Nanocrystalline AlNiCoFeCrTi High-Entropy Alloy Resulted from Mechanical Alloying and Annealing

This study reports the structural evolution of multi-component AlNiCoFeCrTi high-entropy alloy from elemental materials to nanocrystalline metastable solid solution during mechanical alloying (MA), and further, to equilibrium phases during subsequent thermal annealing. It was justified experimentally that shot-time mechanical milling of Al-Ni-Co-Fe-Cr-Ti powder mixture during 3 hours resulted in a single-phase nanocrystalline high-entropy alloy (HEA) with a structure of bcc solid solution. During thermal annealing of the bcc solid solution phase transformation take place, and grain growth of equilibrium phases occur. The phase composition of as-MA alloy transforms to fcc and bcc solid solutions with TiC precipitations' when the MA powder was annealed at 1200 degrees C for 1 h. X-ray diffraction and electron microscopy data show that the nanocrystalline powder microstructure is retained in the alloy with no grain growth. The AlNiCoFeCrTi HEA exhibit 7.1 GPa and 9.2 +/- 0.3 GPa in Vickers hardness after mechanical alloying and after thermal annealing, respectively.