形变温度对Ti-Ni合金超弹性弹簧形变行为的影响

采用拉伸试验和应力应变循环试验研究了形变温度及应力应变循环对Ti-Ni_(50.8)超弹性弹簧形变行为的影响。结果表明:当形变温度在247K以下时Ti-Ni_(50.8)弹簧呈形状记忆性,形变温度在247K以上时呈超弹性特性。623~773K退火态Ti-Ni_(50.8)弹簧室温下可获得良好超弹性。当退火温度超过873K后,超弹性衰减。在应力-应变循环早期,弹簧应变恢复率衰减很快,随循环次数增加,衰减变慢。Ti-Ni_(50.8)弹簧预先应力应变循环训练可增强其变形稳定性。     

Ti-50．8Ni-0．3Cr超弹性合金的相变与形变特性

用示差扫描量热仪、X射线衍射仪、拉伸实验和循环实验研究了退火温度、形变温度和应力-应变循环对Ti-50.8Ni-0.3Cr超弹性(SE)合金丝和弹簧相变、形变及应力循环特性的影响.350-600℃退火态Ti-50.8Ni-0.3Cr合金室温下呈SE特性,室温组织由母相B2和TiNi3组成.退火温度显著影响合金的相变类型,随退火温度升高,合金的马氏体相变温度升高,R相变温度先升高后降低,应力诱发马氏体应力先降低后升高;随形变温度的升高,SE弹簧的应力诱发马氏体切应力增加;随应力循环次数增加,SE弹簧的应变恢复率先快速衰减后趋于稳定.预循环训练可增加弹簧SE特性的稳定性.要使该合金弹簧具有良好的SE特性,退火温度应为400-550℃,使用温度应在室温以上.     

退火态Ti-49.8Ni形状记忆合金的组织及性能研究

用光学显微技术及拉伸试验研究了退火温度T_a和形变温度T_d对Ti-49.8Ni(原子分数,%)形状记忆合金(SMA)丝材及弹簧的显微组织与形状记忆行为的影响.结果表明:冷加工态Ti-49.8Ni合金组织呈纤维状;退火后,随T_a升高,其显微组织逐渐从纤维状向等轴状过渡,合金丝和弹簧的马氏体(M)再取向力先减小后增大;退火态合金在室温下呈形状记忆效应,随T_d升高,合金的M再取向力升高,形状记忆效应份额逐渐减少,超弹性效应份额逐渐增加.     

Ti50.6Ni合金弹簧超弹性行为研究

研究了试验温度、退火温度（ Ｔｈ） 及应力—应变循环对Ｔｉ５０ ．６Ｎｉ 合金弹簧超弹性（ＳＥ） 行为的影响。结果表明，冷拔态Ｔｉ５０ ．６Ｎｉ 合金中温退火后，热循环相变类型为Ａ→Ｒ→Ｍ←——— ，组织呈纤维状。该合金弹簧经６２３ ～７７３Ｋ 退火后，室温下可获得ＳＥ。随试验温度升高，弹簧刚度增加。Ｔｈ≥８２３Ｋ时，ＳＥ特性变坏。应力—应变循环初期，弹簧的切应力、切应变恢复率急剧衰减，随循环次数增加，衰减变慢。预循环训练可增强ＴｉＮｉ 合金弹簧超弹性的稳定性。     

Ti49.4Ni50.6超弹性弹簧的相变和形变特性

用示差扫描量热仪、拉伸实验和应力-应变循环实验系统研究了退火温度、变形温度以及热循环和室温应力-应变循环对Ti49．4Ni50．6超弹性(SE)弹簧的相变和形变特性的影响。冷加工加中温退火态Ti49．4Ni50．6合金冷却→←加热时的相变类型为母相B2→←R相→←马氏体B19′。随退火温度升高，马氏体转变温度升高，R相转变温度降低。623-773K退火态Ti49．4Ni50．6弹簧室温下可获得SE特性，随变形温度升高，SE弹簧剐度增加；当退火温度超过823K后，SE持性变差。热循环时SE弹簧的切变量取值越小，其应变恢复率越高。预循环训练可增强SE的稳定性。     

热处理对Ti-Ni-Co超弹性合金变形行为的影响

用拉伸试验和应力-应变循环试验研究退火温度(Ta)、变形温度(Td)和应力-应变循环对Ti-49.8Ni-1.0Co(原子分数,%)超弹性合金丝和弹簧变形行为的影响.结果表明:随Ta升高,Ti-Ni-Co合金丝应力-应变曲线上的平台应力升高,平台应变先降低后升高;随Ta和Td升高,合金弹簧的临界切应力升高;随循环次数增加,合金弹簧的应变恢复率降低;预循环训练可增强Ti-49.8Ni-1.0Co合金弹簧的SE稳定性.     

Ti-Ni-V形状记忆合金及其弹簧的相变和形变特性

用X射线衍射仪、示差扫描量热仪和拉伸实验研究了退火温度Tan和形变温度Td对Ti-50.8Ni-0.5V形状记忆合金丝及其弹簧的相变和形变特性的影响。结果表明:400～600℃退火态合金的室温相组成为B2和R相。冷却/加热时,350～400℃退火态合金发生A→R/R→A(A—母相,R—R相)一阶段可逆相变;450～500℃退火态合金发生A→R→M/M→R→A(M—马氏体相)两阶段可逆相变;550℃退火态合金发生A→R→M/M→A型相变;600℃退火态合金发生A→M/M→A一阶段可逆相变。随Tan升高,R相变温度先升高后降低,M相变温度先升高后趋于稳定,M相变热滞快速降低,而R相变热滞则几乎不受退火温度影响。随Td和Tan升高,退火态Ti-50.8Ni-0.5V合金弹簧的应力诱发M临界切应力升高。     

橡胶弹簧的设计计算及其系列化

前言在弹性系统中,弹性支承除了金属弹簧外,尚有橡胶弹簧。它除了具有良好的减振、隔音和缓冲效果外,还有下列不可代替的优点: (1)橡胶弹簧的形状和尺寸能自由选择、调整,容易满足多向刚度和强度的要求; (2)有适当的阻尼,有利于越过共振区,能衰减高频振动和噪音,因而大为改善工作     

Fe44Co20Nd7Nb4B25大块非晶合金磁性及热稳定性研究

采用铜模吸铸法制备了Fe44Co20Nd7Nb4B25大块非晶合金,利用差示扫描量热仪(DSC)、X射线衍射仪(XRD)、高分辨透射电镜(HRTEM)和振动样品磁强计(VSM)研究了该合金的结构、非晶形成能力、热稳定性及磁性能.结果表明:该合金为完全非晶结构,在室温下表现为良好的软磁性,并具有较好的非晶形成能力和热稳定性,晶化激活能Ep为642 kJ/mol.退火后该合金表现为硬磁性,退火温度为1003 K时,内禀矫顽力iHc达到最大值,为l164kA/m;退火温度为963 K时,剩余磁感应强度研和最大磁能积(BH)max的值最大,分别为0.27 T和15.79 kJ/m3.     

Ti—50.6ni合金弹簧超弹性行为研究

研究了试验温度、退火温度（Ｔｈ）及应力一应变循环对Ｔｉ－５０．６Ｎｉ合金弹簧超弹性（ＳＥ）行为的影响。结果表明，冷技态Ｔｉ－５０．６Ｎｉ合金中退火后，热循环相变类型为Ａ→Ｒ→Ｍ，组织吾纤维状。该合金弹簧经６２３～７７３Ｋ退火后，室温下可获得ＳＥ。随试验温度升高，弹簧刚度增加。Ｔｈ≥８２３Ｋ时，ＳＥ特性变坏。应力一应变循环初期，弹簧的切应力、切应变恢复率急剧衰减，随循环次数增加，衰减变慢。预循环训练     

Embedding of Superelastic SMA Wires into Composite Structures: Evaluation of Impact Properties

Shape memory alloy (SMA) represents the most versatile way to realize smart materials with sensing, controlling, and actuating functions. Due to their unique mechanical and thermodynamic properties and to the possibility to obtain SMA wires with very small diameters, they are used as smart components embedded into the conventional resins or composites, obtaining active abilities, tunable properties, self-healing properties, and damping capacity. Moreover, superelastic SMAs are used to increase the impact resistance properties of composite materials. In this study, the influence of the integration of thin superelastic wires to suppress propagating damage of composite structures has been investigated. Superelastic SMAs have very high strain to failure and recoverable elastic strain, due to a stress-induced martensitic phase transition creating a plateau region in the stress-strain curve. NiTi superelastic wires (A _f = ?15 °C fully annealed) of 0.10 mm in diameter have been produced and characterized by SAES Getters. The straight annealed wire shows the typical flag stress-strain behavior. The measured loading plateau is about 450 MPa at ambient temperature with a recoverable elastic strain of more than 6%. For these reasons superelastic SMA fibers can absorb much more strain energy than other fibers before their failure, partly with a constant stress level. In this paper, the improvement of composite laminates impact properties by embedding SMA wires is evaluated and indications for design and manufacturing of SMA composites with high-impact properties are also given.     

Effects of ECAP and Aging on Mechanical and Superelastic Behaviors of Ti-Mo-Based and Ti-25at.%Nb SMAs

Ni-free Ti-based shape memory alloys (SMAs) are increasingly recognized as promising functional materials for medical applications. The mechanical properties of these metastable Ti-based SMAs are sensitive to aging and thermomechanical treatment. Effects of severe plastic deformation (SPD)-equal channel angular pressing (ECAP) and aging on superelastic behavior of Ni-free Ti-based SMAs, Ti-9.8Mo-3.9Nb-2V-3.1Al?wt.% (TMNVA) and Ti-25at.%Nb, have been investigated. The results show that the yielding strength of TMNVA alloy increases sharply with the number of ECAP processes??to greater than 1,400?MPa after two passes ECAP??but elongation of TMNVA alloy decreases severely and the plasticity is lost completely after two passes ECAP. Both ECAP process and flash annealing treatment have weak contribution to the superelastic recoverable strains of Ti-Mo-based alloy. For Ti-25at.%Nb alloy, after one pass ECAP process at 400?°C, the yielding stress increases obviously, and the recovery strain increases a little. With the further increase in the number of ECAP processes, the yielding stress and the recovery strain change little. Aging treatment at low temperature after ECAP process is in favor of superelasticity of Ti-25at.%Nb alloy. An almost completely recoverable strain of 1.5% is obtained in Ti-25at.%Nb alloy after two passes ECAP and aging at 300?°C for 1?h. The mechanisms of the effects of SPD and aging are also discussed.     

Superelasticity and fatigue in oligocrystalline shape memory alloy microwires

In oligocrystalline shape memory alloys, the total grain boundary area is smaller than the surface area of the specimen, leading to significant effects of free surfaces on the martensitic transformation and related shape memory and superelastic properties. Here we study sample size effects upon the superelastic characteristics of oligocrystalline microwires after one loading cycle and after many. Cu-Zn-Al wires with diameters ranging from ∼100 down to ∼20 μm are fabricated by the Taylor liquid processing technique and characterized through both uniaxial cyclic tensile testing and mechanically constrained thermal cycling. The energy dissipated per superelastic cycle increases with decreasing wire diameter, and this size effect is preserved after extensive cycling despite a significant transient evolution of the superelastic response for early cycles. We also present fatigue and fracture data, indicating that oligocrystalline wires of this normally brittle alloy can exhibit fatigue lifetimes two orders of magnitude improved over conventional polycrystalline Cu-Zn-Al.     

Physical Simulation of the Random Failure of Implanted Braided NiTi Stents

A problem of random clinical failures of the braided esophageal NiTi stents has been addressed by performing physical simulation experiments on helical NiTi springs loaded in cyclic tension in air, water, and simulated biological fluid. Strains and stresses involved in spring deformation were analyzed through simulation by FEM implemented SMA model. It was found that the fatigue life of NiTi springs is significantly lower in fluids than in the air pointing toward the corrosion fatigue mechanism. There is, however, a fatigue limit roughly corresponding to the onset of martensitic transformation in the wire, which is not common for corrosion fatigue. It is proposed that surface TiO₂ oxide cracking plays major role in that. Once the oxide layer on the NiTi wire surface fractures, typically during the first mechanical cycle, cracks in the oxide layer periodically open and close during subsequent mechanical cycling. This leads to the localization of mechanical and corrosion attacks under the oxide cracked regions. Microcracks within the surface oxide layer crossing over into the NiTi matrix were indeed revealed by scanning electron microscopy of FIB sections of fatigued wires. A corrosion assisted mechanism for fatigue crack nucleation at the interface between the surface oxide and NiTi matrix is proposed based on the available evidence. The approach opens a space for a better assessment of the corrosion fatigue performance of superelastic NiTi and ultimately for estimation of the lifetime of implanted braided NiTi stents.     

Superelasticity of NiTi Ring-Shaped Springs Induced by Aging for Cranioplasty Applications

This paper concerns the application of titanium-nickel rings in modeling the cranium. After being fixed to the osseous margins, the ring’s expansion at the same time broadens and shortens the cranium vault. The rings formed from a straight superelastic wire, flattened to an ellipse, do not show the presence of a typical force plateau but rather a pseudoelastic loop during loading-unloading in the relationship between the force and the deflection. Based on the idea that superelasticity in more complex shape-springs may be induced by the precipitation hardening process, the further studies were carried out on alloys with higher nickel contents (51.06 at.% Ni). The rings that had been formed were welded and aged at an optimal temperature and time. The improved superelastic behavior during compression and unloading the rings was obtained by introducing small deformation by drawing the quenched wires before forming the rings and aging. Very positive clinical reshaping by long-term distraction with the superelastic ring-shaped springs was achieved in young children under one year and a less spectacular effect was observed in the group of older children.     

Static and Cyclic Load-Deflection Characteristics of NiTi Orthodontic Archwires Using Modified Bending Tests

Near-equiatomic nickel-titanium (nitinol) has the ability to return to a former shape when subjected to an appropriate thermomechanical procedure. One of the most successful applications of nitinol is orthodontic archwire. One of the suitable characteristics of these wires is superelasticity, a phenomenon that allows better-tolerated loading conditions during clinical therapy. Superelastic nitinol wires deliver clinically desired light continuous force enabling effective tooth movement with minimal damage for periodontal tissues. In this research, a special three-point bending fixture was invented and designed to determine the superelastic property in simulated clinical conditions, where the wire samples were held in the fixture similar to an oral cavity. In this experimental study, the load-deflection characteristics of superelastic NiTi commercial wires were studied through three-point bending test. The superelastic behavior was investigated by focusing on bending time, temperature, and number of cycles which affects the energy dissipating capacity. Experimental results show that the NiTi archwires are well suited for cyclic load-unload dental applications. Results show reduction in superelastic property for used archwires after long-time static bending.     

等温退火对8030铝合金导线组织性能的影响

研究了不同等温退火工艺对8030铝合金导线组织及性能的影响。结果表明:等温退火前后合金均由α-Al基体和Al₆Fe相组成。在同一等温温度下,随着等温时间的延长组织逐渐趋于均匀化;同一等温时间下,随着等温温度的升高,组织趋于均匀化的时间缩短。经过等温退火处理后铝合金导线的导电率均有所提高,在470 ℃均匀化退火24 h后再经240 ℃等温4 h,合金导电率达到最高值57.21%IACS,比未经热处理试样的导电率提高了2.4%IACS。经过等温退火处理后铝合金导线的硬度及抗拉强度均有所降低,塑性大幅度提高。在470 ℃均匀化退火24 h后再经260 ℃等温8 h,合金的伸长率最高可达23.64%。热处理前后合金均为塑性断裂。     

Mechanical and Vibration Characteristics of Laminated Composite Plates Embedding Shape Memory Alloy Superelastic Wires

Currently, there is a great interest in the study of shape memory alloy (SMA) composites, since SMA wires with a small diameter have become commercially available. Many potential uses have been found for SMA composites in shape control, vibration control, and for the realization of structures with improved damage tolerance. In this work, two types of SMA-hybridized composites are presented for investigating the mechanical and vibration characteristics. The first one contains unidirectional superelastic SMA wires, while the other has been realized with embedded knitted SMA layers. The samples from these laminates have been tested according to “Charpy method” (ASTM D256) and static flexural test method (ASTM D790) to evaluate the influence of the integration of thin superelastic SMA wires on the impact behavior and the mechanical properties of the hybrid composites. Moreover, since the SMA wires are expected to give damping capacity, by measuring the vibration mode of a clamped cantilever using laser vibrometry, the influence of both SMA arrangements on the vibration characteristics has been investigated. Finally, further tests have been carried out on composite panels realized by embedding unidirectional steel wires to distinguish the influence of the martensitic transformation from the pure introduction of a metallic wire into the polymeric matrix.     

铜铝复合接触线用银铜合金的抗软化性和再结晶

研究了刚性铜铝复合接触线用银铜合金的抗软化性及再结晶,硬度测试、组织和静态再结晶动力学的分析结果表明,银铜合金的软化温度约为390 ℃,再结晶温度为350～450 ℃.银铜合金退火过程中发生再结晶的激活能为77.68 kJ·mol-1;350 ℃、390 ℃退火时的再结晶完成时间分别约为414.4、167.7 min.