The Observation of Cellular Precipitation in an Ni36Co18Cr20Fe19Al7 High-Entropy Alloy after Quenching and Annealing

Abstract

High-entropy alloys (HEAs) comprise a minimum of five major elements. These alloys show some special characteristics, such as excellent mechanical and high temperature properties. The development of the HEAs requires a knowledge of phase transformations during alloy making procedures. The phase transformations of an Ni36Co18Cr20Fe19Al7 HEA were studied in this research. The alloy underwent hot forging, cold rolling, annealing at and quenching from 1323 K, and isothermal holding at 873 K. The alloy is a single face-centered cubic (FCC) phase in the as-quenched condition. After annealing at 873 K, not only fine coherent L12 particles precipitated homogeneously in the FCC matrix, but lamellae of FCC and L12 phases also developed from the grain boundaries. Both lamellar FCC and L12 grains have a cubic-on-cubic orientation relationship (OR). The composition of the lamellar L12 phase is Ni60Co8Cr6Fe6Al20, and that of the lamellar FCC phase is Ni31Co15Cr28Fe21Al4. Cellular precipitation occurs in the HEA, and the high-temperature FCC (γ) transforms to a lamella of low-temperature FCC (γ1), and an L12 phase, i.e., γ → γ1+L12.