The fracture toughness and its prediction model for Ti-5Al-5Mo-5V-1Cr-1Fe titanium alloy with basket-weave microstructure

The fracture toughness and its prediction model for Ti-5Al-5Mo-5V-1Cr-1Fe titanium alloy with basket-weave microstructure are studied in present paper. Five double annealing processes were used to prepare different microstructure features. The results show that the fracture toughness of Ti-5Al-5Mo-5V-1Cr-1Fe alloy is very sensitive to its microstructure, which shows a variance of about 40 MPam. Moreover, an "abnormal" phenomenon has been found that a microstructure with high yield strength does not necessarily gets low fracture toughness. It is due to that not only the material plastic deformation along the crack path can exert influence on fracture toughness but also its crack path tortuosity. Generally speaking, long and thick α platelets in microstructure is necessary to get rough crack front geometry, which can obviously improve the fracture resistance. According to above findings, a fracture toughness prediction model considering both the intrinsic and extrinsic contributions is built. It is verified that the model can fairly predict the fracture toughness for Ti-5Al-5Mo-5V-1Cr-1Fe alloy with basket-weave microstructure. Moreover, based on the prediction model, the respective contributions of the intrinsic and extrinsic parts to the fracture toughness of Ti-5Al-5Mo-5V-1Cr-1Fe alloy are studied. The results show that the intrinsic contributions for the five microstructures constitute the vast majority of their fracture toughnesses, which do not vary a lot from each other. However, the extrinsic contributions for the five microstructures are dramatically different, indicating that the extrinsic fracture toughness is more sensitive to the basket-weave microstructure features than the intrinsic part. Therefore, pursuing the enhanced extrinsic fracture toughness is exactly the way to optimize the fracture toughness of Ti-5Al-5Mo-5V-1Cr-1Fe alloy with basket-weave microstructure.