing a temperature at a relatively low rate (e.g., less than <NUM>/min) for a heat treatment of a coating may cause the amorphous phase to transition to crystalline phase with substantially no flow such that the microstructure of the coating is effectively "locked in" without the amorphous material flowing into the pores and microcrack of the as-deposited material. In such an example, the porosity (e.g., open porosity and/or microcracks) of the as-deposited coating may not substantially decrease as a result of the heat treatment. In some examples, as described herein, such a heat treatment may be used following the deposition of an abradable coating on an already heat treated EBC. In this manner, the porosity of the as-deposited abradable coating may be maintained at a desirable level (e.g., to function as an abradable coating) while still transitioning at least some of the amorphous phase material of the as-deposited abradable coating to crystalline phase.

Although not wishing to be bound by theory, two possible mechanisms caused by the relatively high heating rate during heat treatment include: <NUM>) the heating rate is fast enough that the amorphous component of the as-deposited coating may become viscoelastic and has sufficient time to flow before the onset of crystallization, thereby closing open porosity and/or healing (e.g., filling) cracks in the coating; and/or <NUM>) the fast heating rate delays the onset of crystallization thereby allowing the coating sufficient time to become viscoelastic and flow. Such delayed onset of crystallization with be consistent with changing the crystallization kinetics of a glass by increasing the heating rate. In some examples, the two mechanisms may be densification mechanisms.

In some examples, the heat treatment of the as-depositing EBC may include heating the as-deposited coating to an elevated heat treatment temperature and maintaining the coating at (or above) that heat treatment temperature for a set period of time. In addition to, or as an alternative to decreasing the porosity and/or microcracks of the EBC, the parameters of the heat treatment (e.g., the heat treatment temperature, the rate of temperature increase to reach the heat treatment temperature, and/or the duration of period of time) may be selected to control the grain size of the crystalline phase of the resulting heat treated EBC. For example, in some instances, the heat treatment temperature, rate of temperature increase, and/or duration may be selected to nucleate a relatively low number of grains during crystallization of the amorphous as-deposited EBC, and then growing those grains during the heat treatment. Compared to a heat treatment that nucleates more grains, resulting heat treated EBC may have a lower amount of grain boundaries within the heat treated layers, thereby decreasing the transport pathways for oxidants within the heat treated coating.

Following the EBC heat treatment, an abradable coating may be deposited on the heat treated EBC and then another heat treatment may be performed. In some examples, the heat treatment of the as-depositing abradable coating may include heating the as-deposited coating to an elevated heat treatment temperature and maintaining the coating at (or above) that heat treatment temperature for a set period of time. The parameters of the heat treatment (e.g., the heat treatment temperature, the rate of temperature increase to reach the heat treatment temperature, and/or the duration of period of time) may be selected to maintain the porous structure of the as-deposited abradable coating. For example, in some instances, the heat treatment temperature, rate of temperature increase, and/or duration may be selected to such that the porosity of the heat treated abradable coating is substantially the same as the as-deposited coating or not significantly reduced compared to the as-deposited coating. In some examples, the heat treatment of the abradable coating may maintain the porosity of the abradable coating above a threshold level. In some examples, the heat treatment of the abradable coating may reduce the porosity of the as-deposited abradable coating a lesser percentage than the percentage of porosity decrease caused by the heat treatment of the as-deposited EBC.

In some examples, the disclosure relates to techniques for densifying or otherwise modifying a plasma sprayed EBC so that the coating will have reduced porosity and microcracks. An EBC will have a lower gas permeability which will enhance the coatings performance as a barrier to protect SiC-based CMC from oxidation and volatilization. The SiC-based CMC component coated with an abradable coating, EBC and an optional bond coat that are deposited by a plasma spray or slurry based processing techniques. The abradable coating and EBC may include a rare-earth (RE) monosilicate, RE disilicate or a mixture thereof, and the bond coat may include silicon, a metal silicide, RE monosilicate, RE disilicate, hafnium silicate, mullite, SiC, a metal oxide or a mixture thereof.

Examples of the disclosure may include one or more post coating deposition heat treatment(s) in air, oxygen, water vapor, inert gas, vacuum or combinations thereof, e.g., for the heat treatment of the EBC only or the heat treatment of the EBC followed by another heat treatment of the abradable coating. The heat treatment of the as-deposited EBC may be implemented at a relatively fast heating rate, e.g. greater than <NUM>/min, such as, about <NUM>/min to about <NUM>/min, or about <NUM>/min. The heat treatment temperature can be set at, e.g., about <NUM> to about <NUM>, with a total time duration of about <NUM> to about <NUM> hours. In some examples, a single heat treatment for the EBC may be comprised of several segments where one segment is aimed to densify or decreasing the porosity and/or microcracks of the coating while another segment is aimed to control the grain size of the coating. Each segment may have a unique temperature and time.

Conversely, the heat treatment of the abradable coating that is being deposited on the heat treated EBC may be implemented at a relatively low heating rate, e.g. less than <NUM>/min, such as, about <NUM>/min to less than <NUM>/min, about <NUM>/min to about <NUM>/min or at about <NUM>/min. In some examples, the relatively low heating rate may be about <NUM>/min to about <NUM> minutes/°C. The heat treatment temperature can be set at, e.g., about <NUM> to about <NUM>, with a total time duration of about <NUM> to about <NUM> hours. As described herein, in some examples, the abradable coating may not undergo a heat treatment following the deposition of the abradable coating on the heat treated EBC.

<FIG> is a conceptual and schematic diagram illustrating an example system <NUM> for depositing an EBC on a substrate, heat treating the as-deposited EBC, subsequently depositing an abradable coating on the EBC, and, optionally, then heat treating the as-deposited abradable coating. The heat treatment of the as-deposited EBC may be configured to decrease the porosity of the as-deposited EBC, control the grain sizes of the heat treated EBC, and/or control the microstructure and distribution of the heat treated EBC (e.g., control the size and distribution of secondary phases such as ytterbium monosilicate in the coating). The optional heat treatment of the abradable coating may be configured to maintain or only slightly reduce the porosity of the abradable coating as compared to the porosity of the coating prior to heat treatment. As shown, system <NUM> includes deposition device <NUM>, heat treatment furnace <NUM>, and transfer device <NUM>.

Deposition device <NUM> may be configured to deposit one or more layers of an EBC and abradable coating system on a substrate to form a coated article, such as article <NUM> in <FIG>, which include coating system <NUM> on substrate <NUM>. In some examples, deposition device <NUM> may be configured to deposit coating <NUM> using a thermal spray process, a slurry deposition process, and/or other process suitable for depositing a coating, such as, EBC <NUM> and abradable coating <NUM>. 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 <NUM> 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 <NUM> may be deposited via deposition device <NUM> in an atmosphere including, for example, air, an inert atmosphere, a vacuum, or the like. In some examples, the deposition of coating <NUM> by deposition device <NUM> may take place in a heated environment or may take place at room temperature. For ease of description, the operation of system <NUM> will primarily be described herein with regard to article <NUM> of <FIG> although other articles formed using system <NUM> are contemplated.

Furnace <NUM> may be configured to heat and maintain article <NUM> at a relatively high temperature following the deposition EBC <NUM> using deposition device <NUM>, e.g., to perform a post-deposition heat treatment of EBC <NUM> on substrate <NUM> as well as a post-deposition heat treatment of abradable coating <NUM> on the heat treated EBC <NUM> and substrate <NUM>. Furnace <NUM> may include an internal cavity sized and otherwise configured to contain article <NUM> after the deposition of EBC <NUM> on substrate <NUM> as well as article <NUM> after abradable coating <NUM> has been deposited on EBC <NUM> and substrate <NUM>. Any suitable type of furnace <NUM> may be used that is capable of functioning as described in this disclosure. Furnace <NUM> 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 <NUM> 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 example, an induction system may be used to directly heat article <NUM> to deliver high heating rates. In some examples, article <NUM> may be heated for heat treatment using an oxy-fuel burner rather than a furnace.

Transfer device <NUM> may be configured to robotically transfer article <NUM> between furnace <NUM> and thermal spray device <NUM>, as desired before and/or after the deposition of EBC <NUM> and abradable coating <NUM> via deposition device <NUM>. For example, transfer device <NUM> may transfer substrate <NUM> to thermal spray device <NUM> for the deposition of EBC <NUM> (and option bond layer <NUM>), then transfer the coated substrate <NUM> to furnace <NUM> for the heat treatment of EBC <NUM>, then transfer the EBC <NUM> and substrate <NUM> back to thermal spray device <NUM> for the deposition of abradable coating <NUM> on the heat treated EBC <NUM>, and then optionally transfer substrate <NUM> with EBC <NUM> and abradable coating <NUM> back to furnace <NUM> for the heat treatment of the as-deposited abradable coating <NUM>. In other examples, article <NUM> may be manually transferred between deposition device <NUM> and furnace <NUM> as described.

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

Controller device <NUM> 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 <NUM> 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 <NUM> may be provided within dedicated hardware and/or software modules.

In one example, system <NUM> may be configured to form an article such as article <NUM> shown in <FIG>, which includes coating system <NUM> on substrate <NUM>. For example, system <NUM> may be configured to deposit one or more layers of coating system <NUM> on substrate <NUM> using deposition device <NUM>, e.g., by slurry deposition, air plasma spraying or other thermal spray deposition process. Following the deposition of EBC <NUM> and optional bond coat <NUM> on substrate <NUM> by deposition device <NUM>, article <NUM> may be moved to furnace <NUM> (e.g., via transfer device <NUM>) for a post deposition heat treatment of EBC <NUM>. As will be described further below, the post-deposition heat treatment in furnace <NUM> may be controlled by controller device <NUM> so that EBC <NUM> is at an elevated temperature (e.g., a temperature at or above the crystallization temperature of EBC <NUM>) for a desired duration of time. Controller device <NUM> 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 <NUM> may provide for a decrease in the open porosity and/or microcracks of EBC <NUM>, e.g., based on the rate of temperature increase, and/or control of the grain sizes within heat treated EBC <NUM>.

Likewise, following the deposition of abradable coating <NUM> on the heat treated EBC <NUM> by deposition device <NUM>, article <NUM> may be moved to furnace <NUM> (e.g., via transfer device <NUM>) for a post deposition heat treatment of abradable coating <NUM>. As will be described further below, the post-deposition heat treatment in furnace <NUM> may be controlled by controller device <NUM> so that abradable coating <NUM> is at an elevated temperature (e.g., a temperature at or above the crystallization temperature of abradable coating <NUM>) for a desired duration of time. Controller device <NUM> 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 <NUM> may maintain or not significantly reduce the porosity of the heat treated abradable coating compared to the as-deposited abradable coating of abradable coating <NUM>, e.g., based on the rate of temperature increase and/or other parameters of the heat treatment. The heat treatment of the abradable coating may convert an amorphous phase of the EBC to crystalline phase while reducing the porosity of the as-deposited EBC.

<FIG> is a conceptual diagram illustrating an example article <NUM> including a substrate <NUM> and coating system <NUM>. Coating system <NUM> includes an optional bond coat <NUM>, an EBC <NUM>, and a abradable layer <NUM>. In some examples, article <NUM> may include a component of a gas turbine engine. For example, article <NUM> 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>, EBC <NUM> may include plurality of voids (e.g., pores, intercolumnar voids, cracks, and/or the like) within the layer. As described herein, heat treatment of coating <NUM> may decrease the porosity of the as-deposited EBC <NUM>, e.g., by rapidly increasing the temperature of EBC <NUM> during post-deposition heat treatment to at least partially fill or close at least some of the voids during the heat treatment.

Substrate <NUM> may include a material suitable for use in a high-temperature environment. In some examples, substrate <NUM> may include a ceramic or a ceramic matrix composite (CMC). Suitable ceramic materials, may include, for example, a silicon-containing ceramic, such as silica (SiO<NUM>) and/or silicon carbide (SiC); silicon nitride (Si<NUM>N<NUM>); alumina (Al<NUM>O<NUM>); an aluminosilicate; a transition metal carbide (e.g., WC, Mo<NUM>C, TiC); a silicide (e.g., MoSi<NUM>, NbSi<NUM>, TiSi<NUM>); combinations thereof; or the like. In some examples in which substrate <NUM> includes a ceramic, the ceramic may be substantially homogeneous.

In examples in which substrate <NUM> includes a CMC, substrate <NUM> 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 (Si<NUM>N<NUM>), an aluminosilicate, silica (SiO<NUM>), a transition metal carbide or silicide (e.g., WC, Mo<NUM>C, TiC, MoSi<NUM>, NbSi<NUM>, TiSi<NUM>), 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 (Si<NUM>N<NUM>), an aluminosilicate, silica (SiO<NUM>), a transition metal carbide or silicide (e.g. WC, Mo<NUM>C, TiC, MoSi<NUM>, NbSi<NUM>, TiSi<NUM>), or the like.

Substrate <NUM> 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 <NUM> may help protect underlying substrate <NUM> from chemical species present in the environment in which article <NUM> 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 <NUM> may also protect substrate <NUM> 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>, optional bond coat <NUM> of coating <NUM> is on substrate <NUM>. 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>, bond coat <NUM> of coating system <NUM> may be directly on substrate <NUM>. In other examples, one or more coatings or layers of coatings may be between bond coat <NUM> of coating <NUM> and substrate <NUM>.

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

In examples in which substrate <NUM> includes a ceramic or CMC, bond coat <NUM> may include a ceramic or another material that is compatible with the material from which substrate <NUM> is formed. For example, bond coat <NUM> may include mullite (aluminum silicate, Al<NUM>Si<NUM>O<NUM>), silicon metal or alloy, silica, a silicide, or the like. Bond coat <NUM> may further include other elements, such as a rare earth oxide or rare earth silicate including an oxide or 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 <NUM> may be selected based on the chemical composition and/or phase constitution of substrate <NUM> and the overlying layer (e.g., EBC layer <NUM> of <FIG>). For example, if substrate <NUM> includes a ceramic or a CMC, bond coat <NUM> may include silicon metal or alloy or a ceramic, such as, for example, mullite.

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

Bond coat <NUM> may be applied on substrate <NUM> 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 <NUM> includes EBC <NUM>, which may be configured to help protect substrate <NUM> against deleterious environmental species, such as CMAS and/or water vapor. EBC <NUM> may include at least one of a rare-earth oxide, a rare-earth silicate, an aluminosilicate, or an alkaline earth aluminosilicate. For example, EBC <NUM> may include mullite, barium strontium aluminosilicate (BSAS), barium aluminosilicate (BAS), or strontium aluminosilicate (SAS). In some examples, EBC <NUM> may include at least one rare-earth oxide, at least one rare-earth monosilicate (RE<NUM>SiO<NUM>, where RE is a rare-earth element), at least one rare-earth disilicate (RE<NUM>Si<NUM>O<NUM>, 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), europium (Eu), samarium (Sm), promethium (Pm), neodymium (Nd), praseodymium (Pr), cerium (Ce), lanthanum (La), yttrium (Y), or scandium (Sc).

EBC <NUM> may be any suitable thickness. For example, EBC <NUM> may be about <NUM> inches (about <NUM> micrometers) to about <NUM> inches (about <NUM> micrometers). In examples in which EBC <NUM> is a non-abradable EBC, EBC <NUM> may have a thickness of about <NUM> inches (about <NUM> micrometers) to about <NUM> inches (about <NUM> micrometers). In other examples, EBC <NUM> may have a different thickness.

Coating system <NUM> includes abradable coating <NUM> on EBC <NUM>. In such a configuration, coating system <NUM> may be configured such that abradable coating <NUM> has a greater porosity than EBC <NUM>, and the porosity of abradable coating <NUM> may be provided such that the outer surface of abradable coating <NUM> is abraded, e.g., when brought into contact with an opposing surface such as a blade tip. Abradable coating <NUM> may be on EBC <NUM>, which may provide for better adhesion of abradable coating <NUM> to optional bond layer <NUM> or substrate <NUM>. In some examples, abradable coating <NUM> may be about <NUM> inches (about <NUM> micrometers) to about <NUM> inches (about <NUM> micrometers) thick. In other examples, abradable coating <NUM> may have a different thickness.

The composition of abradable coating <NUM> may be selected from similar compositions as those listed above for EBC <NUM>. In some examples, the composition of abradable coating <NUM> may be the same or substantially similar to the composition of EBC <NUM>. In other examples, the compositions may be different. Regardless of the composition or the thickness of EBC <NUM> or abradable coating <NUM> of <FIG>, EBC <NUM> and abradable coating <NUM> may include a plurality of voids. For example, EBC <NUM> and abradable coating <NUM> 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 EBC <NUM> and abradable coating <NUM>. 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 <NUM> micrometers (µm) to about <NUM>.

In some example, the porosity of EBC <NUM> and the porosity of abradable coating <NUM> may be different, e.g., with abradable coating <NUM> having a higher porosity than EBC <NUM>. In some examples, EBC <NUM> may include a porosity of less than about <NUM> %, such as about <NUM> % to about <NUM> %, where porosity is measured as a percentage of pore volume divided by total volume of EBC <NUM>. The porosity of EBC <NUM> may be the porosity following the EBC heat treatment described herein. Abradable coating <NUM> may include a porosity of more than about <NUM> %, such as about <NUM> % to about <NUM> % where porosity is measured as a percentage of pore volume divided by total volume of layer <NUM>. The porosity of abradable coating <NUM> may be the porosity following the abradable coating heat treatment described herein. In each case, the porosity of EBC <NUM> and abradable coating <NUM> may be measured using mercury porosimetry, optical microscopy or Archimedean method.

As described herein, in some examples, a post-deposition heat treatment may be used to decrease the porosity and/or microcracks of EBC <NUM> prior to deposition of abradable coating <NUM>. For examples, the as-deposited EBC <NUM> may include open pores (e.g., interconnected pores in the layer) and/or microcrack networks. The open pores and/or microcracks may results in EBC <NUM> being permeable to gas, which may allow for undesirable oxidation and volatilization of article <NUM>. The post deposition heat treatment of EBC <NUM>, e.g., using a temperature increase of greater than <NUM>/min, may decrease the open porosity and/or microcracks in EBC <NUM>, e.g., as compared to the as-deposited EBC and/or a similar coating heat treated using a temperature increase of <NUM>/min or less. The percentage of open porosity and/or microcracks in EBC <NUM> may be decreased to lower the gas permeability of EBC <NUM>, e.g., which will enhance the EBCs performance as a barrier to protect substrate <NUM> from oxidation and volatilization.

The porosity and/or microcracks of EBC <NUM> as deposited may be decreased by heat treatment of EBC <NUM> following deposition. In some examples, the heat treatment of EBC <NUM> may decrease the porosity and/or microcracks of EBC <NUM> by at least about <NUM> percent (e.g., from about <NUM>% to about <NUM>%), at least about <NUM>% (e.g., from about <NUM>% to about <NUM>%), or at least about <NUM> percent (e.g., from about <NUM>% to about <NUM>%), e.g., as compared to the porosity of the as-deposited EBC <NUM> and/or a similar coating that underwent heat treatment with a slower rate of temperature increase (e.g., <NUM>/min or less).

As described herein, in some examples, a post-deposition heat treatment of abradable coating <NUM> may be performed on abradable coating <NUM>. The heat treatment may maintain or only slightly reduce the porosity of abradable coating <NUM>, e.g., while also transforming amorphous phase of the as-deposited abradable coating <NUM> to crystalline phase. In some examples, the porosity of abradable coating <NUM> may be substantially the same before and after the heat treatment, or may be reduced by less than about <NUM> % compared to the porosity of abradable coating <NUM> before the heat treatment, such as less than about <NUM> % or less than about <NUM> % or less than about <NUM> %.

In some examples, the porosity of the as-deposited EBC <NUM> and abradable coating <NUM> may be created and/or controlled by plasma spraying the coating material using a co-spray process technique in which the coating material and a coating material additive are fed into a plasma stream with two radial powder feed injection ports. The feed pressures and flow rates of the coating material and coating material additive may be adjusted to inject the material on the outer edge of the plasma plume using direct <NUM>-degree angle injection. This may permit the coating material particles to soften but not completely melt, and the coating material additive to not burn off, but rather soften sufficiently for adherence within coating <NUM>.

In other examples, the porosity of EBC <NUM> and abradable coating <NUM> may be controlled by the use of coating material additives and/or processing techniques to create the desired porosity. For example, to form an abradable layer such as abradable coating <NUM> of coating <NUM> in <FIG>, a fugitive material that melts or burns at the use temperatures of the component (e.g., a blade track) may be incorporated into the coating material that forms abradable coating <NUM>. The fugitive material may include, for example, graphite, hexagonal boron nitride, or a polymer such as a polyester, and may be incorporated into the coating material prior to deposition of the coating material on substrate <NUM> to form abradable coating <NUM>. The fugitive material then may be melted or burned off in a post-formation heat treatment, or during operation of the gas turbine engine, to form pores in coating <NUM>. The post-deposition heat-treatment may be performed at up to about <NUM> for a component having a substrate <NUM> that includes a CMC or other ceramic.

In other examples, the porosity of coating system may be created or controlled in a different manner, and/or coating system <NUM> may be deposited on substrate <NUM> using a different technique. For example, coating system <NUM> 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 <NUM> or abradable coating <NUM> has a columnar microstructure, EBC <NUM> and/or abradable coating <NUM> may be deposited on substrate <NUM> 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, EBC <NUM> and/or abradable coating <NUM> including a columnar microstructure may include a dense vertically cracked (DVC) coating, which in some cases, may be deposited on substrate <NUM> using an air plasma spray technique.

<FIG> is a flow diagram illustrating an example technique for forming a coating system on a substrate such as coating system <NUM> of article <NUM> on substrate <NUM>. The technique of <FIG> will be described with respect to system <NUM> of <FIG> and article <NUM> of <FIG> for ease of description only. A person having ordinary skill in the art will recognize and appreciate that the technique of <FIG> may be implemented using systems other than system <NUM> of <FIG>, may be used to form articles other than article <NUM> of <FIG>, or both.

As shown in <FIG>, substrate <NUM> may be positioned within deposition device <NUM> and controller device <NUM> may control deposition device <NUM> to deposit optional bond layer <NUM> and EBC <NUM> on substrate <NUM> (<NUM>). For example, deposition device <NUM> may deposit each of bond layer <NUM> and EBC <NUM> by thermal spraying (e.g., air plasma spraying) or slurry deposition under the control of controller device <NUM> (<NUM>). In some examples, a tape casting process may be used to deposit bond layer <NUM> and EBC <NUM>. The temperature within deposition device <NUM> may be approximately room temperature or elevated above room temperature.

As deposited, EBC <NUM> and/or bond layer <NUM> may have a relatively high amorphous phase concentration, e.g., due to the high cooling rates/quenching of the particles upon impact with substrate <NUM>. For example, EBC <NUM> may have an amorphous phase of at least about <NUM> weight percent (wt%), such as, at least about <NUM> wt%. Conversely, EBC <NUM> may have a crystalline phase of less than about <NUM> wt%, such as less than about <NUM> 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 EBC <NUM> and optional bond layer <NUM> on substrate <NUM>, the article may be transferred to furnace <NUM> by transfer device <NUM> for a first post-deposition heat treatment (<NUM>). Once within furnace <NUM>, controller device <NUM> may control the temperature of furnace to heat treat the as-deposited EBC <NUM> by heating EBC <NUM> to or above a selected temperature for a selected period of time (<NUM>). In some examples, the first post-deposition heat treatment may take place before or after EBC <NUM> cools to room temperature following its deposition. The post-deposition heat treatment temperature and duration within furnace <NUM> may be controlled by controller device <NUM> and may be selected to increase the crystalline phase concentration of EBC <NUM> on substrate <NUM>. For example, furnace <NUM> may be at a treatment temperature of at or above the crystalline temperature of the layer(s) of EBC <NUM>.

In accordance with some examples of the disclosure, the post-deposition heat treatment of EBC <NUM> may be configured to decrease the porosity and/or microcrack networks of EBC <NUM>. In some examples, the heat treatment may include increasing the temperature of EBC <NUM> at a relatively fast rate (e.g., a rate greater than <NUM>/min, such as, about <NUM>/min to about <NUM>/min). In some examples, EBC <NUM> may be at approximately room temperature (e.g., about <NUM>) at the beginning of the first heat treatment. The temperature of EBC <NUM> may be increased (e.g., by heating in furnace <NUM>) at the relatively high rate to the desired elevated heat treatment temperature. In some examples, the high heating rate may be accomplished by pre-heating furnace <NUM> prior to transfer of EBC <NUM>, bond layer <NUM>, and substrate <NUM> to furnace <NUM>. In some examples, the heat treatment temperature may be at or above about <NUM> to about <NUM>. EBC <NUM> may be held at or above the heat treatment temperature for a desired period of time (e.g., about <NUM> hours to about <NUM> hours). Controller device <NUM> may control furnace <NUM> 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, the combination of EBC <NUM>, bond layer <NUM>, and substrate <NUM> may be held within furnace <NUM> at the heat treatment temperature such that EBC <NUM> reaches a temperature at or above the crystalline phase temperature of EBC <NUM>. The combination of EBC <NUM>, bond layer <NUM>, and substrate <NUM> may be held within furnace <NUM> at the heat treatment temperature such that EBC <NUM> reaches a temperature at or above the temperature at which the amorphous phase transitions to a crystalline phase. The combination of EBC <NUM>, bond layer <NUM>, and substrate <NUM> may be held within furnace <NUM> for heat treatment for a suitable amount of time to provide for a desired amount of crystalline phase in EBC <NUM>.

In some examples, the relatively high rate of temperature change to the elevated heat treatment temperature may allow the amorphous phase of the as-deposited coating to flow, e.g., to fill the pores (e.g., interconnected pores), microcracks, and/or other voids of the as-deposited coating, before transitioning to crystalline phase. The filling of the pores, microcracks, and/or other voids may reduce the gas permeability of the one or more layers EBC <NUM> and/or bond layer <NUM>. In some examples, the porosity and/or microcracks of EBC <NUM> and/or bond layer <NUM> may be decreased by the first heat treatment (<NUM>). In some examples, the heat treatment of EBC <NUM> may decrease the porosity and/or microcracks of EBC <NUM> by at least about <NUM> percent (e.g., about <NUM>% to about <NUM>%), at least about <NUM>% (e.g., from about <NUM>% to about <NUM>%), or at least about <NUM> percent (e.g., from about <NUM>% to about <NUM>%), e.g., as compared to the porosity of the as-deposited EBC <NUM> and/or a similar coating that has been heat treated with a slower rate of temperature increase (e.g., <NUM>/min or less). In some examples, EBC <NUM> and/or bond layer <NUM> may be substantially hermetic following the post deposition heat treatment.

In some examples, as will be described further below, in the case of an abradable layer, the heat treatment of abradable coating <NUM> following the heat treatment of EBC <NUM> without abradable coating <NUM> may maintain or only decrease the porosity and/or microcracks of abradable layer <NUM> by about <NUM> percent or less, such as about <NUM> % to about <NUM> % or about <NUM> % to about <NUM> %, compared to the porosity of the as-deposited abradable coating <NUM>.

Additionally, or alternatively, the first heat treatment of EBC <NUM> may be configured to control the grain size and/or amount of crystalline phase in the heat treated EBC <NUM>. In some examples, the rate of temperature change, elevated heat treatment temperature, and/or duration of the heat treatment may be selected to nucleate and grow a relatively small number of grains in the heat treated EBC <NUM>. The relatively small number of grains may be grown to a relatively large size, thus reducing the concentration of grain boundaries in EBC <NUM>. Additionally, or alternatively, the heat treatment of EBC <NUM> may be configured to control the microstructure of EBC <NUM> (e.g., control the size and distribution of secondary phases such as ytterbium monosilicate in the coating).

In some examples, the number of nucleated grains may be dependent upon the heat treatment temperature. The heat treatment duration may also affect the final number of grains remaining. If the heat treatment is high enough in temperature to grow the grains, smaller grains will be consumed at the expense of the larger ones. The heat treatment temperature or temperature ranges may be selected achieve specific nucleation and/or growth characteristics. In some examples, a grain growth portion of the heat treatment may need to be performed at a high enough temperature that allows for sufficient solid state diffusion rates. In some examples, such a heat treatment temperature may have a lower limit of about <NUM> degrees Celsius.

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

Following the first heat treatment step (<NUM>), the combination of EBC <NUM>, bond layer <NUM>, and substrate <NUM> may be transferred to deposition device <NUM> and controller device <NUM> may control deposition device <NUM> to deposit abradable coating <NUM> on EBC <NUM> (<NUM>). For example, deposition device <NUM> may deposit abradable coating <NUM> by thermal spraying (e.g., air plasma spraying) or slurry deposition under the control of controller device <NUM> (<NUM>). In some examples, a tape casting process may be used to deposit abradable coating <NUM>. The same deposition device that was used to for the deposition of EBC <NUM> and bond layer <NUM> may be used to deposit abradable coating <NUM>, or a different deposition device may be used. The same deposition process that was used to for the deposition of EBC <NUM> and bond layer <NUM> may be used to deposit abradable coating <NUM>, or a different deposition process may be used.

In some examples, the as-deposited abradable coating <NUM> may have a relatively high porosity (e.g., greater than about <NUM> %, such as, about <NUM> % to about <NUM>%). The porosity of the as-deposited coating <NUM> may be achieved by removing as fugitive material from the abradable coating as described above. The as-deposited abradable coating <NUM> may have a greater porosity than the heat treated EBC <NUM>.

Following the deposition of abradable coating <NUM> on EBC <NUM> (<NUM>), article <NUM> may or may not undergo a second heat treatment step to heat treat abradable coating <NUM>. In some examples, following the deposition of abradable coating <NUM> on EBC <NUM>, article <NUM> may be transferred to furnace <NUM> by transfer device <NUM> (<NUM>) for an optional second post-deposition heat treatment (<NUM>). Once within furnace <NUM>, controller device <NUM> may control the temperature of furnace to heat treat the as-deposited abradable coating <NUM> by heating abradable coating <NUM> to or above a selected temperature for a selected period of time (<NUM>). In some examples, the second post-deposition heat treatment may take place before or after abradable coating <NUM> cools to room temperature following its deposition. The second post-deposition heat treatment temperature and duration within furnace <NUM> may be controlled by controller device <NUM> and may be selected to increase the crystalline phase concentration of abradable coating <NUM>. For example, furnace <NUM> may be at a treatment temperature of at or above the crystalline temperature of the layer(s) of abradable coating <NUM>.

In accordance with some examples of the disclosure, the second post-deposition heat treatment of abradable coating <NUM> may be configured to maintain the porosity and/or microcrack networks of abradable coating <NUM>. In some examples, the second heat treatment may include increasing the temperature of abradable coating <NUM> at a relatively slow rate (e.g., a rate less than <NUM>/min, such as, less than or equal to about <NUM>/min). In some examples, abradable coating <NUM> may be at approximately room temperature (e.g., about <NUM>) at the beginning of the second heat treatment. The temperature of abradable coating <NUM> may be increased (e.g., by heating in furnace <NUM>) at the relatively slow rate to the desired elevated heat treatment temperature. In some examples, the slow heating rate may be accomplished by not pre-heating furnace <NUM> prior to transfer of article <NUM> to furnace <NUM>. In some examples, the second heat treatment temperature may be at or above about <NUM> to about <NUM>. Abradable coating <NUM> may be held at or above the heat treatment temperature for a desired period of time (e.g., about <NUM> hours to about <NUM> hours). Controller device <NUM> may control furnace <NUM> 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, the heating rate, cooling rate, duration, and/or heat treatment temperature of the second heat treatment (<NUM>) may be different than the first heat treatment (<NUM>).

In some examples, the heat treatment of abradable coating <NUM> may be tailored to maintain or only nominally reduce the porosity of the abradable coating <NUM> prior to the heat treatment. As described above, it has been found that is some cases, increasing a temperature at a relatively low rate (e.g., less than <NUM>/min, such as about <NUM>/min) for a heat treatment of a coating may cause the amorphous phase to transition to crystalline phase with substantially no flow such that the microstructure of the coating is effectively "locked in" without the amorphous material flowing into the pores and microcrack of the as-deposited material. In such an example, the porosity (e.g., open porosity and/or microcracks) of the as-deposited coating may not substantially decrease as a result of the heat treatment. In some examples, the porosity of abradable coating <NUM> may be substantially the same as the porosity of abradable coating <NUM> prior to the heat treatment, or to be reduced by less than approximately <NUM> percent, such as about <NUM> percent to about <NUM> percent. In some examples, the porosity of abradable coating <NUM> following the second heat treatment (<NUM>) may be greater than about <NUM> % such as, about <NUM> % to about <NUM> %. The porosity of abradable coating <NUM> following the heat treatment may be greater than the porosity of the heat treated EBC <NUM>.

The technique of <FIG> is one example of a process for forming an article having both an EBC and abradable coating, wherein the EBC is heat treated prior to the deposition of the abradable coating. In some examples, the abradable coating is heat treated following the deposition rather than only heat treating the EBC with the abradable coating. In some examples, after thermal spraying of the EBC (or otherwise deposited) and before deposition of the abradable coating, the EBC may be heat treated under a particular set of conditions that promote a dense EBC, for example a high heating/cooling rate of about <NUM>/min. After the EBC is heat treated and abradable coating is thermally sprayed (or otherwise deposited) on top of the EBC, a second heat treatment is performed with a second set of conditions that maintain the porous structure of the abradable coating, for example a slow heating/cooling rate of <NUM>/min.

<FIG> illustrates a perspective diagram of an example article <NUM> that may be used in a high-temperature mechanical system. As described above, article <NUM> includes a substrate <NUM>, EBC <NUM> deposited on substrate <NUM>, and an abradable coating <NUM> deposited on EBC <NUM> and substrate <NUM>. Optional bond layer <NUM> is not shown in <FIG>.

Article <NUM> may be a component of a high-temperature mechanical system, such as, for example, a gas turbine engine or the like. In some examples, article <NUM> may include a gas turbine blade track or gas turbine blade shroud. However, while the description herein may be directed to a gas turbine blade track or shroud, it will be understood that the disclosure is not limited to such examples. Rather, abradable coating <NUM> and EBC <NUM> may be deposited over any article which requires or may benefit from an abradable coating and EBC. For example, abradable coating <NUM> and EBC <NUM> may be deposited on a cylinder of an internal combustion engine, an industrial pump, a housing or internal seal ring of an air compressor, or an electric power turbine.

While operating article <NUM> in high-temperature environments, a rotating component (e.g., blade tip <NUM>) may abrade abradable coating <NUM> to cut track <NUM> in abradable coating <NUM>. The thickness of abradable coating <NUM> may be selected such that track <NUM> does not penetrate all the way through abradable coating <NUM> into EBC <NUM>. In the case of a turbine, as the turbine blade rotates, tip <NUM> of the turbine blade contacts abradable coating <NUM> and wears away a portion of coating <NUM> to form track <NUM> in the abradable coating corresponding to the path of the turbine blade. The intimate fit between the blade tip and abradable coating provides a seal that can reduce the clearance gap between the rotating component and an inner wall of the track or shroud, which can reduce leakage around a tip of the rotating part to enhance the power and efficiency of the gas turbine engine.

The techniques described in this disclosure may be implemented, at least in part, in hardware, software, firmware, or any combination thereof. 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. 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.

Claim 1:
A method comprising:
depositing an environmental barrier coating (EBC) on a ceramic or ceramic matrix composite (CMC) substrate to form an as-deposited EBC;
heat treating the as-deposited EBC following the deposition of the as-deposited EBC on the substrate to form a heat treated EBC having a first porosity;
subsequently depositing an abradable coating on the heat treated EBC to form an as-deposited abradable coating; and
subsequently heat treating the as-deposited abradable coating to form a heat treated abradable coating having a second porosity that is greater than the first porosity of the heat treated EBC;
wherein heat treating the as-deposited EBC includes heating the as-deposited EBC at a first controlled rate,
wherein heat treating the as-deposited abradable coating includes heating the as-deposited abradable coating at a second controlled rate that is less than the first controlled rate, and
wherein the EBC and abradable coating each includes at least one of rare earth (RE) monosilicate or RE disilicate.