Wear and oxidation resistances of AlCrFeNiTi-based high entropy alloys

Based on the AlCoCrFeNi high entropy alloy, by replacing Co with Ti, new cobalt-free high entropy alloys AlCrFeNiTi and its derivative AlCrFeNiTiMn0.5 were designed and prepared by arc melting, and as-cast micro-structures, wear and oxidation behaviors were investigated. The results show that two alloys are all composed of an ordered body centered cubic (BCC) and a disordered BCC phases, and typical dendritic structures including dendritic (DR), interdentritic (ID) and 'eutectic phase' areas were observed, implying the feature of near-eutectic high entropy alloys for AlCrFeNiTi and AlCrFeNiTiMn0.3 . Adhesive wear mechanisms for these two alloys are indentified mainly as delamination wear, while oxidative wear is gradually dominated in AlCrFeNiTi. The wear resistance declines with addition of a half mole of Mn into AlCrFeNiTi due to rising wear coefficients of alloys. The oxidation kinetics of AICrFeNiTi and AlCrFeNiTiMn0.3 alloys oxidized at 900 degrees C meet the exponential rate law, and the oxidation rate of AICrFeNiTi is lower than that of AlCrFeNiTiMn0.3, suggesting a better oxidation resistance. Comparing with AlCrFeNiTi, a new Mn2O3 subscale was formed between the outer TiO2 scale and the underlying Al2O3 subscale on surfaces of AlCrFeNiTiMn0.5, which is consistent with theoretical analysis from the view of forming ability level by the first principles calculations.