Sprayed coating, method for manufacturing sprayed coating, sprayed member and spraying material

1. A sprayed coating having a multilayer structure comprising a lower layer made of a sprayed coating comprising a rare earth oxide, and a surface layer made of another sprayed coating comprising a rare earth fluoride and/or a rare earth oxyfluoride, wherein

said sprayed coating having the multilayer structure has a volume resistivity at 23° C. and a volume resistivity at 200° C., the volume resistivity at 23° C. being 1×10 9 to 1×10 12 Ω·cm, and a temperature index of the volume resistivities defined by the ratio of the volume resistivity at 200° C. to the volume resistivity at 23° C. being 0.1 to 10.

2. The sprayed coating of claim 1 wherein the surface layer comprises RF 3 , or RF 3 and at least one selected from the group consisting of R 5 O 4 F 7 , R 7 O 6 F 9 , and ROF, wherein R is at least one selected from rare earth elements inclusive of Y and Sc, and each R may be the same or different.

3. The sprayed coating of claim 1 wherein the lower layer comprises R 2 O 3 , or R 2 O 3 and at least one selected from the group consisting of RF 3 , R 5 O 4 F 7 , R 7 O 6 F 9 , and ROF, wherein R is at least one selected from rare earth elements inclusive of Y and Sc, and each R may be the same or different.

4. The sprayed coating of claim 1 wherein the lower layer has a multilayer structure consisting of at least two sub-layers of sprayed coatings, and at least one of the sub-layer consists of a sprayed coating comprising a rare earth oxide.

5. The sprayed coating of claim 1 wherein the lower layer has a thickness of 50 to 300 μm, and the surface layer has a thickness of 10 to 200 μm.

6. The sprayed coating of claim 1 wherein the surface layer has a Vickers hardness of at least 500.

7. The sprayed coating of claim 1 wherein the surface layer has a porosity of up to 1%.

8. The sprayed coating of claim 1 wherein the surface layer has a centerline average roughness Ra of 0.1 to 6 μm.

9. A sprayed member comprising a metal substrate, a ceramic substrate or a carbon substrate, and the sprayed coating of claim 1 formed thereon.

10. The sprayed member of claim 9 wherein the metal substrate is composed of an aluminum alloy, an anodized aluminum alloy or a stainless steel, the ceramic substrate is composed of alumina, zirconia, quartz glass, silicon carbide or silicon nitride.

11. A method for manufacturing the sprayed coating of claim 1 , comprising the steps of:

thermal spraying a rare earth oxide powder on a substrate to form the lower layer by atmospheric plasma spraying, and

thermal spraying a slurry comprising an organic solvent and a rare earth fluoride powder dispersed therein on the lower layer to form the surface layer by suspension plasma spraying.

12. The method of claim 11 wherein the slurry further comprises a rare earth oxide powder, and a weight ratio of fluoride powder/oxide powder is 99/1 to 90/10.

13. A method for manufacturing the sprayed coating of claim 1 , comprising the steps of:

thermal spraying a rare earth oxide powder on a substrate to form the lower layer by atmospheric plasma spraying, and

thermal spraying a powder comprising a rare earth fluoride and a rare earth oxide to the lower layer to form the surface layer by atmospheric plasma spraying.

14. A spraying material in a form of a slurry comprising an organic solvent and a rare earth compound powder dispersed therein, the rare earth compound powder comprising an RF 3 powder, and R being at least one selected from rare earth elements inclusive of Y and Sc,

wherein the RF 3 powder has an average value of roundnesses of at least 0.9, the roundness being defined by the following expression (1):

(Roundness)=(Circumferential length of an assumed circle having the equivalent area in planar view to an area of an observed particle)/(Circumferential length of the observed particle in planar view)  (1).

15. The spraying material of claim 14 wherein the RF 3 powder has a BET specific surface area of up to 2 m 2 /g, and a volume basis average particle size D 50 of 2 to 6 μm.

16. The spraying material of claim 14 wherein the RF 3 powder has a particle hardness of 7 to 12 GPa as measured by nanoindentation method.

17. The spraying material of claim 14 wherein the RF 3 powder has a total volume of pores having a diameter of up to 10 μm in the range of up to 0.5 cm 3 /g as measured by mercury porosimetry.

18. A spraying material in a form of a slurry comprising an organic solvent and a rare earth compound powder dispersed therein, the rare earth compound powder comprising an RF 3 powder, and R being at least one selected from rare earth elements inclusive of Y and Sc, wherein the spraying material further comprises an R 2 O 3 powder, R being at least one selected from rare earth elements inclusive of Y and Sc, and a weight ratio of RF 3 powder/R 2 O 3 powder is 99/1 to 90/10.

19. The spraying material of claim 18 wherein the R 2 O 3 powder has a volume basis average particle size D 50 of 10 to 500 nm.

20. The spraying material of claim 18 wherein the RF 3 powder has a BET specific surface area of up to 2 m 2 /g, and a volume basis average particle size D 50 of 2 to 6 μm.

21. The spraying material of claim 18 wherein the RF 3 powder has an average value of roundnesses of at least 0.9, the roundness being defined by the following expression (1):

(Roundness)=(Circumferential length of an assumed circle having the equivalent area in planar view to an area of an observed particle)/(Circumferential length of the observed particle in planar view)  (1).

22. The spraying material of claim 18 wherein the RF 3 powder has a particle hardness of 7 to 12 GPa as measured by nanoindentation method.

23. The spraying material of claim 18 wherein the RF 3 powder has a total volume of pores having a diameter of up to 10 μm in the range of up to 0.5 cm 3 /g as measured by mercury porosimetry.