共查询到19条相似文献,搜索用时 78 毫秒
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采用热压法将0.26mm的NiTi合金丝复合于铝中,利用SEM,DSC,热膨胀仪等实验手段研究了热循环对预应变为4%的NiTi合金丝/铝基复合材料马氏体逆相变的影响。结果表明,在第一次加热过程中,马氏体逆转变开始温度明显升高;第二次加热过程中逆转变开始温度比未预应变样品略有降低;随热循环次数增加,逆相变开始温度降低;当循环次数超过30次后,逆转变温度几乎保持不变。并对热循环过程中的马氏相变过程进行了分析讨论。 相似文献
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用电阻、恢复率同步测量的方法,研究了热循环对Ni47Ti44Nb9合金马氏体相变和记忆性的影响,并通过X-射线衍射、金相观察等方法对其微观机理进行了探讨。结果表明,随着热循环次数的增加,合金Ms明显下降;但热循环下不能诱发R相变,并对合金记忆性无明显影响。 相似文献
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采用球磨工艺使高温熔盐合成的NiTi粉末的相变行为发生改变,进而研究了球磨过程中球磨转速、球磨时间、摘要过程控制剂和时效处理对NiTi相变的影响。利用差示扫描量热法(DSC)、X射线衍射(XRD)和扫描电子显微镜(SEM)等现代检测手段对NiTi粉末的成分、组织形貌以及NiTi的相变行为进行了相应的分析研究。 相似文献
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用超声脉冲反射法测试了NiTi形状记忆合金(SMA)在相变过程中的纵波声速,研究了合金声速随温度变化的规律。结果表明:在非相变温度范围内,NiTi合金声速随温度缓慢变化,但在发生相变的温度范围内,声速的变化趋势发生明显改变;测得NiTi合金的各相变温度与常规电阻法基本一致,与电阻法等其他测量相变温度的方法相比,纵波声速法具有简单易行、测量方便以及对工件无损伤等优点。 相似文献
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采用爆炸焊将两块原子百分比不同的NiTi合金制成大块成分不均匀的NiTi/NiTi复合板,并在此基础上对其相变行为以及相应的回复应变特征进行了研究。结果表明焊后的复合板具有良好的界面结合和可逆马氏体相变;冷变形后NiTi/NiTi合金的逆相变温度及其相变温度范围随预应变量的增大而升高;同时,在较宽的温度范围内得到两步回复应变。 相似文献
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本文依据固体经验电子理论,建立了NiTi形状记忆合金马氏体晶胞的键络模型,并就合金化元素Cu对NiTi合金Ms点的影响进行了电子结构分析。为揭示该类功能材料中成分-性能-结构之间的内在联系做了初步探索,从电子结构的层次上初步解释了Cu对NiTi合金Ms点的作用机制。 相似文献
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In this paper, differential scanning calorimeter (DSC) was used to study the effects of predeformation and plate thickness
on the reverse martensitic transformation of explosively welded NiTi/NiTi alloy. Results showed that there was a constraint
between Ni50.4Ti (NiTi-1) and Ni49.8Ti (NiTi-2), which led to that the thickness of NiTi-1 or NiTi-2 strongly affected the reverse martensitic transformation
behavior because residual stress variations in thickness wound enable bias force to be built inside the composite. The DSC
measurements showed that after deformation, the reverse martensitic transformation temperature of the composite was increased
with the increasing thickness of NiTi-2. Also, the XRD results revealed that the microstructure of NiTi/NiTi alloy changed
from B2 phase to B19’ phase along the thickness direction. 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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Experimental observations are reported for the non-proportional multiaxial transformation ratchetting of super-elastic NiTi shape memory alloy performed under the stress-controlled cyclic tension–torsion loading conditions and at room temperature. The effect of axial mean stress on the evolutions of transformation ratchetting strain and dissipation energy per cycle during the cyclic tests is discussed firstly; and then the dependence of multiaxial transformation ratchetting on the different non-proportionally loading paths (e.g., linear, square, hourglass-typed, butterfly-typed, rhombic and octagonal paths) is investigated. The results show that the multiaxial transformation ratchetting occurs mainly in the axial direction because only the non-zero axial mean stress is used and the mean shear stress is set to be zero in the all prescribed multiaxial loading paths; and the axial peak and valley strains increase with the increasing axial mean stress and also depend significantly on the shapes of loading paths. Comparison with the corresponding uniaxial ones illustrates that the multiaxial stress states are more helpful to promote the development of transformation ratchetting, especially for the non-proportional ones. 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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The vacuum electron beam welding (EBW) technique was employed to weld Ni50.8Ti49.2 shape memory alloy sheets, and the microstructure, transformation behaviors and mechanical behaviors of the welding joints were investigated systematically. The microstructure observation showed that the weld seam was composed of coarse columnar crystals at the center and relatively fine columnar crystals near the fusion line. The abnormal high intensity of B22 0 0 peak in XRD patterns and preferred orientation in EBSD indicated that the grains in the weld seam have grown preferentially along the 〈1 0 0〉 crystal orientation. Differential scanning calorimetry (DSC) curves exhibited an increase of the martensite start temperature (Ms) of the weld seam, which led to the mixed microstructure of martensite and austenite at room temperature. As a result, the ultimate tensile strength of the welding joint was 85% as high as that of the base metal at room temperature, while it could reach 93% at 223 K when both the weld seam and the base metal were in pure martensitic state. 相似文献
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The use of NiTi in complex shaped components for structural applications is limited by the material cost and machinability and adequate joining techniques have been investigated to minimize the thermal cycle effect on the superelastic and shape memory effects exhibited by NiTi. Laser welding is the most used joining process for this material. However, existing studies mainly address the functional properties of laser welded NiTi wires, and the superelastic cycling tests are limited to either a low number of cycles (maximum 100) or to low strains (below 6%). This paper discusses the results of the cycling behavior exhibited by laser butt welded 1 mm thick NiTi plates, when tested to high strains (up to 10%) and for a large number of cycles (600). The superelastic effect was observed and the microstructural changes induced by the laser welding procedure, namely the extension of the thermal affected regions, were seen to influence the evolution of the accumulated irrecoverable strain. Thus, it is possible, by controlling the heat input introduced during welding, to tune the maximum superelastic recovery presented by NiTi laser welds. 相似文献
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利用变形约束时效的方法制作了双程记忆弹簧,采用DSC和温度-位移记录仪表征了弹簧的相变行为和双程记忆效应。DSC和双程记忆动力学曲线均表明弹簧在升温过程的形状变化由马氏体逆相变M/R→A控制,而冷却过程受A→R→M两阶段相变控制,并且R相变对双程记忆应变量的贡献比马氏体相变的贡献大。与马氏体相变相比,R相变诱发的双程记忆效应具有较窄的动作滞后温度以及很高的记忆稳定性,这与变形约束时效时所获得的一定取向的Ti3Ni4相共格内应力场有关。结果表明:变形约束时效是获得双程记忆弹簧的良好途径,制作方法相对简单,获得的双程记忆应变量大,且稳定性高,尺寸制作具有很强的可设计性以及动作温度的可控性。 相似文献