Effect of Al content on the microstructure and mechanical alloying behavior of AlCoCuMnNi and Al0.25CoCuMnNi high entropy powders

Abstract

The concept of high entropy alloys (HEAs) is an emerging subject in materials science and engineering. The presence of at least four elements in equiatomic or near equiatomic composition in HEAs has led to superior properties and vast unexplored alloying space. In this study, we investigated two new HEA powders, AlCoCuMnNi and Al0.25CoCuMnNi, by subjecting mechanically milled (MM) powders to a series of analyses over a 60 h ball milling process. It was found that alloying starts after 20 h of MM and after 45 h, full elemental integration into the host lattice was detected. Meanwhile, further milling to 60 h can cause powder contamination. The High-Resolution Transmission Electron Microscopy (HRTEM) results validated the XRD findings and provided further insights into the substantial influence of Al content on the microstructure and the extent of amorphization within the milled powders. Differential Thermal Analysis (DTA) analysis on the MM powders showed one exothermic peak for AlCoCuMnNi and one for Al0.25CoCuMnNi at high temperatures, which may suggest the formation of the BCC or second FCC phases for these alloys. The results confirmed the significant influence of the increased Al content on increasing both the lattice constant and lattice strain while decreasing thermal stability of the investigated MM powders. The present results provided insights needed for consolidation of such HEA powders.