Microstructure Evolution and Microhardness of Al_xNi_2−xCoCrFe Alloys After Long-Time Annealing

The phase constituents of Al_xNi_2−xCoCrFe (x = 0.25−1.75) alloys were thermodynamically calculated and experimentally investigated. The experimental results indicate that when 0.5 ≤ x < 1.0, the as-cast Al_xNi_2−xCoCrFe alloys consist of fcc + B2 phase, with the volume fraction of fcc phase decreasing as the Al content increases. When x ≥ 1.0, the as-cast alloys contain only the B2 phase. After 1000 °C annealing, large bcc blocks precipitate in the alloy Al_1.25Cr_0.75CoFeNi, with an increase Al content in the B2 phase. After 800 °C annealing, very fine B2 and or σ particles precipitated from the as-cast fcc phase when 0.5 ≤ x < 1.0, and Al-poor bcc phase precipitated from the as-cast B2 phase. Moreover, the hardness of the as-cast or 800 °C annealed Al_xNi_2−xCoCrFe alloys increased linearly with increasing Al content.