Microstructure evolution and high temperature oxidation of LSM CoNiCrAlY alloy

This study systematically characterized the effect of a Y3Al5O12 (YAG)/Al2O3 composite pre-oxidation layer induced by laser surface melting (LSM) on the oxidation behavior of CoNiCrAlY binder alloys. The as-cast CoNiCrAlY alloys were first vacuum heat-treated at 1100 °C for 2 h, followed by LSM treatment in air at a laser power of 400 W and a scanning speed of 200–800 mm/min. Both the heat-treated (HT) and LSM-treated samples were then oxidized at 1100 °C for 100 h. The results showed that the β phase was significantly refined after LSM treatment and re-precipitated and segregated along the grain boundaries. Simultaneously, due to the high oxygen affinity of Y and Al, a composite pre-oxidation layer composed of YAG and Al2O3 was formed in situ on the alloy surface during the LSM process. Further research revealed that the YAG/Al₂O₃ composite pre-oxidation layer formed under conditions of 200-600 mm/min effectively suppressed the growth of subsequent oxide layers and prevented the depletion of the β phase during oxidation. This is mainly attributed to the stable YAG forming a barrier at the grain boundaries, thereby inhibiting the inward diffusion of oxygen and the outward diffusion of Al. However, at the highest scan rate of 800 mm/min, due to the cracking and local exfoliation of the composite pre-oxidation layer, the protective effect was reduced, and oxygen diffused inward along the defect channels, forming a new Al₂O₃ layer below the original pre-oxidation layer, accompanied by a corresponding β-phase depletion region.