The Effect of Stress and Temperature on the Extent of Primary Creep in Directionally Solidified Nickel-Base Superalloys

Abstract

The primary creep strain (PCS) of most directionally solidified nickelbase superalloys at intermediate temperature of 700-800°C and high stress of 490-784 MN/m2 is evidently higher than that of conventionally cast alloys. That is due to the shearing of the y' particles and the large gliding distance of dislocations. PCS increases with increasing stress. The longitudinal PCS of DSK3 at intermediate temperature is quite low, similar to that of the conventionally cast CCK3 alloy. Directional solidification does not increase the longitudinal PCS of K3 alloy at intermediate temperature and high stress. This is due to the creep mechanism of dislocation climbing-over y' particles. PCS increases slightly with increasing creep stress. The transverse PCS of the directionally solidified alloys is the same of the corresponding conventionally cast alloys. The larger the degree of Y-Y' lattice misfit and the higher the strength, the lower the longitudinal PCS of directionally solidified alloys. At high temperature of 850-9800C and low stress of 196-343 MN/mz, the PCS of DS nickel-base superalloy is similar to that of conventionally cast alloys. At high temperature, the PCS of all alloys increases slightly with the increasing creep stress.