Role of microstructure in plastic deformation and crack propagation behaviour of an α/β titanium alloy

Abstract

The deformation and crack propagation behaviour have been comparatively investigated in a titanium alloy with bimodal microstructure (BM) and bilamellar microstructure (BLM). The results show that higher fracture toughness (58 MPa m1/2) was obtained for the BLM than that BM one (45 MPa m1/2). The deformed microstructure, crack initiation and propagation and surface damage morphology were observed by SEM and EBSD. Fatal cracks easily nucleated at the larger primary α phase, especially at the equiaxed αe/β interface and primary α lath (αl), and often grow along a straight line, which accelerated the crack propagation and leaded to non tortuous crack path in BM. For the BLM, slip hardly transferred the αl/βtrans interface due to the secondary α(αs) precipitation in the β lamellas. Cracks initiated at the boundaries of α colony and propagated with a zig-zag way, which leaded to a high branch and fluctuation of the crack of BLM and generated a relatively superior fracture toughness performance. These results indicate that a small amount of αl colony surrounded with βtrans matrix is beneficial to the improvement of fracture toughness, which can provide a good theoretical support to tailor the microstructure and mechanical performance of titanium alloys.