Analysis of hybrid fracture in α/β titanium alloy with lamellar microstructure

An integrated experimental-numerical method combining a realistic microstructure-based isotropic crystal-plasticity (CP) model and fracture surface analysis was adapted to analyze the fracture behavior of the titanium alloy Ti-6Al-4V. A hybrid fracture mode consisting of cleavage facets and elongated dimples was observed and analyzed. With the help of numerical simulations and post-mortem SEM, the micro-mechanism of the hybrid fracture mode was revealed. The results show that ruptured α lamellae can be linked to cleavage facets induced by the development of voids. Simultaneously, hard β lath can function as walls that separate two neighboring arrays of voids or micro-cracks within the α lamellae. The origin of this behavior can be associated with a heterogeneous stress/strain distribution in the α/β phases, which was revealed via numerical simulations. Further, the influence of the α grain orientation on the void evolution was investigated by varying the Schmid factor of the grains in simulations.