Effect of Al Content on Phase Compositions of FeNiCoCrMo0.5Alx High Entropy Alloy

The FeCoNiCrMo0.5Alx system with x up to 2.13 was analyzed from the point of view of evolution of the phase composition and microstructure. Cast samples were synthesized by induction melting and analyzed by X-ray diffraction, energy dispersive spectroscopy, scanning electron microscopy, and Vickers microhardness test methods. Phase compositions of these alloys in dependance on Al concentration consist of FCC solid solution, sigma-phase, NiAl-based B2 phase, and BCC solid solution enriched with Mo and Cr. Phase formation principles were studied. Al dissolves in a FeCoNiCrMo0.5 FCC solid solution up to 8 at.%.; at higher concentrations, Al attracts Ni, removing it from FCC solid solution and forming the B2 phase. Despite Al not participating in sigma-phase formation, an increase in Al concentration to about 20 at.% leads to a growth in the sigma-phase fraction. The increase in the sigma-phase was caused by an increase in the amount of B2 because the solubility of sigma-forming Mo and Cr in B2 was less than that in the FCC solution. A further increase in Al concentration led to an excess of Mo and Cr in the solution, which formed a disordered BCC solid solution. The hardness of the alloys attained the maximum of 630 HV at 22 and 32 at.% Al.

Automated summary

The phase composition and microstructure evolution of the FeCoNiCrMo0.5Alx system were analyzed, revealing that Al concentration significantly affects the alloy's phase composition and hardness. Increasing Al concentration leads to changes in the phases present in the alloy, with hardness peaking at 630 HV at certain Al concentrations.