Dislocation induced FCC twinning at the HCP/FCC interfaces in a deformed Ti-5at.%Al alloy: Experiments and simulations

Abstract

This paper proposes a new formation route for the face-centered cubic (FCC) twins at the hexagonal close-packed (HCP)/FCC interface in a deformed Ti-5at.%Al alloy. Experimental results show that a FCC band satisfying a prismatic-type (P-type) orientation relationship (OR) with the HCP matrix (defined as “P-type FCC band”) is surrounded by a group of FCC lamellae that align in parallel and satisfy a basal-type (B-type) OR within the HCP matrix (defined as “B-type FCC lamellae”). High-resolution transmission electron microscopy reveals a local {111} twinning relation between the P-type FCC band and the B-type FCC lamellae at their contact boundaries. Molecular dynamics simulations indicate that basal stacking faults initiate from the misfit regions and evolve into the B-type FCC lamellae at the relaxed P-type HCP/FCC interfaces. Then mismatch provides the nucleation source for a full dislocation that continues to slip in the initial FCC grain. Repeating these two processes produces the {111} twinning relation between the new-forming FCC lamellae and the initial FCC grain. Lattice correspondence analysis further interprets the formation route for the {111} twins proposed in the present study from the aspect of crystal geometry.