On the substructure evolution and its distinct role on dynamic strain aging in a multi-component cobalt base alloy at intermediate temperatures (300 to 700 °C)

Abstract

Manifestations of dynamic strain aging (DSA) in a solid-solution multi-component cobalt-base alloy was evaluated over wide temperature [25–1000 °C] and strain rate range [10−4–10−1 s−1]. Trends in serration onset strain with temperature together with kinetic analysis revealed the features of Portevin-Le Chatelier effect (PLC) and inverse-PLC. Besides, distinct dependence of strain rate sensitivity on the strain rate jump direction is observed between 10−4 and 10−3 s−1 and >550 °C. Detailed post-deformation characterization was done using transmission electron microscopy. In the initial stages (∼0.05 strain), multipoles were found to be the predominant local obstacles responsible for DSA, and strain accumulation occurs through their unzipping. The substantial presence of widely separated (∼23 nm) extended dislocations indicates the strong dominance of Suzuki segregation. Besides, a continuous evolution of heterogeneous to homogeneous slip vis-à-vis multipole density and their arrangement with temperature is observed. This study provides new insights into substructural evolution and its role on DSA mechanisms in multi-component alloys.