NiTi形状记忆合金垫片的压缩回弹性能及其本构关系

主要以NiTi形状记忆合金垫片为对象,制作了NiTi合金垫片试样,研究不同预紧力下的压缩回弹力学性能,并建立相应的本构方程。结果表明:NiTi合金垫片在压缩载荷作用下具有典型超弹性特性,其回弹率达到99%以上;并且建立的NiTi合金的本构方程与试验数据非常吻合。     

NiTi形状记忆合金回复应力-温度模型改进与实验研究

针对NiTi形状记忆合金的马氏体不完全逆转变带来的回复应力模型预测误差,开展了NiTi形状记忆合金一维回复应力-温度模型研究。在Brinson的形状记忆合金(SMA)一维本构模型基础上,增加马氏体回复因子为内变量,给出了马氏体回复因子与预应变的关系,综合考虑温度和应力对马氏体体积分数的影响,构造NiTi形状记忆合金回复应力-温度改进模型,通过实验测试了不同预应变量的NiTi合金回复应力与温度关系曲线。研究表明:本研究提出的改进模型预测的NiTi形状记忆合金回复应力-温度曲线,与实验曲线吻合较好。     

NiTi形状记忆合金回复力-温度模型改进与实验研究

摘要: 针对NiTi形状记忆合金的马氏体不完全逆转变现象带来的回复力模型预测误差,开展了NiTi形状记忆合金一维回复应力-温度模型研究。在Brinson的形状记忆合金(SMA)一维本构模型基础上,增加马氏体回复因子为内变量,给出了马氏体回复因子与预应变的关系,综合考虑温度和应力对马氏体体积分数的影响,构造NiTi形状记忆合金回复应力-温度改进模型,通过实验测试了不同预应变量的NiTi合金回复应力与温度关系曲线。研究表明：本文提出的改进模型预测的NiTi形状记忆合金回复应力-温度曲线,与实验结果曲线吻合较好,本研究结果对于提高NiTi形状记忆合金回复力预测精度具有重要意义。     

峰值应力对NiTi形状记忆合金循环变形塑性行为的影响

对单轴循环加载下,峰值应力对NiTi形状记忆合金(SMA)塑性行为的影响进行了研究。考虑到实际工况,对NiTi形状记忆合金在3种应力条件下(恒定峰值应力、阶梯峰值应力以及震荡峰值应力)的峰值应变、残余应变以及耗散能的变化进行实验分析。对于恒定峰值应力,发现峰值应力越高,NiTi形状记忆合金的超弹性劣化现象就越明显;对于阶梯峰值应力和震荡峰值应力,发现加载历史对于NiTi形状记忆合金塑性行为有显著影响。相较于恒定峰值应力,非恒定峰值应力可以引起更明显的NiTi形状记忆合金的超弹性劣化。     

电弧增材NiTi形状记忆合金构件的可控变形有限元数值分析

形状记忆合金(SMA)是一种具有广阔应用前景的新型智能材料,具有形状记忆效应和超弹性,在航空航天学等领域具有很好的应用前景。文中基于航天器智能结构对可展开性的具体要求——升空前为节省空间对结构进行压缩,减少装载体积,抵达目标地后实现主动展开以备使用,对NiTi形状记忆合金智能结构"折叠-主动变形展开"过程中的关键技术进行了研究。通过电弧增材的方式制备了NiTi合金构件,并通过DSC测试表明,室温下增材件组织是完全奥氏体组织,且存在完整的形状记忆效应相变过程。又基于Workbench软件,采用Auricchio本构,建立了三维NiTi合金几何模型,模拟了热驱动实现构件的主动展开过程,试验验证了模型的有效性。     

NiTi形状记忆合金超弹性的研究进展

近年来 ,有关NiTi形状记忆合金的研究取得了很多进展 ,本文主要介绍了NiTi形状记忆合金超弹性的基础研究、力学行为、在耐磨损性能方面的应用研究以及数学方面的某些进展和重要问题     

NiTi形状记忆合金超弹性的研究进展

近年来，有关NiTi形状记忆合金的研究取得了很多进展，本文主要介绍了NiTi形状记忆合金超弹性的基础研究、力学行为、在耐磨损性能方面的应用研究以及数学方面的某些进展和重要问题。     

形状记忆合金的本构关系

利用DSC分析了热流-温度曲线和马氏体体积分数与自由能增量间的微分关系,建立了一个新的余弦型形状记忆合金马氏体相变模型;推导了一个新的形状记忆合金本构方程.研究表明:Liang和Rogers的马氏体相变模型和本构方程分别为本文建立的马氏体相变模型和本构方程所描述的一种特殊情况;本文建立的马氏体相变模型和本构方程比Liang和Rogers及其它现存马氏体相变模型和本构方程能更准确地描述形状记忆合金的相变行为和力学行为.     

热爆反应合成多孔NiTi形状记忆合金的性能

利用热爆方法来制备了多孔NiTi形状记忆合金.研究了在不同热爆温度下制备出的样品与其机械性能之间的关系.结果表明:在1 223 K下热爆反应制备的NiTi合金,具有大的孔隙度,高开孔率和基本各向同性,同时表现出较好的超弹性.对断口分析发现,断裂为脆性断裂和韧性断裂的复合.这表明改善孔洞分布和形态,可以极大地提高多孔NiTi形状记忆合金的机械性能和超弹性.     

高熵形状记忆合金的研究进展

高熵形状记忆合金是在等原子比NiTi合金的基础上,结合高熵合金的概念,逐渐发展起来的一种新型高温形状记忆合金。近年来,已开发出了综合性能优异的(TiZrHf)50(NiCoCu)50系和(TiZrHf)50(NiCuPd)50系高熵形状记忆合金,引起了广泛的关注和研究兴趣。本文从物相组成、微观组织、马氏体相变行为、形状记忆效应和超弹性等角度出发,综述了高熵形状记忆合金的研究进展,并对高熵形状记忆合金未来的研究重点进行了展望。     

Investigation of the role of Ti oxide layer in the size-dependent superelasticity of NiTi pillars: Modeling and simulation

Recent compression tests of NiTi pillars of a wide range of diameters have shown significant size dependency in the strain recovered upon unloading. In this paper, we propose a numerical model supporting the previously proposed explanation that the external Ti oxide layer may be responsible for the loss of superelasticity in the small pillars. The shape memory alloy at the center of the pillar is described using a nonlocal superelastic model, whereas the Ti oxide layer is modeled as elastoplastic. Voigt average analysis and finite element calculations are compared to experiments for the available range of pillar sizes. The simulation results also suggest a size-dependent strain hardening due to the constraint on the phase transformation effected by the confining Ti oxide layer.     

Designing a novel functional-structural NiTi/hydroxyapatite composite with enhanced mechanical properties and high bioactivity

Clinical applications require porous biomaterials, however, higher porosity levels and hydroxyapatite (HA) content hampers the mechanical properties like superelasticity. Here, a functional-structural composite consisting of a central NiTi shape memory alloy core with an outer macro-porous NiTi/HA layer was fabricated by spark plasma sintering (SPS). The central NiTi alloy provides desirable mechanical properties like high strength and superelasticity, while the outer layer with controllable pore size and bioactive HA, which strongly boosts the bioactivity. This work might provide a strategy for designing and fabricating multifunctional biocompatible materials that could be promising for bone implants.     

Microstructure and Mechanical Properties of NiTi Shape Memory Alloys by In Situ Laser Directed Energy DepositionEI北大核心CSCD

以Ni粉与Ti粉为原料,采用激光定向能量沉积(LDED)技术制备NiTi形状记忆合金。利用XRD、物相拟合、SEM、EDS和DSC等测试方法,对NiTi合金的显微组织、物相含量和物相转变进行分析,随后采用压缩圆柱样品进行形状记忆效应测试,并评估其形状记忆效应。激光能量密度较低时,NiTi合金中产生大量Ni_(4)Ti_(3)相沉淀,随着激光能量密度增加,Ni_(4)Ti_(3)相消失。激光能量密度为20.0 J/mm^(2)时,NiTi合金具有2878 MPa的压缩断裂强度与34.9%的压缩失效应变,且样品在循环20 cyc后具有88.2%形状记忆恢复率。     

Equal channel angular extrusion of NiTi shape memory alloy tube

As a new attempt, equal channel angular extrusion (ECAE) of nickel–titanium shape memory alloy (NiTi SMA) tube was investigated by means of process experiment, finite element method (FEM) and microscopy. NiTi SMA tube with the steel core in it was inserted into the steel can during ECAE of NiTi SMA tube. Based on rigid-viscoplastic FEM, multiple coupled boundary conditions and multiple constitutive models were used for finite element simulation of ECAE of NiTi SMA tube, where the effective stress field, the effective strain field and the velocity field were obtained. Finite element simulation results are in good accordance with the experimental ones. Finite element simulation results reveal that the velocity field shows the minimum value in the corner of NiTi SMA tube, where severe shear deformation occurs. Microstructural observation results reveal that severe plastic deformation leads to a certain grain orientation as well as occurrence of substructures in the grain interior and dynamic recovery occurs during ECAE of NiTi SMA tube. ECAE of NiTi SMA tube provides a new approach to manufacturing ultrafine-grained NiTi SMA tube.     

Effects of Solution and Aging Treatments on Corrosion Resistance of As-cast 60NiTi Alloy

60NiTi alloy has become a competitive candidate for bearing applications due to its shape memory effect, superelasticity, high strength, hardness, excellent abrasion resistance and corrosion resistance, etc. However, the relationship between its corrosion resistance and heat treatment is not clearly understood. Therefore, we used OM, XRD, SEM and EDS to study the evolution of microstructure in as-cast, solution-treated and aged 60NiTi alloy. Besides, the potentiodynamic polarization and salt spray test were used to compare corrosion resistance of 60NiTi alloy and 316 stainless steel and to study the effect of microstructures on corrosion resistance of 60NiTi alloy. The results show that the corrosion resistance of as-cast 60NiTi alloy is comparable to that of 316 stainless steel, but the corrosion resistance of solution-treated and aged 60NiTi alloys is much superior. The significantly reduced Ni₃Ti phase after the solution and aging treatments is responsible for the remarkable improvement in the corrosion resistance of as-cast 60NiTi alloy.     

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-Nb原位复合材料的准线性超弹性变形EI北大核心CSCD

据文献报道,Nb纳米线增强NiTi记忆合金复合材料可展现超常的准线性超弹特性。为揭示该准线性超弹特性的产生和变形机制,通过真空感应熔炼、锻造、拔丝方法原位合成了NiTi-Nb复合材料丝材。TEM显微分析表明,Nb纳米线沿丝材轴向平行分布在纳米晶NiTi基体中。该材料在经历一次9%的预变形后会展现准线性超弹特性,其屈服强度达1.7 GPa,表观Young's模量约34 GPa,准线性超弹性应变接近5.5%。同步辐射高能X射线原位拉伸实验结果表明,准线性超弹性的产生与以下2点原因有关:(1)复合材料经历预变形后,Nb纳米线和NiTi基体间会产生耦合力,再次加载时,NiTi所受的耦合拉应力可以将局部区域应力诱发马氏体相变所需的外应力降低到零附近,并且耦合力越大,加载初期的相变速率越高,经过适当的预变形后,加载初始就能够持续发生高速率相变;(2) NiTi中耦合拉应力呈梯度分布,使相变应力-应变曲线不再是常见的“平台型”,转变为“硬化型”斜线。     

Nb合金化对电弧增材制造NiTi基形状记忆合金的影响

NiTi合金是一种应用广泛的形状记忆合金,其中Ti₄₇Ni₄₄Nb₉成分的合金是一种可靠的航空管接头材料. 采用双丝电弧增材制造(WAAM)的方法制备了Ni₅₂Ti₄₈合金,并以Nb元素进行了原位合金化得到了Ti₄₇Ni₄₄Nb₉合金,研究了其典型组织、压缩性能、相变温度与形状记忆效应,分析了Nb元素的添加对WAAM镍钛合金组织及性能的影响. 结果表明,加入Nb元素后,合金的组织除B2相晶粒外,还在晶界处有细小的β-Nb相析出,使得合金的压缩强度在横向与纵向上分别增加了7.9%与3.1%,形状记忆回复率则下降了4.0%,相变温度滞后从?6.4 ℃提升至40.9 ℃,使得该材料作为记忆合金管接头时更加利于储存与装配.