Complexion-mediated martensitic phase transformation in Titanium

The most efficient way to tune microstructures and mechanical properties of metallic alloys lies in designing and using athermal phase transformations. Examples are shape memory alloys and high strength steels, which together stand for 1,500 million tons annual production. In these materials, martensite formation and mechanical twinning are tuned via composition adjustment for realizing complex microstructures and beneficial mechanical properties. Here we report a new phase transformation that has the potential to widen the application window of Ti alloys, the most important structural material in aerospace design, by nanostructuring them via complexion-mediated transformation. This is a reversible martensitic transformation mechanism that leads to a final nanolaminate structure of alpha" (orthorhombic) martensite bounded with planar complexions of athermal omega (a-omega, hexagonal). Both phases are crystallographically related to the parent beta (BCC) matrix. As expected from a planar complexion, the a-omega is stable only at the hetero-interface.