The dynamic recrystallization behavior of single-crystal（SC） superalloy SR.R99 at low strain rate was investigated by high-temperature creep testing.The results show that dynamic recrystallization may take place after the uncoated samples have been creep-tested in air at high temperature and low stress for a long time.Both the threshold temperature and strain for the dynamic recrystallization of SC superalloy SRR99 at low strain rate are lower than those for the static recrystallization.Dynamically recrystallized grains with the depth less than 15 μm are only located in the surface γ＇-free layers,and the recrystallized grains are well-developed grains without columnar y＇precipitates within them.The dynamic recrystallization behavior of SC superalloy SRR99 at low strain rate is mainly related to high-temperature oxidation.Suitable protective coating can effectively prevent the dynamic recrystallization of SC superalloy components in service.In addition,the dynamic recrystallization behavior of SC superalloy SRR99 at high strain rate was also studied by high-temperature compression testing.At high strain rate,a higher temperature and larger strain are needed for the occurrence of dynamic recrystallization than at low strain rate,and the recrystallized grains have cellular structures with an amount of columnar γ＇ precipitates within them.
