导　　师： 张松

学科专业： H0502

授予学位： 硕士

作　　者： ;

机构地区： 沈阳工业大学

摘　　要： 近等原子比的niti形状记忆合金(nitisma)独特的形状记忆效应、超弹性和良好的生物相容性，使其成为最具开发潜力的生物医用材料之一。本试验采用高功率连续波固体nd-yag激光辐照，在置于n2反应室中的niti形状记忆合金表面制备激光气体氮化层。利用扫描电子显微镜(sem)、能谱仪(edx)、x-射线衍射仪(xrd)、傅立叶转换红外光谱(ftir)、恒电位仪、锁相放大器、摩擦磨损试验机对多种功能激光表面改性层的微观组织、结构、表面形貌、电化学腐蚀及摩擦磨损性能进行了系统研究，并对niti形状记忆合金表面改性层在模拟人体体液中的电化学腐蚀性能、类骨磷灰石形成能力进行了探讨。 选择适当的激光辐照工艺参数，可获得致密的tin增强金属基复合材料(mmc)梯度氮化层，氮化层的表面被厚度为1-2μm的tin陶瓷层封闭，氮化层内部tin增强相呈梯度分布。扫描电镜(sem)及能谱(edax)分析结果表明，mmc氮化层与基体niti合金间存在良好的冶金结合，界面处成分均匀过渡，表面ni含量极低。 niti记忆合金激光气体氮化层的硬度随涂层组织呈梯度变化，表层显微硬度可达1300hv以上。氮化层的磨损机制是tin颗粒被挤压和复合材料基体的犁削，表面改性层的存在明显地改善了niti合金的抗磨损性能。基材较氮化层磨损得严重；相同时间内氮化层的磨损量远少于基材的磨损量；氮化层的磨痕深度比基材浅，niti合金经激光气体氮化后其抗磨损性能提高了3倍。 电化学性能测试说明激光气体氮化可以有效的抑制腐蚀反应的发生。经激光表面改性后，腐蚀电位提高了约100mv，击穿电位提高了约500mv，而腐蚀电流却降低了一个数量级。eis测试表明激光气体氮化使niti合金的界面反应电阻相对于基体材料提高了50倍左右，cpe值仅为基体材料的42％，从而可以有效的抑制对人体有害的ni2+的释放。 生物矿化试验说明激光改性所获得的氮化层具有优异的生物相容性。经过适当的酸碱处理后，样品在模拟人体生理溶液(sbf)中浸泡可诱导类羟基磷灰石(ha)的沉积。表面沉积物ca、p摩尔比为1.47，接近人体骨羟基磷灰石摩尔比1.67。在表面生长物的反射红外光谱中，除了观测到羟基磷灰石相关的磷酸根和羟基的振动，还观测到1437cm-1处co32-特征峰和875cm-1处hpo42-特征峰，表明表面沉积物的结构为含有co32-的类羟基磷灰石。 沉积过程中的交流阻抗谱测试与sem结果一致。阻抗谱中时间常数和沉积层电阻值的变化对应表面类羟基磷灰石的生长。拟合数据可以发现，在人体模拟溶液中浸泡相同时间后，激光气体氮化样品表面沉积物的阻抗值远远高于基体材料表面沉积物的阻抗值。 Amongst the most interesting medical alloys developed in the last few years is the NiTi shape memory alloy /(NiTiSMA/) with nearly equiatomic nickel and titanium distribution because of its shape memory effect, superelasticity and good biocompatibility. Laser gas nitrided /(LGN/) layer was fabricated on the surface of the NiTiSMA after irradiated by a continuous wave Nd-YAG laser in N/_2 environment. SEM, EDX, XRD, FTIR, electrochemical, and wear tests were carried out for material characterization. The bone-like apatite formation on the specimens in body simulated fluid was also studied. The following conclusions are drawn:Laser gas nitrided layer, dense and free of crack, was fabricated on the surface of NiTi shape memory alloy /(NiTiSMA/) after irradiated by a continuous wave Nd-YAG laser in N/_2 environment. The modified layer distributed by graduation. Test results indicated that there was a good metallurgical bonding between the modification layer and the NiTi alloy substrateThe hardness of the outmost surface of the modified layer was as high as 1300Hv. The hardness of the nitrided layer changed across the modified layer. The wear resistance was 4 times as much as that of the substrate.The electrochemical tests in the simulated body fluid /(Hank's solution/) at 37℃ showed that the corrosion and biocompatibility of the material were improved by means of laser gas nitriding. The corrosion potential was increased by 100mV and the breakdown potential by about 500mV while the corrosion current and capacitance decreased. EIS tests indicated that the transference resistance increased by about 50 times and the capacitance was 42/% of the substrate.Biomineralization tests showed that the biocompatibility was effectively improved by laser gas nitriding. The modified layer have the ability to induce the formation of bone-like apatite during immersing in simulated body fluid/(SBF/) at 37℃ and thus are considered bioactive. The formed layer has the Ca//P atomic ratio of 1.47 very close to that of bone-apatite, which has the Ca//P atomic ratio of 1.67. The hydroxyl bond stretch, the vibration bands of phosphate and carbonate are observed in FTIR examination. It is believed that the formed layer is composed of bone-like apatite.The results of the EIS tests coincided with those obtained from SEM very well. Time constant and the impedance of the bone-like apatite reflect the whole process of apatite nucleation and growth on the pretreated specimen surfaces.

关 键 词： 形状记忆合金 激光氮化 极化曲线 生物矿化 模拟体液 生物医学材料 镍钛合金

分 类 号： [TG139.6]

领　　域： [金属学及工艺] [一般工业技术] [金属学及工艺]