Effect of heat treatment on microstructure and mechanical properties of spark plasma sintered AlCoCrFeNiTi0.5 high entropy alloy

• High Entropy Alloy nanocomposite was produced by powder metallurgy.
• Formation of TiC nanoparticles by in-situ reaction was achieved.
• The structure exhibited high hardness of 762 HV.
• Prominent hardness of 603 HV even after heat treatment at 1100 °C was retained.
• Detrimental σ phase was successfully eliminated by the heat treatment.

The present work is focused on synthesis and heat treatment on non-equiatomic AlCoCrFeNiTi0.5 high entropy alloy (HEA) with a composite structure reinforced by TiC nanoparticles. The initial alloy was prepared by mechanical alloying (MA) in a planetary ball mill, compacted by spark plasma sintering (SPS) and heat treated at different temperatures. Mechano-chemical reactions during the MA process as well as the microstructure and hardness of the SPS-ed compacts prior to and after the heat treatment were investigated. During MA, Cr-based supersaturated solid solution with the BCC structure was formed. After SPS at 1100 °C, the BCC solid solution decomposed into nano-grained microstructure consisting of FCC and ordered BCC solid solutions, σ phase, and in-situ formed TiC nanoparticles. The high hardness of the alloy (762 HV) was retained after the subsequent heat treatment at 1100 °C (603 HV). It was shown that the fabrication of TiC reinforced nanocomposites from elemental powders without the use of expensive nanograined powders can be achieved.

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