Abstract
Water-based lubrication has attracted wide attention as an oil-free lubrication method owing to its greener and cleaner lubrication means. However, due to operating in the water environment, most moving parts would inevitably suffer from abrasion, rusting, and aging problems. Developing a novel solid-water composite system with ultra-low friction and wear will open new possibilities for innovative lubrication material research and development. Here, we first revealed the water-based lubrication behavior of a high-hardness niobium nitride coating (NbN). In a three-phase contact environment (water, air, and NbN), oxidation and hydrolytic reactions of NbN result in the formation of “colloidal solutions”, containing Nb2O5 colloidal particles between the tribo-pairs. Utilizing the double electric layer repulsion and weak shear action of the “colloidal solution”, NbN achieves ultra-low friction and wear; the corresponding values are as low as 0.058 and 1.79 × 10−10 mm3·N−1·m−1, respectively. In addition, other VB transition metal nitrides (VB TMNs) exhibit the same low friction feature as NbN in the three-phase contact environment; the friction coefficients are even lower than those in an oil-based environment. The water-based lubrication of VB TMNs provides a new reliable scheme for optimizing solid-water composite lubrication systems without additives and is expected to be applied in environments with high humidity or insufficient water coverage.
Highlights
Water-based lubrication can effectively save natural resources and ensure the normal operation of mechanical equipment in a clean environment
VB transition metal nitrides (VB TMNs) with high hardness attained an ultra-low wear rate of ~10–10 mm3·N–1·m–1. These findings identify the VB TMNs as a mechanically strong coating material that exhibits outstanding water-based lubrication behavior, with simultaneous non-additive lubricating functionality and superior protection, guaranteeing the service life and safety of mechanical equipment in an environment with highhumidity or inadequate water cover; the material shows great potential for applications ranging from microdevices to large-scale industrial equipment
niobium nitride coating (NbN) with good crystallization can be obtained if the deposition temperature is properly increased
Summary
Water-based lubrication can effectively save natural resources and ensure the normal operation of mechanical equipment in a clean environment. From a protective mechanical equipment perspective, the deposition of protective coatings with excellent mechanical properties and water-based lubricating behavior on the surface of a moving part should be a simpler and more effective method than the scheme for optimizing the water environment. The VB TMNs exhibit outstanding water-based lubricating behavior when simultaneously exposed to water and air and their friction properties are superior to those of similar nitride coatings in a solid–oil composite lubrication system [25]. VB TMNs with high hardness attained an ultra-low wear rate of ~10–10 mm3·N–1·m–1 These findings identify the VB TMNs as a mechanically strong coating material that exhibits outstanding water-based lubrication behavior, with simultaneous non-additive lubricating functionality and superior protection, guaranteeing the service life and safety of mechanical equipment in an environment with highhumidity or inadequate water cover; the material shows great potential for applications ranging from microdevices to large-scale industrial equipment
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