Quantitative Study on Degree of Lattice Distortion and Solid-Solution Strengthening in Refractory High Entropy Alloys

Refractory high-entropy alloys (RHEAs) have attracted outstanding properties like high strength and microstructural stability at elevated temperatures. In many RHEAs, the lattice distortion plays a major role in their excellent properties , which is caused by the random distribution of the constitutive elements that vary appreciably in atomic size. There have been many efforts to understanding of the solid-solution strengthening effect induced by lattice distortion in BCC single solid-solution RHEAs. The solid solution strengthening effect in high-entropy alloys is determined by two factors: the atomic size mismatch and the shear modulus mismatch, which are closely related with atomic size differences, shear modulus misfit and bonding energy misfit among elements. Especially, it has been reported that the yield strength of many RHEAs with single-phase BCC structure is enhanced by maximizing the lattice distortion. Thus, it is important to understand the relationship between degree of lattice distortion and its resulting strengthening effect to develop novel RHEAs with outstanding mechanical properties.<br/><br/>In this study, to establish the concrete relationship between the degree of lattice distortion and strengthening effect in the RHEAs, we attempted to validate the effect of the lattice distortion on solid-solution strengthening effect in HEAs by systematic alloy design. Specifically, we fabricated a number of equi-atomic refractory alloys, containing BCC single solid-solution phase. Their microstructure evolution and mechanical properties were systematically investigated using neutron diffraction, scanning electron microscopy, electron backscatter diffraction and universal testing machine.