Short-Range Order (SRO) in medium and high entropy alloys: design and characterization

Abstract

Medium and high entropy alloys are a new class of materials that is primarily related to the design of alloys. Due to the presence of multiple principal elements in the matrix phase, understanding atomic-level phenomena becomes challenging. This is the case with short-range order (SRO), which involves first and second atomic neighbors. SRO, favored by chemical preferences between distinct pairs of elements, can affect local composition and, consequently, influence important deformation mechanisms. Examples include twinning-induced plasticity and phase transformation-induced plasticity, which depend on stacking fault energy (inherently affected by chemical composition). These mechanisms help explain the excellent properties of Cantor and CrCoNi alloys, with the latter being classified as one of the toughest engineering materials ever tested. In order to better understand these alloys, recently, high-impact studies have been investigating the occurrence of SRO and its influence on the properties of alloys with multiple principal elements. However, due to the difficulty in detecting this constituent and certain experimental misconceptions, little is still understood. To overcome current challenges, this study proposes the fabrication of CrCoNi alloys with the addition of secondary elements that should promote SRO formation (by reducing the system's mixing enthalpy) and facilitate its detection (due to larger differences in atomic scattering factor). This simple concept will be combined with processing under optimized conditions (long times and lower temperatures) and advanced characterization techniques (transmission electron microscopy, electron diffraction, cryogenic tensile testing, thermal analysis, among others). (AU)