Abstract
Equilibrium or near-equilibrium phase data are crucial to the development and application of high entropy alloys (HEAs). However, the vast majority of published HEA phase data are based on as-cast or shortly annealed conditions. Here, the phase constituents and microstructures in three equimolar CoCrFeNiX alloys (X = B, Al, Ga) after prolonged annealing at 500–1100 °C have been investigated. The CoCrFeNiB alloy was comprised of a dominating FCC phase and various boride phases [(Cr, Fe)2B, (Fe, Co, Ni)3B, Cr2B-tI12] at all annealing temperatures. Annealing at 700 °C led to the additional formation of CrB. The CoCrFeNiAl alloy was comprised of B2, BCC, and FCC phases at 1100 and 500 °C. The BCC phase transformed to the sigma phase at 700 and 900 °C. The CoCrFeNiGa alloy was comprised of BCC and FCC phases at all annealing temperatures, with additional sigma phase formation at 700 °C and 500 °C. The experimental results were compared with CALPHAD predictions. Depending on the alloy system, the accuracy of CALPHAD calculations varied significantly. The accuracies are well-related to the fraction of assessed systems of each alloy. These data here are not only useful as individual alloys. Together with previous parts of this systematic study, which investigated X elements from groups IVB, VB, and VIB (Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W), the holistic dataset offers the basis for new analysis and interpretations when looked at in its totality. We expect that this dataset will be valuable for future studies on the phase formation and other aspects of HEAs.
NSTL
Elsevier