Strain direction dependency of deformation mechanisms in an HCP-Ti crystalline by molecular dynamics simulations

In this work, effects of uniaxial tensile directions on the deformation mechanisms of a hexagonal close-packed (HCP) titanium crystalline were investigated by molecular dynamics simulations. Three uniaxial tensile directions, namely the [21-1-0], [011-0] and [0001] directions, were studied. When the tensile loading was along the [21-1-0] direction, the parent HCP phase transformed firstly into the body-centered cubic (BCC) phase following the Pitsch-Schrader orientation relationship (OR), and then transformed either into the face-centered cubic (FCC) phase following the Bain path or back to the HCP phase following different variants of the Pitsch-Schrader OR. The new-forming and matrix HCP structures were in a {101-1} twinning relationship with each other. The newly formed FCC phase was in a prismatic-type (P-type) OR with the HCP matrix and in a basal-type (B-type) relationship with the new-forming HCP structure at individual contacting interface. The FCC/HCP interfaces in the P-type OR was immobile while that in the B-type OR propagated by the slip of Shockley partial dislocations. Both FCC/HCP interfaces in the P-type and B-type ORs were observed under high-resolution transmission electron microscope. With the tensile loading along the [011-0] direction, deformation mechanism of the system was dominated by the slip and dissociation of prismatic dislocations. The system stretched along the [0001] direction deformed mainly through the slip and dissociation of pyramidal dislocations, as well as through the activation of {101-2} twinning by a pure shuffle mechanism. The present investigation can provide clues in designing titanium alloys with both high strength and good plasticity.