As-Cast Microstructures of High Entropy Alloys Designed to Be TaC-Strengthened

Abstract

In this work two new alloys were obtained by extrapolation from a wellknown high entropy alloy, the equimolar CoNiFeMnCr one. This was doneby the addition of carbon and of tantalum, Ta being one of the strongestMC-former elements. They were produced by conventional casting underinert atmosphere. The obtained microstructures were characterized by X-raydiffraction, metallography, electron microscopy, and energy dispersionspectrometry. Their hardness was also measured by hardness indentation.In parallel, the original CoNiFeMnCr alloy was also synthesized andcharacterized for comparison. The reference HEA alloy is single-phasedwith an austenitic structure, while the two {Ta, C}-added alloys aredouble-phased, with an austenitic matrix and interdendritic script-likeTaC carbides. The matrixes of these HEA/TaC alloy are equivalent toan equimolar CoNiFeMnCr alloy to which 2 wt.% Ta is present in solidsolution. The presence of the TaC carbides caused a significant increase inhardness which suggests that the HEA/TaC alloys may be mechanicallystronger than the HEA reference alloy at high temperature.