Dynamic Strain Aging in a Newly Developed Ni-Co-Base Superalloy with Low Stacking Fault Energy

Characteristics of dynamic strain aging （DSA） in a Ni-Co-base superalloy were studied by tensile tests at temperatures ranging from 250 ℃ to 550 ℃ and strain rates ranging from 3 x 10-5 to 8 x 10-4 s-1. Serrated flow in the tensile stress-strain curves was observed in the temperature range from 300 ℃ to 500 ℃. Normal DSA behavior was found at temperatures ranging from 300 ℃ to 350 ℃, while inverse DSA behavior was observed at temperatures ranging from 400 ℃ to 500 ℃. The yield strength, ultimate tensile strength, elongation, work hardening index, and fracture features were not affected by temperature and strain rates in DSA regime. Negative strain-rate sensitivity of flow stress was observed in DSA regime. The analysis suggests that the ordering of the substitutional solutes around some defects like mobile dislocations and stacking faults due to the thermal activated process may cause the serrations on the tensile curves.