Microstructure evolution and phase transformation in quaternary Co-9Al-10W-4Mo alloy during heat treatment

. Alloy Co-9Al-10W-4Mo was investigated on the microstructure and phase transformation, the following results were obtained. Eutectic Crystal containing the µ phase and B2 phase appeared as cast alloy, and solid solution treatment at 1300 ºC for 8h homogenized the structure to form the µ phase for supersaturation of W. Following aging at 900 ºC for 50 h induces the rod-like DO19 phase precipitation in the γ / γ ´ matrix structure. DO19 phase appeared between µ / γ interface after aging at 900 ºC for 300 h and 600 h and promoted more transformation from the µ phase to DO19 phase. Diffusion of W/Mo between the µ phase and matrix after long term aging is the main factor that induces phase transformation. Addition of Mo to Co-9Al-10W alloy prompts precipitation of the µ phase, and Mo was a W-like element. Formation of the DO19 phase in the interface decreases the interface energy induced by misfit between µ / γ crystallographic parameter.