Effects of Al on crack propagation in titanium alloys and the governing toughening mechanism

Abstract

In this work, molecular dynamics simulation is performed to investigate the effect of Al element on the crack propagation along the {101‾1} twin boundary in Ti alloys with different contents and distribution of Al element during the uniaxial tensile deformation. The results show that increasing Al content obviously promotes the percentage of face-centered cubic (FCC) structure during the deformation process, which hinders the micro-crack propagation and enhances the plasticity and toughness of the Ti–Al alloys. The FCC bands transform from the hexagonal close-packed (HCP) matrix satisfying the basal-type (B-type) orientation relationship (OR) represented by (0001)HCP||(111)FCC and [12‾10]HCP||[11‾0]FCC. The increase of Al element reduces the basal stacking fault (BSF) energy of the HCP structure and thus contributes to the formation of BSFs, which grow into FCC bands with the B-type orientation by the slip of Shockley partial dislocations. The {101‾1} pyramidal SF activated at the crack tip evolves into FCC grains in the Ti–Al alloys following the prismatic-type (P-type) OR with the HCP matrix represented by (101‾0)HCP||(110)FCC and [12‾10]HCP||[11‾0]FCC, during which atomic shear and shuffle is involved.