Structure and high temperature mechanical properties of novel non-equiatomic Fe-(Co, Mn)-Cr-Ni-Al-(Ti) high entropy alloys

Four non-equiatomic Fe-(Co, Mn)-Cr-Ni-Al-(Ti) high entropy alloys, namely Fe36Mn21Cr18Ni15Al10, Fe36Co21Cr18Ni15Al10, Fe35Mn20Cr17Ni12Al12Ti4, and Fe35Co20Cr17Ni12Al12Ti4 alloys, were produced by arc melting. Structures and compression mechanical properties of the as-cast alloys were examined. The Fe36Co21Cr18Ni15Al10 alloy had mostly a face-centered cubic (fcc) structure, while Fe36Mn21Cr18Ni15Al10 mainly consisted of a body-centered cubic (bcc) matrix with embedded B2 precipitates. An addition of Ti resulted in the formation of L21 precipitates of a cuboidal shape mostly in the Fe35Mn20Cr17Ni12Al12Ti4 and of a plate-like shape in the Fe35Co20Cr17Ni12Al12Ti4 alloys. In addition, a significant amount of the fcc phase (0.17) was found in the latter alloy. Good correlation between the average valence electron concentration (VEC) value and the amount of the fcc phase in the experimental alloys was found. The comparison of the experimental data with results obtained using a Thermo-Calc software and a TCHEA2 database demonstrated a lack of credibility in the L21 phase formation predicting. In terms of the mechanical properties, the Fe36Co21Cr18Ni15Al10 alloy was rather soft, while the Fe36Mn21Cr18Ni15Al10 and Fe35Mn20Cr17Ni12Al12Ti4 alloys had high strength at temperatures of ≤400 °C. The Fe35Co20Cr17Ni12Al12Ti4 alloy had the highest strength among the examined alloys and maintained the strength at temperatures up to 600 °C. The correlation between the mechanical properties and structure of the non-equiatomic Fe-(Co, Mn)-Cr-Ni-Al-(Ti) high entropy alloys and a potential for further improvements of the properties are discussed.