Influence of Dynamic Precipitation of γ′ Phase on Dynamic Strain Aging in a Fe-Ni-Based Superalloy

Discontinuous plastic flow due to dynamic strain aging (DSA) in a Fe-Ni-based superalloy was investigated by tensile tests in the temperature range from 500 ºC to 800 ºC with different γ′ fraction. Type A serrations were observed in the solutionized and as-aged specimens at 500 ºC, which was a result of diffusion of carbon atoms. The stress amplitude was affected by the dislocation density induced by the presence of γ′ phase. Type C serrations occurred in the solutionized and under-aged samples at 650 ºC and 700 ºC. With the increase of γ′ phase fraction in the initial microstructure, the stress amplitude and duration of type C serrations decreased at 700 ºC. It was demonstrated that the dominant deformation mechanisms of under-aged specimens at 650 ºC and 700 ºC were weakly-coupled dislocation pairs shearing the fine γ′ particles with slip bands, while the deformation mechanism transformed to dislocation climbing at 800 ºC. The model linking serration amplitude, solute concentration at the dislocation line and dislocation density was used to analyze the effect of γ′ dynamic precipitation on the DSA. The dynamic precipitation of γ′ phase during tensile significantly alters the DSA behavior by removing substitutional solutes responsible for γ′ precipitation from the matrix.