The analysis of fracture toughness and fracture mechanisms of TC4 alloy at different temperatures

This study systematically investigates the fracture toughness and underlying fracture mechanisms of a TC4 alloy featuring a duplex microstructure, with a specific focus on the influence of temperature. Experimental results demonstrate a significant enhancement in fracture toughness, which increases progressively from 56 MPa·m 1/2 at room temperature to 93.1 MPa·m 1/2 at 250 °C. It is observed from the fracture surface through SEM that the fracture mechanism has changed from quasi-cleavage fracture at room temperature to ductile fracture at higher temperatures. Analysis indicates that the intrinsic contribution, primarily governed by inherent plastic deformation capacity, is the key factor responsible for this temperature-dependent toughening. As the temperature rises, the activation of additional slip systems within the α phase significantly enhances plastic deformation capability. This intrinsic change not only alters the fracture mode but also profoundly influences the paths of crack propagation. At all tested temperatures, microstructural interfaces such as grain boundary α (α GB ), primary α phase (α p ) boundaries, and α p /β interfaces consistently act as barriers, inducing crack deflection. However, as the temperature increases, more slip systems within the α phase become active. This not only promotes multiple deflections of cracks within the crystal, increasing path tortuosity, but also significantly enhances the overarching plastic deformation capacity of the material, thereby expanding the plastic zone at the crack tip.