Predicting solid solubility in CoCrFeNiMx (M = 4d transition metal) high-entropy alloys

Abstract

CoCrFeMnNi is a prototype fcc-structured high-entropy alloy. Numerous efforts have been paid to strengthen CoCrFeMnNi, by replacing Mn with other elements for an enhancement of the solid solution strengthening. 4d transition metals, including Zr, Nb, and Mo, are of interest for this purpose, since they have much larger atomic radii than that of Mn. However, Nb and Mo are known to have a low solid solubility in fcc-structured CoCrFeNi. Compared to Nb and Mo, Zr has an even larger atomic radius. The solid solubility of Zr in fcc-structured CoCrFeNi was investigated in this work, combining both experimental studies and thermodynamic calculations. In addition, based on previous results and new results obtained here, methods to predict the solid solubility in CoCrFeNiM x (M ¼ Zr, Nb, and Mo) alloys were developed. Particularly, the average d-orbital energy level, Md, was re-evaluated in the present work, for an improved predictability of the solid solubility in fcc-structured high entropy alloys containing 4d transition metals.

Structure property relationship in (TiZrNbCu)1−xNix metallic glasses

“…The change results in an increase in the number of nearest neighbour atoms (obtained from the radial distribution function) and is therefore consistent with the change from the body centered cubic-to face centered cubic-like local atomic arrangements. A similar type of a change of crystal structure has been observed previously in crystalline HEAs for VEC≥7 [42,44].…”

“…We note that VEC≤7 for x≤0.25 (HEA region) and reaches 8 for x=0.5 (Ni-rich region). Thus, provided the correlation between VEC and crystal structure of numerous solid solution HEAs [42,44] also applies to TE-TL type of multicomponent amorphous alloys, the transition from the HEA to Ni-rich concentration range in our alloys could coincide with a change in the "atomic short range order" (SRO), from say bcc-like to mixed bcc-fcc-like and finally to fcc-like.…”

“…HEAs the "valence electron concentration" (VEC) criterion was proposed [44]. According to this criterion a bcc phase forms for VEC  6.87, a mixture of bcc and fcc phase forms for 6.87  VEC <8, and a fcc phase appears for VEC  8.…”

TCHEA1: A Thermodynamic Database Not Limited for “High Entropy” Alloys

“…The liquid composition changes gradually during solidification. Sheikh et al [48] According to the equilibrium calculation, the black curves in Fig. 23, no Ni 7 Zr 2 phase was predicted.…”

Effect of Al on microstructure and mechanical properties of cast CrCoNi medium-entropy alloy

“…Second, these criteria are referred to as simple solid solutions, but no precise criteria have been available for the disordered and ordered phase transition. In a word, these above-mentioned criteria are considered as necessary conditions for forming simple solid solutions but not suffi cient conditions [39] , because exceptions have been found for many systems [37] . However, they are still useful in predicting the phase evolution in some cases.…”