Investigation On The Tribological Behaviors Of Transitional Metal Nitrides/borides Films In Water-based Environment

Water-based lubrication has attracted wide attention,owing to it is a green and clean lubrication means.However,due to operating in the water environment,most moving parts would inevitably suffer from abrasion,rusting,and aging problems.It is important application prospects to develop a novel solid-water composite system with ultra-low friction and wear.Therefore,the important topic of water-based lubrication research is the development of tribopairs materials under water-based lubrication.Therefore,the development of friction pair materials is a very important topic in the research of water-based lubrication.Transitional metal nitride（boride）is an important protective coating material with prominent high hardness,wear resistance,corrosion resistance,and chemical inertness features.The excellent mechanical properties and environmental stability of transitional metal nitrides（borides）indicate that they have great application potential as protective coatings in water environments.In this article,we take the transitional metal nitrides（borides）films as the research objects,as well as design the three-phase（film,water and air）contact environment and the two-phase（film and water）contact environment covered by water.The dry friction（film and air）environment looks as a comparison item.The tribological behaviors of films in three different environments were systematically studied.The main research contents and conclusions are as follows:1.Investigation on the tribological behaviors of transitional metal nitrides in water-based environment.Here,we prepared niobium nitride（Nb N）film by magnetron sputtering method,and systematically invistigated the tribological properties of Nb N film in three-phase contact environment（water,air and Nb N film）,two-phase contact environment with full water-covered（Nb N film and water）,and dry friction environment（Nb N film and air）.In a three-phase contact environment,oxidation and hydrolytic reactions of Nb N result in the formation of colloidal solutions‖containing Nb₂O₅ colloidal particles between the tribopairs.Utilizingthe double electric layer repulsion and weak shear action of the―colloidal solution‖Nb N achieves the ultra-low friction;and the high hardness of the Nb N film and the mutual repulsion of the double electric layers reduce the direct contact of the tribopair to achieve the ultra-low wear.The corresponding friction coefficient and wear rate values are as low as 0.058 and 1.79×10^-10 mm³/Nm,respectively.In addition,otherⅤB transition metal nitrides（Ta N,VN）also exhibit the same low friction feature as Nb N in the three-phase contact environment with bright prospect;the friction coefficients are even lower than those in thean oil-based environment.2.Study on the superlubrication behavior of transitional metal borides in the three-phase contact environment.In the research,we developed a robust macroscale water-based superlubricity of transition metal diborides（TMB₂）,and expanded the contact area of superlubricating interface to millimeter scale in water environment for the first time.With three-phase contact（TMB₂,water and air）,the friction coefficient for the TMB₂ can remain in the range of 0.001 to 0.006,and excellent anti-wear ability is also obtained(the wear rate reaches～10^-13 m³/Nm).According to the characterization analysis of the friction interface and products,we found that the special contact state promotes the occurrence of tribochemical reaction of TMB₂.First,during the friction process,the friction products（TMO and H₃BO₃）are continuously transported to the water to form negatively charged B（OH）₄^-and neutral（TMO）n H⁺·m B（OH）₄^-.Under the dynamic equilibrium of friction reaction,the difference of the charges properties will lead to the repulsion at the interface and the repulsion at the hydration layer.Secondly,the generated friction products are hydrophilic,can play a role in fixing the hydration layer,so that the weak shear characteristics of water can be fully played.In a word,the realization of superlubrication is the joint action of the repulsion force of the friction interface,the repulsion force of the hydration layer in the friction fluid and the hydration lubrication.In order to explore the application prospect of the system in the three-phase contact environment,we extended the contact area of the dual material to the millimeter level,and confirmed the occurrence of macroscopic overslip phenomenon.In this part,a robust macroscopic water-based superlubrication material system was successfully discovered,and the contact area of the superslippery interface was extended to millimeter scale for the first time.