| Total joint replacements have relatively high success rates at10～15years. However,as the population gets older and more active, higher demands are placed on the implants.Several types of bearing couples are used in hip replacements, such as metal-on-polymer,metal-on-metal, ceramic-on-ceramic, and ceramic-on-metal. The release of metal ions isalso a reason for concern due to toxicity. However, wear particles from UHMWPE mayinduce an inflammatory reaction, which may lead to bone resorption and loosening of theimplant. Furthermore, a risk of catastrophic failure arises when bulk ceramics are used,due to their brittleness. In order to avoid this, the ceramic can be used as a coating on amore ductile (metal) substrate. Advantages with coatings can include reduced wear ratesand an increased corrosion resistance. This study aims at developing a preferableprosthesis material, which has wonderful comprehensive performance of toughness, wearresistance and biological activity, prepared by laser cladding Si3N4/TCP compositebioceramic coatings on TC4substrate.The properties of bioceramic coatings prepared by different laser parameters ofcircular light spot and rectangular spot were investigated. The surface and cross-sectionmorphologies, structures, elements distribution, mechanical properties and biologicalbehavior of the Si3N4/TCP composite bioceramic coatings were tested through ScanningElectron Microscope (SEM), Energy Dispersive Spectrometer (EDS), Vickers hardnesstester, Simulated Body Fluid (SBF) and other analytical equipments. The results showedas follows:1) When laser cladding of500W pulse Nd:YAG laser with circular light spot andGL-HL-7000CO2laser with rectangular spot was under suitable parameters, the Si3N4orSi3N4/TCP composite coatings would form compact bonding interface between thecoating and the substrate. The coating layer was very dense and the cross section kept inproper condition. When TCP content was high in the composite coatings, the crack wasmore likely to form through circular light spot Laser cladding. The cracks were less likelyto emerge through rectangular spot laser cladding.2) Cracks were not likely to form even when the TCP content in the coating is20%by laser cladding composite ceramic coatings with continuous CO2rectangular spot laser.3) The SEM photograph of the cross-section of composite ceramic coatingsfabricated by circular light spot Laser cladding is typical laser cladding microstructure. Metallurgy bond appeared between the matrix and composite ceramic coatings. Atransition region formed between the substrate and the ceramic coating components.Namely, a component gradient interface had formed. This type of coating design canreduce the interface problems and improve the lifetime of the implant materials. Columnarfusion organizations of titanium alloy and composite ceramic formed at the coating bottomnear the substrate. A network structure of Si3N4/TCP and titanium alloy formed In thecoating center. With the transition to the coating surface from the base, the microstructuretransformed from columnar crystal to isometric crystal.The ratio of TC4gradually reduced,and Si3N4/TCP increased, the region close to the coating surface was almost occupied byall Si3N4/TCP. Under the high temperature heat source of laser beam, Si3N4grain formedlong rod-shaped grains though self-propagation.4) The difference of the TCP content in the composite ceramic coatings fabricated bycircular light spot Laser cladding would lead a different bonding interface organizationand structure. With the increase of TCP content in the composite ceramic coatings, thedensity of the composite ceramic coating had increased. In the composite coating, thelong-rod Si3N4grain distributed in the axial Si3N4matrix grains. The Si3N4graingradually slimmed with the increase of TCP content. In the region near the coating surface,the parallel long rod Si3N4grain was growing perpendicularly to the coating surface. Therod-shape Si3N4grains distribute randomly in the coating center.5) The surface microhardness of the Si3N4+20%TCP composite ceramic coatingsfabricated by circular light spot Laser cladding was760HV～856HV, The averagemicrohardness of the interface of coating and substrate was749HV. The microhardness ofcoating center was about580HV.6) The biological activity of pure Si3N4ceramic coating dipped in SBF is a little low.The biological activity increased significantly when TCP was added to the compositecoating. The biological activity of the composite ceramic coating improved with theincrease of TCP content. |
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