Effect of Al on structure and mechanical properties of Fe-Mn-Cr-Ni-Al non-equiatomic high entropy alloys with high Fe content

Microstructure and mechanical properties of the Fe-Mn-Cr-Ni-Al system non-equiatomic high entropy alloys with a different Al content (x = 0-14 at.%) were studied in the present work. The Fe40Mn25Cr20Ni15 alloy was composed of the face-centered cubic (fcc) matrix phase with a small amount of coarse bodycentered cubic (bcc) particles. Addition of a small amount of Al (x = 2-6) resulted in an increase in the fraction of the bcc phase to 26% and the formation of fine B2 precipitates within the bcc phase. At higher amounts of Al (x = 10 and x = 14) the microstructure consisted of coarse bcc matrix grains with the B2 precipitates inside. The alloys tend to become stronger with an increase in the Al content from 0 to 10 at.%; further increase in Al concentration did not influence strength considerably. The alloys exhibited pronounced softening with an increase in testing temperature from 25 to 400 degrees C-600 degrees C. Ductility of the alloys was high enough (>50%) at all temperatures. A quasi-binary Fe40Mn25Cr20Ni15-Al phase diagram was constructed using a ThermoCalc software and a TCHEA2 database; reasonable agreement between the experimental and predicted phase compositions of the alloys was obtained. It was suggested that an addition of the strong bcc-stabilizing and compound-forming Al to a bcc-prone Fe40Mn25Cr20Ni15 alloy is beneficial for the development of the alloys with the disordered bcc matrix and the embedded B2 precipitates having attractive mechanical properties. (C) 2018 Elsevier B.V. All rights reserved.