Abstract
In the present work, the adiabatic shear characteristics of our recently designed α + β dual-phase Ti alloy at different strain rates have been investigated by hat shaped specimen. The deformation process is divided into three stages: work hardening stage, steady stage, and unstable thermal softening stage. Along or near the shear deformation paths, the microvoids and the cracks can be captured at the strain rate of 1.8 × 104 s−1, 2.0 × 104 s−1, and 2.3 × 104 s−1, both of which contribute to the stable and unstable softening. It is found that dynamic stored energy of cold work will be significantly improved by the enhanced high strain rate. In the view of coupling analysis of inverse pole figure and grain boundary map, it seems that low angle grain boundaries present a good resistance to the formation of cracks and thermal softening. On the contrary, high angles grain boundaries are typically located in ASBs and their affecting regions, which is in line with the reported results. While the geometrical necessary dislocation (GND) density of adiabatic shear band (ASB) and its surroundings increased significantly, the width of the ASB becomes wider as the strain rate increases, which is consistent with the theory of sub-grain rotation dynamic recrystallization model. The formation of multiple ASBs in the corner position is schematically illustrated and the average elastic modulus and hardness of the ASB region are lower than the α and β phases, combined with the GND analysis, which proves that the ASB is a thermal softening zone in this experiment.
Highlights
Ti alloys are considered as ideal structural materials in aerospace and aircraft application, because of the characteristics of low density, high specific strength at both ambient and elevated temperatures, and excellent corrosion resistance (Lütjering and Williams, 2007)
Under the high strain rate, the narrow-sheared regions generally undergo the severe plastic deformation with intense enhanced temperature in a short time, which will result in the microstructure evolution in local region to form the so-called adiabatic shear band (ASB)
ASB will be yielded at the high strain rate attributing to the competition between thermal softening and strain/stress-rate hardening within the local regions (El-Azab, 2008; Rittel et al, 2008; Guo et al, 2019; Hao et al, 2021)
Summary
Ti alloys are considered as ideal structural materials in aerospace and aircraft application, because of the characteristics of low density, high specific strength at both ambient and elevated temperatures, and excellent corrosion resistance (Lütjering and Williams, 2007). ASB in Advanced Ti Alloys transition in the shear bands formed under extreme conditions. Under the high strain rate, the narrow-sheared regions generally undergo the severe plastic deformation with intense enhanced temperature in a short time, which will result in the microstructure evolution in local region to form the so-called adiabatic shear band (ASB). It is essential to investigate the strain-rate-dependent mechanical properties and structural evolutions of advanced metal materials (Rittel et al, 2008; Guo et al, 2019; Reddy et al, 2020), to reveal the foundations of corresponding plastic deformation behaviours (Hao et al, 2021)
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