Effects of annealing at 800 and 1000 °C on phase precipitates and hardness of Al7Cr20Fe Ni73− alloys

Abstract

The effects of Fe content on the microstructure, phase constituents and microhardness of the as-cast, 800 °C- or 1000 °C-annealed Al 7 Cr 20 Fe x Ni 73− x ( x =13−66) alloys were investigated. Not all these alloys are composed of the single FCC phase. The BCC and B 2 phases are found. It is confirmed that the BCC phase in the Al 7 Cr 20 Fe 66 Ni 7 alloy is transformed from the FCC phase at about 900 °C during cooling. While in the 800 °C-annealed Al 7 Cr 20 Fe 60 Ni 13 alloy, the FCC phase is stable and the hardness decreases. After annealing at 1000 °C, for the precipitation of the B 2 particles, the Al content in the FCC phase decreases, which results in decreasing of the alloy hardness. Moreover, after annealing at 800 °C, a small amount of Al-rich B 2 particles precipitate at the phase boundary and some nanocrystal BCC phase precipitates in the FCC matrix, which increases the hardness of the Al 7 Cr 20 Fe x Ni 73− x ( x =41−49) alloys. These results will help to the composition design and processing design of the Al−Cr−Fe−Ni based high-entropy alloys.