Influence of microstructure on void nucleation and growth in a near-α titanium alloy IMI 685

Abstract

Fracture at room temperature by void nucleation and growth has been investigated in IMI 685, a near-α aircraft titanium alloy containing nominally (by wt.%) 6Al, 5Zr, 0.5Mo and 0.25Si. Three different microstructures, namely coarse-aligned α(A_α), basket-weave α(B_α) and martensitic α(M_α), were obtained after solution treatment in the β range followed by cooling at different rates. Progress of fracture as a function of strain was investigated through measurements of the volume fraction, number density and size distribution of the voids as well as the length of the longest void. Void nucleation occurred at α-β interfaces in A_α and along the α platelets and/or martensitic laths as also α-α intersections in B_α and M_α. Void growth was along the α-α or α-β interfaces. Fracture strain was inversely proportional to the longest void growth rate. A linear relationship was observed between the fracture stress and the length of the longest void at fracture.