The analysis of fracture toughness and fracture mechanism of Ti60 alloy under different temperatures

Fracture toughness and fracture mechanism of Ti60 alloy with duplex microstructure under different temperature conditions were investigated in the present work. The experimental result shows that the fracture toughness of CT samples increases from the room temperature (40 MPa m(1/2)) to 400 degrees C (71.45 MPa m(1/2)) but declines at 600 degrees C (62.55 MPa m(1/2)). It is observed from fracture surface through SEM that the predominant fracture mechanism has changed from quasi-cleavage fracture at room temperature to ductile fracture at higher temperatures. In addition, the tortuosity of crack propagation path has a limited impact on the fracture toughness. Path selections for crack propagation are obtained through SEM observation which can be summarized as: cut through lamellar a, parallel to lamellar a, bypass the equiaxed alpha(p) and cut through the equiaxed alpha(p). Moreover, it is found that the intrinsic contribution is the primary reason leading to the change of the fracture toughness of Ti60 alloy under different temperatures. Meanwhile, it is noteworthy that the area of the crack tip plastic zone increases from RT to 400 degrees C but decreases at 600 degrees C, which is seen as the main impact of temperature on fracture toughness. To be exact, the CT sample with a larger area of the plastic zone could provide a higher K-1C value. Furthermore, a prediction model of K-1C based on tensile properties is established, which has a good accuracy with experimental results. The model is useful in predicting the fracture toughness of Ti60 alloy at different test temperatures. (C) 2019 Elsevier B.V. All rights reserved.