Austenite stability and mechanical properties of nanocrystalline Fe-Mn alloy fabricated by spark plasma sintering with variable Mn content

The effects of Mn content on the austenite stability and mechanical properties of nanocrystalline Fe-(4-10)%Mn alloys were investigated by means of micrograph observation, X-ray analysis, and mechanical testing. The Fe-Mn alloy samples with nanosized crystallite were successfully fabricated by spark plasma sintering because of an extremely short densification time, not only to reach the theoretical density value but also to prevent grain growth. The increased Mn content reduced the crystallite size and increased the volume fraction of austenite. In particular, the volume fractions of austenite in the nanocrystalline Fe-Mn samples were more than approximately four times higher than the equilibrium values. The progress of the compressive deformation increased the volume fraction of strain-induced martensite from the austenite decomposition. The kinetics of the strain-induced martensite formation were evaluated using the empirical equation considering the austenite stability factor. Both larger Mn content and smaller crystallite resulted in the increase in the austenite stability, contributing to not only a higher volume fraction of austenite after sintering, but also an improvement in its mechanical properties during the deformation.