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

Abstract

This study reports the structural evolution of multicomponent 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 °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.

Synthesis Route, Microstructural Evolution, and Mechanical Property Relationship of High-Entropy Alloys (HEAs): A Review

“…Furthermore, the formation of the supersaturated BCC solid solution in the FeNiCrCo 0.3 Al 0.7 HEA is attributed to the energy stored in the grain boundaries, high entropy of mixing, and solid solubility extension [ 114 , 131 ]. Partial BCC phases in the FeNiCrCo 0.3 Al 0.7 HEA after MA evolved to a more stable FCC phase during the SPS process at 1000 °C.…”