Preparation and characterisation of the Al-Cr-Fe-Mn-Mo high-entropy alloy reinforced by in-situ formed carbides

This study aimed to prepare a composite of the high-entropy alloy from the Al-Cr-Fe-Mn-Mo system reinforced by in-situ formed carbides using powder metallurgy techniques. The alloyed powder was prepared by mechanical alloying in ball-mill devices from pure elemental powders with the addition of a process control agent, namely stearic acid. Then, the alloyed powder was consolidated by hot-press sintering. The structure and microstructure of powder and bulk samples were investigated. The mechanical properties of the bulk sample were evaluated. The investigations revealed two bcc phases in the mechanically alloyed powder. The powder annealing at 950 degrees C triggered the phase transformations, which led to the formation of the multielement matrix bcc phase (a = 2.91 angstrom) reinforced by two carbides molybdenum-rich M6C (a = 11.15 angstrom) and chromium-rich M23C6 (a = 10.66 angstrom). A similar composite structure was present in the bulk sample. The investigations suggested that the primary carbon source for carbide formation was the process control agent - stearic acid. The produced bulk composite revealed promising mechanical properties, such as very high hardness up to 1223 +/- 99 HV2 and Young's modulus of 246 +/- 10 GPa.