医用NiTi形状记忆合金表面改性

对NiTi形状记忆合金表面生物活性化处理及生物相容性的发展方向进行了综合评述。讨论了制备TiN保护层、TiO2氧化膜、HA涂层、多孔钛涂层的常用方法,对NiTi合金改性技术的发展方向进行了探讨,并指出在人体模拟溶液中的长期跟踪研究将是NiTi形状记忆合金的研究热点。     

NiTi形状记忆合金的氢致表面损伤

研究了近等原子比NiTi形状记忆合金在阴极充氢后时效过程中表面的相变与破坏,认为时效裂纹的产生与奥氏体不锈钢类似,为氢释放和氢致马氏体分解导致表面收缩产生较大张应力所致,时效过程中裂纹扩展持续时间超过5天。氢致马氏体微观形貌与应力诱发马氏体相似,二者形貌上不可区分。氢化物与基体的界面和氢致马氏体与奥氏体相界面在时效过程中可能成为裂纹源。     

Surface Characterization of Laser Surface Melted NiTi Shape Memory Alloy in Hanks'''' Solution

LASER processing is a relative new surfaceengineering technique for improving the surfaceperformance of metal materials.Both themicrostructure and the distribution of elements in therapidly resolidified surface layer resulted from lasersurface melting(LSM)can be greatly modified.Manycommercially used biomaterials such as Ti-6Al-4V,austenitic stainless steel and titanium were processedby laser,which consequently resulted in improvedcorrosion resistance and biocompatibility.Our previousstudy…     

Temperature Variation in NiTi Shape Memory Alloy During Cyclic Phase Transition

Superelastic NiTi shape memory alloy (SMA) has high recoverable strain and outstanding damping capacity, and has been used as a damping material for many applications. When subjected to displacement-controlled cyclic deformation, the material exhibits distinctive temperature and stress oscillations due to the release of latent heat and hysteresis heat and the heat transfer with the ambient. In this paper, we establish a model to predict the temperature variation of NiTi SMA wire specimen under the cyclic phase transition by lumped heat transfer analysis. Closed-form solution on the evolution of the temperature is obtained. It is shown that, for all the test frequencies, steady-state cyclic thermal response of the specimen can be reached after a certain number of loading cycles in a transient stage, exhibiting a kind of ??thermal shake down.?? In the steady state, the temperature profile oscillates around a mean temperature plateau. We show that the temperature oscillation is mainly due to the release/absorption of latent heat during cyclic phase transition, while the mean temperature rise of the specimen is caused by the accumulation of the hysteretic heat of the phase transition. The model predictions agree well with the experimental results.     

退火工艺对NiTi形状记忆合金恢复力的影响

通过力学性能测试、显微组织观察和预应变后约束下的恢复力测试等手段,研究了退火工艺对Ni50.2Ti49.8合金恢复力的影响.结果表明,预应变为12%时,恢复力达到最大;退火温度升高,恢复力下降.合金的屈服强度是影响恢复力的重要因素,屈服强度越高,在马氏体逆相变过程的相界面迁移能力越强,恢复力就越大.     

激光表面重熔NiTi形状记忆合金组织及腐蚀性能

采用2kWNd：YAG激光器对NiTi合金进行表面重熔处理，利用扫描电镜、X射线衍射、X光电子能谱分析重熔层成分和组织结构，利用电化学测试研究重熔层耐腐蚀性能。结果表明：NiTi合金经过激光重熔处理后，可得到致密的重熔层；根据激光处理参数的不同，在重熔层中会出现TiNi、TiNi3等新相，重熔层表面Ti／Ni及Ti^4 /Ti比显著提高；电化学极化曲线表明激光重熔后NiTi合金的耐蚀性得到了显著改善。     

NiTi形状记忆合金回复力-温度模型改进与实验研究

摘要: 针对NiTi形状记忆合金的马氏体不完全逆转变现象带来的回复力模型预测误差,开展了NiTi形状记忆合金一维回复应力-温度模型研究。在Brinson的形状记忆合金(SMA)一维本构模型基础上,增加马氏体回复因子为内变量,给出了马氏体回复因子与预应变的关系,综合考虑温度和应力对马氏体体积分数的影响,构造NiTi形状记忆合金回复应力-温度改进模型,通过实验测试了不同预应变量的NiTi合金回复应力与温度关系曲线。研究表明：本文提出的改进模型预测的NiTi形状记忆合金回复应力-温度曲线,与实验结果曲线吻合较好,本研究结果对于提高NiTi形状记忆合金回复力预测精度具有重要意义。     

镍钛合金的形状记忆效应稳定化

ＮｉＴｉ合金的形状记忆效应受其化学成分、退火工艺以及加载条件的影响很大 ,因此这些参数也是人们多年来研究的重点。ＮｉＴｉ合金经过反复多次形状记忆循环之后 ,其单向形状记忆效应的稳定性也是其中研究的重点。美国华盛顿大学力学工程系的智能材料和智能系统中心研究了镍钛合金单向形状记忆效应的稳定化 ,研究用的试样是由Ｔｉ 49 9% (质量 )Ｎｉ合金锭制取的 ,由 2 0 3ｍｍ的铸锭锻成 6 3ｍｍ的坯料 ,再热轧成14ｍｍ的棒材 (热轧温度为 90 0℃左右 ) ,合金棒材经过 85 0℃× 2 0ｍｉｎ固溶热处理后水淬 ,该棒材再以 30 %冷加工…     

Effect of Aging Treatment on the Compressibility and Recovery of NiTi Shape Memory Alloys as Static Seals

The improvement of the compressibility and recovery of the gaskets can decrease the leakage occurrence in bolted flange connections. In this study, the effect of aging treatment on the compressibility and recovery of NiTi shape memory alloys is investigated as static seals together with thermal analysis. The experimental results indicate that different phase transformations of NiTi alloys are exhibited in the DSC curves during aging treatment. The recovery coefficient of NiTi alloys aged at 500 °C for 2 h is quite low accompanied with a large residual strain. With increasing aging time at the aging temperature of 400 °C, the residual strain and area of hysteresis loop of NiTi alloys are both increased, whereas the recovery coefficient is decreased. Since the deformation associates the phase transformation behavior, aging treatment could improve the compressibility and recovery of NiTi alloys as static seals.     

NiTi形状记忆合金加热相变过程的DSC研究

采用差示扫描量热法研究了时效处理对NiTi形状记忆合金加热相变过程的影响规律。结果表明：当时效温度低于瓦（特征转折温度）时,相变温度（As和Af）随时效温度的升高而升高;当时效温度高于瓦时,相变温度随时效温度的升高而下降。对于As,当时效15min时,T0=500℃,当时效30rain时,T0=400℃;对于Af,T0均为400℃。在300℃、400℃和500℃时效15min,加热相变过程为M→R和R→P两阶段,在600℃和700℃时效15min时,加热相变过程为M→P一阶段;当时效时间延长至30min时,加热相变过程由M→R和R→P两阶段相变过程变为M→P一阶段。时效温度为500℃和700℃时,体积转变率与温度关系曲线的斜率较大。     

镍钛合金表面锆膜磁控溅射制备与组织结构研究

通过直流平衡磁控溅射法在NiTi形状记忆合金基底上制备纯Zr膜,并采用SEM、XRD、XPS等对Zr膜的组织结构进行研究.结果表明:Zr膜具有晶带T型结构,组织保持细小致密的纤维状特征,没有空洞和锥状形态,表面平整,与基体结合良好;膜和其块体Zr靶材晶体结构一致,出现少量的生物惰性ZrO2陶瓷相.最后,对磁控溅射沉积Zr膜的机制进行了探讨.     

能量输入对SLM成形金属零件致密度的影响

研究了选区激光熔化(SLM)成形单熔道的形态及其形成原因:随着扫描速度的增加,单熔道形态逐渐从连续态过渡到断续态、球化态.在单熔道成形基础上进行正交试验,并讨论了SLM成形高致密度金属零件的能量输入条件及其对成形零件致密度的影响:当能量输入低时,致密度随着能量输入的增加迅速增大;随着能量输入的增加,致密度增加缓慢,进入...     

NiTi形状记忆合金中B2-R相变的计算机模拟

以多孔NiTi合金为研究对象建立了B2-R的相场模型,分析了孔隙率、孔隙尺寸以及孔隙形状对R相生长动力学行为的影响。结果表明,R相尺寸和尺寸分布均匀性都随孔隙率的增加而增大,然而R相的分布特征和尺寸均匀性对孔隙大小以及孔隙形状不敏感。     

医用NiTi合金改性进展

NiTi合金因其独特的形态记忆性、超弹性等特点被广泛应用于临床,但随着合金的植入,镍离子在机体内被溶解释放,该离子可导致机体致敏及毒性反应,而如何减少镍离子溶出的问题已在业内被广泛研究.同时,已经通过多种方法对镍钛合金进行表面改性,并制备出了不同的具有生物相容性的合金材料,本文将对该领域取得的成就进行综述.     

固溶处理对NiTi薄膜中位错密度的影响

用磁控溅射法将NiTi薄膜沉积在纯Cu箔片上，在800℃分别固溶30min，45min，60min和120min：采用X射线傅氏线形分析法计算各固溶时间的位错密度及位错分布参量。随固溶时间的增加，平均位错密度不断下降；亚晶粒尺寸D逐渐增加；平均位错分布参量基本不变。由位错密度及位错分布参量计算得到NiTi薄膜材料的显微硬度值，随固溶时间的增加，显微硬度计算值明显低于测量值。     

Stress-Induced Martensite in Front of Crack Tips in NiTi Shape Memory Alloys: Modeling Versus Experiments

NiTi-based shape memory alloys (SMAs) exhibit an unusual stress distribution at the crack tip as compared to common engineering materials, due to a stress-induced martensitic transformation resulting from highly localized stresses. Understanding the fracture mechanics of NiTi-based SMAs is critical to many of their applications. Here, we develop an analytical model, which predicts the boundaries of the transformation region in the crack tip vicinity of NiTi-based SMAs. The proposed model is based on a recent analytical approach which uses modified linear elastic fracture mechanics concepts to predict the crack tip stress distribution and transformation region in SMAs but, unfortunately, it applies only to the plane stress condition. To overcome this limitation, the proposed model accounts for stress triaxiality, which plays an important role in restricting crack tip plastic deformations in common ductile metals as well as the stress-induced martensite in NiTi SMAs. The effects of triaxial stress at the crack tip are taken into account by including a new parameter, the transformation constraint factor, which is based on the plastic constraint factor of elasto-plastic materials. The predictions of the model are compared with synchrotron x-ray micro-diffraction observations and satisfactory agreement is observed between the two results. Finally, the evolution of crack tip transformation boundaries during fracture tests of miniature compact tension specimens is predicted and the effects of applied load and crack length are discussed.     

NiTi形状记忆合金在蒸馏水介质中的微动磨损特性

NiTi形状记忆合金是一种极具发展前景的医用植入材料.采用SRVⅢ摩擦磨损试验机考察了NiTi形状记忆合金在蒸馏水介质中的微动磨损性能,研究法向载荷对NiTi合金磨损机制的影响规律.利用扫描电子显微镜及能谱仪分析NiTi形状记忆合金表面磨痕形貌及磨损产物成分.用形貌仪测量样品表面磨痕深度,并对磨损体积进行计算.实验结果表明:NiTi合金在蒸馏水介质中的微动磨损摩擦系数、磨损体积均随着载荷的增大而增大.微动磨损失效机制以磨粒磨损以及疲劳剥层断裂为主.     

镍钛合金光催化高级氧化表面改性与生物相容性

在UV/H2O2光催化体系中,通过高级氧化法在NiTi SMA表面生成贫Ni的Ti氧化膜.通过亲水性试验、血小板黏附试验以及MTT细胞毒性试验对改性后试样的生物相容性进行了系统的评价,研究发现改性后试样的亲水性得到明显改善.表面血小板黏附数量减少,变形和团聚现象得到抑制,形成血栓的可能性降低,血液相容性得到提高.改性后试样的细胞相对增殖率(RGR)高于化学抛光的试样,试样周围细胞分裂增生良好,与材料边缘结合自然,改性处理同样提高了试样的细胞相容性.结果表明光催化高级氧化是提高NiTi SMA生物相容性的一种有效方法.     

脉冲高能量密度等离子体陶瓷刀具表面改性研究进展

对刀具涂层技术的发展现状与趋势进行了综述,提出了提高涂层刀具性能的"五化"措施:沉积工艺复合化、薄膜组成多元化、薄膜结构多层化、薄膜组成和显微结构梯度化、薄膜晶粒纳米化.基于这个思想,提出了用高能量密度脉冲等离子体技术进行陶瓷刀具表面改性,并在最近几年用高能量密度脉冲等离子体同轴枪对硬质合金和氮化硅陶瓷刀具进行了镀膜改性尝试.使用该复合表面改性技术,所制备涂层刀具结构独特,很好地满足了"五化"思想,材料性能得到显著提高.在优化的工艺条件下,所得TiN、TiCN和TiAlN涂层刀具硬度高,纳米硬度分别为26～28 Gpa、50～53 Gpa和38～40 Gpa;膜基结合力强,纳米划痕临界载荷达80～110 Mn.所得TiN、TiCN和(Ti,Al)N涂层硬质合金刀具能够在工业条件下对硬度高达HRC 58～62 的淬硬CrWMn钢进行干切削,实用切削速度可提高2～10倍,且刀具磨损较小;涂层氮化硅陶瓷刀具加工淬硬钢和灰铸铁(HB 2200～2300 Mpa)工件时,比未涂层刀具后面磨损降低6～10倍.预示该技术是一种非常有前途的陶瓷刀具改性技术.     

Effect of Cross-linking Density on Creep and Recovery Behavior in Epoxy-Based Shape Memory Polymers (SMEPs) for Structural Applications

Epoxy-based shape memory polymers (SMEPs) are gaining importance in the area of aerospace structures due to their high strength and stiffness which is a primary requirement for an SMEP in structural applications. The understanding of viscoelastic behavior of SMEPs is very essential to assess their shape memory effect. In the present work, three types of SMEPs with varying cross-linking densities were developed by curing an aromatic epoxy resin with aliphatic amines. Glass transition temperature (T _g) was measured for these SMEPs using advanced rheometric expansion system, and from the T _g measurements, a range of temperatures from glassy to rubbery regimes were chosen. At selected temperatures, creep-recovery tests were performed in order to evaluate the viscoelastic behavior of SMEPs and also to investigate the effect of temperature on creep-recovery. Further, a three-parameter viscoelastic model (Zener) was used to fit the data obtained from experiments. Model parameters like moduli of the springs and viscosity of the dashpot were evaluated by curve fitting. Results revealed that Zener model was well suited to describe the viscoelastic behavior of SMEPs as a function of test temperatures.