Title: Tailoring ordering-disorderingtransition in high-entropy alloy

Abstract

While X-ray and electron diffraction techniques are typically exploited to identify the existence of short range order (SRO) in metallic solid solutions, systematical approach to reveal the degree or tendency of SRO is still lacking due to its very tiny length-scale dimension. Further, impact of the SRO tendency on the mechanical properties in metals and alloys still remains a prime challenge in the field of high-entropy alloys with complex chemical flexibility. We report here a strategy that determines the degree or tendency of SRO in a face-centered cubic (FCC) high-entropy alloy (HEA) by monitoring the intensity of diffuse scattering in electron diffraction patterns, by detecting synchrotron X-ray diffuse scattering, and by observing specific heat evolution reaction. When an interstitial Fe40Mn40Cr10Co10 (at%) disordering HEA was subjected to tensile loading at 77 K, both the ductility and the ultimate tensile strength of the alloy increased with increasing strain rate, but there was no significant change in yield strength. This phenomenon of neither stress- nor strain-controlled failure is attributed primarily to the advent of deformation-induced SRO domains and their development in disordered structure. The current approach quantitatively demonstrates that tension at high strain rates enhances the intensity of SRO-induced electron scattering as well as an exothermic reaction. Any other TEM laboratory can verify the existence of SRO phenomenon as well as its tendency in other FCC base disordering solid solutions. Further important message in this talk is that disordering-to-ordering transition is common in metallic solid solutions, which are driven by alloy compositions, loading temperatures, and loading rates.