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 degrees C. It is found that Co addition has no obvious effect on the yield strength below 650 degrees C, but significantly increases the yield strength at 650-800 degrees 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 gamma'. 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 anchor deformation twinning, which may be responsible for the enhanced strength at intermediate temperatures. (c) 2012 Elsevier B.V. All rights reserved.