Fabrication And Properties Of Biomedical Porous TiNi(Nb) Alloy

Near-equiatomic TiNi shape memory alloys are promising materials for hard tissue replacement in the biomedical field, due to their superelastic biomechanical properties, similar with some human hard tissues such as bones and tendons, and their shape memory effect, excellent biocompatibility and corrosion resistance. However, the high stiffness of dense TiNi alloy often leads to large stress-shielding from the surrounding bone tissues. This does not favor the formation of new tissues consequently giving rise to poor fixation between the implant and tissues and even the final failure.As mentioned above, this study is designed to investigate the biomimetic porous TiNi alloy with the optimization of structure properties and mechanical properties. In order to further explore the potential of porous TiNi shape memory alloy, the nearly full density, general porosity and high porosity of TiNi alloys were prepared by vacuum hot pressing method, vacuum sintering method and template impregnating with sintering method, respectively. The composition, microstructure and mechanical properties of TiNi alloys were evaluated and the factors influencing these properties were investigated, respectively.The TiNi alloy was prepared by vacuum hot pressing sintering, and the properties of the alloy were closely related to raw material powder. The relative density of the alloy fabricated by pre-alloyed powder is higher than that of alloy fabricated by mixed powder. The tensile strength and elastic modulus of the pre-alloyed powder TiNi alloy are677.34MPa and5.348Gpa, respectively. The TiNi alloy with medium porosity was prepared by vacuum sintering, which property can be adjusted by changing the sintering temperature. With the temperature increasing, the composition of TiNi alloys are more and more homogeneous, and the relative density increases from56.36%to62.99%, and the tensile strength raises from72.43MPa to160.72MPa. The high porosity of TiNi alloy which is similar to human cancellous bone is prepared by template impregnating, and completely preserves pre-alloy powder pure phase.The Mechanical properties of TiNi alloy is closely related to its porosity under the same preparation condition. Therefore, the mechanical strength and elastic modulus of TiNi alloy exhibit trends consistent with the relative density. The different properties of TiNi alloy can be adjusted by changing preparation methods and technological factors. The porosity is adjusted to obtain the appropriate porosity and mechanical properties of porous TiNi alloy. Mechanical properties of TiNi alloy is adjusted in a wide range to meet the different implant requirements. Especially, high porosity TiNi alloy was prepared by impregnation, which is not only easy to get similar pore property to human bone tissue, but also easy to get similar mechanical properties to bone tissue that can avoid stress shielding by selecting template and adjusting the solid content.The porous TiNiNb alloy, in which Nb element was the substitution for Ni, was prepared by vacuum sintering. With the addition of Nb, the property of TiNiNb alloy is quite different from TiNi binary alloy. When Nb content increase from0to10at.%, the alloy matrix phase is TiNi parent phase, and Nb particles dispersed in the matrix phase. Nb is a solid solution element in Ti matrix, and can modestly increase the sintering activity of TiNiNb alloy. With the Nb content increasing, the alloy becomes contract obviously and the relative density continued to increased. Meanwhile, tensile strength and elastic modulus of alloy effectively improved with the increase of Nb content. Furthermore, Nb can moderately improved biological property of TiNi alloy.The results of biology research show that TiNi alloy has excellent biological safety and compatibility. The porous TiNi alloy, especially three-dimensional connective porous TiNi alloy prepared by impregnation has higher potential than the dense TiNi alloy as bone tissue engineering scaffolds. Pore structure of material would enhance its surface energy, which is conducive to interaction between implant and organism. Porous TiNi alloy not only shows the good ability to apatite deposits, but also ensure adequate space for the delivery of nutrients and metabolic waste due to its rich connectivity and excellent three- dimensional pore structure. Porous structure can promote the biological tissue ingrowth through the pore channels inside the TiNi alloy, which would enhance the biomechanical strength between tissue and implants, and improve the stability and healing process of TiNi alloy implants.