Structure, Density and Hardness of Spark Plasma Sintered Fe-Mn Alloys

This study examines the effect of Mn content on phase evolution, density, and its correlation with the hardness of Fe-Mn alloys produced through mechanical milling followed by a spark plasma sintering technique. Alloys with Mn concentrations of 5, 10, 15, and 20 wt% were examined, revealing phase compositions primarily consisting of BCC (-Fe, ferrite), FCC (-FeMn, austenite), and HCP (-FeMn, martensite), with minor occurrences of MnO. The Mn content significantly affected the phase distribution, strain, crystallite size, and relative density. The evolution of phase structure—particularly the balance between hard BCC, HCP, and softer FCC—emerges as a critical factor in determining hardness. The alloy with 10 wt% Mn exhibited the highest hardness (595.34 Hv) despite not having the highest density, indicating that densification and the nature and proportion of constituent phases governed the mechanical properties. While ferrite and martensite enhance hardness, increasing the Mn content promotes the formation of a more ductile austenite phase, which offsets the strengthening effects and contributes to the observed decrease in hardness at higher Mn levels. These findings highlight the complex interplay between phase transformation, microstructure, and hardness in Fe-Mn alloy systems.

BCC; Density; Fe-Mn; Hardness; Spark plasma sintering

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