Investigation On The Preparation Of TiCN/SiO2Bioceramic Coating Via Laser Cladding Technology And Its In Vitro Bioactivity

TiCN/SiO2bioceramic coating was obtained on Ti-6Al-4V substrate via laser cladding TiCN/SiO2precursors. A pulsed YAG laser with average power of500W was used to carry out laser processing. ABAQUS finite element analysis was utilized to simulate the temperature filed distribution and analyse the characteristics of temperature filed to provide a theoretical reference for laser cladding technology. The phase constituents, surface morphology, microsturcture of the coating were investigated with X-ray diffraction (XRD), Optical Microscopy (OM), Scaning Electron Microscopy (SEM) equipped with Energy Disperse Spectroscopy (EDS), and Laser Scanning Confocal Microscopy (LSCM), respectively. The surface energies of the coatings were calculated through contact angle measurement by statistic drop method to evaluate the wettabiligy of the coating. Simulated Body Fluid immersion experiments were carried out to explore the in vitro bioactivity of the coatings.ABAQUS soft ware was used to simulate the temperature distribution characteristics. The simulation results show that laser processdure presents a rapid-heat and rapid-cooling cracteristic. A huge temperature gradient was observed. This result in a highest temperatute was up to4250℃at the distance about0.2mm under the suface of melt pool. The temperature filed distribution was influenced by laser parameters such as laser scanning speed and defocus distance of laser beam. It also revealed that the depth of the laser melt pool increased with the decreasing of laser scanning speed, both of the temperature in the middle of melt pool and the temperature gradient increased. The depth of melting pool decreased with increasing of defocus distance of laser beam. Compared to the influence of laser scanning speed on the temperature filed distribution, that of the defocus distance of laser beam was not obvious. The results from ABAQUS finite element simulation are coinsident with the results from the following experiments.TiCN/SiO2mixture powder with a certain weight ratio was used the precursor and pre-pasted on the surface of Ti-6A1-4V substrate, followed by laser processing procedure. The influences of laser technologies on the phase constituents and the surface morphology of the coating were investigated by XRD, LSCM, SEM, and EDS methods. The results revealed that the main factors influencing the phase constituents and surface morphology include laser scan speed, defocus distance and the ambient. The appropriate parameters to achieve a sound coating are that laser pulse width is3ms, pulse duration15Hz, laser scan speed in the range of2mm/s to3mm/s, the defocus value of15mm, and the pressure of nitrogen gas of0.2MPa. With the above parameters, a desirable weight ratio of TiCN to SiO2is8:2, and a composite coating with the main phases of TiCN, TiN, and Ti-Si-C was achieved. The results of Laser Scanning Confocal Microscope showed that a sound topography of the coating was achieved. The average surface roughness is about7.93μm。 SEM results revealed that three typical zones, namely cladded zone, transformation zone, and heat affected zone were observed. Between the substrate and the heat affected zone, a metallurgical bonding zone was also observed, indicating a typical metallurgical bonding was obtained after laser processing. The microstructure can be characterized as dentrites with a uniform distribution in the cladded zone. Microhardness measurement for the20wt.%SiO2-TiCN coated sample reavealed that the microhardness in the cladded zone is up to1376HV0.2, which is more than4times of that of Ti-6A1-4V substrate。Wettability and in vitro bioactivity of laser processed TiCN/SiO2coating was investigated. Contact angle between coating surface and different fluids was measured by static drop method to calculate the surface energy of the coating. The results showed that laser processed SiO2substituted samples presented a higher surface energy compared to the bare Ti-6A1-4V.. For20wt.%SiO2-TiCN coated sample, the surface energy is57.32±0.45mJ/m2, indicating that the wettability of the coating was significantly improved after the addition of SiO2. Simulated Body Fluid immersion experiments were carried out. The phase constituent and the surface morphology of the surface after SBF immersion were studied. XRD and EDS results of the samples after immersion in SBF for3days,6days, and9days, Hydroxyapatite coating was detected on the surface of laser processed samples. For20wt.%SiO2-TiCN coated sample, after9days immersion in SBF, a large area CaP layer was observed.