Toughening alpha-Ti by dislocation-induced phase transformation at crack tips

H Zhang and XQ Ou and S Ni and M Song, MECHANICS OF MATERIALS, 151, 103629 (2020).

DOI: 10.1016/j.mechmat.2020.103629

In this paper, molecular dynamics simulation was used to investigate the crack propagation along the 10 (1) over bar1 twin boundary in titanium bi-crystals during uniaxial tensile deformation. The whole deformation process can be divided into two periods according to the crack propagation speed: (1) the quick crack propagation period in the early deformation stage and (2) the slow crack propagation period in the later deformation stage. The results show although the pyramidal and basal stacking faults induced from crack tips can reduce the stress concentration in the early deformation stage, they are nonetheless inadequate to inhibit the quick crack propagation with a velocity over 100 m/s. Comparatively, the formation of new face-centered cubic (FCC) grains at crack tips in the later deformation stage can blunt the crack, retard crack propagation and thus promote the toughness of the material. The nucleation and growth of the newly formed FCC grains are controlled by different mechanisms. During the quick crack propagation period, complex interactions between partial dislocations on pyramidal planes and dislocations on prismatic planes induce retained stacking faults in FCC lamella and new pyramidal stacking faults in hexagonal close-packed (HCP) matrix. The retained stacking faults develop into FCC nuclei as the tensile strain increases. During the slow crack propagation period, the FCC nuclei grow towards HCP phase and develop into a coarser grain that pins the further propagation of the adjacent crack tip. The growth of FCC nuclei is governed by a prismatic-type phase transformation mechanism, which involves atomic shear, shuffle and extra lattice distortion.

Return to Publications page