Effect of Milling Time on the Structure Stability of FeMnNiCrAl Non-equiatomic High-Entropy Alloy.

A non-equiatomic Fe_34.9Ni_30.2Mn_18.6Cr_9.3Al₇ high-entropy alloy (HEA) was synthesized by mechanical alloying using different milling times. To study the effect of milling time on the structure stability, X-ray diffraction (XRD), scanning electron microscopy and energy-dispersive X-ray spectroscopy were conducted. For comparison, an Al-free alloy (Fe_37.5Ni_32.5Mn₂₀Cr₁₀) was produced at 25 h milling. XRD indicated a single FCC phase alloy after 5 h milling time and a dual FCC and BCC phase at 25 h milling time. Clearly, it is found that Al addition is not necessarily the main factor leading to BCC phase formation as reported for similar HEAs produced by casting route. Increasing the milling time, the lattice strain increased reaching an average maximum value of 0.8% with an increase in d-spacing while the crystallite size was reduced to about 5.7 nm. A dual-phase structure formation was related to a decrease in the accumulated strain (ca.32%) confirming a strain-induced transformation. [ABSTRACT FROM AUTHOR]