Strain-hardening properties of the high-entropy alloy MoNbTaTiVZr processed by high-pressure torsion

Abstract

An equiatomic MoNbTaTiVZr refractory high-entropy alloy (HEA) produced by arc melting was processed by high-pressure torsion (HPT) at room temperature. Thermodynamic calculations and experimental results indicated a dual-phase microstructure composed of about 85% BCC Zr-depleted and 15% BCC Zr-rich phase in the as-cast condition. HPT causes grain refinement and an increase in dislocation density without the formation of new phases. After four revolutions, the Zr-depleted phase was hardened to $$\sim $$ ∼ 540 HV, while the Zr-rich phase exhibited softening with a decrease in hardness to $$\sim $$ ∼ 480 HV. The occurrence of a vortex-like microstructure and the analysis of elemental concentrations indicated a shear-induced mechanical homogenization, which was supposed to be the cause of the observed softening.

Deformation-induced homogenization of the multi-phase senary high-entropy alloy MoNbTaTiVZr processed by high-pressure torsion

“…Two groups of BCC peaks with a pronounced asymmetry to the peaks of the major BCC phase are also visible. According to our previous study [17], the RHEA has a grain size of approximately 100 µm and consists of dendritic regions depleted of Zr and interdendritic regions enriched in Zr.…”

“…Such a strain localization might be due to the large deformation of V-rich inclusions. Since in our previous study [17] no pronounced enrichment of vanadium is found in the dendritic region, it can be assumed that the V-rich inclusions are mainly dissolved in the interdendritic region. This assumption could be confirmed by the lattice parameter of the interdendritic region in Fig.…”

“…Disk-shaped samples with a diameter of 6 mm and a thickness of 0.8 mm were sliced from the ingot using electric discharge machining and a wire diamond saw. More details of the sample preparation can be found in [17].…”

“…This is due to the fact that the soft phase is more prone to deformation compared to the hard phase in HPT-processing. In our previous study [17], a strain softening behavior was observed by probing the average ultra-microhardness of the interdendritic region. As shown in Figs.…”