Massive transformations in titanium alloys: Role of relative orientation of adjacent parent grains
Shenglu Lu, Dandan Han, Dongyang Qin, Tingting Song, Dong Qiu, Milan Brandt, Huiping Tang, Ma Qian
Abstract
Massive transformations occur in both additively and conventionally manufactured titanium (Ti) alloys. Unlike martensitic transformations, massive transformations can result in patch-like massive phases (αm) that traverse the parent prior-β grain boundaries (GBs). However, the conditions favouring the formation of these trans-GB αm-phases in Ti alloys remain largely unexplored. Through characterising the trans-GB αm-phases in α-β Ti alloys fabricated by additive and conventional processes, we find that their formation always occurs when two neighbouring prior-β grains share or nearly share a {110} pole, without exception. These trans-GB αm-phases exhibit concentrated {0001} poles while their {112¯0} poles spread widely. In addition, as metastable phases, they tend to decompose into ultrafine α-β lamellae. The role of relative orientation of adjacent parent grains in massive transformations and the implications for microstructural innovations in α-β Ti alloys are discussed.