MoSi2 induced core-β/shell-Laves structure to achieve enhanced oxidation resistance of CoNiCrAlY alloys fabricated by oscillating laser-directed energy deposition

Abstract

To improve the oxidation resistance of CoNiCrAlY alloys, varying contents of MoSi₂ were introduced into the alloys fabricated via oscillating laser-directed energy deposition (OL-DED). The microstructural evolution and isothermal oxidation behavior of the CoNiCrAlY-xMoSi₂ alloys (x = 0, 5, 7, 10, and 12 wt.%) were systematically investigated. Results show that greater MoSi₂ additions facilitate β phase formation and lower the Al threshold required to develop a continuous Al₂O₃ scale. This leads to a transition in the oxide scale from a double-layer structure (Co(Ni)Cr₂O₄ + Al₂O₃) to a single-layer Al₂O₃. Notably, when the MoSi₂ content exceeds 5 wt.%, Laves phase precipitates form around the β phase, creating a unique core-β/shell-Laves structure. This structure effectively suppresses grain boundary diffusion of Al atoms, promoting lattice diffusion and facilitating the formation of a uniform and dense Al₂O₃ scale. The optimal MoSi₂ addition of 10 wt.% results in a weight gain of only 0.36 mg/cm² after oxidation at 1000 °C for 500 h, representing a 62.1 % reduction compared to the undoped CoNiCrAlY alloy. These findings demonstrate that the OL-DED-fabricated CoNiCrAlY-10MoSi₂ alloy exhibits superior oxidation resistance, outperforming other MCrAlY alloys at 1000 °C.