Microstructure and microhardness of high entropy alloys with Zn addition: AlCoFeNiZn and AlCoFeNiMoTiZn

Abstract High entropy alloys were designed from equiatomic multicomponent systems using powder metallurgy including mechanical alloying and sintering. The structure and morphology of the resulting alloys were characterized by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy techniques and their hardness values were also determined in the Vickers scale. The results indicate under the milling conditions used, the AlCoFeNiZn, AlCoFeNiMoTi and AlCoFeNiMoTiZn alloys crystallized forming BCC structures whereas the AlCoFeNi alloy presented two different phases, one with FCC structure and the other one with BCC. The synthesis method resulted in alloys with grain sizes in the nano scale having values between 4.1 and 9.4 nm on the powder form up to 40.1 nm after sintering phenomenon which lead to phase transformations which were more evident in the Mo-containing alloys. In addition, the AlCoFeNiZn and AlCoFeNiMoTiZn alloys did not show Zn traces after sintering as it was suggested by chemical analyses using energy dispersive spectroscopy, suggesting it is lost by evaporation during sintering process. Mo-containing systems exhibited the highest microhardness in both milled and sintered conditions.