Ultrahigh grain boundary strengthening ability of VCoNi medium entropy alloy

Tensile tests of VCoNi medium-entropy alloy with different grain sizes were conducted at 77 K, 194 K and 293 K. The results show that the grain boundary strengthening ability characterized by the Hall-Petch slope of the alloy increases with decreasing temperature and is evidently higher than that of FCC pure metals, Cu-Al alloys, and some common FCC high-entropy alloys/medium-entropy alloys at room temperature. A new model correlated to intrinsic stacking fault energy and lattice friction stress is derived to describe the high grain boundary strengthening ability. The high grain boundary strengthening ability and its temperature dependence of the VCoNi medium-entropy alloy are mainly attributed to the high lattice friction stress of the VCoNi alloy. The findings provide a possibility for designing the single-phase FCC medium-entropy alloy with ultra-high yield strength and considerable plasticity.

Automated summary

The tensile tests of VCoNi medium-entropy alloy with different grain sizes were conducted at low temperatures. The results showed that the alloy exhibited a high grain boundary strengthening ability, which increased with decreasing temperature. This ability was significantly higher than that of other materials at room temperature. A new model was proposed to describe the high grain boundary strengthening ability, based on the intrinsic stacking fault energy and lattice friction stress. The high grain boundary strengthening ability of the VCoNi medium-entropy alloy was mainly attributed to its high lattice friction stress.