High temperature oxidation behavior of laser clad Co–Cr–Mo coating on γ-TiAl substrate

Abstract

In this work, Co–Cr–Mo powder is used to form laser clads on a γ-TiAl substrate. The oxidation behavior of Co-Cr-Mo alloys in air at 900 °C for 10 and 480 h has been studied. The results show that the uniform, fine, and defect-free microstructure of Co-Cr-Mo coating was prepared by laser cladding. The clad coating consisted of γ-Co (fcc), ε-Co (hcp), and Cr23C6. The specific mass gain as a function with the number of cycle plot was parabolic, which indicated that diffusion has controlled the oxidation process. At short time (10 h), the oxide scale formed on the surface was composed mainly of Cr2O3. With the increase in the duration of oxidation from 10 to 480 h, the thickness of the oxide film increased from about 1–1.5 to 6–6.5 μm. The analyses of oxide scale formed after long time (480 h) showed that layer II composed of CoCr2O4 formed on the Cr2O3 (layer I). When the thickness of the Cr2O3 layer increased, the defects such as porosity and microchannels were formed in oxide scale. Cobalt diffused from these defects to surface and with increasing the oxidation time, CoCr2O4 formed and covered the surface of oxide scale.