化学修饰对NiTi形状记忆合金氧化膜的影响

用X光电子能谱（XPS）研究了NiTi形状记忆合金经酸、碱处理后表面氧化膜成分和结构的变化。结果表明，未经处理的NiTi合金表面最外层氧化膜主要由TiO2、TiO和少量的Ni组成，酸、碱处理后，最外层氧化膜由TiO2、Ni2O3组成，但经碱处理后，氧化膜的厚度大大增加。     

Analysis of the mechanical and shape memory behaviour of nitrogen ion-implanted NiTi alloy

Experimental results of an accumulation and return strain behaviour of the modified surface of NiTi alloy, as well as mechanical and shape memory behaviour, are shown in this paper.Surface of equiatomic NiTi shape memory alloy (in martensitic form) has been modified by high-dose ion-implantation technique using nitrogen ion beam. The low-energy (65 keV) and following high doses have been used: 1×10¹⁷, 5×10¹⁷ and 1×10¹⁸ J/cm². Correlation between subsurface layers elemental composition of NiTi alloy, microstructure and shape memory properties is shown.     

Detecting NiTi two-way shape memory effect based on microstructural and macromechanical parameters

ABSTRACT

The two-way shape memory effect in NiTi shape memory alloys is identified according to the evolution of the apparent modulus of the martensite during mechanical cycling. The microstrain and texture index of the NiTi samples are evaluated with synchrotron data to relate the evolution to the changes in the NiTi microstructure caused by mechanical cycling. The results show that a progressive decrease in the apparent modulus of the martensite during load, together with an increase in the apparent modulus of the reoriented martensite, are a sign that the NiTi sample is developing the two-way memory effect by mechanical cycling. When the two moduli show the same value, the two-way shape memory effect is fully developed in the NiTi alloy.

This paper is part of a thematic issue on Titanium.     

材料状态对NiTi形状记忆合金相变行为的影响

用金相显微镜观察了冷加工和固溶状态的显微组织形貌,用示差热量扫描法(DSC)系统研究了冷加工、固溶和时效处理对近等原子比的NiTi形状记忆合金的相变温度的影响。试验结果表明,冷加工态NiTi合金组织形态呈纤维状,固溶处理后组织形态呈等轴状。冷加工带来的大量变形缺陷抑制了热弹性马氏体的相变;冷加工态NiTi合金直接进行时效发生了P→M相变;经固溶处理后再进行时效则发生了P→R→M相变。NiTi合金在不同的热处理条件下发生了不同类型的热弹性马氏体相变。分析认为,应力、位错密度及析出相对NiTi合金热弹性马氏体的相变行为有重要的影响。     

Surface alloying of Mg alloys after surface nanocrystallization

Surface nanocrystallization using a surface mechanical attrition treatment effectively activates the surface of magnesium alloys due to the increase in grain boundary diffusion channels. As a result, the temperature of subsequent surface alloying treatment of pure Mg and AZ91 alloy can be reduced from 430 degrees C to 380 degrees C. Thus, it is possible to combine the surface alloying process with the solution treatment for this type of alloy. After surface alloying, the hardness of the alloyed layer is 3 to 4 times higher than that of the substrate and this may significantly improve the wear resistance of magnesium alloys.     

镍钛合金在医疗器械领域应用和表面改性研究进展

镍钛合金基于特有的超弹性、形状记忆效应,广泛应用于医疗器械领域。其中超弹性表现为大变形下的弹性应变,应用于血管和腔道介入器械、口腔正畸丝、根管器械等;形状记忆效应可实现低温下易变形、体温下自回复,应用于热激活正畸丝、骨科、矫形外科、缝线等。此外,可通过多样化的表面改性技术,提升镍钛合金的生物相容性、腐蚀抗性、摩擦磨损性能,优化产品性能,拓展其在医疗器械制品中的应用范围。     

Physical and tribological characteristics of porous NiTi SMA fabricated by powder metallurgy

This paper presents the mechanical and tribological characteristics of the NiTi shape memory alloy (SMA) fabricated by powder metallurgy. This material has prominent applications in micro-electromechanical systems, medical implants, actuator, space and aerospace industries, etc. In every field, wear characteristics plays a dominating role. In present work dry-abrasion wear behavior is determined for NiTi alloy by varying binder percentage. With increasing binder percentage from 2.5 to 15 %, density decreases from 6.5 to 5.3 g/cm3 while porosity increases from 19 % to 51 %. Increasing rotational speed and binder percentage at a constant load the wear rate increases in the NiTi alloy. Due to the presence of hard particles, NiTi exhibits a very small wear rate. The coefficient of friction is also computed for the alloys in present research work. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction were used for the investigation of surface morphology and phases in the NiTi alloy.     

Effect of Ta2O5/TiO2 thin film on mechanical properties,corrosion and cell behavior of the NiTi alloy implanted with tantalum

The NiTi shape memory alloy has been modified by plasma immersion ion implantation (PIII) with Ta at different incident currents to improve the corrosion resistance and other surface and biological properties. The surface topography, chemical components, mechanical properties, corrosion resistance and cytocompatibility are investigated. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) revealed that Ta implantation led to the formation of compact Ta₂O₅/TiO₂ nano-film on the surface of the NiTi alloy. The results of Auger electron spectroscopy (AES) showed that Ni was suppressed in the superficial surface layer of the modified NiTi alloy samples. The results of nano-indentation illustrated a lower level of nano-hardness and Young's modulus after Ta implantation. Potentiodynamic anodic polarization curves showed that the corrosion resistance of NiTi alloys was enhanced by Ta implantation. Cells reached confluency and a double-layered structure had developed after cultured for three days. The NiTi alloy modified by a moderate incident current possesses a uniform and slippery surface morphology and the largest surface roughness, leading to the best corrosion resistance and the highest cell proliferation rate, respectively.     

Mechanical response of nitrogen ion implanted NiTi shape memory alloy

In the paper a change of material (mechanical) parameters of NiTi shape memory alloy subjected to ion implantation treatment is investigated. The spherical indentation tests in micro- and nano-scale and tension test have been performed to study an evolution of local superelastic effect in different volumes of nonimplanted and nitrogen ion implanted NiTi alloy. The differential scanning calorimetry has been applied to measure the change of characteristic temperatures due to ion implantation treatment. The structure of implanted material has been investigated using electron microscopy technique. It has been found that the ion implantation process changes the properties not only in a thin surface layer but also in bulk material. In the layer the pseudoelastic effect is destroyed, and in the substrate is preserved, however its parameters are changed. The characteristic phase transformation temperatures in substrate are also modified.     

三元Ni-Ti基形状记忆合金的研究现状

针对二元NiTi形状记忆合金在应用中所显示出的局限性,三元NiTi基形状记忆合金通过第三组元的加入,改善了二元NiTi形状记忆合金的某些性能,弥补了其在应用中的不足,降低了成本,进一步扩大了NiTi基形状记忆合金的应用范围,从而一直受到研究者的广泛关注.综述了三元NiTi基形状记忆合金的研究现状,总结了存在的不足:首先,对于合金体系还需要大量的量化研究,确定出不同应用条件下合金的有效成分范围是其实用化的基础;其次,合金制备过程熔炼介质对合金产生的影响等重视不够;同时,应用性能研究还有待加强,性能的长效性与稳定性是关键,这方面的研究还缺乏充分而有效的数据.     

NiTi合金生物医用材料表面改性的研究进展

NiTi合金由于其形状记忆效应、超弹性和低模量等优良性能在生物医学领域得到广泛应用。然而,在生理环境中镍离子释放会诱发毒性和炎性反应,因此需要对其进行表面改性。从表面氧化、表面涂层和表面接枝大分子等方面综述了近年来国内外NiTi合金表面改性的研究进展,评述了各种表面改性技术的优势和缺陷,指明了NiTi合金表面改性的未来发展趋势。     

Surface nanocrystallization of Ni3Al by surface mechanical attrition treatment

The mechanical property and microstructure evolutions of Ni₃Al intermetallic compound subjected to surface mechanical attrition treatment (SMAT) were investigated in relation to surface nanocrystalization. Grain size in topmost surface of SMATed Ni₃Al alloy was refined to a minimum size of about 10 nm, and then increased with the enhancement of the depth from surface to matrix. The original ordered L1₂ phase transformed to Ni (Al) solid solution with a disordered face-centered cubic structure. The maximum nanohardness of the deformed Ni₃Al alloy was near 12 GPa. The microstructure evolution including the variation of defects during the SMAT as well as post-annealing processes showed that the surface nanocrystallization of Ni₃Al intermetallic compound was predominantly controlled by dislocations which divided the coarse grains. The different microstructures at each sublayer illustrated that the nanocrystallization process was decided by the accumulated energy resulted from plastic strain.     

医用NiTi形状记忆合金表面氧化改性研究进展

氧化是NiTi形状记忆合金表面改性的重要手段,常用的氧化工艺包括热氧化、微弧氧化、阳极氧化和化学氧化。虽然四种工艺都依靠合金自身的Ti元素在合金表面原位生成以晶态或非晶态TiO2为主的氧化膜,但四种氧化工艺的原理及所制备的膜层形貌、结构等均不相同。本文评述了四种表面改性工艺的优势和缺陷,并对NiTi合金表面改性的发展方向进行了展望。     

Surface nanocrystallization of Ni3Al by surface mechanical attrition treatment

In this paper, the possibility of surface nanocrystallization of Ni₃Al intermetallic by surface mechanical attrition treatment was explored. The microstructure and hardness of treated sample were characterized through scanning electronic microscope, transmission electronic microscope, X-ray diffraction and nanoindentation examination. The results showed surface nanocrystallization was realized on Ni₃Al intermetallic by surface mechanical attrition method. The nanocrystalline in top surface was about 10 nm and a deformed layer about 10–30 μm formed. Nanoindentation examination showed the nanohardness increased sharply to a maximum and then decreased in a narrow depth till to a stable level with the depth from treated surface. The maximum nanohardness of surface was near 12 GPa.     

Manufacturing and processing of NiTi implants: A review

NiTi is categorized as a shape memory alloy that found interesting applications in vast areas of engineering from aerospace to biomedical; the latter applications are due to its biocompatibility in addition to its unique properties. The unique properties such as shape memory and pseudoelasticity make NiTi an excellent candidate in many functional designs. However, the manufacturing and processing complications of this alloy pose impediments to widespread applications. This paper discusses challenges and opportunities in making NiTi parts for biomedical applications such as implants. To this end, common manufacturing processes for NiTi from casting and powder metallurgy to machining are discussed. Also, new opportunities in additive manufacturing processes such as laser and electron beam techniques towards making 3D components from NiTi are described. Finally, the challenges in heat treatment and shape-setting of NiTi parts in order to attain desired shape memory properties are reviewed.     

Effect of micro-arc oxidation surface modification on the properties of the NiTi shape memory alloy

In this paper, the effects of micro-arc oxidation (MAO) surface modification (alumina coatings) on the phase transformation behavior, shape memory characteristics, in vitro haemocopatibility and cytocompatibility of the biomedical NiTi alloy were investigated respectively by differential scanning calorimetry, bending test, hemolysis ratio test, dynamic blood clotting test, platelet adhesion test and cytotoxicity testing by human osteoblasts (Hobs). The results showed that there were no obvious changes of the phase transformation temperatures and shape memory characteristics of the NiTi alloy after the MAO surface modification and the coating could withstand the thermal shock and volume change caused by martensite-austenite phase transformation. Compared to the uncoated NiTi alloys, the MAO surface modification could effectively improve the haemocopatibility of the coated NiTi alloys by the reduced hemolysis ratio, the prolonged dynamic clotting time and the decreased number of platelet adhesion; and the rough and porous alumina coatings could obviously promote the adherence, spread and proliferation of the Hobs with the significant increase of proliferation number of Hobs adhered on the surface of the coated NiTi alloys (P?<?0.05).     

多孔NiTi形状记忆合金的制备及性能

采用球磨后的NiTi合金粉末为原料,添加尿素作为造孔剂,利用粉末烧结法制备多孔NiTi形状记忆合金.研究烧结温度、保温时间和预成型压力等条件对制备的多孔NiTi合金组织结构和力学性能的影响.结果表明:相对于传统的Ni粉和Ti粉近等原子比混合烧结方法,此方法制备的多孔NiTi合金的相组成更加纯净.且随烧结温度升高,多孔N...     

NiTi合金形状记忆效应的微观机制研究进展

NiTi合金具有优异的形状记忆功能和良好的生物体兼容性,近年来对它的应用研究受到工程界和医学界的重视,同时对NiTi合金形状记忆效应的微观机制的研究也在逐步深入.介绍了NiTi合金的主要特性及影响其形状记忆功能的主要因素,总结了NiTi合金的形状记忆效应和超弹性的微观机制研究现状,并指出了需对该合金进一步研究的一些问题.     

NiTi合金表面化学沉积羟基磷灰石生物活性层机理的研究

用化学方法对NiTi合金表面进行处理,用SEM观察了表面形貌,测定了表面Ca/P层的成分。用热力学方法对可能获得表面结构进行了推算,表明表面结构可能为羟基磷灰石。     

Mechanical properties of additive laser-welded NiTi alloy

Laser welding would be a suitable joining technique for NiTi shape memory alloy if the mechanical properties of laser weld were improved. With this purpose, effects of additive on mechanical properties of laser-welded NiTi alloy have been experimentally studied. Welding specimens used in this study were 2 mm thick hot-rolled plates with a chemical composition of Ni50.9Ti49.1. (Ni50.9Ti49.1)-Ce2 (at.%) alloy foil or Ni47Ti44Nb9 plate was used as filler metal to add Ce or Nb element into NiTi laser weld metal. Both tensile strength and the toughness of additive-welding specimens were improved significantly compared with non-additive-welding specimen. The mechanical property improvement was attributed to the fine solidification NiTi grains and good grain-linking in weld center. The microstructure control mechanisms of these two additive welds were discussed.