Evolution behavior of oxide scales of TiAlCrN coatings at high temperature

Abstract

Coating oxidation performance is a major concern in modern machining and other high temperature applications. This study presents TiAlCrN composite coatings with different Cr content prepared on a magnetron sputtering device. SEM, AFM and XRD were used to determine the structure of the coatings. It was found that the coatings show a solid solution of B1-NaCl face-centered cubic structure with [200] preferential orientation. As the Cr content increases, the particle size and roughness of the coating increase slightly, while the hardness of the coating decreases. Oxidation tests revealed that no significant oxidation occurs in all coatings below 800 °C. However, as the oxidation temperature increases to 1000 °C, the Ti0.32Al0.38Cr0.30N coating undergoes severe oxidation and the Ti0.17Al0.19Cr0.64N coating remains good. The oxide scale of the coatings after oxidation test is analysis by XPS depth profiling in details. XPS results revealed that the oxide scale of the Ti0.32Al0.38Cr0.30N coating changes from a dense Al rich oxide layer (800 °C) to a loose and discontinuous TiAl rich oxide layer (1000 °C), which is the main reason for its poor oxidation resistance. However, the Ti0.17Al0.19Cr0.64N coating shows a top loose TiAl rich oxide layer and a dense bottom CrAl rich oxide layer. The presence of this dense and continuous CrAl rich oxide layer can limit the rapid diffusion of Ti atoms to the surface while preventing the oxygen atoms from diffusing into the interior, which is the key to excellent oxidation resistance of the Ti0.17Al0.19Cr0.64N coatings.