RELATED APPLICATIONS

The present application is a National Phase of International Application Number PCT/JP2017/027843 filed Aug. 1, 2017 and claims priority to Japanese Application Number 2016-175520 filed Sep. 8, 2016.

TECHNICAL FIELD

The present invention relates to a coating method of forming a coating layer, for example, on an inner surface of a shroud of a gas turbine, a coating layer formed by the coating method, and a turbine shroud on which the coating layer has been provided by the coating method.

BACKGROUND ART

For example, a gas turbine is used for an engine of an aircraft such as a helicopter and a jet aircraft. Such a gas turbine for aviation is configured with a compressor, a combustor, and a turbine. Therefore, the compressor compresses an air taken from an air intake port, so as to generate a compressed air having a high temperature and high pressure. Fuel is supplied in this compressed air, and the fuel is combusted by the combustor, and thus a combustion gas having a high temperature and high pressure is generated. The turbine is driven by the combustion gas. In a case of a helicopter, a rotor rotates by a driving force of the turbine. In a case of a jet aircraft, a thrust is obtained by energy of an exhaust gas.

In the gas turbine, a combustion temperature in the combustor is highly set in order to improve efficiency, and a rotor blade, a stator blade, a shroud, and the like of the turbine, which are exposed to the combustion gas (exhaust gas) having a high temperature have a thermal barrier coating (TBC) provided on surfaces thereof. In the thermal barrier coating, a top coating is provided on the surface of a base material with a bond coating interposed between the top coating and the base material. The top coating is formed by thermal spraying a thermal spraying material having small thermal conductivity.

In order to improve the efficiency of the engine of an aircraft, utilizing a material which is lightweight and excellent in heat resistance is required. Thus, applying ceramics matrix composites (CMC) exceeding characteristics of a metal-based heat resistant material has been examined. That is, a heat resistant coating layer is formed on the inner surface of a shroud produced with the CMC. In this case, the CMC and the top coating (for example, zirconia top coating) have thermal expansion coefficients different from each other. Thus, thermal stress is reduced by interposing a bond coating having an intermediate thermal expansion coefficient between the CMC and the top coating. However, if a bond coating is formed by thermal spraying an alumina coating material onto the CMC, the alumina coating material turns into an amorphous state just after the application. The alumina coating material may be crystallized at a use temperature, and cracks may occur.

As a method of forming a bond coating having high durability, a method of spraying powder slurry or performing dipping into the powder slurry and then performing sintering is provided. As such a coating method, for example, a method disclosed in PTL 1 is provided. In the coating method disclosed in PTL 1, dispersion treatment is performed on fine alumina powder with a dispersion medium and a dispersant. Then, the resultant is mixed with a coarse alumina powder, and thereby generating a coating material. The slurry of the generated coating material is applied onto the surface of a base material and then drying is performed. Then, heat treatment is performed.

CITATION LIST

Patent Literature

[PTL 1] Japanese Unexamined Patent Application Publication No. 10-330958

SUMMARY OF INVENTION

Technical Problem

In the above-described coating method in the related art, a slurry of a coating material generated by mixing fine alumina powder and coarse alumina powder is applied onto the surface of a base material and is dried. Then, heat treatment is performed. If the coarse alumina powder is mixed with the fine alumina powder, it is possible to suppress sintering shrinkage occurring in the heat treatment. However, there are problems as follows. That is, bonding between particles in a bond coating is weakened by the coarse alumina powder. When a coating material is thermally sprayed onto the surface of the bond coating, the top coating is delaminated along with the bond coating.

To solve the above-described problems, an object of the present invention is to provide a coating method, a coating layer, and a turbine shroud for improving heat resistance and adhesion.

Solution to Problem

In order to achieve the above object, according to the present invention, a coating method includes a slurry deposition step of depositing a slurry including a coarse ceramixs particle and a fine ceramixs particle on an oxide-based ceramics matrix composite such that a proportion of coarse particles decreases towards a surface of the base material, a bond coating formation step of forming a bond coating by performing a heat treatment on the base material on which the slurry has been deposited, and a top coating formation step of forming a top coating by thermal spraying a ceramic onto the bond coating.

Thus, a bond coating is formed in a manner that a slurry including a coarse ceramixs particle and a fine ceramixs particle is deposited on a base material configured with an oxide-based ceramics matrix composite, and then a heat treatment is performed. A top coating is formed by thermal spraying a ceramic onto the bond coating. At this time, in the bond coating, the slurry is deposited such that the proportion of coarse particles decreases towards the surface of the slurry. Therefore, the bond coating largely contains the coarse ceramixs particle on the base material side, and thus it is possible to relieve stress occurring by sintering shrinkage. In addition, since the coarse ceramixs particle is contained small on the top coating side, bonding between particles in the ceramic increases. Thus, hardness becomes high, and it is possible to suppress erosion when the top coating is formed. As a result, it is possible to improve heat resistance and adhesion of a coating layer.

According to the present invention, in the coating method, the slurry deposition step includes a first slurry deposition step of depositing a first slurry in which the coarse ceramixs particle and the fine ceramixs particle are mixed at a first proportion which has been set, on the base material, and a second slurry deposition step of depositing a second slurry in which the coarse ceramixs particle and the fine ceramixs particle are mixed at a second proportion having a proportion of coarse particles, which is lower than that in the first proportion, on the surface of the first slurry.

Thus, the first slurry in which the coarse ceramixs particle and the fine ceramixs particle are mixed at the first proportion is deposited on the base material, and the second slurry in which the coarse ceramixs particle and the fine ceramixs particle are mixed at the second proportion having a proportion of coarse particles, which is lower than that in the first proportion is deposited on the surface of the first slurry. Accordingly, it is possible to easily cause the proportion of coarse particles in the first bond coating on the base material side to be different from the proportion of coarse particles in the second bond coating on the top coating side. It is possible to simplify a coating production process and to reduce cost.

According to the present invention, in the coating method, the proportion of coarse particles in the first slurry is in a range of 60% to 80%, and the proportion of coarse particles in the second slurry is in a range of 40% to 60%.

Thus, the proportion of the coarse particles in each of the first bond coating and the second bond coating is set to be the optimum value. Accordingly, it is possible to relieve stress occurring by sintering shrinkage in the entirety of the bond coating. In addition, since the coarse ceramixs particle is contained small on the top coating side, bonding between particles in the ceramic increases. Thus, hardness becomes high, and it is possible to suppress erosion when the top coating is formed.

According to the present invention, in the coating method, the oxide-based ceramics matrix composite is an alumina⋅silica type oxide-based ceramics matrix composite, and the coarse ceramixs particle and the fine ceramixs particle are alumina-based powder.

Thus, a ceramic having a thermal expansion coefficient positioned at an intermediate position between the thermal expansion coefficients of the base material and the top coating is applied as the coating material of the bond coating, and thus it is possible to reduce an influence of thermal stress occurring in sintering.

According to the present invention, in the coating method, the oxide-based ceramics matrix composite is a pure alumina type oxide-based ceramics matrix composite, and the coarse ceramixs particle and the fine ceramixs particle are alumina-based powder and zirconia-based powder.

Thus, a ceramic having a thermal expansion coefficient positioned at an intermediate position between the thermal expansion coefficients of the base material and the top coating is applied as the coating material of the bond coating, and thus it is possible to reduce an influence of thermal stress occurring in sintering.

According to the present invention, in the coating method, the top coating is a zirconia abradable top coating.

Thus, since the zirconia abradable top coating is used as the top coating, the top coating obtains a self-wearing type impact absorbing function, and thus, when the coating layer is brought into contact with the peripheral member, it is possible to relieve an impact force by the top coating being worn, and to prevent wear or breakage of the peripheral member.

According to the present invention, a coating layer includes a bond coating obtained by sintering a coating material including a coarse ceramixs particle and a fine ceramixs particle on a base material configured with an oxide-based ceramics matrix composite such that a proportion of coarse particles decreases towards a surface of the base material, and a top coating formed by thermal spraying a ceramic onto the bond coating.

Thus, in the bond coating, since the coating material is sintered such that the proportion of coarse particles decreases towards the surface side of the slurry, the bond coating largely contains the coarse ceramixs particle on the base material side, and thus it is possible to relieve stress occurring by sintering shrinkage. In addition, since the coarse ceramixs particle is contained small on the top coating side, bonding between particles in the ceramic increases. Thus, hardness becomes high, and it is possible to suppress erosion when the top coating is formed. As a result, it is possible to improve heat resistance and adhesion of a coating layer.

According to the present invention, in the coating layer, the bond coating includes a first bond coating obtained by sintering a first coating material in which the coarse ceramixs particle and the fine ceramixs particle are mixed at a first proportion which has been preset, and a second bond coating obtained by sintering a second coating material in which the coarse ceramixs particle and the fine ceramixs particle are mixed at a second proportion having a proportion of coarse particles, which is lower than that in the first proportion, on a surface of the first bond coating.

Thus, it is possible to easily cause the proportion of coarse particles in the first bond coating on the base material side to be different from the proportion of coarse particles in the second bond coating on the top coating side. It is possible to simplify a coating production process and to reduce cost.

According to the present invention, there is provided a turbine shroud in which the coating layer is provided on the inner surface thereof.

Thus, regarding the bond coating, it is possible to relieve stress occurring by sintering shrinkage on the base material side. In addition, since bonding between particles in the ceramic increases on the top coating side, hardness becomes high, and it is possible to suppress the erosion when the top coating is formed. As a result, it is possible to improve heat resistance and adhesion of a coating layer and to improve durability of a turbine shroud.

Advantageous Effects of Invention

According to the coating method, the coating layer, and the turbine shroud of the present invention, when a bond coating and a top coating are formed on a base material configured with an oxide-based ceramics matrix composite, in the bond coating, the proportion of coarse particles of the ceramic decreases towards the surface side of a slurry. Thus, the coarse ceramixs particle is largely contained on the base material side, and it is possible to relieve stress occurring by sintering shrinkage. In addition, since the coarse ceramixs particle is contained small on the top coating side, bonding between particles in the ceramic increases, and thus hardness becomes high, and it is possible to suppress the erosion when the top coating is formed. As a result, it is possible to improve heat resistance and adhesion of a coating layer.

