Quantitative relationship between impact toughness and quasi-static tensile properties of Ti-652 titanium alloy

Abstract

Opinions regarding the relationship between impact toughness and quasi-static properties of titanium alloys remain divided to this day. In this paper, quasi-static tensile property parameters were introduced into the classical model of elastic-plastic fracture toughness. Utilizing the absorbed energy during the elastic and plastic stages, as conveyed by the integral of the quasi-static tensile stress-strain curve, the description of elastic and plastic work within the fracture toughness model was provided. Additionally, for the first time, a quantitative model relating impact toughness to quasi-static tensile property parameters in high-strength titanium alloys was proposed and applied to the high-strength Ti-652 titanium alloy. Decoupling the elastic and plastic segments of stress-strain curve, it was found that plasticity contributes more to impact toughness than strength, especially for high-strength metallic materials. Comparing the mechanical properties of Ti-652 titanium alloy with 9 kinds of microstructure, M9 was found to have the highest impact toughness (53.713 J/cm2) which features a duplex microstructure and underwent more severe plastic deformation during the test of samples, leaving shear bands and “ripple-like” patterns on the quasi-static tensile and impact fractures. Besides, statistics of dislocation density assisted by TEM images demonstrate that the dislocation density (ρ̅GND=4.82 ×1014 m−2) of high-impact toughness specimens are apparently higher than that (ρ̅GND=3.86 ×1014 m−2) of low-impact toughness specimens. Severe plastic deformation increased the energy consumption during the fracture process, resulting in high impact toughness of specimen.