Coarsening behavior of γʹ precipitates and compression deformation mechanism of a novel Co–V–Ta–Ti superalloy

Abstract

The coarsening behavior of γʹ precipitates at different temperatures and the compression deformation mechanism of a novel Co–V–Ta–Ti superalloy are investigated. It is found that the coarsening behavior of the γʹ precipitates follows the classical Lifshitz-Slyozov-Wagner (LSW) model based on measured results of the temporal evolution of the mean radius, volume fraction, and number density of the γʹ precipitates. The coarsening rate constant, K, of the γʹ precipitates is strongly dependent on the aging temperature, and it increases nearly ten times with the aging temperature rising from 800 to 900 °C. Within this temperature range, the activation energy for coarsening of the γʹ precipitates is determined to be 230 kJ/mol. This value is close to the activation energy for the diffusion of V in Co, suggesting that the coarsening rate of γʹ precipitates is limited by the diffusion of V element. A lot of slip bands are observed in the alloy after compression deformation, which shows the crystal slip is the primary deformation mechanism for the Co–V–Ta–Ti alloy. It is found that the dislocations bypass the γʹ precipitates below 700 °C in the alloy, and pairs of dislocations shear the γʹ precipitates with a high density of stacking faults (SFs) above the peak temperature of 700 °C.