Tribological performance of hydrogenated diamond-like carbon coating deposited on superelastic 60NiTi alloy for aviation selflubricating spherical plain bearings

It is imperative to develop a novel matching of metallic substrate and self-lubricating coating for aircraft spherical plain bearing in a wide range of service conditions.As a new type of superelastic material,60NiTi alloy meets the performance requirements of aerospace bearing materials,but exhibits poor tribological performance,especially under the conditions of dry sliding friction.A Hydrogenated Diamond-Like Carbon(H-DLC)coating was deposited on the 60NiTi alloy to improve its tribological performance.The microstructure and mechanical behavior of the 60NiTi alloy and its H-DLC coating were explored.Results show that improvement of friction and wear performance of the H-DLC coating deposited on the 60NiTi substrate is mainly achieved by graphitization at the friction interface and the transfer film produced on the counterpart ball.The increased friction load leads to intensification of graphitization at the friction interface and formation of continuous and compact transfer film on the surface of the counterpart ball.

Metastable hybridized structure transformation in amorphous carbon films during friction-A study combining experiments and MD simulation

Amorphous carbon films have attracted substantial interest due to their exceptional mechanical and tribological properties.Previous studies revealed that the amorphous carbon films exhibited lower coefficient of friction(COF)because of the transformation in bond structure from sp^(3)-C to sp^(2)-C during friction processes.However,the mechanism for such a transformation during friction is not well understood.This study is conducted to get an insight into the metastable transformation in amorphous carbon film during friction by means of experiments and molecular dynamics(MD)simulation.Relevant wear tests showed that wear of the film changed from an abrasive wear mode to a mixture of abrasion and adhesive wear,resulting in a decrease in growth rate of the wear rate after the running-in stage.It is worth noting that the sp^(3)-C atoms were increased during the running-in stage when the films contained lower sp^(3)/sp^(2) ratios.However,the formed sp^(3)-C atoms could only be short-lived and gradually transformed to sp^(2)-C atoms with the graphitization generated on the wearing surface of the films.The radial distribution function and translational order parameter indicated that the films'high sp^(3)/sp^(2) ratio led to an increased sp^(2)-C proportion on the wear scar after friction,which caused an increased structural ordering.

Electronic characteristic,tensile cracking behavior and potential energy surface of TiC(111)/Ti(0001)interface:A first principles study

The preparation of TiC coating on Ti alloy surface to improve the wear resistance has attracted attention from researchers in aerospace field.The service life of TiC coating is related to the interfacial adhesion properties between TiC coating and Ti alloy substrate.However,it is difficult to explain its interfacial adhesion mechanism by experimental methods.Based on the termination of atoms on the TiC surface,two TiC/Ti interface models named as the C-terminated-TiC(111)/Ti(0001) and Ti-terminated-TiC(11)/Ti(0001) interface were constructed by first-principles.The interfacial electronic characteristic of C-Ti bond is a mixture of polar covalent and metal bonds,and that of Ti-Ti bond is the metal bond.The tensile strains of both C-terminated-TiC(111)/Ti(0001) and Ti-terminated-TiC(111)/Ti(0001) interface in the fracture stage are ranged from 12% to 14%.Their maximum tensile stresses are 16.201 GPa and 15.590GPa,respectively.The sliding potential energy surface maximum of C-terminated-TiC(111)/Ti(0001) and Ti-terminated-TiC(111)/Ti(0001) interface are 5.387 J/m^(2) and 0.271 J/m^(2),respectively.And the sliding potential barriers on the minimum energy path are 2.094 J/m2and 0.136 J/m^(2) with an ideal shear strength of 20.32 GPa and 1.61 GPa,respectively.In summary,the interfacial adhesion property of C-terminated-TiC(111)/Ti(0001) interface is better than that of Ti-terminated-TiC(111)/Ti(0001) interface.