Study On Friction And Wear Properties Of Ni-graphite Self-lubricating Laser Cladding Layer

Titanium alloy has many advantages such as light weight,high strength,high rigidity and toughness,good welding performance,and excellent corrosion resistance.It has been applied and developed in aerospace,marine,automotive,textile,agriculture and animal husbandry industries.Laser cladding is one of the common technical methods for surface modification of titanium alloys.Adding an appropriate solid lubricant to the laser cladding material can impart self-lubricating properties to the laser cladding layer and show excellent friction reduction during friction and wear.In this paper,a nickel-clad graphite self-lubricating and wear-resistant coating is prepared on the surface of TC4 titanium alloy substrate using Ni60,TC4 and nickel-clad graphite（hereinafter referred to as Ni-graphite）as the cladding material through coaxial powder feeding laser cladding technology.The effects of the amount of nickel-clad graphite added on the forming quality,phase composition,microhardness,anti-friction property and wear resistance of laser cladding layers were investigated,and the proportion of laser cladding materials was optimized.It provides experimental and theoretical basis for improving the friction and wear resistance of titanium alloy surface,and has certain industrial application value.The main research work of this article is:（1）The effects of Ni-graphite addition amount on the forming quality and microstructure uniformity of laser cladding layer were studied.The optimal amount of Ni-graphite in the cladding material was 35wt.%.When the amount of Ni-graphite was 35wt.%,the number of cracks in the cladding layer was the smallest,and the graphite content in the coating was more and the distribution was more uniform.The reason was that too little Ni-graphite was liable to decompose the graphite completely,while too much Ni-graphite resulted in agglomeration and segregation of graphite in the coating and increased residual stress.（2）The effects of the addition amount of Ni-graphite on the phase composition and properties of the laser cladding layer were explored.The main phases in the cladding layer include the ceramic phases TiC and Ti B₂,the intermetallic compound Ti₂Ni,the matrixα-Ti,and the lubricant phase graphite.The hardness of the coating decreased with the increase of the amount of Ni-graphite,and the wear resistance also decreased.The anti-friction property of the coating with Ni-graphite added at or above35wt.%was improved compared to the TC4 substrate.When the amount of Ni-graphite added was 35wt.%,The coating could simultaneously improve the substrate hardness,friction reduction and wear resistance.（3）The microstructure and element distribution of the coating were analyzed when Ni-graphite was added at 35wt.%.Ti C-Graphite and TiC-Ti₂Ni composite structures with two semi-coherent relationships were generated in the coating,which was helpful to prevent graphite from detaching from the matrix and increased the uniformity of coating structure distribution.