Effect of La2O3 on Microstructure and Properties of Ti-BN-G Composite Coatings Prepared by Argon Arc Cladding
TC4 alloy(Ti-6Al-4V)is the titanium alloy with the most industrial applications.It is widely used in the biomedical,petrochemical,aerospace,and military industries because of its advantages,which include a low density,high specific strength(strength/density),good corrosion resistance,and good low-temperature performance.It is especially prominent in the field of offshore equipment.TC4 alloy is in great demand for ship structures,where it is mainly used for engine parts,pressure-resistant shells,propellers,seawater pipelines,and other key components.However,TC4 alloy is susceptible to oxidation and has poor wear resistance,low hardness,and other defects,which limit its further development in these application areas.With the continuous development of China's science and technology,the wear-and-tear failure of part surfaces is becoming increasingly prominent.Therefore,it is urgent to use surface engineering technology to repair failed parts or strengthen the surfaces of critical parts used under harsh service conditions.In the field of surface engineering,the moderate addition of the rare earth La2O3 can increase the hardness and wear resistance of a coating.The addition of too small or an excessive amount of the rare earth La2O3 can prevent the composite coating performance from reaching the optimal level.In order to investigate the effects of different mass percent contents of this rare earth(La2O3)on the compositions and performances of composite coatings,La2O3/Ti-BN-G composite coatings were prepared on the surface of TC4 specimens using argon arc cladding technology.Ti powder,BN powder,graphene powder,and La2O3 were used as the raw materials.Measured quantities of these powders were placed in an onyx research body and fully milled to obtain a homogeneous mixture.It was then pre-coated on the surface of the TC4 alloy,and Ti-BN-G coatings with different La2O3 contents were prepared using argon arc melting and cladding technology.An X-ray diffractometer,scanning electron microscope,and energy spectrum analyzer were used to analyze the physical phases and microstructures of the coatings,and the microhardness of each coating was tested using a micro-Vickers hardness tester.A friction wear tester was used to test the wear rate and friction factor of each coating to analyze its wear resistance.The results showed that the coating phase consisted of granular and dendritic Ti(C,N),needle and rod TiB,and α-Ti phases.The organization changed with an increase in the La2O3 content.When the mass percentage content of La2O3 was 4 wt％,the composite coating had the best tissue refinement effect and most uniform distribution.A surface scan analysis showed that the rare earth La elements were uniformly distributed in the composite coating,which inhibited the growth of the tissues.Thus,the properties were further optimized,and the microhardness of the composite coating was increased by 3.7 times compared with that of the substrate,and the wear resistance was improved by 9.6 times.The wear mechanism was abrasive grain wear.When the mass percentage of La2O3 was 5 wt％,the composite coating was coarse and unevenly distributed,and the hardness and wear resistance were reduced.Finally,it was concluded that the most significant organizational densification and refinement effect was obtained for the composite coating when the mass percentage content of La2O3 was 4 wt％.This coating exhibited high hardness and excellent wear resistance,with further improvements in the mechanical properties of the TC4 alloy.By optimizing the mass percentage of this rare earth(La2O3)to obtain a high-performance coating,the research results provided an experimental basis and theoretical foundation for solving the problem of wear loss on the surfaces of parts.
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