| Ti6Al4V alloy has been widely used in aerospace,automobile and other fields,because of its high specific strength,high temperature resistance and good biocompatibility.However,with the development of technology in aerospace,military,petrochemical and other fields in China,higher requirements are put forward for the hardness,wear resistance and heat transfer performance of Ti6Al4 V alloy.Therefore,using surface modification technology to improve the hardness and wear resistance of titanium alloy has important practical significance.Laser cladding is a surface modification technology with high efficiency and low cost,which has a wide application prospect in aerospace,petrochemical and mechanical manufacturing.In this paper,Graphene(Gr)/Ti6Al4 V composite powder was used as the research object.The metal/ceramic composite coating was prepared by laser cladding on the surface of titanium alloy.The effect of the second phase in the composite on the nucleation of titanium matrix and the interfacial bonding strength of heterogeneous phase were studied by first principles.The results are as follows:(1)Laser cladding technology was used to cladding Gr/Ti6Al4 V composite powder and Ti6Al4 V alloy powder on Ti6Al4 V alloy surface.In the process of laser cladding Gr/Ti6Al4 V composite powder,in-situ reaction occurs: Ti + C ? TiC,forming a new phase TiC.TiC is feather like and homogeneously distributed in ?' acicular martensite,and ?-Ti was refined,which plays the role of grain refinement.At the top of the composite coating,the amount of TiC was low and it was not homogeneously distributed.In the middle of the coating,the TiC was homogeneously distributed and the number of TiC particles significantly higher.The bottom of the composite coating bonded well with Ti6Al4 V substrate.At the same time,it is found that there are still some Gr in the composite coating,which is well combined with Ti6Al4 V substrate.(2)The interfacial stability of ?-Ti(0001)/TiC(111)and ?-Ti(1-100)/TiC(111)was studied by first principles,and the nucleation analysis was carried out.The results show that in the calculation of ?-Ti(0001)/TiC(111)and ?-Ti(1-100)/TiC(111)interface models,it is found that compared with Ti-termination interface,the interface adhesion work of C-termination interface is larger,and the interface spacing and interface energy are both smaller.It is shown that this interface model is more conducive to the stability of interface structure,and Ctermination hollow-sited interface is the most stable interface with the minimum interface spacing,the maximum interface adhesion work and the minimum interface energy.According to the curve analysis of charge differential density and split-wave density of states,when the atom on the end face of TiC surface is C atom,a strong Ti-C covalent bond is formed between the Ti atom and C atom at the interface,and the charge transfer is obvious,which is more conducive to strengthening the stability at the interface.The results of nucleation analysis show that the C-termination hollow-sited interface of ?-Ti(0001)/TiC(111)is the best way of ?-Ti/TiC interface bonding.(3)The effects of Gr addition on the hardness,friction and wear and electrochemical corrosion properties of the composite coatings were studied.The microhardness of the composite coating was about 57% higher than that of Ti6Al4 V substrate.Compared with Ti6Al4 V substrate,the TiC hard particles and the self-lubrication of graphene improved the wear resistance of composite coating.And the wear mechanism changed from more serious abrasive and adhesive wear to a mild wear with fine scratches.Under high temperature friction and wear,the composite coating and substrate also have serious oxidation wear.At the same time,compared with that of the substrate,the self-corrosion potential of the composite coating positively shifted significantly,and the corrosion current density decreased.The corrosion resistance of the composite coating was also improved.The corrosion morphology was local pitting,while that of Ti6Al4 V substrate was denudation.(4)The effects of different loads and sliding speeds on the tribological behavior of laser cladding TiC/Gr/Ti6Al4 V composite coatings were obtained.The results show that the wear rate and friction coefficient of TiC/Gr/Ti6Al4 V composite coating decrease with the increase of sliding speed under a certain load.When the sliding speed is 0.4 m/s,the wear mechanism is abrasive wear and slight oxidation wear.When the sliding speed is 1.0 m/s,the wear mechanism changes into slight delamination wear and severe oxidation wear.At a certain sliding speed,the wear rate of TiC/Gr/Ti6Al4 V composite coating increases with the increase of load,but the friction coefficient is on the contrary.With the increase of load,the wear mechanism changes from slight abrasive wear and oxidation wear to delamination wear,fatigue wear and oxidation wear.The friction and wear properties of TiC/Gr/Ti6Al4 V composite coating can be effectively improved by Gr and in-situ synthesized TiC ceramic particles. |
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