Coated member, coating material, and method of manufacturing coated member

Abstract

A coated member includes a heat-shielding coating layer made of a zirconia-dispersed silicate in which ytterbia-stabilized zirconia is precipitated as a dispersed phase in a matrix phase which is any one of a rare earth disilicate, a rare earth monosilicate, and a mixed phase of the rare earth disilicate and the rare earth monosilicate. The rare earth disilicate is a (Y.sub.1-a[Ln.sub.1].sub.a).sub.2Si.sub.2O.sub.7 solid solution wherein Ln.sub.1 is any one of Sc, Yb, and Lu, or a (Y.sub.1-c[Ln.sub.2].sub.c).sub.2Si.sub.2O.sub.7 solid solution wherein Ln.sub.2 is any one of Nd, Sm, Eu, and Gd. The rare earth monosilicate is Y.sub.2SiO.sub.5, [Ln.sub.1].sub.2SiO.sub.5, a (Y.sub.1-b[Ln.sub.1]b).sub.2SiO.sub.5 solid solution wherein Ln.sub.1 is any one of Sc, Yb, and Lu, or a (Y.sub.1-d[Ln.sub.2].sub.d).sub.2SiO.sub.5 solid solution wherein Ln.sub.2 is any one of Nd, Sm, Eu, and Gd.

Claims

1. A method of manufacturing a coated member, the method comprising: forming a heat-shielding coating layer on a substrate by spraying particles onto the substrate made of a silicon-based ceramic or a ceramic fiber-reinforced ceramic matrix composite, the particles being obtained by mixing any one of rare earth disilicate powder, rare earth monosilicate powder and mixed powder of the rare earth disilicate powder and the rare earth monosilicate powder with ytterbia-stabilized zirconia powder containing ytterbia in a content of 8 wt % or more and 27 wt % or less and diffusion heat-treating the obtained mixed powder at a temperature of 1300 C. or more and 1700 C. or less, wherein the rare earth disilicate powder is made a (Y.sub.1-a[Ln.sub.1].sub.a).sub.2Si.sub.2O.sub.7 solid solution (here, Ln.sub.1 is any one of Sc, Yb, and Lu, a is 0.05 or more and less than 1 when Ln.sub.1 is Sc, and a is 0.2 or more and less than 1 when Ln.sub.1 is Yb or Lu, and the rare earth monosilicate powder is made of a (Y.sub.1-b[Ln.sub.1].sub.b).sub.2SiO.sub.5 solid solution (here, Ln.sub.1 is any one of Sc, Yb, and Lu, and 0<b0.5).

2. The method of claim 1, wherein the substrate is made of an oxide-based ceramic fiber-reinforced oxide-based ceramic matrix composite or a SiC fiber-reinforced SiC matrix composite.

3. The method of claim 2, wherein the oxide-based ceramic fiber-reinforced oxide-based ceramic matrix composite is an Al.sub.2O.sub.3 fiber-reinforced Al.sub.2O.sub.3 matrix composite.

4. The method of claim 1, wherein an addition amount of the ytterbia-stabilized zirconia in the particles is 50 vol % or more and 90 vol % or less.

5. The method of claim 1, wherein any one of the rare earth disilicate powder, the rare earth monosilicate powder, and the mixed powder thereof is mixed with the ytterbia-stabilized zirconia at a mixing ratio at which a difference in thermal expansion coefficient between the substrate and the heat-shielding coating layer is less than 310.sup.6/K.

6. A method of manufacturing a coated member, the method comprising: forming a heat-shielding coating layer on a substrate by spraying particles onto the substrate made of a silicon-based ceramic or a ceramic fiber-reinforced ceramic matrix composite, the particles being obtained by mixing any one of rare earth disilicate powder, rare earth monosilicate powder and mixed powder of the rare earth disilicate powder and the rare earth monosilicate powder with ytterbia-stabilized zirconia powder containing ytterbia in a content of 8 wt % or more and 27 wt % or less and diffusion heat-treating the obtained mixed powder at a temperature of 1300 C. or more and 1700 C. or less, wherein the rare earth disilicate powder is made of any one of a (Y.sub.1-c[Ln.sub.2].sub.c).sub.2Si.sub.2O.sub.7 solid solution (here, Ln.sub.2 is any one of Nd, Sm, Eu, and Gd, c is 0.1 or more and less than 1 when Ln.sub.2 is Nd, Sm, or Eu, and c is 0.2 or more and less than 1 when Ln.sub.2 is Gd, and the rare earth monosilicate powder is made of a (Y.sub.1-d[Ln.sub.2].sub.d).sub.2SiO.sub.5 solid solution (here, Ln.sub.2 is any one of Nd, Sm, Eu, and Gd, and 0<d0.5).

7. The method of claim 6, wherein the substrate is made of an oxide-based ceramic fiber-reinforced oxide-based ceramic matrix composite or a SiC fiber-reinforced SiC matrix composite.

8. The method of claim 7, wherein the oxide-based ceramic fiber-reinforced oxide-based ceramic matrix composite is an Al.sub.2O.sub.3 fiber-reinforced Al.sub.2O.sub.3 matrix composite.

9. The method of claim 6, wherein an addition amount of the ytterbia-stabilized zirconia in the particles is 50 vol % or more and 90 vol % or less.

10. The method of claim 6, wherein any one of the rare earth disilicate powder, the rare earth monosilicate powder, and the mixed powder thereof is mixed with the ytterbia-stabilized zirconia at a mixing ratio at which a difference in thermal expansion coefficient between the substrate and the heat-shielding coating layer is less than 310.sup.6/K.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic cross-sectional view of a coated member according to a first embodiment.

(2) FIG. 2 is a graph illustrating a relationship between a temperature and a crystal structure of a rare earth disilicate.

(3) FIG. 3 is a view illustrating a change in crystal structure by heat-treatment of a Y.sub.2Si.sub.2O.sub.7 spray coating film.

(4) FIG. 4 is view illustrating a change in crystal structure by heat-treatment of a (Y.sub.0.8Yb.sub.0.2).sub.2Si.sub.2O.sub.7 solid solution spray coating film.

(5) FIG. 5 is view illustrating a change in crystal structure by heat-treatment of a (Y.sub.0.8Gd.sub.0.2).sub.2Si.sub.2O.sub.7 solid solution spray coating film.

(6) FIG. 6 is a schematic cross-sectional view of a coated member according to a second embodiment.

DESCRIPTION OF EMBODIMENTS

First Embodiment

(7) FIG. 1 is a schematic cross-sectional view of a coated member according to a first embodiment. A coated member 100 includes a heat-shielding coating layer 102 on a substrate 101.

(8) The substrate 101 is a turbine member of an aircraft engine or a gas turbine member for powder generation such as a shroud, a combustion liner, or the like. In detail, the substrate 101 is made of a silicon (Si)-based ceramic or a ceramic fiber-reinforced ceramic matrix composite. The silicon-based ceramic means a ceramic containing silicon such as SiC, Si.sub.3N.sub.4, or the like. The ceramic fiber-reinforced ceramic matrix composite is an oxide-based ceramic fiber-reinforced oxide-based ceramic matrix composite exemplified by a SiC fiber-reinforced SiC matrix composite or an Al.sub.2O.sub.3 fiber-reinforced Al.sub.2O.sub.3 matrix composite.

(9) In the present embodiment, the heat-shielding coating layer 102 is a layer made of a zirconia-dispersed silicate in which ytterbia-stabilized zirconia (YbSZ) is precipitated as a dispersed phase in a matrix phase which is any one of a rare earth disilicate, a rare earth monosilicate, and a mixed phase of the rare earth disilicate and the rare earth monosilicate. A thickness of the heat-shielding coating layer 102 is 50 m or more and 500 m or less.

(10) In the present embodiment, YbSZ is zirconia (ZrO.sub.2) to which ytterbia (Yb.sub.2O.sub.3) is added as a stabilizer in a content of 8 wt % or more and 27 wt % or less. YbSZ has excellent high-temperature stability at a high temperature (for example, about 1300 C. to 1400 C.) and imparts erosion resistance to the heat-shielding coating layer 102. When an addition amount of ytterbia is less than 8 wt %, phase stability is deteriorated. When the addition amount of ytterbia is more than 27 wt %, mechanical properties are deteriorated.

(11) The rare earth disilicate is any one of a (Y.sub.1-a[Ln.sub.1].sub.a).sub.2Si.sub.2O.sub.7 solid solution (here, Ln.sub.1 is at least one of Sc, Yb, and Lu, a is 0.05 or more and less than 1 when Ln.sub.1 is Sc, and a is 0.2 or more and less than 1 when Ln.sub.1 is Yb or Lu), Sc.sub.2Si.sub.2O.sub.7, Yb.sub.2Si.sub.2O.sub.7, and Lu.sub.2Si.sub.2O.sub.7.

(12) Alternatively, the rare earth disilicate is any one of a (Y.sub.1-c[Ln.sub.2].sub.c).sub.2Si.sub.2O.sub.7 solid solution (here, Ln.sub.2 is at least one of Nd, Sm, Eu, and Gd, c is 0.1 or more and less than 1 when Ln.sub.2 is Nd, Sm, or Eu, and c is 0.2 or more and less than 1 when Ln.sub.2 is Gd), Nd.sub.2Si.sub.2O.sub.7, Sm.sub.2Si.sub.2O.sub.7, Eu.sub.2Si.sub.2O.sub.7, and Gd.sub.2Si.sub.2O.sub.7.

(13) FIG. 2 is a graph illustrating a relationship between a temperature and a crystal structure of a rare earth disilicate (Reference of the graph: A. J. F. Carrion et al., Structural and Kinetic Study of Phase Transitions in LaYSi.sub.2O.sub.7, Journal of the European Ceramic Society, Vol. 32 (2012) PP. 2477-2486, A boundary line of the crystal structure is added by the present inventor). In FIG. 2, a horizontal axis indicates an ionic radius of a rare earth element, and a vertical axis indicates a temperature.

(14) An ionic radius of Y.sup.3+ is 0.90 , and referring to FIG. 2, phase transition ( phase.fwdarw. phase) occurs at about 1280 C. That is, when the coated member is used in a temperature environment higher than 1300 C., phase transformation accompanied with a volume change is generated by repetitive cooling and heating.

(15) Referring to FIG. 2, an ionic radius on a boundary line between the phase and the phase at 1300 C. is 0.897 . That is, when the ionic radius of the rare earth element is 0.897 or less, crystal stability of the rare earth disilicate can be secured up to 1300 C. An ionic radius on a boundary line between the phase and the phase at 1400 C. is 0.885 . That is, when the ionic radius of the rare earth element is 0.885 or less, crystal stability of the rare earth disilicate can be secured up to 1400 C.

(16) In the (Y.sub.1-a[Ln.sub.1].sub.a).sub.2Si.sub.2O.sub.7 solid solution in which Y is substituted with a separate rare earth element, an average ionic radius of rare earth elements (Y and Ln.sub.1) is changed depending on a substitution amount. In order to allow the average ionic radius to be smaller than that of Y, Y is substituted with a rare earth element having an ionic radius smaller than that of Y. Referring to FIG. 2, the elements having an ionic radius smaller than that of Y are Sc, Yb, Lu, Tm, and Er. Particularly, in the cases of Sc, Yb, and Lu, the ionic radius is small as compared to Y, and a phase of disilicate is stably present up to a high temperature.

(17) Table 1 illustrates a substitution amount of a substitution element (Sc, Yb, or Lu) in the (Y.sub.1-a[Ln.sub.1].sub.a).sub.2Si.sub.2O.sub.7 solid solution and an average ionic radius of the rare earth elements.

(18) TABLE-US-00001 TABLE 1 Substitution Element a Sc Yb Lu 0 0.9 0.9 0.9 0.05 0.892 0.898 0.898 0.1 0.885 0.897 0.897 0.2 0.869 0.894 0.894 0.3 0.854 0.89 0.89 0.4 0.838 0.887 0.887 0.5 0.823 0.884 0.884

(19) Referring to Table 1, the average ionic radius is to be 0.897 or less if a is 0.05 or more for Sc, and 0.1 or more for Yb or Lu. That is, when a is equal to or higher than the above-mentioned range, the coated member can withstand an operation temperature of 1300 C.

(20) Further, referring to Table 1, the average ionic radius is to be 0.885 or less if a is 0.1 or more for Sc, and 0.5 or more for Yb or Lu. That is, when a is equal to or higher than the above-mentioned range, the coated member can withstand an operation temperature of 1400 C. or more.

(21) In the case in which a rare earth element has a larger ionic radius as that of Y, there is a boundary between an phase and a phase as illustrated in FIG. 2. Referring to FIG. 2, an ionic radius on a boundary line between the phase and the phase at 1300 C. is 0.905 . That is, when the ionic radius of the rare earth element is 0.905 or more, crystal stability of the rare earth disilicate can be secured up to 1300 C. An ionic radius on a boundary line between the phase and the phase at 1400 C. is 0.91 . That is, when the ionic radius of the rare earth element is 0.91 or more, crystal stability of the rare earth disilicate can be secured up to 1400 C.

(22) In order to allow the average ionic radius to be larger than that of Y, Y is substituted with a rare earth element having an ionic radius larger than that of Y. As a difference in ionic radius between a rare earth element and Y is increased, an effect of changing an average ionic radius of the rare earth elements is increased. Therefore, it is advantageous to select an element having an ionic radius larger than that of Gd in FIG. 2. Meanwhile, Pr, Ce, and La have high reactivity with steam, such that steam resistance of the coating film is deteriorated. Therefore, Gd, Eu, Sm, and Nd are suitable as a substitution element of Y.

(23) Table 2 illustrates a substitution amount of a substitution element (Gd, Eu, Sm, or Nd) in (Y.sub.1-c[Ln.sub.2].sub.c).sub.2Si.sub.2O.sub.7 and an average ionic radius of the rare earth elements.

(24) TABLE-US-00002 TABLE 2 Substitution Element c Nd Sm Eu Gd 0 0.9 0.9 0.9 0.9 0.1 0.908 0.906 0.905 0.9038 0.2 0.917 0.912 0.909 0.9076 0.3 0.925 0.917 0.914 0.9114 0.4 0.933 0.923 0.919 0.9152 0.5 0.942 0.929 0.924 0.919

(25) Referring to Table 2, the average ionic radius is to be 0.905 or more if c is 0.1 or more for Nd, Sm, or Eu, and 0.2 or more for Cd. That is, when c is equal to or higher than the above-mentioned range, the coated member can withstand an operation temperature up to 1300 C.

(26) Further, referring to Table 2, the average ionic radius is to be 0.91 or more if c is 0.2 or more for Nd or Sm, and 0.3 or more for Eu or Gd. That is, when c is equal to or higher than the above-mentioned range, the coated member can withstand an operation temperature up to 1400 C.

(27) In the case in which the rare earth disilicate is (Y.sub.1-a[Ln.sub.1].sub.a).sub.2Si.sub.2O.sub.7 (here, Ln.sub.1 is at least one of Sc, Yb, and Lu), the rare earth monosilicate is Y.sub.2SiO.sub.5, [Ln.sub.1].sub.2SiO.sub.5, or a (Y.sub.1-b[Ln.sub.1].sub.b).sub.2SiO.sub.5 solid solution (here, Ln.sub.1 is any one of Sc, Yb, and Lu, and 0<b0.5).

(28) In the case in which the rare earth disilicate is (Y.sub.1-c[Ln.sub.2].sub.c).sub.2Si.sub.2O.sub.7 (here, Ln.sub.2 is at least one of Nd, Sm, Eu, and Gd), the rare earth monosilicate is Y.sub.2SiO.sub.5 or a (Y.sub.1-d[Ln.sub.2].sub.d).sub.2SiO.sub.5 solid solution (here, Ln.sub.2 is any one of Nd, Sm, Eu, and Gd, and 0<d0.5).

(29) Since the rare earth monosilicate has a low activity of SiO.sub.2 as compared to the rare earth disilicate, the rare earth monosilicate has high steam resistance. Among the rare earth monosilicates, Y.sub.2SiO.sub.5 is cheap. Sc.sub.2SiO.sub.5, Yb.sub.2SiO.sub.5, Lu.sub.2SiO.sub.5, Nd.sub.2SiO.sub.5, Sm.sub.2SiO.sub.5, Eu.sub.2SiO.sub.5, and Gd.sub.2SiO.sub.5 have almost similar properties to those of Y.sub.2SiO.sub.5. Therefore, as the rare earth monosilicate, one of these compounds may be used alone or Y in Y.sub.2SiO.sub.5 can be substituted with at least one of Sc, Yb, and Lu, or at least one of Nd, Sm, Eu, and Gd.

(30) As the rare earth monosilicate, Y.sub.2SiO.sub.5 (substitution amounts b=0, and d=0) can be used, but in order to prevent concentrations of the rare earth elements from being changed by interdiffusion with the rare earth disilicate, (Y.sub.1-aLn.sub.1a).sub.2Si.sub.2O.sub.7 and (Y.sub.1-c[Ln.sub.2].sub.c).sub.2Si.sub.2O.sub.7, coexisting in the mixed phase, it is preferable that the substitution amounts b and d are the same as the substitution amounts a and c of the rare earth disilicate. When the substitution amounts b and d are large, cost is increased, such that upper limits of b and d are 0.5.

(31) In a coated member 100 corresponding to a laminate, when a difference in thermal expansion coefficient between the substrate 101 and the heat-shielding coating layer 102 is large, thermal stress is generated in the heat-shielding coating layer 102. Cracks, or the like, occur in the heat-shielding coating layer 102 due to thermal stress generated in the heat-shielding coating layer 102 by repeating operation and stop of equipment (aircraft engine or gas turbine). In order to alleviate thermal stress generated in the heat-shielding coating layer 102, a difference between the thermal expansion coefficient of the heat-shielding coating layer 102 and the thermal expansion coefficient of the substrate 101 needs to be less than 310.sup.6/K, and preferably, less than 210.sup.6/K (at room temperature to 1200 C.)

(32) A thermal expansion coefficient of a mixture is changed depending on a mixing ratio of each component. In order to allow the difference in thermal expansion coefficient to be above-mentioned range, a mixing ratio between the rare earth silicates and YbSZ, the kinds of rare earth disilicate and rare earth monosilicate, a substitution amount of the rare earth element, and a mixing ratio between the rare earth monosilicate and the rare earth disilicate in the case in which the mixed phase of the rare earth monosilicate and the rare earth disilicate is used as the matrix phase are determined depending on the kind of substrate 101.

(33) For example, the thermal expansion coefficient of the substrate 101 is 610.sup.6/K to 810.sup.6/K (at room temperature to 1200 C.) if the substrate 101 is made of the Al.sub.2O.sub.3 fiber-reinforced Al.sub.2O.sub.3 matrix composite, the thermal expansion coefficient of the substrate 101 is 3.510.sup.6/K to 4.510.sup.6/K if the substrate 101 is made of the SiC fiber-reinforced SiC matrix composite, the thermal expansion coefficient of the substrate 101 is 4.510.sup.6/K if the substrate is made of SiC, and the thermal expansion coefficient of the substrate 101 is 3.310.sup.6/K if the substrate is made of Si.sub.3N.sub.4.

(34) A thermal expansion coefficient of YbSZ (8 to 27 wt % Yb.sub.2O.sub.3ZrO.sub.2) is 10.310.sup.6/K (at room temperature to 1200 C.). The thermal expansion coefficient of the rare earth monosilicate is 7.110.sup.6/K to 10.110.sup.6/K (for example, a thermal expansion coefficient of Y.sub.2SiO.sub.5 is 7.410.sup.6/K) (at room temperature to 1200 C.), and the thermal expansion coefficient of the rare earth disilicate is 3.710.sup.6/K to 4.210.sup.6/K (for example, a thermal expansion coefficient of Y.sub.2Si.sub.2O.sub.7 is 3.710.sup.6/K) (at room temperature to 1200 C.)

(35) YbSZ has a large thermal expansion coefficient as compared to the substrate. In the case in which an addition amount of YbSZ is large, thermal stress is generated in the heat-shielding coating layer 102. Meanwhile, in the case in which the addition amount of YbSZ is small, sufficient erosion resistance cannot be obtained. Therefore, it is preferable that the addition amount of YbSZ is 50 vol % or more and 90 vol % or less.

(36) In the case in which the substrate 101 is made of the Al.sub.2O.sub.3 fiber-reinforced Al.sub.2O.sub.3 matrix composite, even though the matrix phase is made of the rare earth monosilicate, a difference in thermal expansion coefficient between the substrate 101 and the heat-shielding coating layer 102 is small, thereby suppressing thermal stress in the heat-shielding coating layer 102. This combination is advantageous in that a heat-shielding coating layer 102 having excellent steam resistance can be obtained.

(37) Meanwhile, in the case in which the substrate 101 is made of a material of which a thermal expansion coefficient is significantly different from that of YbSZ, such as the SiC fiber-reinforced SiC matrix composite or the silicon-based ceramic, thermal stress in the heat-shielding coating layer 102 can be suppressed by selecting the rare earth disilicate, which is a material having a small thermal expansion coefficient, as a matrix phase. Further, in the case of using the mixed phase of the rare earth disilicate and the rare earth monosilicate as the matrix phase, it is possible to impart excellent steam resistance to the heat-shielding coating layer 102 while decreasing the thermal expansion coefficient of the heat-shielding coating layer 102.

(38) The heat-shielding coating layer 102 according to the present embodiment is formed by a spray method. Spray particles are prepared by the method described below.

(39) The rare earth disilicate and the rare earth monosilicate corresponding to the matrix phase are prepared by the method described below.

(40) As raw material powder of the rare earth disilicate, SiO.sub.2 powder, Y.sub.2O.sub.3 powder, [Ln.sub.1].sub.2O.sub.3 (here, Ln.sub.1 is any one of Sc, Yb, and Lu), and [Ln.sub.2].sub.2O.sub.3 powder (here, Ln.sub.2 is any one of Nd, Sm, Eu, and Gd) are weighed and mixed with each other so as to have a predetermined composition.

(41) As raw material powder of the rare earth monosilicate, SiO.sub.2 powder, Y.sub.2O.sub.3 powder, [Ln.sub.1].sub.2O.sub.3 (here, Ln.sub.1 is any one of Sc, Yb, and Lu), and [Ln.sub.2].sub.2O.sub.3 powder (here, Ln.sub.2 is any one of Nd, Sm, Eu, and Gd) are weighed and mixed with each other so as to have a predetermined composition.

(42) The mixed powder is heat-treated, thereby obtaining rare earth disilicate powder and rare earth monosilicate powder. As a method of performing heat-treatment, there is a method of performing heat-treatment at 1300 C. or more using an electric furnace, a method of performing plasma heat-treatment, a method of melting the raw material powder and grinding the obtained melt, or the like.

(43) Since a reaction by heat-treatment can be promoted by using fine powder having a particle size of 1 m or less as the raw material powder, it is possible to decrease a heat-treatment time while removing un-reacted particles.

(44) The powder after heat-treatment was pulverized and classified into 1 m to 50 m or so.

(45) Alternatively, commercial Y.sub.2Si.sub.2O.sub.7 powder, [Ln.sub.1].sub.2Si.sub.2O.sub.7 powder, [Ln.sub.2].sub.2Si.sub.2O.sub.7 powder, [Ln.sub.1].sub.2SiO.sub.5 powder, and [Ln.sub.2].sub.2Si.sub.2O.sub.5 powder may be used as the raw material powder.

(46) In the case in which the mixed powder of the rare earth disilicate powder and the rare earth monosilicate powder is used as the matrix phase, the rare earth disilicate powder and the rare earth monosilicate powder prepared as described above are weighed and mixed with each other to have a predetermined composition ratio.

(47) In order to obtain YbSZ, ZrO.sub.2 powder and Yb.sub.2O.sub.3 powder in a predetermined ratio (8 wt % or more and 27 wt % or less) are mixed together with a suitable binder and a suitable dispersant in a ball mill, thereby preparing slurry. This slurry is granulated and dried by a spray drier, and subjected to diffusion heat-treatment at 1300 C. to 1700 C. so that Yb.sub.2O.sub.3 and ZrO.sub.2 are solid-solubilized, thereby obtaining YbSZ powder.

(48) The YbSZ powder after heat-treatment was pulverized and classified into 1 m to 50 m or so.

(49) The rare earth disilicate powder, the rare earth monosilicate powder, or a mixed powder of the rare earth disilicate powder and the rare earth monosilicate powder is mixed with the YbSZ powder at a predetermined ratio.

(50) Zirconia-dispersed silicate powder is obtained by performing heat-treatment on the mixed powder. As a method of performing heat-treatment, there is a method of performing heat-treatment at 100 C. or more using an electric furnace, a method of performing plasma heat-treatment, a method of melting the raw material powder and grinding the obtained melt, or the like.

(51) The mixed powder is prepared by using fine powder having a particle size of 1 m or less, such that a reaction by heat-treatment can be promoted, and it is possible to decrease a heat-treatment time while removing un-reacted particles.

(52) The particles after heat-treatment are pulverized and classified, and particles having a size of 10 m to 200 m are used for spraying as a coating material.

(53) In order to verify phase stability of the rare earth disilicate, spray powder of Y.sub.2Si.sub.2O.sub.7, a (Y.sub.0.8Yb.sub.0.2).sub.2Si.sub.2O.sub.7 solid solution, and a (Y.sub.0.8Gd.sub.0.2).sub.2Si.sub.2O.sub.7 solid solution were prepared by the method as described above. Further, spray coating films were manufactured using these powder.

(54) The manufactured spray coating film was heat-treated at 1300 C. for 100 hours and 1400 C. for 100 hours, and a change in crystal phase was determined by X-ray diffraction (XRD). As illustrated in FIG. 3, in the case of Y.sub.2Si.sub.2O.sub.7, a coating film was amorphous in the as-sprayed state, and after heat-treatment at 1300 C. for 100 hours, the coating film was composed of a -Y.sub.2Si.sub.2O.sub.7 phase and an X.sub.2Y.sub.2SiO.sub.5 phase. After heat-treatment at 1400 C. for 100 hours, the coating film was composed of two phases, that is, a -Y.sub.2Si.sub.2O.sub.7 phase and the X.sub.2Y.sub.2SiO.sub.5 phase. Therefore, it may be appreciated that at 1300 C. or more, phase transformation from -Y.sub.2Si.sub.2O.sub.7 to -Y.sub.2Si.sub.2O.sub.7 occurred.

(55) Meanwhile, FIG. 4 illustrates the results obtained by heat-treating a (Y.sub.0.8Yb.sub.0.2).sub.2Si.sub.2O.sub.7 solid solution spray coating film in which Y was partially substituted with Yb at 1300 C. for 100 hours and at 1400 C. for 100 hours. It may be appreciated that in the cases of heat-treatment at 1300 C. for 100 hours and at 1400 C. for 100 hours, there was almost no change in a diffraction peak, and thus, phase transformation was suppressed.

(56) Meanwhile, FIG. 5 illustrates the results obtained by heat-treating a (Y.sub.0.8Gd.sub.0.2).sub.2Si.sub.2O.sub.7 solid solution spray coating film in which Y was partially substituted with Gd at 1300 C. for 100 hours and at 1400 C. for 100 hours. It may be appreciated that in the cases of heat-treatment at 1300 C. for 100 hours and at 1400 C. for 100 hours, there was almost no change in a diffraction peak, and thus, phase transformation was suppressed.

Second Embodiment

(57) FIG. 6 is a schematic cross-sectional view of a coated member according to a second embodiment. In a coated member 200, a bond coat 202 and a top coat 203 are sequentially laminated on a substrate 201. The top coat 203 is composed of three layers. An outermost layer of the top coat 203 is a heat-shielding coating layer 206.

(58) The substrate 201 is made of the same material as in the first embodiment.

(59) The bond coat 202 is to secure good adhesion between the substrate 201 and the top coat 203. The bond coat 202 is made of Si, silicide such as MoSi.sub.2, LuSi, or the like, mullite (3Al.sub.2O.sub.3-2SiO.sub.2), barium strontium aluminosilicate (BSAS, (Ba.sub.1-xSr.sub.x)OAl.sub.2O.sub.3SiO.sub.2), or the like. The bond coat 202 may be made of one of the above-mentioned materials or formed by laminating a plurality of materials. The bond coat 202 has a thickness of 20 m or more and 200 m or less.

(60) The bond coat 202 is formed by a spray method, a sintering method, or the like.

(61) A first layer 204 of the top coat is composed of a mixed phase of a rare earth disilicate and a rare earth monosilicate. A thickness of the first layer 204 is 20 m or more and 400 m or less.

(62) In detail, the first layer 204 is composed of a mixed phase of a rare earth disilicate represented by a (Y.sub.1-e[Ln.sub.3].sub.e).sub.2Si.sub.2O.sub.7 solid solution (here, Ln.sub.3 is any one of Sc, Yb, and Lu, e is 0.05 or more and 0.5 or less when Ln.sub.3 is Sc, and e is 0.2 or more and 0.5 or less when Ln.sub.3 is Yb or Lu), and a rare earth monosilicate represented by a Y.sub.2SiO.sub.5 or a (Y.sub.1-f[Ln.sub.3].sub.f).sub.2SiO.sub.5 solid solution (here, Ln.sub.3 is any one of Sc, Yb, and Lu, and f is more than 0 to 0.5 or less).

(63) Alternatively, the first layer 204 is composed of a mixed phase of a rare earth disilicate represented by a (Y.sub.1-g[Ln.sub.4].sub.g).sub.2Si.sub.2O.sub.7 solid solution (here, Ln.sub.4 is any one of Nd, Sm, Eu, and Gd, g is 0.1 or more and 0.5 or less when Ln.sub.4 is Nd, Sm, or Eu, and g is 0.2 or more and 0.5 or less when Ln.sub.4 is Gd), and a rare earth monosilicate represented by a Y.sub.2SiO.sub.5 or a (Y.sub.1-h[Ln.sub.4].sub.h).sub.2SiO.sub.5 solid solution (here, Ln.sub.4 is any one of Nd, Sm, Eu, and Gd, and h is more than 0 to 0.5 or less).

(64) When e and g of the rare earth disilicate in the first layer 204 are within the above-mentioned ranges, the coated member can withstand an operation temperature of 1400 C. or more. If e and g are large, an amount of the substitution element is increased. Therefore, in consideration of raw material cost, cost for substitution is increased by using Sc, Yb, and Lu, or Nd, Sm, Eu, and Gd, which are expensive elements. Therefore, there is an upper limit in the substitution amounts of Sc, Yb, and Lu, or Nd, Sm, Eu, and Gd. In detail, it is preferable that upper limits of e and g are 0.5.

(65) As the rare earth monosilicate, Y.sub.2SiO.sub.5 (substitution amount f=0, and h=0) can be used. However, in order to prevent concentrations of rare earth elements from being changed by interdiffusion with the rare earth disilicate, coexisting in the mixed phase, it is preferable that the substitution amounts f and h are the same as substitution amounts e and g of the rare earth disilicate. Meanwhile, when the substitution amounts f and h exceed the above-mentioned ranges, raw material cost is increased, which is not preferable.

(66) In order to alleviate thermal stress in the top coat 203, a difference in thermal expansion coefficient between the first layer 204 and a base (substrate 201 including the bond coat 202) is less than 310.sup.6/K, and preferably, less than 210.sup.6/K (at room temperature to 1200 C.). In order to allow the difference in thermal expansion coefficient to be in the above-mentioned range, a composition of the rare earth disilicate, a composition of the rare earth monosilicate, and a mixing ratio between the rare earth disilicate and the rare earth monosilicate are determined depending on the kinds of substrate 201 and bond coat 202.

(67) The first layer 204 is formed by a spray method. Spray particles for forming the first layer 204 are prepared by the same process as that in the first embodiment described above. That is, rare earth disilicate powder and rare earth monosilicate powder having predetermined compositions are prepared in advance. The rare earth disilicate powder and the rare earth monosilicate powder are mixed with each other at a predetermined ratio and subjected to heat-treatment using the method described in the first embodiment. The powder after heat-treatment are pulverized and classified into 1 m to 50 m or so.

(68) A second layer 205 of the top coat 203 is made of a rare earth monosilicate represented by Re.sub.2SiO.sub.5. Here, Re may be one of rare earth elements or a plurality of rare earth elements may be selected. In detail, the second layer 205 is made of Y.sub.2SiO.sub.5, Yb.sub.2SiO.sub.5, Lu.sub.2SiO.sub.5, (Y, Yb).sub.2SiO.sub.5, (Y, Lu).sub.2SiO.sub.5, or the like. Considering raw material cost, it is preferable that the second layer 205 is made of Y.sub.2SiO.sub.5 or a rare earth monosilicate, (Y, Re).sub.2SiO.sub.5 (here, Re is another rare earth element except for Y) in which Y is partially substituted with another rare earth element. Considering interdiffusion with the rare earth disilicate, it is preferable that a substitution element Re is Sc, Yb, Lu, Nd, Sm, Eu, or Gd. It is particularly preferable that the substitution element Re is the same material as the rare earth element contained in the first layer 204. Considering raw material cost, it is preferable that a substitution amount of Re is 0.5 or less.

(69) The second layer 205 is formed by a spray method. A thickness of the second layer 205 is 50 m or more and 300 m or less.

(70) In the case of applying the composite oxide containing a rare earth element selected from the plurality of rare earth elements to the second layer 205, particles solid-solubilized by heat-treatment after weighing and mixing raw material powder so as to have a predetermined substitution ratio can be used as the spray particles. In this way, uniformity of the composition in the second layer 205 is secured.

(71) A difference in thermal expansion coefficient between the first layer 204 and the second layer 205 is less than 310.sup.6/K, preferably, less than 210.sup.6/K (at room temperature to 1200 C.). A material of the second layer 205 is selected so that the difference in thermal expansion coefficient described above is secured.

(72) The third layer 206 of the top coat 203 is the heat-shielding coating layer, and the same material as that in the first embodiment is used therein. It is possible to prevent the substrate 201 from being eroded by steam in a high-temperature environment by forming the third layer 206 made of YbSZ and rare earth monosilicate which have excellent steam resistance.

(73) Considering thermal stress of the top coat 203 under a use environment, a difference in thermal expansion coefficient between the second layer 205 and the third layer 206 is less than 310.sup.6/K, preferably, less than 210.sup.6/K (at room temperature to 1200 C.). A material of the third layer 206, that is, a composition of a matrix phase, and an addition amount of YbSZ are selected so that the difference in thermal expansion coefficient described above is secured.

Example

(74) Table 3 illustrates a difference in thermal expansion coefficient between a substrate and a heat-shielding coating layer (at room temperature to 1200 C.) in the case of forming a coated member having a configuration illustrated in FIG. 1. As the substrate, an Al.sub.2O.sub.3 fiber-reinforced Al.sub.2O.sub.3 matrix composite (AS-N610, COI Ceramics, thermal expansion coefficient: 810.sup.6/K (at room temperature to 1200 C.), or AS-N720, COI Ceramics, thermal expansion coefficient: 6.310.sup.6/K (at room temperature to 1200 C.)) was used.

(75) In Table 3, YbSZ is stabilized zirconia to which 16 wt % of Yb.sub.2O.sub.3 was added.

(76) TABLE-US-00003 TABLE 3 Comparative Comparative Example 1 Example 2 Example 3 Example 4 Example 5 Example 1 Example 2 Heatshielding YbSZ + YbSZ + YbSZ + YbSZ + YbSZ + YbSZ YbSZ Coating Layer 10 vol % 50 vol % 25 vol % 25 vol % 25 vol % Yb.sub.2SiO.sub.5 Yb.sub.2SiO.sub.5 Yb.sub.2SiO.sub.5 + Yb.sub.2SiO.sub.5 + (Y.sub.0.8Yb.sub.0.2).sub.2SiO.sub.5 + 25 vol % 25 vol % 25 vol % Yb.sub.2Si.sub.2O.sub.7 Yb.sub.2Si.sub.2O.sub.7 (Y.sub.0.8Yb.sub.0.2).sub.2Si.sub.2O.sub.7 Substrate AS-N610 AS-N610 AS-N610 AS-N720 AS-N720 AS-N610 AS-N720 Difference in 2 0.85 0.1 1.7 1.7 2.3 4 Thermal Expansion Coefficient ( 10.sup.6/K)

(77) As illustrated in Table 3, since in Examples 1 to 5, the difference in thermal expansion coefficient between the heat-shielding coating layer and the substrate was 310.sup.6/K or less, thermal stress in the top coat was alleviated. Particularly, in Examples 2 to 5, the difference in thermal expansion coefficient was less than 210.sup.6/K, and heat cycle durability was improved as compared to Comparative Examples 1 and 2.

(78) Table 4 illustrates a difference in thermal expansion coefficient between a substrate and a heat-shielding coating layer (at room temperature to 1200 C.) in the case of forming a coated member having a configuration illustrated in FIG. 6. As the substrate, a SiC fiber-reinforced SiC matrix composite (Tyrannohex, Ube Industries, Ltd., thermal expansion coefficient: 410.sup.6/K (at room temperature to 1200 C.)) was used.

(79) In Table 4, YbSZ is stabilized zirconia to which 16 wt % of Yb.sub.2O.sub.3 was added.

(80) TABLE-US-00004 TABLE 4 Comparative Example 6 Example 7 Example 8 Example 9 Example 3 Third Layer Yb.sub.2SiO.sub.5 + 15 vol % (Y.sub.0.8Yb.sub.0.2).sub.2Si.sub.2O.sub.7 + Yb.sub.2SiO.sub.5 + Yb.sub.2SiO.sub.5 + YbSZ 50 vol % YbSZ 15 vol % (Y.sub.0.8Yb.sub.0.2).sub.2SiO.sub.5 + 50 vol % YbSZ 50 vol % YbSZ 70 vol % YbSZ Second Layer Yb.sub.2SiO.sub.5 Yb.sub.2SiO.sub.5 Yb.sub.2SiO.sub.5 Y.sub.2SiO.sub.5 Y.sub.2SiO.sub.5 First Layer 50 vol % 50 vol % (Y.sub.0.8Yb.sub.0.2).sub.2Si.sub.2O.sub.7 + 50 vol % 50 vol % (Y.sub.0.8Yb.sub.0.2).sub.2Si.sub.2O.sub.7 + 50 vol % (Y.sub.0.8Yb.sub.0.2).sub.2Si.sub.2O.sub.7 50 vol % (Y.sub.0.8Gd.sub.0.2).sub.2Si.sub.2O.sub.5 (Y.sub.0.8Gd.sub.0.2).sub.2Si.sub.2O.sub.7 + 50 vol % Y.sub.2SiO.sub.5 Y.sub.2Si.sub.2O.sub.7 + 50 vol % 50 vol % 50 vol % Y.sub.2SiO.sub.5 (Y.sub.0.8Yb.sub.0.2)SiO.sub.6 (Y.sub.0.8Yb.sub.0.2).sub.2SiO.sub.5 Bond Coat Si Si Si Si Si Difference in Thermal 1.5 1.5 1.5 1.5 2.9 Expansion Coefficient between Third and Second Layers (10.sup.6/K) Difference in Thermal 1.9 1.9 1.8 1.9 1.9 Expansion Coefficient between Second and First Layers (10.sup.6/K) Difference in Thermal 1.5 1.5 1.6 1.5 1.5 Expansion Coefficient between First Layer and Base (10.sup.6/K)

(81) As illustrated in Table 4, since in Examples 6 to 9, the differences in thermal expansion coefficient between the first layer and the base, between the first and second layers, and between the second and third layers were 310.sup.6/K or less, thermal stress in the top coat was alleviated. Particularly, in Examples 6 to 9, the difference in thermal expansion coefficient was less than 210.sup.6/K, and heat cycle durability was improved as compared to Comparative Example 3.

REFERENCE SIGNS LIST

(82) 100, 200 Coated member 101, 201 Substrate 102 Heat-shielding coating layer 202 Bond coat 203 Top coat 204 First layer 205 Second layer 206 Third layer