Solid-state cold spraying of FeCoCrNiMn high-entropy alloy: an insight into microstructure evolution and oxidation behavior at 700-900 °C

About 3 mm thick five-element equimolar high-entropy alloy (HEA) FeCoCrNiMn was successfully deposited by solid-state cold spraying (CS). The high-temperature oxidation behavior of the CSed HEA was investigated at 700-900 °C. Heat treatment was performed on the CSed HEA before oxidation to heal the incomplete interfaces between the deposited particles. Results show that the microstructure of the CSed HEA is characterized by grain refinement and abundant interparticle incomplete interfaces. Post-spray heat treatment promotes recrystallization and grain growth in the CSed HEA. After oxidation testing, the oxide scales are composed of multi-layers: a Mn₂O₃ (or Mn₃O₄) outer layer, a Mn-Cr spinel intermediate layer and a Cr₂O₃ inner layer. The CSed HEA exhibits higher parabolic rate constants and more favorable internal oxidation than the bulk HEAs that have similar compositions in the literature. Such a discrepancy becomes pronounced at higher temperatures. The grain refinement and numerous particle boundaries are responsible for such a distinctive performance of the CSed HEA.