Study On Surface Modification Technology Of Titanium Alloy By HVAF Spraying

Titanium alloy has developed rapidly since the 20th century.Due to its low density and high strength,it is widely used in aerospace,automotive,chemical,ocean,electronics and many other fields.While under some crucial working conditions,the surface hardness of titanium alloy is not high enough to withstand wear and corrosion,resulting in the decline of service life and even damage of parts.This situation limits its wider use in industry.At present,many surface modification technologies have been applied to the surface modification of titanium alloy.However,most of them have their own shortcomings,such as high cost,complex process,limited coating thickness and so on.In this paper,two kinds of composite coatings were prepared on the surface of titanium alloy by HVAF.The microstructure and phase composition of the composite coatings were characterized by X-ray diffraction（XRD）,optical microscope（OM）,scanning electron microscope（SEM）and electron probe micro-analyzer（EPMA）;Vickers hardness tester was used to measure the hardness of coating section;the bending strength and impact toughness of the sample were tested;The wear resistance and corrosion resistance of the samples were measured by friction wear tester and electrochemical workstation.In this experiment,the orthogonal test is setting the three process parameters of powder feeding rate,spraying distance and raw material mixing ratio as variables.The range analysis is carried out,which based on the performance of the samples to judge the influence of the changes of various parameters on the different performance of the samples,and it is expected to obtain a set of optimized process.The experimental results show that the powder feeding speed has the greatest influence on the comprehensive properties of the coating.The properties of WC-Cr C-Ni/TC4 coating optimized by orthogonal experiment are improved,and the porosity is 1.64%;The average hardness of the section is 831 HV_{0 3};The impact toughness is low,67.8 J/cm²;Bending strength 1901 MPa;The average friction coefficient is 0.398.The dense B₄C/Ni composite coating was prepared on TC4 titanium alloy by supersonic flame spraying.It was found that the main phases of the composite coating were B₄C,Ni₃B,C and so on;The porosity of the composite coating is about 2.3%;The average hardness is 591HV_{0 3},about 1.9 times of the base material;In the form of dry friction,the friction process of the coating is dominated by abrasive wear,with an average friction coefficient of about 0.41and a wear rate of 4.997×10^-5 g_*m^-1,about 20%higher than the substrate;At 3.5wt.%The corrosion resistance of B₄C/Ni coating in Na Cl solution is significantly improved,and its corrosion current density is 3.992×10^-8 A·cm^-2,better than WC coating.Therefore,the B₄C/Ni composite coating prepared by supersonic flame spraying has high comprehensive properties.