Abnormal grain growth behavior of an Oxide Dispersion Strengthened Superalloy

Abstract

To obtain a superior high temperature creep strength, the transformation of fine-grained structure to large elongated grains by abnormal grain growth is an important process for oxide dispersion strengthened superalloys. The present study investigated the abnormal grain growth behavior of TMO-2, an experimental alloy possessing higher creep strength than existing ODS alloys. It was found that abnormal grain growth was triggered by oxide dispersoid coarsening rather than γ′ dissolution. Preanneal increased the grain growth temperature and decreased the grain growth rate in the same manner as low-γ′ or γ′-free ODS alloys. However, with regard to stored energy, far fewer dislocations were found, and grain growth was considered to be driven predominantly by surface energy. The allowance of normal grain growth during preanneal or hot work to preserve abnormal grain growth ability was investigated and correlated with the amount of softening.