ATOMIC-SCALE ANALYSIS OF MARTENSITIC-TRANSFORMATION IN TITANIUM ALLOYED WITH VANADIUM .2. 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 (RID) simulat ions 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 b arrier) path involves a simultaneous operation of the {110}[<(1)over b ar 10>] shuffling and the {112}[11(1) over bar] shear processes, and t hat the transformation is initially dominated by the shuffling. The b. c.c. structure is unstable in Ti, that is there is no energy barrier a long 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 incompl ete in Ti-15V and completely absent in Ti-25V. The progress of the tra nsformation is significantly effected by the b.c.c. --> h.c.p. mismatc h stresses which develop during the transformation. The matrix constra ints and free surfaces play an important role in the martensitic trans formation, affecting the type of the variant and even the crystal stru cture of the product phase.