Fabrication And Characterization Of Laser Cladded Bioceramic Hydroxyapatite Coatings

The typical materials for hard tissue treatment are metallic materials, polymers and ceramics. And bioactive ceramic hydroxypaptite(HA) has received a great deal of attention. But the inherent mechanical properties of ceramic such as low tensile strength and brittleness have restricted it from many load bearing applications. The bioceramic HA coatings on metal substrate fabricated by various surface modified techniques would combined the advantages of metal and bioceramic.A bioceramic composite coating with high HA content metallurgically bonded to substrate, was obtained by double laser cladding pre-placing mixed powders of CaCO3, CaHPO4·2H2O and Ti on the TC4surface, and followed by appropriate heat treating process. Thermodynamic calculation for main reactions happening in the process of fabricating hydroxyapatite(HA) composite coating by laser cladding using the mixture of the calcium carbonate (CaCO3) and calcium hydrogen phosphate dihydrate (CaHPO4·2H2O) and temperature field simulation during cladding process are carried out to choose the processing parameters. The main research results are as follows.1. The thermodynamic calculation of the main reactions during laser synthesizing HA coating using the mixture of CaCO3and CaHPO4·2H2O indicates that The major reaction of synthesizing HA satisfies the thermodynamic condition when the temperature is below1500K, which means that the way of synthesizing HA by laser cladding using CaCO3and CaHPO4·2H2O is feasible.2. The temperature field simulation of transitional coating laser cladding onto TC4substrate is conducted by ANSYS software in consideration of the changes of materials, dynamic boundary conditions, latent heat and dynamic thermal resistance. Moreover, the results of simulation are compared to the experiments in the way of the depth, width and shape of molten pool of the substrate to verify the accuracy of the model. The effects of process parameters and coating thickness on the temperature field are analyzed to choose the process parameters.3. The bioceramic composite coatings are prepare with precursor powders of titanium, CaCO3and CaHPO4·2H2O by double laser cladding with different process parameters. The bonding state between coatings and substrate is fine metallurgical bonding without apparent cracks. The effects of process parameters, Ca/P and heat treatment on the composition, surface morphology and section morphology of coating are analyzed.4. The bioceramic composite coatings with high HA content and good bonding were fabricated onto TC4substrate by laser cladding with the processor powders of titanium, CaCO3and CaHPO4·2H2O, and followed by appropriate heat treating process. It would be benefit for the research of bioceramic HA coating fabricated by laser cladding.