Preparation And Tribological Properties Of TiC Reinforced Metal Matrix Composite Coatings Obtained Via EDC Using A Reduced Graphene Oxide Nanosheet Mixed Dielectric

Nano titanium carbide?Ti C?particles have excellent mechanical properties,which can greatly improve the tensile strength,hardness and wear resistance of the composite when added to the metal matrix.It has a wide application prospect in the fields of aerospace,electronic power,and mechanical friction.The technology of electrical discharge coating is a kind of surface strengthening technology,which produces a plasma beam channel between the electrode and the workpiece,melts the electrode material and reacts with the liquid-phase medium,and then deposits it on the workpiece surface to form a modified layer.By selecting the appropriate tool electrode material and liquid medium,metal carbide reinforced metal matrix composite coating can be quickly generated on the workpiece surface.However,the electrical discharge coating has the disadvantages of uneven pulse discharge energy distribution and difficulty in control.The resulting coating is often accompanied by defects such as cracks and micropores,which greatly limits the development and the application of electrical discharge coating.According to the theory of impurity discharge,adding solid fine particles to the liquid working medium is beneficial to reduce the breakdown strength of the working medium,increase the discharge gap,and disperse the energy of pulse discharge.Therefore,adding suitable solid fine particles in the working medium is expected to suppress cracks,micropores and other coating formation defects.In view of the thin thickness of graphene atoms,the unique two-dimensional planar structure and good thermal conductivity,this study used alkyl-modified graphene nanosheets and alkane mixture as the working medium between the semi-sintered titanium tool electrode and the workpiece Pulse discharge to prepare nano-Ti C particles reinforced metal matrix composite coating on the surface of the workpiece.The research content and results are as follows:1.Alkyl modification of graphene nanosheets.Based on the principle of similar miscibility,graphene oxide nanosheets were alkyl-modified by octadecylamine.The modified graphene oxide nanosheets were characterized by infrared spectroscopy,XRD,Raman,SEM and other methods.The results show that the amine group of the octadecylamine molecule reacts with the epoxy group of graphene oxide to.The alkyl modification significantly improves the dispersion and stability of graphene in alkane liquid,and maintains the two-dimensional morphology of graphene nanosheets.2.Preparation and friction and wear properties of nano-Ti C particles reinforced iron-based composite coating.Using a mixture of alkyl-modified graphene nanosheets and alkane as the working medium,pulse discharge is applied between the semi-sintered titanium tool electrode and the H13 steel workpiece,and a titanium carbide particle reinforced iron-based composite coating is prepared on the H13 steel surface.Study the influence of process parameters on the morphology,microstructure and hardness of the composite coating.The fine structure and friction and wear properties of the composite coating under optimized process parameters were studied.Research indicates:?1?The relative optimized process parameters are discharge time=0.5h,peak current=10A,pulse time=8?s,and concentration of alkyl-modified graphene nanosheets=0.15g/L.?2?The thickness of the coating is uniform and there are no obvious defects such as cracks and micropores,which is significantly better than the coating prepared in pure alkane liquid.The reason for the improvement of coating quality can be attributed to the fact that graphene dispersed uniformly in alkane liquid is beneficial to reduce the breakdown strength of the working medium,increase the discharge gap,and disperse the energy of pulse discharge.?3?The microhardness of the coating surface reaches 1813HV_0.2,which is 5.3 times and 1.8times of H13 steel and pure alkane medium coating,respectively.?4?The microstructure of the coating is a composite structure with multi-size titanium carbide particles distributed on the martensite matrix,and the titanium carbide particles exhibit a hierarchical distribution:the surface is nano-sized titanium carbide particles and self-assembled into column morphology,below is coarse titanium carbide particles.?5?Under a 30N load,the average COF of the coating is about 0.2,which is 69%and 52%lower than those obtained by H13 steel and pure alkane medium,respectively.The wear those obtained by H13 steel and pure alkane medium,respectively.The wear mechanism of the coating is dominated by mild abrasive wear.3.Preparation and friction and wear properties of multi-scale Ti C particles reinforced copper-based composite coatings.Multi-scale Ti C particles reinforced copper-based composite coatings were prepared by electrical discharge coating and aging treatment two-step method.In the first step,using a mixture of alkyl-modified graphene nanosheets and alkane as the working medium,a pulse discharge is applied between the semi-sintered titanium tool electrode and the copper workpiece to prepare a titanium carbide particle reinforced copper-based composite coating on the copper surface.The second step is to convert Ti atoms and C atoms dissolved in the copper matrix into nano-sized titanium carbide particles through aging treatment and disperse and distribute them in the copper matrix.The effect of the aging process on the microstructure,hardness and friction and wear properties of the multi-scale Ti C particle-reinforced copper-based composite coating was mainly studied.The research results show that:?1?The relatively optimized aging process parameters are:aging time 0.5h,aging temperature 500?.?2?The coating microstructure is a composite structure in which primary Ti C particles generated by pulse discharge,secondary Ti C particles precipitated by aging treatment and a small amount of intermetallic compounds??-Cu₄Ti and?-Cu₄Ti?are distributed on the copper matrix.?3?The surface hardness of the coating reaches 1384HV_0.2,which is 15%higher than that of the titanium carbide particle reinforced copper-based composite coating without aging treatment.The increased hardness mainly comes from the dispersion strengthening of secondary Ti C particles precipitated by aging treatment.?4?The average friction factor of the coating under a load of 20N is about 0.2,and the wear rate is 1.24×10^-5 mm³ N^-1 m^-1,compared with the titanium carbide particle reinforced copper-based composite coating without aging treatment,The average friction factor is reduced by 33%,and the wear resistance is 3.7 times higher.The main wear mechanism of the coating is slight abrasive wear and oxidative wear.