Microstructure evolution and degradation process of AlCrTiSiN coatings with different Si contents at high temperatures

Abstract

The microstructure evolution of AlCrTiN and AlCrTiSiN coatings containing 4, 6.8, and 10.6 at.% Si was studied at temperatures ranging from 800 to 1100 °C. The AlCrTiN coating exhibits a single-phase fcc-(Al,Cr,Ti)N structure, while the AlCrTiSiN coatings transition from a nanocomposite structure, composed of fcc-(Al,Cr,Ti)N and amorphous a-Si_xN_y, to a fully amorphous structure as the Si content increases. The hardness and adhesion strength of coatings initially rise, peaking at 24 GPa and 44 N respectively, due to the formation of the nanocomposite structure. However, these properties decline as the coatings become fully amorphous. At elevated temperatures, severe oxidation leads to the gradual formation of layered oxides. Concurrently, phase transformation, spinodal decomposition, and crystallization occur within the nitride layer. The addition of Si enhances oxidation resistance by promoting the rapid formation of a dense and protective oxide layer, and by reducing nitrogen release and TiO₂ formation. However, at 1000 and 1100 °C, the coating with 10 at.% Si exhibits slightly faster oxidation compared to the 6.8 at.% Si coating, as the increased Si content reduces the Al content, limiting the coating's ability to regenerate the protective oxide layer.