Dynamic Strain Aging in Ni Base Alloys with Different Stacking Fault Energy

Cobalt in a 23wt.% Cobalt containing Ni-base superalloy was systematically substituted for by Ni in order to investigate the effects of stacking fault energy (SFE) on dynamic strain aging. The results showed that adding Co had little effect on the phase constituents, but the SFE of γ matrix decreased continuously with increasing Co content. Mechanical properties tests showed that all the alloys exhibited serrated flow during tensile deformation due to dynamic strain aging (DSA) within a temperature ranges of 200°C-500°C. The starting temperature for serration improved from 200°C to 300°C with increasing the Co content from 5wt% Co in Alloy1 to 23wt% Co in Alloy3. In the serrated flow regime, all the alloys clearly exhibited the normal and inverse DSA behaviors. The tensile properties such as yield stress, ultimate tensile strength and fracture feature in DSA regime were not influenced by temperature, strain rate and Co content. A relation between high density of SF and the inverse DSA effect was found in Alloy3 with low stacking fault energy. Analysis of the results suggested that the mechanism for the inverse DSA is related to the locking of the mobile dislocation by substitutional elements.