Achieving low wear in a complex concentrated alloy CrFeNiNb with multi-phase hierarchical microstructure

We propose a strategy to achieve low wear in a complex concentrated alloy (CCA) CrFeNiNb with multi-phase hierarchical microstructure. The CCA comprises a matrix of ultrafine-grained hexagonal close-packed (HCP) Laves phase (80.3 vol%), a secondary face-centered cubic (FCC) phase (18.3 vol%), a minor amount of (Nb,Cr)-oxides and a trace amount of uniformly dispersed nanoscale precipitates. The CrFeNiNb CCA exhibits an ultrahigh hardness of 993 (±22) HV and an extremely low wear rate of 7.4 (±0.6) × 10−6 mm3/(N·m) when sliding against a silicon nitride (Si3N4) ball. To elucidate the wear mechanism, we characterized the morphology, chemical composition and cross-sectional microstructure of the wear track. The results indicate that the cracked oxide layer, subgrain formation in the FCC phase, and the Shockley partial and full dislocations-triggered intragranular prismatic slip in the C14 Laves phase synergically contribute to the exceptional wear resistance. Furthermore, we conducted a detailed analysis of the chemical composition and crystal structure of the cracked oxide layer, along with a compressive discussion of the subsurface deformation of HCP/FCC phases. These findings offer significant insights into designing wear-resistant alloy through the formation of multi-phase hierarchical microstructure.