Studies On The HA/316L Stainless Steel Biological Functionally Gradient Materials

Hydroxyapatite(HA) has excellent biocompatibility and bad mechanical properties, which restricts its usage for bearing bone reconstruction. 316L stainless steel(316L) has broad applications in clinic, but it always lead to ill reaction such as inflammation because of its unqualified biocompatibility. Preparation of the composites having both advantages has become the heat point in biomaterials field. Surrounding this important task, HA/316L biocomposites were fabricated with powder metallurgy in this paper. Aim at the question of heat stress mismatch between HA and 316L phase, heat stress relaxed HA/316L biological functionally gradient materials(FGM) were prepared. At the same time, systemic researches including mechanical properties, phase structure, microstructure and biocompatibility evaluation of the FGM were carried out.HA and ZrO₂ ( CaO ) nano powder were prepared firstly. The results show that crystal degree of hydroxyapatite enhance with the increase of calcinated temperature and the optimal preparing technique is maintaining 2h at 750℃ with temperature-rising speed of 5℃·min^-1. Activated energy of HA can be calculated as 24.8 kJ·mol^-1 according to the relationship between grain size and calcinated temperature. HA's growing mechanism is interficial diffusion controlling mechanism. ZrO₂ ( CaO ) nano powder is prepared by azeotropic distillation and chemical coprecipitation method with heat treatment between 600 ℃ and 1 100 ℃ . Transformation temperature of tetragonal phase to monoclinic phase is 1 234.5 ℃ in ZrO₂ ( CaO ) nano powder, which is higher than that of pure ZrO₂ because of the existence of stabilizer CaO.HA/316L power, HA/316L fibre and HA-ZrO₂ (CaO) /316L fibre biocomposite series were fabricated by vacuum sintering. The results show that comprehensive mechanical properties can be ranked as HA/316L power system2 (CaO) /316Lsystem. Microstructure of all biocomposite systems change regularly with the components of HA and interface of HA/316L powder(or HA/316L fibre) combines tightly. Some element interdiffusion takes place between both phases in HA/316L power system and Ca, P element' s diffusibility in HA is laeger than that of Fe element in 316L powder. While there only exists diffusion of Fe element in 316L fibre to the matrix in HA/316L fibre and HA-ZrO2 (CaO) /316L systems.The approaches also address that diameter and length of 316L fibre have influence to the mechanical properties of HA-ZrO2 (CaO) /316L biocomposites. Composite's mechanical properties with fibre diameter of 40 u m is better than that of 50 U m and fibre length of 0.8-1.2mm is better that of 2³mm. Micropores increase with volume fraction of 316L fibre because of contact among fibres, which become microflaws and lead to descending of mechanical properties. Thereof, it can be concluded that HA-ZrO2 (CaO) /316L fibre biocomposite having 20vol% with fibre diameter of 40 u m and fibre length of 0.8¹.2mm has optimal mechanical properties with bending strength, Young's modulus and fracture toughness equal tol40.1MPa, 117.8GPa and 5.81 MPa-m m, 87.1%, respectively.HA-ZrO2 (CaO) /316L fibre symmetrical and asymmetrical biological FGMs were fabricated under 1100°C by use of hot isostatic pressing(HIP) technique. The results show that there is no distortion in the FGMs and no microcracks on their surface. 316L fibre is evenly distributed in the FGMs. 316L fibre is enwrapped in the HA-ZrO2 ( CaO ) matrix and both integrate each other tightly. The combining mechanism of matrix to 316L fibre is physical adhering force. With increase of HA contents, both fracture toughness and Young's modulus of the gradient layer in HA-ZrO2 (CaO) /316L fibre FGMs decrease gradually, which results in mechanical properties relaxation design of the FGMs. It can be deduced that fibre pulling out and interbedded crack deflexion are the major toughing mechanism in the FGMs.HA/316L powder symmetrical and asymmetrical FGMs werefabricated by hot pressing(HP) technique. The results show that obvious gradient changes on the macroscopic are shown in the FGMs. While the components changes continuously in microcosmic and the interfaces among all gradient layers unites tightly. The addition of 316L powder changes the fracture way of the composites and improves their mechanical properties. There exists several toughing mechanism including interbedded crack deflexion, crack deflexion and crack bridging in the FGMs.HA contents in HA/316L biological FGMs change regularly with different gradient layer, which is coincided with the componets design. Grain size of 316L grows gradually with the decrease of HA contents, which suggests HA has restraining erTect on the growth of 316L grain size. Major sub-structure of 316L component are dislocation and stacking. Conbining circumstance of phase interface is very well and both phase bite into each other at the interface. There approximately exists 20 nm transition area at the interface. The two phases of HA and 316L powder dissolve into each other in some degree during hot pressing and the combining mechanism is dissolving behavior.Acute toxicity experiment, sub-acute toxicity experiment, heat resource experiment, bacteria-restraining experiment, blood-dissolving experiment, skin-implanting experiment, Ames experiment and cell toxicity experiment were carried out to HA/316L powder FGMs. The results show that HA/316L powder FGMs have excellent biocompatibility and possess broad clinical value in bearing bone reconstruction.