Effect of annealing on microstructure, grain growth, and hardness of nanocrystalline Fe–Ni alloys prepared by mechanical alloying

Fe–xNi alloys from x = 0 to x = 15 with an as-milled grain size and hardness in the range of 8–11 nm and 8.5–9.5 GPa, respectively, were synthesized by ball milling. Microstructural changes, hardness, and grain growth due to annealing were characterized using X-ray diffractometry, microhardness, focused ion beam channeling contrast imaging, and optical microscopy. It was found that the composition range of single bcc phase was extended by ball milling. Subsequent annealing of MA samples resulted in reduction of hardness and extensive grain growth. It indicates that nickel has no significant effect on thermal stabilization of iron. Retained austenite was observed for Fe–8Ni and Fe–10Ni alloys annealed in the two-phase region and effect of as-milled structure on retained austenite formation was discussed.