Effects of solutes on thermal stability, microstructure and mechanical properties in CrMnFeCoNi based alloys after high pressure torsion

The equiatomic Cantor alloy and Ni-enriched derivates of it ((CrMnFeCo)(x)Ni1-x with x = 0.8, 0.4, 0.08 and 0) were deformed by high pressure torsion to the saturation regime and subsequently annealed in a wide temperature range. The microstructural stability of the alloys was investigated in terms of grain growth and decomposition tendencies with an emphasis on Ni92 and Ni60 that are marking a transition from dilute solid solutions to HEA alloys. Ni92 and Ni100 show a larger grain size after HPT than the HEA type alloys Ni20 and Ni60, yet, they do exhibit a lower resistance to grain growth. Both HEA type alloys exhibit decomposition tendencies in the form of secondary phases (Ni20) or nanosized Cr-rich precipitates and Mn segregations to grain boundaries (Ni60), that reduce the grain boundary mobility. A comparison of the activation energies for grain growth and diffusion coefficients of the alloys shows a good qualitative agreement. The differences in microstructural stability are also reflected by the mechanical properties. All alloys show a small amount of hardening after annealing, followed by a softening for higher temperatures in case of dilute solid solutions. In contrast, the hardness of the HEA type alloys remains constant up to 450 degrees C (Ni60) or even increases up to 500 degrees C (Ni20) followed by a softening at higher annealing temperatures. The second phase formation with limited volume fractions has no effect on the modulus. (C) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

In this study, the microstructural stability and mechanical properties of the equiatomic Cantor alloy and its Ni-enriched derivates were investigated through high pressure torsion deformation and annealing treatment. The results showed that Ni92 and Ni100 alloys had larger grain sizes but lower resistance to grain growth. Both HEA type alloys exhibited decomposition tendencies, reducing the grain boundary mobility. Additionally, the hardness of the HEA type alloys remained constant at higher annealing temperatures, while dilute solid solutions exhibited softening.