Phase stability and yield stress of Ni-base superalloys containing high Co and Ti

Ni-base superalloys containing high Co (> 20 wt pet) and Ti (> 5.5 wt pet) were designed in order to study the effects of Co16.9 wt pet Ti addition on phase stability and mechanical property. These new alloys, though they contained high Ti, mainly consisted of gamma and gamma' phases. Ni3Ti (eta) phase was observed along the grain boundaries in some of the alloys. The formation of eta phase was mainly related to the Ti/Al ratio, Ti content, and alloy composition. Tensile and compression tests showed that these new alloys exhibited higher yield stress than that of the baseline alloy, TMW-1(U720LI). The possible strengthening mechanisms were discussed in terms of solid-solution and precipitation strengthening effects by the Co16.9 wt pet Ti additions. Preliminary results show promising trends for the development of new superalloys for turbine disc applications.