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Experimental observations are performed to investigate the non-proportional multiaxial whole-life transformation ratchetting and fatigue failure of superelastic NiTi SMA micro-tubes in stress-controlled loadings at human-body temperature (310 K). The effects of axial mean stress and stress hold on the whole-life transformation ratchetting and fatigue life are investigated with uniaxial, torsional and five different multiaxial loading paths. The results show that the stress holds on the upper or lower transformation plateaus will both promote forward and reverse transformation, and lead to shorter fatigue life. The multiaxial fatigue lives of NiTi shape memory alloy depend significantly on loading paths and applied stress levels. 相似文献
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In this paper, the effect of test temperature on the transformation ratchetting of super-elastic NiTi shape memory alloy was first investigated in the cyclic tension-unloading tests. It is shown that all the residual strain, dissipation energy, the start stress of martensite transformation and their evolutions during the cyclic loading depend greatly upon the test temperature. Based on the experimental observations, a new one-dimensional constitutive model is constructed by considering two different inelastic deformation mechanisms (i.e., martensite transformation and transformation-induced plasticity). The proposed model employs a new evolution rule of transformation-induced plasticity which considers the physical mechanism of the plastic deformation, i.e., the dislocation slipping in the austenite phase near the austenite–martensite interfaces. Furthermore, the interaction between dislocation and martensite transformation is also taken into account in the proposed model. The capability of the proposed model to predict the uniaxial temperature-dependent transformation ratchetting of NiTi shape memory alloy is verified by comparing the predictions with the experimental data. 相似文献
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NiTi形状记忆合金薄膜的制备及形变特性 总被引:4,自引:0,他引:4
研究了适用于微器件的溅射态NiTi形状记忆合金薄膜.讨论了溅射工艺及织构对薄膜结构和相变特征的影响.利用薄膜热相变特性制成了微驱动器,观察并分析了该器件的形变特性.结果表明:原位加热溅射可以获得具有织构的晶化薄膜;用该薄膜制备的驱动器回复率为0.76%. 相似文献
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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. 相似文献
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表面氧化及离子注氮对NiTi形状记忆合金耐腐蚀性能的影响 总被引:9,自引:0,他引:9
采用电化学测试的方法,研究了表面氧化以及表面氧化-离子注氮两种表面改性方式对NiTi形状记忆合金在人体生理模拟液(Hank′s溶液)中腐蚀行为的影响。腐蚀电位和极化曲线的测量结果表明表面氧化-离子注氮的方法使NiTi合金材料的腐蚀电位正移。雏钝电流密度下降,钝化电位区间扩大,合金表面耐蚀性明显提高。尤其是NiTi合金在进行氮离子注入后,测得击穿电位显著上升.增强了表面膜的抗局部腐蚀能力。因而表面氧化-离子注氮的改性方法可使材料的耐蚀性达到最佳。通过XPS的分析发现,离子注氮后合金表面形成氮化钛相以及富含羟基的化学效应,使NiTi基体的电化学性能得到提高。 相似文献
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《材料科学技术学报》2019,35(10):2238-2242
It is a challenge to develop complex-shaped NiTi shape memory alloy parts by traditional processing methods, due to the poor machinability of NiTi alloy. It is reported that selective laser melting (SLM) of additive manufacturing could overcome this problem. However, the reported SLM-produced NiTi exhibits poor tensile ductility due to the inner defects and adverse unidirectional columnar grains from SLM process. In this work, the defect-less SLM-NiTi with nondirective columnar grains was fabricated by optimizing the intraformational laser scanning length and interformational laser scanning direction. The obtained lath-shaped SLM-NiTi sample exhibits tensile strain of 15.6%, more than twice of the reported maximum result (˜7%). Besides, the SLM-NiTi part with complex geometry displays a shape memory recovery of 99% under compressive deformation of 50%. 相似文献
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In this paper we present a novel method for depositing NiTi thin film by DC sputtering. The film has transformation temperatures very close to that of the target. The new process involves heating the target and does not require compositional modification of the NiTi target. Results from X-ray diffraction, differential scanning calorimeter, four-point probe, Rutherford backscattering, and transmission electron microscopy are presented. These results indicate that compositional modification can be produced by varying the target temperature. Films produced from hot targets have compositions similar to the target while films produced from cold targets were Ti deficient. Films that were produced by gradual heating of the target have compositional gradation through the film thickness. The gradated films exhibit the two-way shape memory effect. 相似文献
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In this paper the corrosion behavior of NiTi thin films fabricated by sputtering from Ni and Ti targets has been studied by cyclic potentiodynamic polarization tests in Hank's and Ringer's solution at 310 K. For comparison, bulk NiTi Shape Memory Alloy (SMA) has also been studied to elucidate the different corrosion behavior of bulk and thin film material. The electrochemical experiments reveal that thin film NiTi SMA has comparable corrosion current density (icorr), much higher pitting corrosion potentials and wider passive range than the bulk NiTi. We show that NiTi SMA vapour deposited thin films are less susceptible to pitting corrosion than the bulk. 相似文献
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采用真空阴极电弧沉积技术,在NiTi记忆合金表面沉积了TiAlBN和TiAlCrFeSiBN多元膜和TiN薄膜,研究了薄膜成份及沉积工艺对NiTi合金性能和组织的影响.结果表明,在NiTi合金表面沉积TiAlBN和TiAlCrFeSiBN多元膜和TiN薄膜均可降低合金在Hank溶液中的Ni溶出速率,其中多元膜的Ni溶出速率最小;提高偏压对沉积了TiAlBN多元膜的NiTi合金的Ni溶出速率无明显影响,但使沉积了TiAlCrFeSiBN膜的NiTi合金的Ni溶出速率降低.在TiAlBN和TiAlCrFeSiBN多元膜表面存在较多细小的钛滴和孔隙,钛滴与薄膜基体之间的融合良好;在TiN薄膜表面存在一些大钛滴和孔隙,钛滴与薄膜基体之间的融合不好.镀膜后,NiTi基体的加热相变点移向低温区,其幅度与薄膜成份及沉积工艺有关,提高偏压使沉积了两种多元膜的NiTi基体的相变点移动幅度增大,但却使沉积了TiN膜的NiTi基体的相变点的移动幅度减小.镀膜过程均使NiTi中的M体尺寸增大. 相似文献
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为了研究热循环对NiTi合金激光焊接接头相变行为的影响,用激光点焊了φ0.5 mmTi-50.6%Ni合金细丝,利用金相显微镜观察了母材和接头的显微组织,通过示差热分析仪研究了热循环对点焊接头相变行为的影响.结果表明,NiTi合金激光点焊接头,熔化区为树枝晶,热影响区由粗大等轴晶和细小等轴晶组成.热循环可改变接头的相变行为,使马氏体相变由B2→B19'转变为B2→R→B19'.随着热循环次数的增加,正相变过程中Rs点升高,R相变温度范围变宽,Ms点降低;逆相变的相变温度都降低. 相似文献
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C. Velmurugan V. Senthilkumar Krishanu Biswas Surekha Yadav 《Advanced Powder Technology》2018,29(10):2456-2462
The effect of particle size and sintering temperature on the densification and microstructural characteristics of nickel-titanium shape memory alloy (NiTi-SMA) has been investigated using spark plasma sintering (SPS) process. The Ni and Ti elements in different particle sizes were alloyed in the composition of Ni50.6Ti49.4. The milled NiTi powders were consolidated using SPS process in a temperature range of 700–900?°C. The densification was characterized by plotting temperature, current and relative displacement of punch as a function of holding time. The results showed that a maximum relative density of ~98% can be achieved for NiTi-SMA with an average particle size of 10?µm at a sintering temperature of 900?°C. The microstructure of the sintered NiTi-SMA was examined using scanning electron microscope (SEM) and composition of NiTi alloy was analyzed using energy dispersive spectroscopy (EDS) analysis. The effect of sintering temperature on the microstructural evolution and transformation was also studied. 相似文献
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F. Chen Y.X. TongX.L. Lu X. WangB. Tian L. LiY.F. Zheng C.Y. ChungL.W. Ma 《Materials Letters》2011,65(7):1073-1075
In this investigation, the effect of graphite addition on martensitic transformation and damping behavior of Ni50Ti50 (at.%) shape memory alloy has been studied. It is found that martensitic transformation temperature decreases obviously with the addition of graphite. Microstructural observation shows that TiC precipitates and forms whiskers when the carbon content is increased beyond ~ 0.6%. With the increase of graphite content, the damping capacity during reverse transformation increases initially and then decreases while the damping capacity of full martensite is remarkably improved by the addition of graphite particles. It is proposed that the enhancement of damping capacity can be ascribed to the high damping capacity of graphite itself, as well as, the increase of the amount of interface between martensite and austenite can be beneficial to the damping capacity. 相似文献
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承受各种循环加载的TiNi形状记忆合金的超弹性变形行为 总被引:6,自引:0,他引:6
TiNi形状记忆合金由于其优良的机械性能、抗腐蚀能力和生物适应性得到广泛的使用。超弹性是TiNi形状记忆合金重要的力学性能之一。本文通过实验研究了不同加载速率和不同实验温度下承受完全循环加载以及部分加载卸载的TiNi形状记忆合金超弹性变形行为。分析了循环变形期间马氏体相变应力和弹性模量变化的特性。研究表明在完全循环加载过程中,由于残余应变的存在,马氏体相变应力随循环增加而减小。马氏体相变应力的变化量(即残余应力)与残余应变成线形关系。对于受过循环变形的机械训练的TiNi形状记忆合金,研究了部分加载和卸载情况下其超弹性变形,分析了相变开始与结束的应力特性。 相似文献
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A series of experimental studies have been carried out on nearly equi‐atomic NiTi shape memory alloy wires. The effects of fatigue cycles, displacement rates as well as testing temperatures on the superelastic capabilities have been studied. Under cycling loading, the threshold stresses for martensitic transformation decrease and the residule strains increase. Saturation is reached after 100 cycles. With increasing displacement rates, the critical stresses required for the martensitic transformation increase and the slopes of the upper plateau in the stress‐strain curves rise. The dissipated energy increases rapidly with increasing displacement rate, reaches a maximum value at around 6.0mm/min and then decreases as the displacement rate continues to increase. Tests also show that the threshold stresses characterizing the forward/reverse transformations increase linearly with increasing test temperature. 相似文献