Microstructure evolution and work hardening behaviour during cold deformation of Haynes 214 superalloy

Abstract

Using uniaxial compression tests, the microstructure evolution and work hardening behaviour of Haynes 214 superalloy were investigated in the strain rate range of 0.01–5 s−1. The true strain-stress relationship was formulated based on a modified Tian model. The alloy exhibited a four-stage work hardening response similar to that previously reported for low stacking fault energy (SFE) face-centred cubic alloys. At strain lower of ∼0.07 (stage I), the work hardening rate decreased. At stage II (strain between 0.07 and 0.16), because of dislocation cross-slip, the dislocation movement was difficult, and the rate of work hardening increased. At stage III (strain between 0.16 and 0.48), work hardening showed the second decreasing stage. This stage was attributed to the appearance of high angle boundaries (HAGBs) as well as deformation twins, which consumed dislocation, relieved stress concentration, changed the crystal orientation, and produced some slip systems in a favourable orientation. When strain was greater than 0.48 (stage IV), as the number of deformation twins increased and they crossed one another, a final, slightly consistent hardening regime was observed. In addition, work hardening behaviour was considerably influenced by the strain rate. The true stress was the highest at medium strain rate of 1 s−1, and the second stage work-hardening rate at this strain rate was also larger than that at other rates, which was related to the generation of deformation twins at a high strain rate of 5 s−1.