Research On Ultrasonic Vibration-assisted Laser Cladding Process And Properties Of Bioinert Ceramic Coatings

The bioinert ceramic coating prepared by traditional laser cladding technique has some problems,such as internal defects,uneven microstructure and so on,which cannot meet the requirements of artificial joint surface.In this paper,the bioinert ceramic coatings were prepared by ultrasonic vibration-assisted laser cladding process by using the cavitation effect of ultrasonic for further improving the quality and performance of the coating.The main works and innovations of this paper are as follows:(1)An ultrasonic vibration-assisted laser cladding system was designed and built,and the effects of ultrasonic vibration on the microstructure and mechanical properties of Ti C/Ti B ceramic coatings prepared by laser cladding in-situ synthesis were investigated.The ultrasonic vibration improved the macroscopic morphological quality of the coating and reduced the pores number in coating.The appropriate ultrasonic vibration power increased the relative content of ceramic phase in the coating.With the increase of ultrasonic vibration power,Ti B transformed from dendrites to granular crystals,while Ti C remained existing in the form of granular crystals.In the simulated body fluid(SBF)environment,the wear resistance of the coatings prepared with ultrasonic vibration assisted at power of 400 W increased by about 120%and the friction coefficient decreased by 50%compared with the coatings prepared without ultrasonic vibration assisted.(2)The effects of ultrasonic vibration on the microstructure and mechanical properties of Ti C ceramic coatings prepared directly by laser cladding were investigated.Based on the orthogonal experimental method,the laser power P and scanning speed V were taken as the influencing factors,and the porosity area A_S and the height difference HD of the coating were taken as the evaluation indexes,and a set of optimal process parameters were obtained:laser power P=400 W,scanning speed V=5mm/s.The Ti C ceramic coatings prepared under the optimum process parameters had good forming quality.With the increase of ultrasonic vibration power,the root of Ti C dendrites were fused,the grains were refined,and the micro-hardness and wear resistance of the coating were improved.(3)The effects of ultrasonic parameters on cavitation bubble morphology,microjet velocity,and collapse time were investigated,and the grain refinement mechanism of coatings prepared by ultrasonic vibration-assisted laser cladding was identified.A two-phase flow calculation model of laser cladding molten pool was constructed by COMSOL,and the evolution law of cavitation bubble under the ultrasonic action was analyzed.The results showed that within the experimentally preferred parameter range,using relatively low frequency and high power ultrasonic assisted laser cladding process,it was possible to obtain relatively larger microjet velocity and shorter collapse time,which could intensify the cavitation effect in the molten pool and promote the refinement of coating grains.