Effect of Grain Size on Mechanical Properties of Single Phase Co-Ni-Cr-Mo Based Superalloy

초록

A recrystallized Co-Ni-Cr-Mo based superalloy was produced by cold working of 72% and subsequent recrystallization heat treatment. Microstructural observation revealed that a full recrystallization of the cold-worked alloy occured when heat treatment was performed at and above 1273K for 1h. So that, recrystallization heat treatment was carried out in a temperature range from 1273K to 1473K for 1h~24h, by which the average grain size was controlled to 28?▲238?. Tensile tests were carried out from room temperature (RT) to 1073K in order to understand the effect of grain size on the mechanical properties of the Co-Ni-Cr-Mo based superalloy. At RT and 943K, yield strength, tensile strength and elongation of the recrystallized alloy were improved with decreasing grain size. The alloy having a grain size less than 42? exhibited a steady-state flow behavior in the true stress-true strain curve at 943K. However, the alloy having a grain size of 28? showed lower yield strength than that of 42? at 1073K. It was found that the steady state flow is closely related to the occurrence of {111}<112> deformation twinning in the Co-Ni-Cr-Mo based superalloy.