Critical stress for the bcc-hcp martensite nucleation in Ti-6.25at.%Ta and Ti-6.25at.%Nb alloys

Martensitic transformation is an important deformation mechanism in titanium alloys. Using density functional theory calculations, we establish the lattice constants and the associated energetics of the bcc-hcp transformation in Ti-6.25at.%Ta and Ti-6.25at.%Nb alloys. We present a bcc-hcp nucleation model based on the Peierls Nabarro formalism, incorporating the elastic strain energy of the dislocations participating in the transformation process, and subsequently obtain the theoretical stress required to nucleate an hcp martensite from a perfect bcc crystal. The stress levels for hcp nucleation calculated in the present analysis for Ti-6.25at.%Ta and Ti-6.25at.%Nb alloys are 114 MPa and 95 MPa respectively.