Massive transformations in titanium alloys: Role of relative orientation of adjacent parent grains

Massive transformations occur in both additively and conventionally manufactured titanium (Ti) alloys. Unlike martensitic transformations, massive transformations can result in patch-like massive phases (alpha(m)) that traverse the parent prior-beta grain boundaries (GBs). However, the conditions favouring the formation of these trans-GB alpha(m)-phases in Ti alloys remain largely unexplored. Through characterising the trans-GB alpha(m)-phases in alpha-beta Ti alloys fabricated by additive and conventional processes, we find that their formation always occurs when two neighbouring prior-beta grains share or nearly share a {110} pole, without exception. These trans-GB alpha(m)-phases exhibit concentrated {0001} poles while their {11 (2) over bar0} poles spread widely. In addition, as metastable phases, they tend to decompose into ultrafine alpha-beta lamellae. The role of relative orientation of adjacent parent grains in massive transformations and the implications for microstructural innovations in alpha-beta Ti alloys are discussed.