Effect of Friction Surfacing on the Microstructure and Corrosion Behavior of CoCrFeMnNi High-Entropy Alloy

In recent years, CoCrFeMnNi high-entropy alloy (HEA) has attracted considerable attention owing to its exceptional mechanical properties, thermal stability and corrosion resistance. Friction surfacing (FS), as a solid-state additive manufacturing technology that can avoid point defects such as pores, has great application potential in the fabrication of HEA coatings. However, relevant research has been extremely limited so far. In this article, a CoCrFeMnNi HEA coating was successfully fabricated on 304 stainless steel substrates via FS. The microstructure and corrosion behavior of as-cast HEA, solution-treated HEA and HEA coating prepared by FS were systematically analyzed. The results showed that the as-cast alloy exhibited severe dendritic segregation of Mn and Ni elements, with large-sized MnCr2O4-MnS composite inclusions widely distributed. Solution treatment could alleviate this segregation and partially suppress the corrosion rate. In contrast, the thermo-mechanical coupling imposed by FS eliminated the dendritic segregation and promoted compositional homogeneity. Moreover, FS effectively fragments the inclusions in the HEA, leaving only small-sized MnCr2O4 observable. These effects substantially reduced the defect density in the passive film on the FSed-coating surface, leading to a marked enhancement in corrosion resistance. The corrosion current density (icorr) of the coating decreased from 0.55 μA/cm2 in the as-cast state to 0.11 μA/cm2, and the pitting potential increased from −120.3 mV to 125.7 mV.