Dependence of the fracture behaviour and property on the microstructural parameters of TA15 titanium alloy with trimodal microstructure

The optimization of fracture property of trimodal microstructure plays a critical role in the service of important structural components of titanium alloys. However, trimodal microstructure (TMM), composed of lamellar α ( α _l), equiaxed α ( α _p), and transformed β ( β _t), involves numerous microstructural parameters, and their changes can interactively affect the propagation paths of microscopic crack and macroscopic fracture property. To this end, the dependence of crack propagation behaviour and fracture toughness on microstructural parameters (content and size of α _p, length and thickness of α _l) of TMM was investigated by using a multiscale finite element model. It is found that the influence of microstructural parameters on crack propagation features and fracture toughness is non-monotonic. Specifically, as the α _p content or α _l length increases, the features of crack propagation path (tortuosity and energy consumption) and fracture toughness of TMM increase first, and then decrease. As the α _p size increases, the crack propagation features increase first and then decrease, and fracture toughness decreases first, and then increases. As the α _l thickness increases, the crack propagation features and fracture toughness present a fluctuating trend. On these bases, the principles for regulating microstructural parameters can be summarized as: the content of α _p ≈ 23 %, the size of α _p ≥ 18.5 μm, the length of α _l ≈ 17.7 μm, thickness of α _l ≥ 2.9 μm. The conclusions can provide guidance for determining the regulation objectives of TMMs to optimize the fracture properties.