| HA is a new type of biological material which is very similar with the main inorganic constituents of human bone, however, due to its own poor mechanical properties, low strength, brittleness, these cause it can not be used directly in human as biological materials. Currently, the majority of domestic and foreign researches have been tended to the preparation of hydroxyapatite composite in order to toughen themselves, moreover, the toughening phase should also meet the biological material requirement which doesn’t affect the biological properties of HA bioceramic. NiTi shape memory alloy (atomic ratio1:1) as the most common application of a class of alloys meet all the requirements of the biological materials, the performance of its unique thermal martensitic transformation creates memory effect and super-elastic at the macro renderingshape. This study is use of such thermoelastic martensitic transformation in NiTi alloys to toughen HA ceramics, This toughening mechanism is essentially different from the normal ZrO2phase transformation toughening, the martensitic transformation of NiTi alloys can be generated by the stress-induced at room temperature, which doesn’t require the matrix phase binding to aid in the conduct of this phase transition. In addition, NiTi shape memory alloy particles also have a general dispersion toughening mechanisms, we can take advantage of its own plastic deformation in toughening material further. NiTi alloy particles toughening HA bioceramics, is completely a brand new attempt which has great prospects, this study implementing a combination of the most common biomedical inorganic materials (HA) and alloy (NiTi) is expected to produce a classmore ideal biomedical composites.In this paper,HA powders are prepared by chemical precipitation, Ca (NO3)2and (NH4)2HPO4as the main raw material, these powders that can be obtained by parameter adjustment as well as burn-in processing are nano-level crystallinity powders,whose morphology is the short rod, diameter within the range of80～100 nm, short diameter in the range of20～30nm, and the particle size distribution is more uniform. Powder prepared by HA and NiTi particles, according to the quality of NiTi than3%,5%,7%and10%for uniform mixing, then put the composite powders into hot pressing sintering furnace,in condition of argon protective atmosphere with pressure at30MPa, the sintering temperature of1000℃,1100℃and1200℃carriying out for1h, all of these result in the NiTi/HA composite materials; According to flexural strength and fracture toughness tests, the density of composite sample in different proportions at different sintering temperatures is basically unchange with the addition of NiTi phase in the composite, composite bending strength will be part of the loss with the increase of NiTi phase, However, the fracture toughness will show this phenomenon that first increases and then declines with the increase of NiTi phase. By comparing the test will select1100℃as the optimum sintering temperature of theNiTi/HAcomposite, the best ratio of at this sintering temperature is that the mass fraction of NiTi is5%, corresponding to this point the fracture toughness will reach to1.375MPa·m1/2, about30%increase than the pure HA in the same temperature. In the transmission electron microscopy and metallographic microscope observation of NiTi/HA composite, the presence of NiTi alloy martensite can be observed, which proves to achieve the desired effect of martensitic transformation toughening;Moreover, on the surface morphology of composite materials, it can be seen that NiTi alloy is indeed played the inhibition of crack propagation and toughening effect of crack deflection occurs in the fracture process. |
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