Effects of mechanical activation on chemical homogeneity and contamination level in dual-phase AlCoCrFeNi high entropy alloy

AlCoCrFeNi High Entropy Alloys were here synthesized by the combination of Planetary Ball Milling and Spark Plasma Sintering at 1100 °C. The relatively low rotating speed led to a peculiar agglomerate state referred to as “Mechanical Activated”. The reactive sintering of activated agglomerates leads to a unique dualphase microstructure: the sintered sample exhibited a distinctive nanostructured lamellar microstructure consisting of two main phases (FCC and BCC). Atom Probe Tomography (APT) was used to ensure that the sintered sample was chemically homogeneous at the nanoscale in each phase. APT also revealed the presence of a Cr-rich sigma phase and oxide nanoprecipitates. X-ray Photoelectron Spectrometry (XPS) results demonstrated that most of the oxygen originated from the commercial powders. Calphad calculations revealed that the presence of oxides could alter the microstructure by modifying the global chemical composition. •5-element agglomerates consisting of a BCC and an FCC phase are produced by medium-energy ball milling.•After Spark Plasma Sintering, the sample exhibited a distinctive nanostructured dual-phase microstructure.•Atom Probe Tomography was used to ensure that the sintered sample was chemically homogeneous at the nanoscale in each phase.•Combined oxygen quantification and XPS demonstrated that a non-negligible amount of oxygen originated from the commercial powders.