Microstructure and corrosion of non-equimolar multi-principal element alloys hardened by metastable precipitates

The design and corrosion resistance of five single-phase Ni-Fe-Cr-Mo-W-X (X = Mn, Al, and Cu) multi principal element alloys (MPEAs) has been recently reported. In this study, these alloys were heat treated at 800 degrees C for up to 160 h starting from the solutionized single-phase to allow precipitation of secondary phases that provide increased hardness and strength. During heat treatment at 800 degrees C, Sigma-phase rich in Cr, Ru, Mo and W precipitated at the grain boundaries in each alloy. Furthermore, copious in-grain precipitation was observed in the MPEAs containing Mn and Al. After aging, the hardness of the MPEA containing Al showed the most significant increase in hardness, about 90%, due to the precipitation. Multiple phases that were different from those predicted to exist at thermodynamic equilibrium were identified in the microstructure of the aged MPEAs using electron microscopy. During cyclic potentiodynamic polarization experiments in 0.6 M NaCl, all five aged MPEAs were found to be spontaneously passive. Only the MPEAs containing Mn, Cu or Al became susceptible to localized corrosion at higher potentials due to breakdown at the interface between the matrix and precipitate. (c) 2021 Elsevier B.V. All rights reserved.

Automated summary

The research focused on the design and corrosion resistance of five single-phase Ni-Fe-Cr-Mo-W-X multi principal element alloys, which were heat treated at 800 degrees C to increase hardness and strength through the precipitation of secondary phases. After aging, the MPEA with Al showed the most significant increase in hardness, about 90%. Electron microscopy revealed the presence of multiple phases in the aged MPEAs that differed from those predicted at thermodynamic equilibrium.