Microstructure And Properties Of Laser Cladding Diamond-nickel Based Composite Coating On Titanium Alloy Surface

Titanium alloy has limited its development in many fields due to its poor wear resistance.It is the current mainstream research direction to improve the surface wear resistance of titanium alloy.Laser cladding technology has attracted much attention because of its good metallurgical effect with the substrate.It is an effective method to prepare high-performance and defect-free coatings.Among many materials to improve the wear resistance,diamond is favored by researchers because of its excellent high hardness and wear resistance.In order to improve the comprehensive properties of titanium alloy,Ni-based titanium-plated diamond coating is prepared on the surface of titanium alloy by laser cladding technology.The main conclusions are as follows:The effect of laser power and the content of titanium-plated diamond on the nickel-based coating on the surface of titanium alloy was investigated by the full combination test method.The results showed that when the laser power was 1300W,the diamond in the coating was retained completely,and the coating formed a good metallurgical bond with the substrate.Adding proper amount of titanium-plated diamond to the coating can reduce the thermal expansion coefficient of the coating and effectively reduce the crack sensitivity at the interface between the coating and the substrate.The cladding layer is mainly composed of diamond,Ti C,Cr₂₃C₆,Ni Ti₂ and other phases.The microhardness and wear resistance of the cladding layer can be improved by adding appropriate amount of titanium-plated diamond.When the laser power is 1300W and the content of Ti-coated diamond is 4%,the microstructure of the cladding layer is obviously refined,the precipitation of Ti C hard phase increases and dislocation strengthening effect is produced,which effectively improves the microhardness of the cladding layer.The hardness of the cladding layer reaches 67.95HRC,the wear coefficient is 0.45,and the longitudinal change between the coating and the friction pair during friction and wear is 0.0556mm.The influence of pretreatment quality,substrate surface roughness and whether the substrate surface is corroded or not on the shear resistance at the interface between the coating and substrate was studied by orthogonal test.Through visual analysis and variance analysis,the best pretreatment process parameters are obtained:preset mass（3.0g）,substrate surface roughness（800-900nm）,and whether the substrate surface is acid etched（acid etched）.The validation test is carried out on the significant factors（preset mass）obtained by variance analysis.The results show that the validation test conforms to the experimental law,the best preset mass of coating（3.2g）,and the shear resistance at the coating interface is 95.2N.In order to further optimize the comprehensive performance of the coating and explore the effect of friction load,time and speed on the friction and wear of the coating surface,Ta element was added to the coating on the basis of the previous test,and the effect of Ta content on the coating was discussed by single factor test method.The results show that when the content of Ta is 6%,the pores and cracks can be eliminated,and the excessive damage of the diamond on the top of the coating can be avoided.With the increase of load,the friction coefficient of the coating does not change significantly,and the friction loss of the silicon nitride ball changes linearly.With the increase of rotating speed,the friction coefficient of the coating decreases,and the friction loss of the silicon nitride ball decreases.The diamond on the coating surface can maintain good holding force under different load and rotating speed.