Comparison of the Sliding Wear of Single-Phase F.C.C Carbon-Doped Fe40.4Ni11.3Mn34.8Al7.5Cr6 and CoCrFeMnNi High-Entropy Alloys at Cryogenic Temperature

The sliding wear behavior of pins of the face-centered cubic high-entropy alloys (HEAs), carbon-doped Fe40.4Ni11.3Mn34.8Al7.5Cr6 (CHEA) and equiatomic CoCrFeMnNi (Cantor), was determined at cryogenic temperatures. Sliding wear tests were run both in dry cryogenic sliding conditions and under liquid nitrogen cryogenic conditions (wet conditions). Scanning electron microscopy, energy-dispersive X-ray analysis, X-ray photoelectron spectroscopy, atom probe tomography, and scanning transmission electron microscopy were used to characterize the worn pin surfaces. It was found that at cryogenic temperatures, the CHEA generally had lower wear rates compared to the Cantor HEA pins, except for the wet high-speed sliding condition. Comparison with previous room temperature tests (Guo et al. in Mater Charact 170:110693, 2020, https://doi.org/10.1016/j.matchar.2020.110693 ) revealed much higher wear rates in low-speed conditions at room temperature, while cryogenic tests had higher wear rates in high-speed conditions. Oxides found on the CHEA pins were much more stable and adherent than those on the Cantor HEA pins, and they played a role in the CHEA’s overall better wear resistance. Large amounts of soft transition metal oxides seen in the Cantor HEA at dry high-speed condition allowed easy removal and therefore the highest wear rate of all conditions. Twins exclusively appeared in the CHEA samples while planar faults mainly appeared in the Cantor HEA ones. Both indicate that plastic deformation had occurred during sliding. Precipitation of secondary phases in the CHEA pins was also found and, coupled with evidence of twinning, also provided explanation for increased wear resistance of the CHEA. Wear mechanisms of cryogenic dry samples varied with sliding speed. Oxidational wear dominated at lower speeds, evidenced by composition of the surface oxide and mechanically mixed sublayer. At high sliding speeds, delamination and adhesive wear were the main mechanisms, with less useful contribution from the surface oxide layer.