Enhanced strength at intermediate temperatures in a Ni-base disk superalloy with high Co addition

Influence of high Co addition, i.e. 15–30 wt%, on the compressive yield strength of a Ni-base disk superalloy (U720Li) has been investigated from room temperature to 1000 °C. It is found that Co addition has no obvious effect on the yield strength below 650 °C, but significantly increases the yield strength at 650–800 °C if Co content is below 25 wt%. The microstructure observations indicate that high Co addition up to 30 wt% has no significant effect on the phase constituent, but affects the size of secondary γ′. The deformation mechanisms are discussed according to a newly developed model. It is suggested that high Co addition induces the transition of deformation mechanisms from dislocation pairs cutting to SF shearing and/or deformation twinning, which may be responsible for the enhanced strength at intermediate temperatures.