Application of modern technology in metallurgy has led to tailoring of alloys with excellent mechanical, corrosive, wear and oxidation resistance properties, coupled by unique solid solution structures. In particular, high entropy alloys (HEAs) which are normally designed by combining at least five metallic components in equal or nearly equal molar ratios have gained much popularity in the scientific community. Research has shown that HEAs form stable solid solutions with simple crystal structures instead of too many complex intermetallic compounds due to their high entropy effect, lattice distortion, sluggish diffusion and cocktail effects. Although the design strategy of HEAs implies that there would be hundreds of new alloy systems, recent studies have mainly focused on CrFeNi-based alloys.
Generally, all HEAs have good wear resistance attributable to their high hardness. Regardless, there are different wear mechanisms for these HEAs. At present, a plethora of literature exists regarding various wear mechanisms of HEAs, unfortunately, none provides a plausible understanding of both wear and oxidation behaviors of high entropy alloys with eutectic structures.
Recently, Shenyang Aerospace University researcher: Dr. Zhi-Sheng Nong in collaboration with his doctoral advisor Professor Jing-Chuan Zhu at Harbin Institute of Technology investigated wear and oxidation behaviors of a new type of high entropy alloy AlCrFeNiTi and its derivative AlCrFeNiTiMn0.5 alloy. In particular, they focused on exploring the wear mechanism and oxidation kinetics for these two HEAs. Their work is currently published in the research journal, Intermetallics.
In brief, based on the AlCoCrFeNi high entropy alloy, by replacing Cobalt with Titanium, new cobalt-free high entropy alloys AlCrFeNiTi and its derivative AlCrFeNiTiMn0.5 were designed and prepared by arc melting. The authors adopted the WK-Π vacuum arc melting furnace carrying electromagnetic stirring system for the synthesis of ingots of the two aforementioned HEAs, after which wear and oxidation behaviors were investigated. The raw materials used for this study were high purity metals, namely: aluminum, iron, nickel, titanium, manganese and chromium.
Generally, the researchers observed that there were no significant changes of structures and morphologies with addition of a half mole of Manganese into AlCrFeNiTi, while more Chromium and Titanium entered into dendritic and interdendritic regions in AlCrFeNiTiMn0.5 alloy, respectively. Additionally, better oxidation resistance in both AlCrFeNiTi and AlCrFeNiTiMn0.5 alloys was observed, based on exponential oxidation kinetic curves.
In summary, the study by Zhi-Sheng Nong and colleagues demonstrated microstructures, wear and oxidation behaviors of Cobalt-free AlCrFeNiTi-based high entropy alloys. The results showed that the two alloys were all composed of both ordered and disordered body centered cubic phases. More so, typical dendritic structures including dendritic, interdendritic and ‘eutectic phase’ areas were also observed, implying the feature of near-eutectic high entropy alloys for AlCrFeNiTi and AlCrFeNiTiMn0.5. Furthermore, comparing with AlCrFeNiTi, a new manganese (III) oxide subscale was formed between the outer Titania scale and the underlying alumina subscale on surfaces of AlCrFeNiTiMn0.5, which was seen to be consistent with theoretical analysis from the view of forming ability level by the first principles calculations.
Zhi-Sheng Nong, Yu-Nong Lei, Jing-Chuan Zhu. Wear and oxidation resistances of AlCrFeNiTi-based high entropy alloys. Intermetallics, volume 101 (2018) page 144–151.Go To Intermetallics