Cherniavsky V. Generalized correlation of structure and mechanical properties formation in high entropy alloys of Al-Cu-Ni-Fe-Cr-Ti-V system during mechanical alloying and sintering

The present study reports synthesis of nanostructured high entropy solid solutions in Al-Cu-Ni-Fe-Cr-Ti-V system by mechanical alloying (MA). Milling was carried in high energy planetary ball mill and attritor mill. Petrol and ethanol was used as a process controlling agent. MA in petrol in planetary ball mill finished the fastest. The alloying rate is found to correlate best with the melting point of the elements among metallurgical factors. The mechanism for this correlation is explained through the effect of melting point on solid-state diffusion and mechanical disintegration which are critical for the final alloying. During MA, a supersaturated solid solutions consisting of a metastable BCC phase were formed. The phase composition transforms to new BCC and one or two FCC solid solutions when the MA powders were annealed or sintered. The BCC and FCC solid solution structure without intermetallic and other phases can be maintained even after the alloy was annealed at 1000 °C. The alloyed powders were consolidated by pressure sintering (PS) and spark plasma sintering (SPS). The Vickers's hardness of PS and SPS nanocrystalline equiatomic AlCuNiFeTi HEA is 11,22±0,30 GPa and 9,85±0,31 GPa, respectively, and equiatomic AlCuNiFeCr HEA is9,18±0,25 GPa and 8,50±0,37 GPa, respectively. PS compared with SPS increases the mechanical properties of the samples to 10-15 %, saved nanocrystalline structure and phase state (as MA).