自蔓延高温合成NiTi形状记忆合金的热力学计算与分析

对自蔓延高温合成Ni-Ti反应体系的标准吉布斯自由能(ΔGT)进行了计算表明,Ni3Ti、NiTi2和NiTi都有可能存在于反应过程中.根据热力学原理编程计算了NiTi反应时的绝热温度及其与稀释剂w(NiTi)含量和预热温度的关系.     

自蔓延高温合成TiNi多孔体合金

为了开发新型的生体材料，本文对自蔓延高温合成TiNi多孔体合金——人造骨材料进行了研究。以单质钛粉和镍粉作原料，在氩气保护条件下，采用预热点燃模式和热爆模式制得了不同形态的多孔TiNi形状记忆合金。采用SEM和XRD分析了样品的孔洞特征和相组成，测试了其力学性能，并研究了合成条件参数与样品表面形貌和孔隙状态之间的关系。结果表明，用SHS法制备TiNi多孔体合金是可行的。     

原料粉末对NiTi的选区激光熔化成形件性能的影响

分别以Ni+Ti元素混合粉末和NiTi预合金粉末为原料,采用选区激光熔化工艺打印成形.重点研究了在相同打印工艺参数下原料粉末对成形件致密度、物相组成、显微组织、显微硬度的影响,从而反馈说明所用打印粉末对成形件性能的影响.结果 表明:在相同打印工艺参数下,整体上NiTi预合金粉末成形件的致密度较高,而Ni+Ti混合粉末成形件的显微硬度较高.对于同一种粉末,随着能量密度的增大,成形件的致密度先增大后减小,而显微硬度先减小后增大.NiTi预合金粉末成形件有致密的微观结构且相分布均匀,但存在少量孔隙.Ni+Ti混合粉末成形件的微观结构有和构建方向垂直的贯穿式裂纹以及不均匀的基体相,但几乎没有孔隙.     

NiTi合金腐蚀性能研究

研究了稀氯化物溶液(模拟人体生理环境)中NiTi合金的腐蚀行为。NiTi合金的镍离子析出量小于316L不锈钢。NiTi—B合金的耐腐蚀性能优于NiTi—A合金。砂纸抛光 氧化处理的NiTi合金的耐腐蚀性能优于砂纸抛光处理的NiTi合金。NiTi合金的耐腐蚀性能随热处理温度的升高及热处理时间的延长而提高；在500℃／90min时，NiTi合金耐腐蚀性能最佳。NiTi合金的耐腐蚀性能与其表面形成的氧化膜有关。     

NiTi合金的生物医用性能及其在医学领域的应用

介绍NiTi合金作为医用材料的主要性能特点：良好的形状记忆效应最大可恢复应变达9％～10％，独特的超弹性使NiTi合金制成的医疗器件如NiTi丝等具有良好的柔顺性；较低的弹性模量弥补了传统医用金属材料作为骨植入物时容易出现应力遮挡现象从而造成骨质疏松的缺点；除此以外，NiTi合金还具有良好的抗疲劳、耐磨损和耐腐蚀性能；讨论了NITi合金的血液相容性和Ni^2＋离子毒性问题。总结了NiTi合金在医学领域的应用现状以及在新兴医学领域的发展，最后给出了一些NiTi医用性能改良的途径。     

自蔓延高温合成高熔点粉体的研究现状与发展

自蔓延高温合成(SHS)技术是制备高熔点化合物材料的有效方法之一,其具有低能耗、高效率等特点。自蔓延高温合成技术是利用反应体系中自身放热来引发并维持反应的进行。自蔓延高温合成技术在制备粉体材料上应用广泛,并且结合了"化学炉"以及机械诱导等手段提高了合成过程中的效率,目前人们已经通过这种技术制备了硅化物粉体、碳化物粉体、氮化物粉体以及硼化物粉体等,所得产品具有较高的致密度以及较小的颗粒尺寸。目前,二元系高熔点化合物的研究已经基本成熟,而三元系高熔点化合物的研究尚未深入展开。综述了国内外自蔓延高温合成技术在高熔点化合物材料制备上的应用与发展,在总结了二元系自蔓延高温合成技术的基础上进一步总结了三元系高熔点材料的合成,并讨论了现有自蔓延高温合成技术的不足与未来发展趋势。     

Zr离子注入对NiTi形状记忆合金表面硬度和耐磨性影响

研究了Zr离子注入参数（注入剂量和注入电流）对NiTi形状记忆合金表面成分、形貌、硬度和耐磨性的影响.发现Zr离子注入后,Zr离子浓度在NiTi合金表面呈高斯分布,同时降低了合金表面的Ni含量.Zr离子注入后合金表面形貌出现沟槽结构,合金外表层纳米硬度、杨氏模量和显微硬度明显提高.摩擦磨损实验结果表明,Zr离子注入降低了NiTi合金初始摩擦因数,显著延长了维持初始低摩擦因数的时间,同时使磨痕的宽度和深度分别减小了30%~50%和28%~50%.因此,选择适当的注入参数可以使NiTi合金获得最佳的耐摩擦磨损性能.      

烧结气氛及时间对凝胶注模成形多孔NiTi合金性能的影响

多孔NiTi合金由于其优异的形状记忆性能和生物相容性而广泛应用于医用植入材料领域。以雾化Ni粉和机械破碎法制备的TiH_2粉末作为原料,以甲基丙烯酰胺作为单体,通过凝胶注模工艺制备出了性能良好的多孔NiTi合金,研究了不同烧结气氛和保温时间对多孔NiTi合金孔隙率、微观组织及力学性能的影响。结果表明:烧结气氛对烧结体的各项性能均具有较大的影响,同氩气及氢气气氛下烧结相比,真空烧结得到的合金孔隙分布均匀,相组成均一,孔隙率及机械性能较好,是理想的烧结气氛;随着烧结时间的增加,合金孔隙率降低,孔径分布更加均匀,抗压强度和杨氏模量增加,同时物相组成并未出现太大变化,单一的NiTi相很难通过延长保温时间来获得。对于固相体积分数分别为42%和45%的坯体,在真空环境下,烧结时间由1 h增加到4 h,其孔隙率分别由49.58%和48.52%降低到35.01%和33.49%,抗压强度由57.13和98.04 MPa增加到207.34和296.14 MPa,弹性模量由10.12和14.2 GPa增加到17.01和19.96 GPa。     

Ti3AlC2陶瓷材料研究进展

综合阐述了合成Ti3AlC2新型陶瓷材料的研究现状.三元层状陶瓷材料Ti3AlC2具有金属和陶瓷的优点.应用SHS、HP、HIP和SPS等方法可以制得高纯度Ti3AlC2材料,然而自蔓延高温合成有着特殊的优点.本文从自蔓延高温合成方面介绍了新型陶瓷材料Ti3AlC2的研究进展.     

NiTi形状记忆和超弹性合金在应用制品中的推广

随着实用化和加工技术的进步,性能优良的NiTi合金的需要量急剧增长.NiTi合金有两个特殊性能,即形状记忆和超弹性性能.通过改变合金中镍与钛的配比,可使其性能产生较大的变化,以适应不同用途的使用要求.添加第三元素(铜或铌)可以提高NiTi合金的使用性能.目前,Ti—CU和Ni—Ti—Nb等三元合金都已实用化.NiTi合金的形状记忆效应通常为单向的,即在低温马氏体状态下变形,升高温度后合金中产生相变,品体结构由马氏作相变为母相,同时回复到变形前的形态.要得到     

High Strain Rate Compression of Martensitic NiTi Shape Memory Alloy at Different Temperatures

The compressive response of martensitic NiTi shape memory alloy (SMA) rods has been investigated using a modified Kolsky compression bar at various strain rates (400, 800, and 1200 s^?1) and temperatures [room temperature and 373 K (100 °C)], i.e., in the martensitic state and in the austenitic state. SEM, DSC, and XRD were performed on NiTi SMA rod samples after high strain rate compression in order to reveal the influence of strain rate and temperature on the microstructural evolution, phase transformation, and crystal structure. It is found that at room temperature, the critical stress increases slightly as strain rate increases, whereas the strain-hardening rate decreases. However, the critical stress under high strain rate compression at 373 K (100 °C) increase first and then decrease due to competing strain hardening and thermal softening effects. After high rate compression, the microstructure of both martensitic and austenitic NiTi SMAs changes as a function of increasing strain rate, while the phase transformation after deformation is independent of the strain rate at room temperature and 373 K (100 °C). The preferred crystal plane of the martensitic NiTi SMA changes from (\( 1\bar{1}1 \))_M before compression to (111)_M after compression, while the preferred plane remains the same for austenitic NiTi SMA before and after compression. Additionally, dynamic recovery and recrystallization are also observed to occur after deformation of the austenitic NiTi SMA at 373 K (100 °C). The findings presented here extend the basic understanding of the deformation behavior of NiTi SMAs and its relation to microstructure, phase transformation, and crystal structure, especially at high strain rates.     

浅析NiTi形状记忆合金的疲劳机理

由于NiTi形状记忆合金具有可逆的热弹性马氏体相变效应等不同与一般金属的特性，使得其疲劳机理也不同于一般的工程材料。为此，本文侧重分析了温度变化对NiTi形状记忆合金疲劳机理的影响和应力诱发马氏体相变等特征相变过程，以及相关的研究方法与主要结果，将为进一步研究其疲劳过程及增韧工艺提供理论参考依据．     

Effect of solution treatment under load on microstructure and fabrication of porous NiTi shape memory alloy by self-propagating high temperature synthesis

Abstract

Porous NiTi shape memory alloy was fabricated by self-propagating high temperature synthesis. Effects of solution treatment under load applied on the microstructure were investigated. The densities of the phases changed insignificantly with solution treatment but the intermetallic phases such as Ti₂Ni, Ni₄Ti₃ and Ni₃Ti₂ disappeared and the density of B2(NiTi) phase increased with the load applied during solution treatment. Consequently, porous NiTi SMA with ideal pore characteristics, high chemical homogeneity and high strength for hard tissue implants was obtained.     

The effect of aging temperature on transformation parameters of porous NiTi shape memory alloy fabricated by SHS

This study reports some different and efficient approaches for the aging temperatures which cause changes in the transformation parameters of porous NiTi (Ti-50.5 at % Ni) shape memory alloy (SMA) with porosity of 55.3% fabricated by self propagating high temperature synthesis (SHS). Changes which occurred in phase transformations due to the effects of various thermal procedures have been investigated by using X-ray diffraction. The micro structure was investigated using a scattering electron microscope and a light optical microscope. The shape memory behavior and transformation temperatures were studied through the differential scanning calorimetry (DSC). During the compression tests, it was observed that the compressive strength of the specimens was higher than the compact human bone, and that it increased with increasing aging temperature.     

Progress in the understanding of NiTi shape memory alloys

Shape memory alloys (SMAs) are a special class of metallic materials which respond with a considerable change in their properties to small changes in temperature or stress. The SMAs offer two interesting characteristics, viz., shape memory effect (SME) and superelasticity (SE), also called pseudoelasticity which make them attractive for applications in engineering and biomedical fields. Among the various SMAs, NiTi base alloys have been the most commercially exploited ones because of their superior SME and SE, mechanical properties, corrosion resistance and biocompatibility. Since the pioneering discovery of NiTi SMA in early 1960s, significant progress has been made in the processing and understanding of the behaviour of these alloys. In spite of these efforts, the NiTi SMAs continue to offer challenges to the scientists and engineers, and new findings are being made continuously. This paper provides an overview of the developments in NiTi SMAs.     

Transformation behavior of sintered porous NiTi alloys

TiH₂ powder is added as a reactant and pore-forming agent to produce porous NiTi shape-memory alloys (SMAs). The transformation behavior of porous NiTi alloys is investigated because it is relevant to the engineering and medical applications of SMAs. It is found that the transformation behavior of porous NiTi alloys is different from that of cast NiTi alloys. It is demonstrated for the first time, by in situ X-ray diffraction (XRD), that there is no R-phase transformation in porous NiTi alloys, and a broadened, two-peak phenomenon observed with a differential scanning calorimeter (DSC) is not associated with R-phase transformation. The characteristic transformation temperatures of porous NiTi alloys are independent of sintering temperature, sintering time, TiH₂ content, and the heating/cooling rate during thermal cycling between +123 and +423 K. Further, the latent heats of transformation are associated with the TiH₂ content and the sintering conditions.     

NaCl造孔剂添加量对多孔NiTi合金孔结构和力学性能的影响

选用Na Cl作为造孔剂,采用压制+烧结法制备孔结构和弹性模量可控的多孔Ni Ti形状记忆合金,采用SEM,XRD和形状回复率检测等测试手段研究造孔剂添加量对Ni Ti形状记忆合金的孔结构和力学性能的影响。结果表明:随Na Cl添加量增加,多孔体孔隙率从39%上升到72%,孔径大于50μm的孔隙数量明显增加;多孔体主要由Ni Ti奥氏体相(B2)和马氏体相(B19′)组成,并存在少量Ni Ti2,Ni3Ti和Ni4Ti3等相;合金的弹性模量随造孔剂的添加从30%时的10.8 GPa下降到70%时的1.5 GPa;当添加量为50%时,多孔体孔隙分布均匀,大于50μm的孔隙占45%,弹性模量为4.8 GPa,形状回复率达到最高值83%,最适合多孔植入体的要求。     

Modeling the effects of stress state and crystal orientation on the stress-induced transformation of NiTi single crystals

A model that combines the phenomenological theory of martensite with a generalized Schmid’s law has been used to predict the principal stress combinations required to induce the martensitic transformation in unconstrained NiTi shape memory alloy (SMA) single crystals. The transformation surfaces prescribed by the model are anisotropic and asymmetric, reflecting the unidirectional character of shear on individual martensite habit planes. Model predictions of the transformation strain as a function of stress axis orientation for a uniaxial applied stress further demonstrate the anisotropy of the stress-induced transformation in NiTi single crystals. Model results for the uniaxial stress case compare favorably with previously published experimental observations for aged NiTi single crystals.     

Experimental Investigation on the EBM-Based Additively Manufactured Prismatic Nickel–Titanium SMA Components

Russian Journal of Non-Ferrous Metals - Additive manufacturing (AM) of the nickel–titanium (NiTi) shape memory alloys (SMA) have provided novel component solutions with a variety of design...     

Modeling the stress-induced transformation behavior of shape memory alloy single crystals

The phenomenological theory of martensite crystallography has been used to determine habit plane/shear direction combinations for stress-induced transformation of NiTi, Cu-Ni-Al and NiAl shape memory alloys (SMA) to twin-related martensite correspondence variant pairs. By considering the habit plane/shear direction combinations as unidirectional shear systems, generalized Schmid's law is then used to predict the mechanical response of unconstrained single crystals of each SMA. Model results include axial transformation strain, and plane stress transformation surfaces as a function of crystal orientation. Comparison of the predicted mechanical response results with the habit plane/shear direction combinations reveals a link between the anisotropy and asymmetry of the mechanical response of SMA single crystals, and the crystallography of the martensitic transformation.