Increased thermal stability of Ti1 − xAlxN/TiN multilayer coatings through high temperature sputter deposition on powder-metallurgical high-speed steels

Abstract

Although spinodal decomposition of metastable cubic Ti1−xAlxN-based coatings and the underlying mechanisms are widely understood, investigations on the influence of high deposition temperatures are lacking. It is thus the aim of this work to elucidate structure, properties, thermal stability and wear performance of Ti1−xAlxN/TiN multilayer coatings sputter deposited on powder-metallurgical high-speed steels at substrate temperatures between 375 and 575°C. At higher substrate temperatures, sharper column boundaries and sharper transition zones in the multilayer arrangement yield increased hardness in the as-deposited state, while the detrimental formation of wurtzite AlN during vacuum annealing is retarded by 50°C according to Rietveld refinement of X-ray diffractograms. Tribological tests at room temperature and up to 650°C corroborate the high potential of increased coating temperatures, while demonstrating the crucial importance of using a substrate material with adequate hot hardness. Cutting tests with coated high-speed steel end mills verify the high temperature deposition approach showing a tool life increase of ~40%.