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Gradient Bioceramic Composite Coating Fabricated By Wide-Band Laser Cladding And Its Biocompatibility

Posted on:2006-03-28Degree:DoctorType:Dissertation
Country:ChinaCandidate:Q B LiuFull Text:PDF
GTID:1101360152985488Subject:Materials Science and Engineering
Abstract/Summary:PDF Full Text Request
To eliminate thermal stress during laser cladding and to raise bonding strength between substrate and coating, composition gradient coatings are designed and fabricated by using wide-band laser cladding technique on a Ti alloy.Guided by thermodynamic and kinetic calculations, the effects of technical parameters of wide-band laser cladding on morphology and sinterability of the bioceramic composite coatings are revealed and the optimized working parameters are obtained, i.e. laser output power P=2.5kw, scanning velocity V=150mm/min, laser beam size D=16mm×2mm. A numerical simulation of the transient temperature field shows that the highest temperature in the melting pool (1919℃) is lower than the upper limit (1927℃) for the formation of HA bioceramic, which validates the feasibility of using the present technique to obtain bioceramic composite coatings.The Rare Earth oxide addition on the formation of HA and 3 -TCP in the bioceramic composite coatings is investigated. When the Y2O3 content falls in the range of 0.4 0.6wt.%, the HA and β -TCP phase contents are the highest. However, above 0.8wt.% Y2O3, the HA and β -TCP phase contents in coatings decrease. The mechanism of such a rare earth catalyzing effect is discussed.The gradient bioceramic composite coatings consist of an alloyed transition layer and the bioceramic coating. The alloyed transition layer is comprised of Ti(Al,P,Fe,V) as the matrix phase, a white eutectic structure Fe2Ti4O+AlV3 and white particles Al3V0.333Ti0.666- In the bioceramic coatings, the matrix phase is mainly comprised of HA ,CaTiO3 and CaO, embedded with α -TCP, β -TCP and TiO particlesThe bonding strength between the coating and the substrate is fairly high, above 38.8MPa. The highest microhardness is obtained for the coating containing 0.6wt.%Y2O3 1062HV0.1 and 1405HV0.1, respectively at the bioceramic coating and the alloyed transition layer. The average tensile strength, bending strength, and elastic modules of the bioceramic coatings are 767.83MPa, 1671.65MPa, and 13.98GPa, respectively. It is particularly noted that the elastic modules is quite closer to that of human bone. The fracture toughness ranges from 3.89 to ,6.46 MPa · m1/2. The wear resistance of the gradient bioceramic coating is excellent.Acute toxicity experiment of mice indicates that after muscle injection of the largest medicine amount, the mice do not show obvious acute toxicity reaction. The implanting into rabbits femur for 1, 2 and 3 months does not exhibit hypersusceptibility , rejection and pathological changes. The amount of leucocyte andneutral cell is normal and the value of Ca2+ and P(PO3',HPO42",H2PO4') nearly keeps equivalent to that of normal animals. In addition, carbamide and CO2 combination rate is in approximately normal level, which demonstrates that the bioceramic coating has a good biocompatibility.After the implantation of the bioceramic coatings into dogs' femur for 6, 12, and 24 weeks, hypersusceptibility , rejection and pathological changes are not found. No fiber cyst, necrosis of bone tissue and chronic inflammation obviously appear through slice observation of hard tissues. The bioceramic coating with different ratios of Ca : P have different abilities to induce osteogenesis. At Ca:P=1.4 and 0.6wt.% Y2O3, the bioceramic coating totally combines with new bones after implanted for 6 weeks, while other coatings are not totally linked with new bones, which indicates that this sample is of best bioactivity and biocompatibility.
Keywords/Search Tags:Wide-band laser cladding, Gradient, Bioceramic composite coating, Bioactivity, Biocompatibility
PDF Full Text Request
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