Robust Low-Friction and Low-Wear TiNbMoTaCr High-Entropy Film Enabled by Periodically Inserting Curved MoS₂ Sheets

The well-known integration of physical, chemical, and mechanical properties enables high-entropy alloys (HEAs) to be applied in various fields; however, refractory HEAs are brittle and susceptible to abrasive wear at high coefficients of friction (COF), resulting in insufficient mechanical durability against abrasion. Herein, curved MoS₂ nanosheets are periodically introduced into the TiNbMoTaCr film for triggering the self-assembly mixed metal oxides @MoS₂ nanoscrolls, which contain hard mixed metal oxides cores and the low-shearing lubricant MoS₂ shells, during the friction in the air environment; such mixed metal oxides@MoS₂ nanoscrolls in the friction interfaces can contribute to the robust low friction and low wear. Compared to the pure TiNbMoTaCr film (with high COF of ∼0.78, low abrasive durability identified by worn-out event), the periodic incorporation of 10 nm thickness curved MoS₂ sheets can successfully achieve a low COF of ∼0.08 and low wear rate of ∼9.561 × 10^-8 mm³/ Nm, much lower than the pure MoS₂ film (COF = ∼ 0.21, wear rate = ∼ 1.03 × 10^-6 mm³/ Nm). Such superior tribological properties originate from the cooperative interaction of TiNbMoTaCr nanolayers and curved MoS₂ nanosheets, accompanied by the self-assembly of mixed metal oxides@MoS₂ nanoscrolls. In these nanoscrolls, TiNbMoTaCr can act as an 'air-absorbing agent' to form high-loading mixed metal oxide cores and serve as an 'oxygen sacrificer,' preventing the low-shearing lubricant curved MoS₂ nanosheets from oxidation. In addition, even with the soft MoS₂, the hardness of the TiNbMoTaCr/MoS₂ nanomultilayers can still be well maintained and increased above the calculated values by mixing law, further favoring superior mechanical durability. The synergetic effect of TiNbMoTaCr and curved MoS₂ nanosheets during the friction in air can provide a route to design HEA films with enhanced tribological properties for better mechanical durability and broader application prospects.