Research on Diamond Coating as Wear-Resistant Film for Mechanical Parts in Spacecraft

Abstract

In lunar exploration, many mechanisms require a solid lubricant coating with high wear resistance. The lunar surface is covered in dust particles that cause aggressive wear when they get between sliding surfaces. Conventional wear-resistant coatings for tools have high friction coefficients in vacuum, and they have inadequate wear resistance to lunar dust. This study focused on diamond coatings. A diamond coating deposited by CVD has excellent wear resistance against dust particles in vacuum, although its coefficient of friction is not as low as other solid lubricants. Also, it is difficult to coat metal surface with diamond because of the difference in their coefficients of thermal expansion. Our study approached the solution to the problem of applying a diamond coating to sliding mechanical surface on the Moon. One approach to finding a suitable coating for metal and ceramic substrates was to change the deposition method and conditions. Another approach was to deposit an intermediate layer between the diamond coating and the substrate to mitigate the internal stress of the coating. Our study showed that a hard diamond coating could be deposited on a metal surface with an intermediate layer if its coefficient of thermal expansion and compatibility with diamond coating were optimized. A diamond coating could be deposited at 250 ºC lower temperature than normal method, and the coating had almost the same tribological characteristics as coating at normal temperature. Low wear was observed for the coatings under low load in vacuum.