Alloying, thermal stability and strengthening in spark plasma sintered Al_xCoCrCuFeNi high entropy alloys

Abstract

Al_xCoCrCuFeNi (x = 0.45, 1, 2.5 and 5 mol) multi-component high entropy alloys synthesized by mechanical alloying were spark plasma sintered to produce high dense compacts. X-ray diffraction and scanning electron microscopy studies reveal that these sintered alloys exhibit varying microstructures from single phase to three phases depending on Al content. The thermal stability studies carried out in the temperature range of 400–600°C for duration of 2–10 h in Ar atmosphere suggest that these alloys exhibit excellent thermal stability in terms of phases and crystallite size. Highest specific hardness of 160 (HV/g cm⁻³) is achieved in the sintered Al₅CoCrCuFeNi alloy and there is no significant change in the hardness after heat treatment of Al_0.45CoCrCuFeNi and AlCoCrCuFeNi alloys. Hall–Petch analysis based on hardness measurements carried out on sintered samples reveals that solid solution strengthening seems to increase with increase in Al content.