Microstructure And Tribological Properties Of Plasma Sprayed Al₂O₃wt%TiO₂ Coatings After Laser Post-treatment Processing

Ti-7.5Nb-4Mo-2Sn is potential to be used as biomaterials due to its good corrosion resistance, low elastic modulus, excellent biocompatibility and mechanical properties. However, it has some shortcomings such as low hardness and poor wear resistance, which limit its application in practice.Laser cladding and Plasma spraying are two advance surface modification technologies, and each has its advantages and disadvantages. The combination of these two technologies is expected to eliminate the defects of the coat prepared by thermal to promote the bonding force between coat and substrate. Moreover, more materials with high hardness and high melt point can be used as coating materials by using the combination techonology.Therefore, in this thesis, the Al2O3-13wt%TiO2was first sprayed on the surface of the substrate by the Plasma spraying technology,and then the coating was remelted by laser claddingmethod. The microstructure of the coating was observed and characterized by XRD, SEM and EDS. Meanwhile, the hardness and wear behavior in the simulating human body liquid(PBS) of the coat were studied using micro hardness tester and high speed reciprocating friction and wear testing machine. The main conclusions are as follows:(1) The Al2O3-13wt%TiO2 ceramic coat was sprayed on the surface of Ti-7.5Nb-4Mo-2Sn by Plasma spraying method,and the microstructure of the coat was characterized. It is found that the coat exhibits layered structure, which is unsound with many pores in different sizes existing in it.(2) The ceramic coating obtained by Plasma spraying method was remelted by laser cladding technology, and the microstructure of the coating was observed. The effects of the laser parameters on the evolution of the microstructure were investigated. The result shows that, by laser remelting, a sound coat, mec metallurgically bonded with the substrate can be obtained. Moreover, it is found that increasing laser scanning rate can refine the microstructure of the coat, and with the increase of the laser scanning rate, the content of Al2O3 in the coat increase, and the dilution ratio due to the substrate melting decreases, which are favor to the increase of the hardness of the coat.(3) The hardness and wear resistance of the laser remelted ceramic coat were evaluated, and the impacts of the microstructure on the wear performance of the coat were investigated. The results show that the microhardness of the laser remelted coatdecreased gradually from the outside to the inside, which shows obvious gradient change. The highest hardness is up to 1157HV0.2, which is 4-5 times of the alloy substrate(225HV0.2). The friction coefficient exhibits a decreasing trend with the increase of the scanning rate. The lowest friction coefficient(0.189) of the coat after laser remelting is 26% of that of the substrate(0.717) and 42% that of the plasma spraying coat(0.448). Consequently, the laser remelted coat significantly improves the friction properties of the alloy surface. The wear of the laser remelted coat is mainly in the spalling wear, combining with abrasive wear and adhesive wear Modes.