Microstructure Of In-situ Synthesized Multiphase Particle Reinforced Titanium Matrix Composite Coating By Argon Arc Cladding And Wear Resistance Research

As science and technology in China is advancing constantly,the industrial field has put forward higher requirements for the quality and performance of metal materials,and the key to the quality of metal materials is wear failure.TC4 alloy is widely used in marine engineering equipment,aerospace,medical equipment and other fields due to its high specific strength,lightweight and other characteristics,but the defects of poor wear resistance and low hardness limit the practical application of TC4 alloy in industry.Therefore,Ti+BN+G_x/La₂O₃composite coating was prepared on the surface of TC4alloy by argon arc cladding using Ti powder,BN powder,graphene powder and rare earth La₂O₃powder.The effects of argon arc cladding process parameters,graphene and La₂O₃content on the microstructure and properties of Ti+BN+G_xcomposite coatings were investigated by X-ray diffraction,optical microscope,scanning electron microscope,micro-hardness tester and friction and wear testing machine.The molar ratio of Ti to BN powder was fixed at 3:2,and the surface morphology and microhardness of the coatings obtained under different cladding parameters were studied.The results show that the coatings have smooth surface,no obvious defects,metallic luster and high microhardness under the conditions of 100 A of cladding current,3 mm/s of cladding speed,10 L/min of argon flow rate and 1 mm of pre-deposited powder thickness.In order to improve the hardness and wear resistance of TC4 alloy coating,the effects of graphene content（0wt.%,1wt.%,3wt.%,5wt.%,7wt.%）on the microstructure and properties of Ti+BN+G_xcoating were investigated.It is found that with the addition of graphene,the reinforcement phase in the coating changes from Ti N to Ti（N,C）.According to the analysis of thermodynamics and Hume-Rothery rule,the infinite solid solution of C element and N element in the molten pool is replaced,Ti（N,C）is formed by intermittent nucleation,and the microstructure is refined to a certain extent.With the increase of graphene content and C element in the molten pool,the Ti（N,C）particle reinforcement phase continues to grow,and the microstructure of the coating is gradually coarse,thus reducing the performance of the coating.When the content of graphene is 5wt.%,the microstructure refinement of the coating is the most obvious,the microhardness is 3 times higher than that of the substrate,and the wear resistance is 4.7times higher than that of the substrate.The wear mechanism of the coating is abrasive wear and slight adhesive wear.Therefore,when the content of graphene is 5wt.%,the Ti+BN+G_xcoating has the best mechanical properties.On the basis of 5wt.%graphene,the performance of the coating was further improved by adding different amounts of rare earth La₂O₃（1wt.%,2wt.%,3wt.%,4wt.%,5wt.%）.It is found that the addition of rare earth La₂O₃does not affect the phase composition of the composite coating,and the reinforcing phases in the composite coating are composed of granular and dendritic Ti（N,C）and needle-like Ti B.The surface scanning analysis shows that the rare earth La element is uniformly distributed in the composite coating,which inhibits the growth of the structure and plays a role in refining the grain.With the increase of La₂O₃content,the microstructure of the composite coating is gradually refined.When the content of La₂O₃is 4wt.%,the microstructure of the composite coating is refined and distributed more uniformly and compactly.Compared with the substrate,the microhardness and wear resistance of composite coating are increased by 3.7 times and 9.6 times,respectively,and the wear mechanism is abrasive wear.When the content of La₂O₃is 5wt.%,the microstructure of the composite coating is coarse and the distribution is uneven,which reduces the hardness and wear resistance of the composite coating.