Needle-like χ phase precipitation induced by stacking fault in novelCo-based superalloys

To explain the precipitation mechanism of χ phase in Co-based superalloys, the microstructural evolution of Co-Ti-Mo superalloys subjected to aging was investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that the needle-like χ phase is mainly composed of D0 19 -Co 3 (Ti, Mo), which is transformed from L1 2 - γ′ phase, and a specific orientation relationship exists between them. χ phase is nucleated through the shearing of γ′ phase due to the influence of stacking fault. The crystal orientation relationship between L1 2 and D0 19 can be confirmed as {111} L12 //{0001} D019 , and 〈112〉 L12 //〈100〉 D019 . The growth of D0 19 - χ phase depends on the diffusions of Ti and Mo, and consumes a large number of elements. This progress leads to the appearance of γ′ precipitation depletion zone (PDZ) around D0 19 - χ phase. The addition of Ni improves the stability of L1 2 - γ′ phase and the mechanical properties of Co-based superalloys.