Microstructural evolution of Fe–32%Ni alloy during large strain multi-axial forging

High-resolution electron backscatter diffraction (EBSD) and transmission electron microscope (TEM) were used to study the microstructural development of Fe–32%Ni alloy during large strain multi-axial forging. The forgings were carried out at the temperature of 773 K and strain rate of 10−2 s−1. The EBSD enables more detailed quantitative measurements to be made than possible with the TEM. The results show that two main microstructural changes take place as the cumulative strain increases. Firstly, the grains are obviously refined and become randomly distributed. Secondly, the volume fraction of high angle boundaries increases. Change in the strain path might be the reason why the volume fraction of high angle boundaries increases with increasing cumulative strain. Grain subdivision and rotation are regarded as the mechanism of structure refinement. The mechanism is termed as continuous dynamic recrystallization (CDRX).