Atomic-scale analysis of martensitic transformation in titanium alloyed with vanadium Part II: molecular dynamics simulations

The martensitic phase transformation in Ti-base TiV b.c.c. alloys is studied using the Embedded Atom Method (EAM) interatomic potentials to quantify the atomic interactions and Molecular Dynamics (MD) simulations to determine the temporal evolution of atomic positions. The EAM-based total energy calculations showed, and the MD simulation results confirmed, that the actual b.c.c. → h.c.p. transformation (minimum barrier) path involves a simultaneous operation of the {110}〈110〉 shuffling and the {112}〈111〉 shear processes, and that the transformation is initially dominated by the shuffling. The b.c.c. structure is unstable in Ti, that is there is no energy barrier along the b.c.c. → h.c.p. transformation path, and the transformation is complete. The addition of vanadium, however, stabilizes the b.c.c. structure, causing the b.c.c. → h.c.p. transformation to be incomplete in Ti15V and completely absent in Ti25V. The progress of the transformation is significantly effected by the b.c.c. → h.c.p. mismatch stresses which develop during the transformation. The matrix constraints and free surfaces play an important role in the martensitic transformation, affecting the type of the variant and even the crystal structure of the product phase.