The Initial Study Of Gradient Bioceramic Coatings Preparated Technique, Physical Property And Chemical Property By Laser Rapid Forming

Pure titanium and titanium alloys have been widely used as implant materials in clinical applications. Although they have excellent mechanical properties and good biocompatibility, they do not have bioactivity. So, titanium and titanium alloys can not form bone bonding with living bone directly. To solve the problem, the concept of preparing functionally gradient materials by laser rapid forming is developed to prepare gradient bioceramic compositie coatings on the pure titanium. Technical parameter and feeding powders is optimized by evaluating the effects of technical parameters of laser rapid forming on phase structure of bioceramic composite coatings. Then, the phase, microstructure, bonding strength, physical property, chemical property and mechanical property of the prepared bioceramic composite coatings are analyzed. It is expected that the new method of gradient bioceramic coatings preparated by laser rapid forming technique can be established.Methods1.The method of statistics orthogonal design and factorial experiment was was used on single cladding by laser rapid forming. XRD was used to characterize the phase of coatings. The effects of technical parameters of laser rapid forming on phase of bioceramic composite coatings were evaluated to optimize the technical parameter and feeding powder.2.The microstructure, compositoion and phase structure of the bioceramic composite coatings prepared by laser rapid forming were investigated by means of scanning electron microscope (SEM) , X-ray diffraction(XRD) and Energy Disperse Spectroscopy (EDS).3.Hardness, bonding strength, physical property, chemical property and mechanical property of bioceramic composite coatings prepared by laser rapid forming were analyzed according to national standards.Results1. When the laser power was 800W, the scanning speed was 200mm/min, the powder feeding rate was 3.0g/min, the overlap rate was 35%, and the feeding powder was chip-shaped HA, a compact bioceramic gradient coating can be obtained by the method of direct cladding by laser rapid forming. The SEM photos showed that directional and disordered crystal structure on the surface of the bioceramic composite coatings were acquired. The dense microstructure of coatings is cellular and dendritic crystal which is gradient varying from bioceramic to substrate. The EDS and XRD results indicated that the bioceramic coating was mainly made up of phosphorus and titanium elements, while calcium element have been lose during laser cladding. The laser rapid forming bioceramic coating did not contain the biological elements and phase composition .So new methods should be explored to prepare gradient bioceramic coatings.2.When the laser power was 400W,the scanning speed was 100mm/min, the powder feeding rate was 3.0g/min, and the overlap rate was 35%, the feeding powder was 80wt%CaHPO4·2H2O+20wt% CaCO3, a better gradient bioceramic coating was obtained by the method of in situ synthesis by laser cladding. The SEM photos showed that the cellular structure on surface of bioceramic coatings was acquired. The compact microstructure of coatings is cellular and dendritic crystal which is gradient varying from bioceramic to substrate. The EDS and XRD results indicated that TCP main phase in the gradient bioceramic coating. The maxnium hardness value in the bioceramic coating is 500 HV0.1. and the average hardness value in the bioceramic coating is 431.2HV0.1. The bonding strength between bioceramic and substrate is above 40.17 MPa. This bonding strength is higher than that of bonding strength of Plasma spraying bioceramic coating. The modulus of elasticity is about to 117.617 GPa, which is similar to the elastic modulus of pure titanium. The biological corrosion resistance is superior to pure titanium.ConclusionIn situ systhesisi of gradient bioceramic coatings on Ti substrate by laser rapid forming have been successful prepared using mixed powders of CaHPO4·2H2O and CaCO3.The microstructure, composition, phase structure, hardness, bonding strength, physical property, chemical property and mechanical property of gradient bioceramic coating are excellent. The dense gradient bioceramic coating with high bonding strength can be prepared by laser rapid forming. This may provide a good theory guidance and technical support for the next Biological experiments.