Anti-friction And Wear-resistant Of Ceramic Reinforced Graphite Self-lubricating Coating Prepared By Laser Cladding On TC4 Surface

TC4 alloy has the outstanding advantages of light weight,high strength,corrosion resistance,oxidation resistance,wide temperature range applicability and excellent machinability.It can meet the requirements of aircraft lightweight design and improve the transient response ability of engine.It is an important structural material for advanced aircrafts and aeroengine.However,TC4 alloy has many application defects such as low hardness,poor anti-friction and wear resistance,and easy to produce adhesive wear and so on,which severely limits the performance and service cycle of aviation titanium alloy parts,and affects the safety and stability of aircraft.In order to improve the surface hardness,friction reduction and wear resistance of TC4 titanium alloy,the ceramic reinforced graphite self-lubricating antifriction and wear resistance laser cladding layers were prepared by coaxial powder feeding laser cladding technology with TC4+Ni60+Ni-graphite and TC4+Ni60+Ni-graphite+Y₂O₃ as cladding materials.The effects of Ni-graphite and Y₂O₃ addition on the forming quality,microstructure characteristics,phase structure relationship and anti-friction and wear resistance of the cladding layer were studied respectively,and the optimal addition amount of Ni-graphite and Y₂O₃ was determined.It aims to provide a certain theoretical support and experimental reference for the safe application of TC4 alloy in the aviation field.The main contents of this paper are as follows:（1）The results show that the phases of Ni-graphite cladding layer with different addition amount are consistent,mainly including Ti C,Ti B₂,Ti₂Ni,graphite and matrix phaseα-Ti.The35wt.%Ni-graphite coating has the least cracks and the best forming quality.The semi-coherent composite structure phase of Ti C wrapped graphite and the coherent composite structure phase of Ti C and Ti₂Ni interlaced growth are formed in the cladding layer;The semi coherent Ti C coating can alleviate the melting of graphite particles in the molten pool,and the Ti C-Ti₂Ni composite structure phase can effectively refine the Ti₂Ni structure,increase the distribution uniformity of Ti₂Ni and reduce the cracking risk of the coating.（2）With the increase of Ni-graphite addition,the average microhardness of the cladding layer gradually decreases,and the average microhardness of 25wt.%Ni-graphite cladding layer(733.8HV_0.5)is the highest,which is about 1.95 times higher than that of the substrate(376.5 HV_0.5);the addition of Ni-graphite effectively reduces the friction coefficient,and the friction coefficient of 35%Ni-graphite cladding layer is the lowest（0.09）,which is about80.4%lower than that of the substrate（0.46）.And the wear mechanism of Ni-graphite coatings with different content is abrasive wear.（3）The addition of Y₂O₃ increases the thickness of the cladding layer,and the cracks in the cladding layer are effectively restrained.When the Y₂O₃ content is 6wt%,there is no crack on the surface of the cladding layer,and the forming quality is the best.With the increase of Y₂O₃ addition,the reinforcement phase Ti C and the intermetallic compound Ti₂Ni are significantly refined.The results of Bramfitt two-dimensional lattice misfit calculation show that the two-dimensional misfit of Y₂O₃-Ti C and Y₂O₃-Ti₂Ni are 7.09 and 5.75 respectively.Y₂O₃ can be used as heterogeneous nucleation point of Ti C and Ti₂Ni to refine the structure of the cladding layer.（4）With the increase of Y₂O₃ addition,the average microhardness of the cladding layer first increased and then decreased,and the average microhardness(750.4HV_0.5)of the 2wt.%Y₂O₃ cladding layer was the highest.When the Y₂O₃ addition is 4wt.%,the melting amount of substrate increases,which results in the decrease of hardness,but the distribution of microstructure is more uniform,and the wear rate is the lowest(3.58×10^-4 mm³·N^-1·m^-1).The coating has the best wear resistance.The addition of Y₂O₃ leads to the decrease of graphite content in the cladding layer,and the anti-friction performance is lower than that of the cladding layer without Y₂O₃.The wear mechanism of the cladding layer with different addition Y₂O₃ is abrasive wear.