TiNi合金轴向压缩动载荷下的超弹性研究

以高温固溶时效和中温退火处理过的Ti-50．7at％Ni合金为研究对象，考察了合金在试验温度为20℃，加载速率分别为3mm／min、15mm／min、30mm／min、50mm／min作用下的轴向压缩应力-应变行为。结果表明：2种热处理方式处理过的Ti-50．7at％Ni合金具有约4．5％～5．0％的非线性超弹性，高温固溶时效处理的合金由于析出相强化提高了合金母相强度，因而相变超弹性能比中温退火的合金要好，在相同试验条件下，高温固溶时效处理合金的加载-卸载曲线包围面积比中温退火的大，但随着加载速率的增加而减小；在较高加载速率下，中温退火的合金表现出近乎线性超弹性。     

Pseudoelasticity of Metal Nanoparticles Is Caused by Their Ultrahigh Strength

An assembly of hemispherical Ag nanoparticles is prepared by solid‐state dewetting of thin Ag film deposited on the sapphire substrate. The in situ nanomechanical compression testing of the particles with a flat diamond punch inside the scanning electron microscope demonstrates the deformation behavior typical for the nucleation‐controlled plasticity: high elastic deformation followed by an abrupt particles collapse. The latter is associated with the dislocations nucleation in otherwise pristine particle. The average contact pressure in the contact zone at the onset of dislocation‐controlled plasticity is about 8 GPa, and does not depend on particle size. This observation supports the hypothesis that the pseudoelasticity of much smaller Ag nanoparticles is intrinsically related to their ultrahigh strength. A stress‐induced diffusion along the particle–substrate and particle–punch interfaces is identified as a factor controlling the pseudoelastic deformation. The corresponding diffusion model allows estimating the room‐temperature self‐diffusion coefficient of Ag along the Ag–W and Ag–zirconia interfaces, which is quite close to the estimated value of the grain boundary self‐diffusion coefficient in Ag. Based on this finding, the map of pseudoelastic deformation of crystalline materials is proposed.     

形状记忆合金驱动的微执行器

以TiNi基为代表的形状记忆合金（SMA）具有做功密度大、可恢复应变应力大、驱动电压低、良好生物相容性等优点，在微执行器领域具有极为广阔应用前景。本文主要总结了TiNi基SMA丝、薄带、薄膜在微执行器方面的国内外研究应用现状，并对目前SMA在微驱动领域应用所存在的问题及其未来的发展趋势进行了分析讨论。     

基于多微凸体有限元分析的超弹TiNi合金磨损机制

对三种不同超弹性的TiNi合金及20MnV钢表面多微凸体在法向栽荷作用下的模型进行了有限元分析，并对超弹TiNi合金的磨损机制进行了探讨。结果表明，由于TiNi合金具有较高的最大弹性变形量，在相同栽荷下，表面上参加接触的微凸体数目随着超弹性的增加而增多,产生的弹性接触面积及最大Mises弹性应变要明显大于20MnV；塑性接触面积及最大Mises塑性应变相对减小。弹性变形能力的增强和塑性应变的减小可以使TiNi合金缓解外部的冲击并能够在磨损过程中抵抗较多的循环栽荷，从而表现出良好的耐磨性。     

Fe-Mn-Si-Cr-Ni形状记忆合金超弹性的研究

用拉伸实验研究了Ｆｅ－１５．２Ｍｎ－６Ｓｉ－８．３Ｃｒ－７Ｎｉ、Ｆｅ－１６Ｍｎ－５Ｓｉ－９Ｃｒ－４Ｎｉ和３１７Ｌ不锈钢的应力应变曲线。结果表明,铁基形状记忆合金存在显著的超弹性。其应力应变曲线上,卸载时的曲线和再加载时的曲线相比有明显的滞后。合金卸载时存在极大的非线性回弹εｓｂ,εｓｂ随变形量的增加而增加,而超弹性应变εＳＥ在小变形量下随变形量的增加而增加,当总变形量超过一定值时,εＳＥ不再增加。Ｆｅ－１５．２Ｍｎ－６Ｓｉ－８．３Ｃｒ－７Ｎｉ的最大超弹性应变εＳＥ可达到０．７５％。应力诱发马氏体与母相之间界面移动产生超弹性,超弹性受化学驱劝力和母相对马氏体相的弹性约束控制。热形成马氏体和母相强度对超弹性影响不大。     

形状记忆合金的本构模型

借助Tanaka用一维形核动力学方程导出的指数形式的相变分数,建立了一个新的形状记忆合金本构模型,提出承不同相变条件下可恢复形状记忆应变的表达式,考虑了材料在变形过程中马氏体的对优取向作用,克服了Tanaka系列模型不能描述材料处于完全马氏体状态时的力学行为的缺点,本模型比现有的形状记忆合金本构模型简单,其正确怀已得到实验的检验。     

Cu、Mn对TiNi合金伪弹性的影响

在不同目标载荷条件下对添加了Cu、Mn的TiNi合金进行压缩试验,研究了Cu、Mn元素的添加对其伪弹性的影响。结果表明,Cu元素不利于提高合金的伪弹性,随Cu含量的增加,合金的伪弹性降低;在一定条件下,添加了Cu、Mn两种元素的TiNi合金的伪弹性明显优于TiNi二元合金,但经过一定的压缩循环后,前者的伪弹性会突然变差。     

Pseudoelastic behaviour of a natural material is achieved via reversible changes in protein backbone conformation

The egg capsules of marine prosobranch gastropods, commonly know as whelks, function as a protective encapsulant for whelk embryos in wave-swept marine environments. The proteinaceous sheets comprising the wall of whelk egg capsules (WEC) exhibit long-range reversible extensibility with a hysteresis of up to 50 per cent, previously suggested to result from reversible changes in the structure of the constituent protein building blocks. Here, we further investigate the structural changes of the WEC biopolymer at various hierarchical levels using several different time-resolved in situ approaches. We find strong evidence in these biological polymers for a strain-induced reversible transition from an ordered conformational phase to a largely disordered one that leads to the characteristic reversible hysteretic behaviour, which is reminiscent of the pseudoelastic behaviour in some metallic alloys. On the basis of these results, we generate a simple numerical model incorporating a worm-like chain equation to explain the phase transition behaviour of the WEC at the molecular level.     

近等原子比NiTi形状记忆合金的超弹性

研究了冷拔量、热处理工艺参数对Ｔｉ４９．８％Ｎｉ合金丝材的超弹性的影响。结果表明不同冷拔量、不同退火工艺处理的丝材获得完全超弹性的温度区间、超弹性特性都不相同，获得最大超弹性应变量的处理工艺为冷拔量３９％、退火温度７２３Ｋ、保温时间３０ｍｉｎ。     

STRESS-STRAIN HYSTERESIS OF Cu-Zn-Al POLYCRYSTALLINE SMAs─Ⅱ: EXPERIMENTS AND NUMERICAL SIMULATIONS

1.IntroductionAsasmartmaterial,manyapplicationshavebeenfoundforshapelllellioryalloys(SMAs)lllz],sincethealloyscanprovidearelativelargerecoverystressandrecoverystrainuponheating.Itisimportalltinsomeapplicationstocalculatetherecoverystressandtherecoverystrainandtoestimatethetemperatllre,atwlliclltherecoverytakesplace.Tillsrequiresabetterunderstandingofthestress--strain--temperaturerelationofSMAs.Amodelhasbeenproposedl3]forthetemperature--dependentstress--strainhysteresisofSMAs.Itwasintendedt…