Effect of Al/Ni ratio, heat treatment on phase transformations and microstructure of AlxFeCoCrNi2−x (x = 0.3, 1) high entropy alloys

• Successful fabrication of AlxFeCoCrNi2−x (x = 0.3, 1) high entropy alloys by DMD.
• Profound effect of Al/Ni ratio on hardness, microstructure, phase transformations.
• Occurrence of ordering and spinodal decomposition concomitantly.
• Sigma phase transformation on annealing in alloys having Al/Ni ⩾ 1.
• Optimizing Al/Ni ratio, a future direction for better mechanical properties.

Laser-aided direct metal deposition, an additive manufacturing technique, was successfully used to fabricate thin walled high entropy alloy components. In this study, the ratio of aluminum to nickel in the AlFeCoCrNi system was decreased to observe the transition of the solid solution from a body centered cubic to a face centered cubic structure. Aluminum concentration was found to cause ordering and spinodal decomposition concomitantly in two of the compositions. The lattice parameter increased from 0.288 nm to 0.357 nm and the hardness decreased from 670 Hv to 149 Hv respectively. Differential thermal analysis was used to track the solidification paths of each of the compositions. Annealing at high temperature led to σ phase transformation in some of the compositions which along with solid solution strengthening accounted for the high softening resistance of these alloys. The optimization of the Al/Ni ratio in these alloys for better mechanical properties has been discussed with the help of an additional alloy composition as an example.

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