The mechanism for the serrated flow induced by Suzuki segregation in a Ni alloy

Abstract

The occurrence of serrated flow has been well accepted as a prevailing deformation feature in Ni-based alloys during plastic deformation at intermediate temperatures, yet its microstructure origin remains poorly understood. Here, characteristics of dynamic strain aging (DSA) in a Ni alloy 230 are studied by tensile tests over a wide range of temperatures and strain rates. The activation energy, Q, of the DSA effect is calculated to be 104 kJ/mol for temperatures from 523 to 773 K, about 35%–50% of the activation energy for lattice diffusion of Cr, Co or Mo in Ni, indicating pipe diffusion to be the crucial mode for solute segregation. Enrichment of Cr and Co atoms at stacking faults investigated by the state-of-the-art energy dispersive X-ray (EDX) spectroscopy is found in the deformed samples at 773 K with the strain rate of 3 × 10−3 s−1, suggesting that dynamic interactions between dissociated dislocations and substitutional solute atoms, known as Suzuki segregation, is responsible for the DSA effect. Moreover, the calculated diffusion distances of solute atoms through bulk diffusion prove that the pipe diffusion along partial dislocation core is contributing to the tensile process.