Structural Evolution Mechanism On The Sliding Interfaces Of Polycrystalline Diamond Sliding Against Ceramic Materials

Friction and wear are inevitable in almost all mechanical systems with moving parts.It is often the main cause of energy loss,mechanical failure and inefficiency.Reducing friction and wear between macroscopic mechanical motion interfaces is significantly important for energy conservation.In order to reduce the adverse effects of friction,attempts have been made to improve the contact configurations of sliding interface to achieve ultra-low/superlubricity by using various solid or liquid lubricants.The regulation of the frictional interface plays a crucial role in the entire tribological system.The systematic understanding of the structural evolution of the frictional interface is of great significance to reveal the tribological behavior of materials in essence,and can provide an effective strategy for the design of ultra-low/superlubricity pairs.In this work,since polycrystalline diamond(PCD)possesses a micron-sized diamond polycrystalline structure,the exfoliated micron-sized diamond particles gradually evolve into nanodiamond and nano-layered structure stacking during the sliding process,which can achieve an incommensurate contact at the nanoscale scale.The contact interface provides the advantage of multi-layer stacks and is ideal for designing ultra-low/superlubricity friction interfaces.This paper systematically explores the structural evolution of the frictional interface of polycrystalline diamond sliding against ceramic materials,and analyzes the evolution of diamond particles to nanodiamond,nanolayered onion carbon and graphene nanosheets,revealing the structural evolution of interface materials and the effect on the tribological properties of polycrystalline diamond.In essence,the nano-layered material between the rigid interface of polycrystalline diamond and ceramic material and the formation of nano-particles at the interface are known to achieve the incommensurate crystalline contacts of the sliding interface,which is of great significance for achieving stable macroscopic ultra-lubrication.Since the realization of macro-scale super-lubrication is challenging,the revealing of the evolution of interface structure provides an idea for the design to achieve macro-scale stable superlubricity.Based on the above research,the main conclusions of this paper are summarized as follows:(1)The importance of anti-friction and wear-resistance design of polycrystalline diamond for its macroscopic application was uncovered.When polycrystalline diamond slides against different mating materials,they show different interfacial states and carbon rehybridization process accompanied by the different tribological behavior.(2)The formation of colloidal layer was studied.The interaction between the formation of colloidal layer and diamond nanoparticles,multilayer graphene nanosheets and nano carbon-like fullerenes in the interface and the structural reorganization mechanism were uncovered.(3)Observing the spalling of diamond particles and the evolution of micron-sized diamond to nanodiamond is significantly for understanding the rehybridization process of diamond induced by shearing effect.The formation of sp~2-C layer caused by diamond phase transition leading to a disordered surface was revealed.The disordered sp~2-C cluster gradually evolved into ordered layered structure accompanied by the formation of multilayer graphene nanosheets,and formation of nano-multilayered onion fullerenes,which indicates the formation of carbon-based tribofilms.Additionally,the relationship between the formation of carbon based tribofilm and the ultralow and superlubricity states was established.