Microstructure change characteristic and fracture mechanism of Ti-47.5Al-2.5V-1.0Cr-0.2Zr alloy during high temperature tensile deformation

Abstract

Changes in the microstructure characteristics and fracture mechanism of Ti-47.5Al-2.5 V-1.0Cr-0.2Zr alloy during tensile deformation were studied by high temperature tensile tests at 750–900 °C and strain rate of 10−5–10−3 s−1. The experimental results indicate that when the tensile temperature increases or the strain rate decreases, the number of small dimples in the tensile fracture structure increases, the proportion of cross-layer fracture decreases, the dimples have torn edges, and the plastic deformation resistance increases. The higher tensile temperature corresponds to a higher dynamic recrystallization (DRX) ratio, and the number of dislocations near the DRX structure is reduced, which shows that the rheological softening effect is significantly enhanced. A lower strain rate corresponds to a higher proportion of DRX and a smaller proportion of lamellar microstructure. Dislocation slip is the main deformation mode; stacking faults can be observed in DRX grains. The changes in the hot deformation microstructure directly reflect decrease of high temperature tensile strength in macroscopic flow behavior. Under the action of tensile stress, holes usually form at the lamellar grain boundary, and the aggregation of multiple micro-holes will merge and connect to form micro-cracks. Cracks are generated and propagated between layers, and the tendency of holes or cracks generated at lower deformation temperatures or higher strain rates is greater. When the stress concentration reaches a certain critical value, the specimen will eventually fracture.