Effect of Nb-C addition on the microstructure and mechanical properties of CoCrFeMnNi high entropy alloys during homogenisation

Abstract

In the present paper, CoCrFeMnNi(NbC) alloy was designed based on theoretical calculations and proposed as a novel high entropy alloy. The effect of Nb-C microalloy addition on the microstructure and mechanical properties of equiatomic CoCrFeMnNi high entropy alloys were studied during homogenisation. The chemical composition, microstructural evolution, hardness and shear deformation behaviour were analysed using XRF, Leco-combustion technique, optical microscopy, SEM-WDX, XRD, Vickers hardness and shear punch testing. Moreover, the thermal behaviour of both alloys during heating stage was studied by differential thermal analysis technique at a heating rate of 10 °C/min. The experimental results confirmed theoretical calculations based on Scheil-Gulliver solidification model and thermodynamic rules, suggesting a solid solution high entropy alloy with FCC-crystal structure after vacuum arc re-melting and homogenisation. SEM-WDX analysis hardly showed any Nb-containing precipitates in both as-cast and homogenised samples. It was also found that Nb-C addition considerably retarded the growth/coarsening of grain size during homogenisation. Moreover, the results suggested that the hardness and shear strength of CoCrFeMnNiNbC alloy was higher than CoCrFeMnNi alloy, mainly due to solid solution strengthening effect.