Synthesis and Key Characteristics of Nanocrystalline AlCuNiFeCr High-entropy Alloy by Mechanical Alloying and Sintering

The present study is primary addressed to structural evolution of multi-component AlCoNiFeCr high-entropy alloy (HEA) from elemental materials to solid solution during mechanical alloying (MA), and further, to equilibrium phases during subsequent thermal annealing and pressure sintering. It was justified experimentally that MA of Al-Cu-Ni-Fe-Cr powder mixture during 5 hours resulted in a single-phase nanocrystalline HEA with a structure of bcc solid solution. During thermal annealing recovery and recrystallization of the bcc solid solution take place at temperatures ranging from 130 to 500 degrees C, and phase transformation, and grain growth of equilibrium phases occur at higher temperatures. The phase composition transforms to bcc and fcc solid solutions when the MA powder was annealed at 600 degrees C for 1 h. The bcc and fcc solid solution structure can be maintained even after the alloy was annealed at 1000 degrees C. The alloy powder was consolidated by pressure sintering at 800 degrees C with 5 GPa pressure. The sintered samples exhibit 9.2 +/- 0.3 GPa in Vickers hardness.