Development of Complex Concentrated Alloys for High Temperature Applications

Abstract

In the current study, the refractory-based AlCrTiTaMo equimolar high entropy alloy (RHEA) and non-refractory-based AlCoCrFeNi equimolar high entropy alloy (NRHEA) were developed. The structural-property correlation of RHEA and NRHEAs has been investigated using different microstructural, mechanical and thermal characterization techniques such as x-ray diffraction (XRD), field-emission scanning electron microscope (FESEM) equipped with energy dispersive spectroscopy (EDS), micro-hardness and oxidation kinetics. The developed RHEA is composed of a dendritic and inter-dendritic type microstructure. Dendrites were rich in Ta and Mo, while Ti, Cr and Al were detected in the inter-dendritic regions. On the other hand, NRHEA exhibits apparent solute partitioning (Al-Ni rich) from that of its matrix (Co-Cr-Fe rich) in the form of spinodal decomposition. XRD analysis reveals the evolution of BCC and B2 phase microstructure for both RHEA and NRHEA specimens. During oxidation studies in the temperature range of 850 1050 and#8451;, among the RHEA and NRHEA, the latter exhibited around 7-8 times sluggish oxidation kinetics than the former due to the formation of predominant and protective Cr2O3 and Al2O3 layer with no signature of cracks and other defects. The high oxidation resistance of NRHEA is also evident from the low-value oxide scale thickness as compared to RHEA.