The temperature dependence of high-temperature strength and deformation mechanism in a single crystal CoNi-base superalloy

The thermal stability and high-temperature strength of single crystal CoNi-base superalloys, Co-30Ni-10Al-7W (at%) and Co-30Ni-10Al-7W-2Ta-3Ti (at%), containing γ′(L12) phase have been investigated. The investigated CoNi-base superalloy with alloying additions of Ti and Ta exhibits excellent γ′ solvus temperature, 1236 ℃, and high-temperature strength, 622 MPa at 900 ℃, compared to reported γ′-strengthening Co-base superalloys. Detailed analyses of the deformation mechanisms for the investigated alloys were carried out by using the transmission electron microscopy (TEM) characterization. Two different transitions of deformation mechanisms for the γ′ phase, from superpartial dislocation shearing to dislocation bypassing and to stacking fault shear, occurred in the investigated alloys as the deformation temperature increased above the peak temperatures. Meanwhile, the high-temperature strength of the investigated alloys largely decreased as the transitions of deformation mechanism took place. The influence of alloying effects on energies of faults and the relationship between high-temperature strength and deformation mechanisms were discussed.