Alloying effects on phase stability, mechanical properties, and deformation behavior of CoCrNi-based medium-entropy alloys at low temperatures

Abstract

Alloying plays an important role in determining the phase stability and mechanical behavior of medium/high-entropy alloys (M/HEAs). In this work, the effects of Al, Ti, Mo, and W additions on the phase stability, strengthening behavior, and stacking fault energies of CoCrNi alloys are quantitatively investigated by using first-principles calculations. Our results reveal that the Al, Ti, and W additions enhance the structural stability of metastable face-centered cubic structures, whereas Mo is in favor of the formation of hexagonal close-packed structures at low temperatures. Through analyzing the elastic moduli and lattice mismatch based on a Labusch-type model, we show that the solute strengthening effect decreases in the order W > Mo > Ti > Al. The compositional dependence of intrinsic stacking fault energy (ISFE) and unstable stacking fault energy (USFE) of CoCrNi MEAs was calculated, and the results indicate that the Al, Ti, Mo and W additions significantly reduce the USFE, leading to a reduction in the energy barriers of dislocation slips. The alloying effects on the deformation behaviors of CoCrNi MEAs are discussed in terms of the ratio of ISFE to the energy barrier of dislocation slips. The present study not only sheds light on the fundamental understanding of phase stability and deformation mechanisms of M/HEAs but also provides useful guidelines for the alloy design of advanced M/HEAs with superior mechanical properties.