Heat-treated microstructure of Co-Al-W ternary alloys

The effects of Al and W additions on the solidus-liquidus temperature, heat-treated microstructure and hardness of four Co-Al-W ternary alloys were investigated. The results show that the solidus and liquidus temperatures of these Co-Al-W ternary alloys are higher than the liquidus temperatures of Ni-base single crystal superalloys. γ(fcc) single phase existed in the matrix of three alloys after solid solution treatment at 1300°C for 8 h, while μ phase-Co₇W₆ was observed along grain boundaries and in grain interiors in the alloy containing high level of W. γ' phase-Co₃(Al, W) with L1₂ structure precipitated in the γ matrix of four alloys after aging treatments at both 800°C/100 h and 900°C/50 h, similar to the microstructure of Ni-base superalloys. High levels of W and Al additions promoted the precipitation of μ phase-Co₇W₆ and Al-rich phase, respectively. Combined with the results of hardness after different aging treatments, the composition range of these ternary alloys containing γ+γ' two phases was preliminarily determined based on microstructural stability and potential high-temperature mechanical properties.