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Nano Hydroxyapatite/SiC Whisker Composite Bioceramics Material And Its Machining

Posted on:2006-09-29Degree:DoctorType:Dissertation
Country:ChinaCandidate:Z W NiuFull Text:PDF
GTID:1101360152981237Subject:Mechanical Manufacturing and Automation
Abstract/Summary:PDF Full Text Request
Hydroxyapatite(HAP) has become one of the most important artificial bone transplant materials because of its excellent biocompatibility and osteophony. The mechanical properties of synthesized hydroxyapatite are poor, especially its fracture toughness is very low. So that it has been strictly limited to being used in non-dynamic load circumstance. SiC whisker can be adopted to toughen HAP bio-ceramics effectively and enlarge its application range.Thermodynamics analysis on synthesizing nano HAP using sol-gel method was carried out. HAP/SiCw composite micro-powder was synthesized using in-situ composite method, and HAP/SiCw composite bio-ceramics was sintered using hot pressing method. The toughening mechanism of SiCw whisker was theoretically studied and analyzed by FEM, fractal analysis on HAP/SiCw was carried out. The ultrasonic machining of HAP/SiCw composite bio-ceramics was studied.The thermodynamics analysis of the systems of Ca-P2O5-H2O and Ca(OH)2-H3PO4-H2O in the water solution when synthesize hydroxyapatite using Sol-gel method was made the appropriate condition to synthesizing hydroxyapatite was got: using dimethylformamide as dispersant and acting under the temperature of 145-150℃ can get high purity nano HAP and avoid using expensive autoclave. Nano HAP was characterized. Theoretical analysis on hot pressing sintering process was carried out and the expression of hot press densification velocity was got. HAP/SiCw composite micro-powder was synthesized using in-situ composite method. HAP/SiCw composite bio-ceramics was sintered using hot pressing method. The proper sintering technical parameters are: the sintering temperature 1300~ 1310 ℃, the pressure 30-40MPa, the time of heat preservation 30min, and the protection gas nitrogen.The micro-structure and mechanical properties of HAP-SiCw composite bio-ceramics were investigated. The influence on micro-structure and mechanical properties of whisker content was studied. Theoretical calculation results indicate thatthe maximal critical content of SiCw in hydroxyapatite-SiCw composite bio-ceramics is 23.7%. The experimental results show that the mechanical properties are the best when the volume content of SiCw is 23.7%, the bending strength is 190MPa and the fracture toughness is 2.31MPa.m1/2. If the SiCw distributes in the plane parallel with the hot press plane, the mechanical properties are the best in the plane normal to the hot press plane, the mechanical properties are the worst in the plane which is parallel with the hot press plane.The stress expression of the whisker tip was got on the basis of modifying the shear lag theory. The expression to forecast the corporate toughening effect of whisker bridging, whisker evulsion and crackle deflexion was derived. The micro unit of HAP toughening by whisker was analyzed by FEM, and the results show that the stress transfer between the whisker tip and the matrix is the main manner to transfer stress. Therefore, the bonding strength between the whisker tip and the matrix is the key factor that determines the mechanical properties of the composite material.The fracture SEM images of HAP/SiCw composite bio-ceramics were analyzed using fractal theory. The results show that HAP/SiCw composite bio-ceramics has fractal character, the fractal dimension of the material fracture rises with the increase of the whisker content and reaches the maximum when the whisker content is 23.7%, however, the fractal dimension of the material fracture falls when the content is higher than this critical value. The fractal dimension of the material fracture rises with the increase of whisker direction angle. The density of the material decreases with the increase of the fracture fractal dimension, whereas the bending strength and fracture toughness of the material increase with the increase of the fracture fractal dimension.Theoretical analysis and experimental study were carried out upon the ultrasonic machining of HAP/SiCw composite bio-ceramics material. Research results show that the material removal rate and the surface roughnes...
Keywords/Search Tags:Composite material, HAP/SiC_w bio-ceramics, Toughening, Fractal, Ultrasonic machining
PDF Full Text Request
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