NiTi形状记忆合金的相变

用X射线衍射、内耗、电阻和透射电镜等方法研究了等原子NiTi合金在150℃以下的相变。实验结果表明,在40—50℃之间,合金开始发生两类可逆的相变:马氏体相变和R相变。马氏体具有单斜畸变B_(19)结构,R相具有畸变B_2结构。R相变不是预转变,在-185℃,R相仍保持相对的稳定。在等原子NiTi合金中,相变依下列次序进行: β(?)β R M(B_(19))(?)R M(B_(19))。     

Young’s Modulus of Austenite and Martensite Phases in Superelastic NiTi Wires

Young’s moduli of superelastic NiTi wires in austenite and stress-induced martensite states were evaluated by three different experimental methods (tensile tests, in situ synchrotron x-ray diffraction, and dynamic mechanical analysis) and estimated via theoretical calculation from elastic constants. The unusually low value of the Young’s modulus of the martensite phase appearing in material property tables (<40 GPa) is generally ascribed in the literature to the fact that stress-driven martensitic transformation and/or twinning processes continue even beyond the transformation range and effectively decrease the value of the tangent modulus evaluated from macroscopic stress-strain curve. In this work, we claim that this low value is real in the sense that it corresponds to the appropriate combination of elastic constants of the B19′ martensite phase forming the polycrystalline wire. However, the Young’s modulus of the martensite phase is low only for wire loaded in tension, not for compression or other deformation modes. It is shown that the low value of the martensite Young’s modulus in tension is due to the combination of the unique coincidence of elastic anisotropy of the B19′ martensite characterized by the low elastic constant C55, austenite drawing texture, and strong martensite texture due to the martensite variant selection under tensile stress.     

Microdefects and electron densities in NiTi shape memory alloys studied by positron annihilation

1Introduction NiTi alloys are the most successful shape memory alloys as a result of their combination of good functional properties and excellent mechanical strength[1,2].The thermal and mechanical shape memory behavior in these alloys is dependent upon …     

NiTi形状记忆合金刷镀工艺研究

研究了刷镀新工艺在NiTi合金表面处理中的应用.结果表明改进活化效果是提高镀层质量的关键.在大量实验的基础上确定了合适的刷镀工艺,获得了外观、结合力良好的镀层.     

NiTi形状记忆合金马氏体相变研究

以NiTi合金为研究对象,在万能试验机上采用原位拉伸方法研究其马氏体相变的失稳情况。结果表明,NiTi合金马氏体形核时的应力应变曲线具有非线性变化特征。马氏体合并时,相变潜热增加了马氏体的形核功。马氏体分裂时,应力波动值较低。     

NiTi形状记忆合金的加工方法

对ＮｉＴｉ形状记忆合金的多种加工方法如锻造、热挤压、轧帛昨拉拔、冷加工、粉末成形、包套碎片挤压成形、溅射沉积加工等进行了详细介绍。     

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形状记忆合金的热循环试验

研制了能评价线圈状NiTi形状记忆合金材料在一定载荷下热循环特性的试验装置,并利用该装置研究了相变点(Ms点、Af点)及形状回复量随着冷热交变循环的变化。结果表明,冷热交变50次时,相变点变化仅为几摄氏度。同时发现随着交变次数的增加形状回复量缓慢地变化。低温(Mf点以上)时变化量比高温(Af点以下)时大,而且载荷量越大变化量也越大。     

NiTi形状记忆合金及其应用开发

ＮｉＴｉ形状记忆合金及其应用开发具有形状记忆效应的合金至今已发现有数十种，其中已实用化的合金除ＮｉＴｉ合金以外还有ＣｕＺｎＡｌ合金和一部分Ｆｅ系合会ＮｉＴｉ合金因具有优良的形状记忆特性（回复应变，发生力）、超弹性和循环寿命等特性，所以应用范围极广。当...     

Electropolishing parameters of NiTi alloy

Electropolishing has been used in NiTi alloy in several fields for its special characteristics, but its essential details and electropolishing mechanism have not been reported yet as a demand from business competition, which, to a great degree, restricts the application and extension of the electropolishing technology. The effect of processing parameters on nitinol electropolishing was explored. Besides the electrolyte, other factors that influence the electropolishing are temperature, current density, time, spacing between anode and cathode, electrolyte stirring, etc. Studies on the effect of the temperature on the electropolishing process show that the higher the temperature is, the bigger the electropolishing rate is, following the near Gauss law. The relationship between the temperature and the surface roughness follows a near parabolic law, and the relationship between the temperature and the surface reflectivity follows a near sigmoidal law. The relationship between the electropolishing voltage and the current density follows a near cubic law, while that between the electropolishing rate and current density follows a near linear law. The relationship between the electropolishing rate and the time follows a near sigmoidal law. The practical spacing between anode and cathode is confirmed by the Hall bath experiment.     

NiTi形状记忆薄膜的力学性能

利用直流或射频磁控溅射法溅射沉积非晶ＮｉＴｉ合金薄膜,研究了５５０℃晶化热处理０．５ｈ的５１．６％ＮｉＴｉ形状记忆薄膜的力学性能。弯曲和拉伸实验结果表明：自由状态的ＮｉＴｉ薄膜具有良好的形状记忆效应。形状记忆的恢复率几乎接近１００％。与相同组分和相同热处理条件下的块体合金材料的形状记忆性能的实验数据相比较是相当的。     

NiTi形状记忆合金的热电行为

研究了形状记忆合金线的热电行为。当合金线被加热到温度高于其相变温度时,由于相的转变而产生一个大的机械力。将 SMA 线用作驱动器,并研究了不同的参数及它们之间的关系。在不同的压力水平下,这些变化的参数分别是弹性应变(位移)、温度磁滞和电阻。通过传递热模型得到安全的加热电流并预测了相变温度。在自然空气对流的条件下,采用680 mA的电流加热、冷却合金线796 s。在43 MPa的应力水平下,应变恢复率为4.33%,相应的电阻变化为11.2%。在加热、冷却循环过程中,电阻变化与位移和电流分别呈线性关系。该研究有助于精确控制有、无外部传感器反馈的SMA线驱动器。     

NiTi合金超细丝的开发

近年来,在各式各样工业领域,进行形状记忆合金的应用开发,成为其主流的是NiTi系形状记忆合金。其用途有使用在汽车、家用电器制品上的感温阀、矫正齿列的超弹性齿列矫正丝及胸罩丝等。NiTi形状记忆合金作为金属网使用时,希望与各种材料复合化。因此超细丝化成为必要条件,但是,NiTi合金是金属间化合物,和不锈钢等铁系合     

医用多孔NiTi形状记忆合金的研究进展

综述多孔NiTi形状记忆舍金的制备工艺、生物力学性能及生物相容性等方面的研究进展。国内外的研究表明，多孔NiTi合金具有优良的生物相容性和高的力学性能，其独特的孔隙结构可保证组织的长入和体液的传输，使植入物与人体骨组织的结合更加牢固可靠，多孔NiTi形状记忆舍金是一种具有良好应用前号的生物医用材料。     

NiTi形状记忆合金高温变形神经网络研究

在Gleeble-1500热模拟机上进行热变形压缩试验,获得了NiTi形状记忆合金在不同应变速率和温度下的真应力-真应变实验数据及微观组织,根据实验数据基于BP神经网络建立模型对NiTi合金的高温变形进行预测。结果表明:随着应变速率的增加,TiNi合金的软化特性变得明显,模型的预测值与试验值误差较小,且预测精度和可靠度高。     

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.