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CoCrFeNiMn high entropy alloy (HEA) owns prominent strain hardening capacity and high tensile elongation but poor wear resistance. In present work, in-situ carbide/CoCrFeNiMn composites with excellent anti-wear properties were fabricated by a flake powder metallurgy route using graphene oxide (GO) and CoCrFeNiMn as original powders. As a result, the hard carbide phase, Cr 7 C 3 , is formed in the soft matrix via in-situ reaction at the GO/HEA interface, which leads to a dense distribution of small-sized Cr 7 C 3 and strong interfacial bonding of the composites. With the addition of 5 wt% GO, the microhardness is improved by 66.7% and the macroscopic wear rate is decreased by 78.3% as compared with CoCrFeNiMn HEA. Increased nano-scratch resistance indicates that the dense distribution of hard Cr 7 C 3 carbide and the strong Cr 7 C 3 -CoCrFeNiMn interfacial bonding play key roles to resist the plastic flow of the HEA matrix during friction and wear. This study may provide a pathway to improve the wear resistance of HEA for engineering applications. [ABSTRACT FROM AUTHOR]

The multi-principal nitride film is known for its high hardness, good corrosion resistance, but its limited toughness severely reduces its wear resistance. This study presents a VCoNiN weak-nitride-forming system with unique microstructure of nanocrystalline embedded in amorphous matrix. The VCoNiN system demonstrates superior hardness to the VCoNi multi-principle alloy film and VN metal nitride film. Moreover, it exhibits the lowest wear rate against Si 3 N 4 at room temperature. The exceptional mechanical properties and excellent oxidation resistance derived from the multi-principal system contribute to the superior wear resistance of VCoNiN. Additionally, the novel microstructure allows for more uniform deformation during wear as the nanocomposite structure accommodates plastic strain without cracking or localized brittle fracture. This provides a promising design strategy for weak-nitride-forming film with enhanced wear resistance by enhancing the plastic deformation ability of brittle nitride. • VCoNiN film exhibits much higher toughness and ultra-lower wear rate than VN. • The structure of nanocrystal embedded in amorphous enhances toughness significantly. • More uniform plastic deformation during the wear greatly reduces the wear rate. [ABSTRACT FROM AUTHOR]

The expected excellent tribological performance of high-entropy alloys (HEAs) is rarely achieved due to the absence of self-lubricating ability on the worn surface. In particular, the situation is more challenging in HEAs with face-centered cubic structure because of the inferior yield strength when used in dry sliding conditions. Unlike conventional soft-solid lubricants, which deteriorate the mechanical properties of HEA matrix, in this study we demonstrate in a protocol model alloy that the proper incorporation of few-layer graphene as reinforcement in CoCrFeNiMn can lead to both surface strengthening and lubrication. This is achieved by a partially chemical interface reaction between graphene and HEA via a tunable fabrication process, resulting in a reduction of wear rate and friction coefficient of 86.03% and 23.87%, respectively. As a result of the interfacial in-situ carbide strengthening together with the self-lubrication of graphene, this tailored composite structure also exhibits superior tribological properties over most HEA-based self-lubrication composites. Besides, the subsurface structure evolution and deformation mechanisms that influence the wear resistance are systematically clarified through microscopic exploration and atomistic simulation. The present study presents an effective strategy for the development of innovative HEA composites suitable for safety-critical applications, which overcomes the inherent compromise and achieves exceptional tribological performance, i.e., self-lubricating and anti-wear. [Display omitted] • The self-lubricating graphene reduces wear rate to an order of magnitude. • The wear rate of Gr/HEA composite surpasses most FCC-structured HEAs. • The in-situ carbides alter the plastic deformation mode from planar to wavy slips. • The graphene significantly alters the plowing and adhesion mechanisms during wear. [ABSTRACT FROM AUTHOR]