Effect of Nb and Ti additions on microstructure, hardness and wear properties of AlCoCrFeNi high-entropy alloy

The use of Nb and Ti in the development of high-performance alloys is strategically important for technological advancement. The effect of Nb and Ti additions on the microstructure, hardness and tribological properties of the High Entropy Alloy (HEA) AlCoCrFeNi was evaluated. The addition of 0.6 mol of Nb led to the formation of Laves phase, resulting in a B2/Laves type hypoeutectic microstructure. Conversely, increasing Ti concentration led to the formation of a dendritic microstructure, with interdendritic region composed of Cr-rich BCC-A2 and Fe-Ti rich Laves phase. The average hardness values obtained were 790 HV, 597 HV and 731 HV for AlCoCrFeNiNb0.6, AlCoCrFeNiTi0.5 and AlCoCrFeNiTi1.2 HEAs, respectively. The high hardness was attributed to the formation of the Laves phase and Cr-rich phases, in addition to solid solution hardening, as confirmed by the increase in the lattice parameter calculated by Rietveld refinement method for both B2 and BCC-A2 phases. While the three compositions exhibited comparable friction coefficient, the alloy containing Nb showed superior wear behavior. This was evidenced by the lower volume of material loss and the lower wear rate, which can be attributed to the fine and homogeneous hypoeutectic microstructure observed in the ingot's cross section. The wear mechanisms were studied, characteristics features of abrasion and adhesion wear were observed.