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A unique three-stage transformation behaviour on cooling has been observed in a Ti-50.2 at% Ni alloy after a low temperature
ageing treatment. The cooling transformation in the aged alloy occurred as a three-stage process of austenite-to-R phase transition
followed by two separate martensitic transformations. The R phase transition developed during ageing with a clear second order
nature initially and gradually evolved into a predominantly first order process. The occurrence of the R transition is not
associated with a decrease in the martensitic transformation temperature during ageing. The reverse transformation to austenite
occurred in one step, regardless of the nature of the forward transformation on cooling. An all-round shape memory effect
was observed in aged samples. These experimental observations suggest that precipitation induced by the ageing treatment is
responsible for the unusual transformation behaviour.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
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In a CuZnAl alloy containing 2.2 wt% of nickel it was found that due to alloy quenching and low temperature ageing, precipitation of NiAl disperse particles takes place resulting in raising of martensitic transformation characteristic temperatures. The ease with which this phase precipitates indicates the low thermal stability of this alloy. At the same time the process of precipitation of NiAl particles offers an opportunity for control of shape recovery temperature by varying quenching temperature, cooling rate and especially ageing time, since variations of characteristic temperatures as a function of ageing time can be expressed by the relation T=At
0.5. It was also ascertained that the two way shape memory effect, as opposed to the one-way effect, is sensitive to processes associated with alloy ageing and also matrix phase transition in the bainite. 相似文献
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ABSTRACTThe two-way shape memory effect in NiTi shape memory alloys is identified according to the evolution of the apparent modulus of the martensite during mechanical cycling. The microstrain and texture index of the NiTi samples are evaluated with synchrotron data to relate the evolution to the changes in the NiTi microstructure caused by mechanical cycling. The results show that a progressive decrease in the apparent modulus of the martensite during load, together with an increase in the apparent modulus of the reoriented martensite, are a sign that the NiTi sample is developing the two-way memory effect by mechanical cycling. When the two moduli show the same value, the two-way shape memory effect is fully developed in the NiTi alloy.This paper is part of a thematic issue on Titanium. 相似文献
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研究了电脉冲时效对Fe14Mn6Si8Cr5Ni合金微观组织及形状记忆效应的影响。研究结果表明预变形后的合金经电脉冲时效其形状记忆效应提高幅度比不预变形合金电脉冲时效幅度大。10%拉伸预变形合金经电脉冲时效1s,其形状回复率便提高到(70.3±1.0)%;时效300s,其形状回复率提高到(87.5±1.0)%,比固溶态合金提高了82.3%,而不预变形直接电脉冲时效合金只比固溶态合金提高了22.3%。经金相和TEM分析,预变形后电脉冲时效的合金中已无热诱发ε马氏体出现,这使得基体奥氏体增多;同时电脉冲能促使预变形时引入的空位和位错迅速崩塌形成层错。正是这两方面的原因使得预变形后电脉冲时效能迅速地提高合金的形状记忆效应。 相似文献
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The effect of thermal cycling under loading on martensitic transformation and two-way shape memory effect was investigated for Ti-49.8 at, pet Ni alloy. It is shown that M-s, and M-f temperature increase with increasing the number of cycles, while A(s) and A(f) temperature decrease during thermal cycling. The total strain at and permanent strain epsilon (p) increase with increasing applied stress and number of cycles. The two-way shape memory effect can be improved by proper thermal cycling training under loading, while excessively high applied stress results in the deterioration of TWSME. The reason for the changes in martensitic transformation characteristics and two-way shape memory effect during thermal cycling under loading is discussed based on the analysis of microstructure by TEM observations. 相似文献
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XianglongMENG WeiCAI K.T.LAU L.M.ZHOU LianchengZHAO 《材料科学技术学报》2003,19(6):590-592
The Effect of the thermal cycling training under constant strain on the two-way shape memory effect (TWSME) in a Ti36Ni49Hfl5 high temperature shape memory alloy (SMA) has been investigated by bending tests. The results indicated that the training procedure is beneficial to get the better TWSME. The two-way shape memory strain increases with increasing the training strain. And it decreases with increasing the training temperature. The TWSME obtained in the present alloy shows poorer stability compared with that obtained in the TiNi alloys. 相似文献
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V Seetharaman 《Bulletin of Materials Science》1984,6(4):703-716
The influence of applied stresses and imposed plastic deformation on the martensitic transformation of a parent phase is described.
Changes in mechanical properties such as flow stress, work hardening rate, fracture toughness, etc brought about by strain-induced
martensitic transformation are briefly examined. In the absence of appreciable dislocation glide, atomic displacements associated
with glissile boundaries are highly ordered and reversible modes of (plastic or nonlinear pseudoelastic) deformation. Such
processes lead to large strains and are encountered in deformation twinning, martensitic transformations and in the reorientation
of martensite units. The reversibility leads to phenomena such as elastic twinning, thermoelastic martensites, superelasticity,
shape memory and two-way shape memory effects, and rubber-like behaviour. These are discussed using a unified approach based
on thermoelastic equilibrium. The shape memory effect suggests several potential applications of the martensitic transformations
in non-ferrous alloys in which the effect is most commonly observed. Recent developments in this area are reviewed with special
reference to the prerequisites for the effect and the influence of metallurgical processing on the extent of shape recovery. 相似文献
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为了进一步提高Fe-14Mn-6Si-8Cr-5Ni合金的形状记忆效应,对固溶态合金采用了形变时效的方法处理,并利用光学显微分析、X射线衍射分析和透射电子显微分析的测试手段分析了时效温度和时效时间对合金形状回复率和相变温度的影响.结果表明,固溶态合金经10%拉伸和600℃时效10 min时,形状回复率提高幅度最大,由固溶态的48%提高到84.7%,并且合金γ→ε马氏体转变的起始温度Ms由固溶态的34℃降低到13.2℃.合金的形状回复率得到提高的主要原因是合金中热诱发ε马氏体已经消失,组织为奥氏体和大量定向α’马氏体,这样的组织特征有利于应力诱发γ→ε马氏体相变以及它们的逆相变. 相似文献
11.
Adam T. Clare Paul R. Chalker Sean Davies Christopher J. Sutcliffe Sozos Tsopanos 《International Journal of Mechanics and Materials in Design》2008,4(2):181-187
Selective laser melting has been used to build high aspect ratio, three-dimensional NiTi micro-electro-mechanical components.
Cantilever beams manufactured in this way have been two-way trained and actuated by ohmic heating demonstrating the suitability
of the process for applications in micro-electromechanical technologies. The influence of laser dwell time and raster pitch
on the density of NiTi shape memory alloy parts and the resolvable feature sizes achievable are discussed. The shape memory
effect properties of solid parts produced by selective laser melting are also reported in contrast to those properties exhibited
by NiTi alloys resulting from other processes. 相似文献
12.
材料辐照效应是入射粒子与物质交互作用造成的物质微观组织结构与宏观性能的变化。辐照效应不仅是改善材料表面性能的重要手段,而且也是特殊环境应用材料可靠性评价的重要组成部分。TiNi基形状记忆合金是一种重要的金属智能材料,具有独特的形状记忆效应和超弹性,已在卫星、空间站等航天器以及生物医学中广泛应用。本文阐述了Ti-Ni基形状记忆合金在空间粒子(质子、电子)以及离子辐照改性的研究进展,辐照效应会对TiNi合金的微观组织结构产生影响,进而改变合金的相变行为和力学行为。然而目前关于TiNi基合金的辐照效应的研究仍处于起步阶段,组织结构和相变行为的变化规律和机理还未研究清楚,有关形状记忆效应的研究较少,仍需深入研究辐照参数、组织结构、相变行为和功能特性之间的内在联系。 相似文献
13.
The effect of ageing on the microstructure, mechanical properties and shape memory effect (SME) in a newly developed Fe-24Mn-5Si-8Co-4Mo shape memory alloy has been studied. It was found that Fe2Mo particles precipitate during ageing and thereby increase hardness and strength of the alloy The SME of the alloy can be remarkably improved by ageing and a maximum SME can be obtained when aged at 873 K. When the ageing temperature is over 873 K, the SME decreases with increasing ageing temperature. The reason for the improvement of SME by ageing in the Fe-Mn-Si-Co-Mo alloy is discussed 相似文献
14.
CuAlBeCr形状记忆合金组织结构与形状记忆效应的研究 总被引:3,自引:0,他引:3
本文研究了热处理制度对含微量Cr的CuAlBe合金的马氏体逆转变及形状记忆效应的影响,并通过正电子湮没Doppler增宽线性参数的测量及金相组织和相结构分析,探讨了组织结构与记忆效应间的内在联系。结果表明,分级淬火态的CuAlBeCr合金具有相对最好的记忆性能(逆变起始温度低,恢复率大),而直接淬火的记忆性能最差。合金中空位型晶体缺陷的浓度显著影响马氏体逆转变开始的温度,空位浓度愈低,则马氏体逆转变开始的温度愈低,所研究的CuAlBeCr合金逆转变完成的区间宽(逆转变终了温度A′_f≈200℃),但该类合金在较高的温度下(≈400℃)具有比CuZnAl合金更好的记忆效应(逆转变动作快,恢复率大)。 相似文献
15.
The transformation sequence and hardening effects of 400 °C aged Ti47.5Ni50.65Al1.85 and Ti49.5Ni50.13Al0.37 shape memory
alloys have been investigated by electrical resistivity tests, internal friction measurements, hardness tests and TEM observations.
Both solution hardening and precipitation hardening are found to occur in these alloys. The hardening effects of Ti47.5Ni50.65Al1.85
alloy are obvious and much higher than those of Ti49.5Ni50.13Al0.37 alloy due to the former having the larger Ni/Ti ratio
and a higher Al solute content in its matrix. The transformation sequence of 400 °C aged Ti47.5Ni50.65Al1.85 alloy shows B2↔R-phase
only for an ageing time of more than 10 h and that of 400°C aged Ti49.5Ni50.13Al0.37 alloy shows the sequence B2↔R-phase↔B19′
or B2↔R-phase with different ageing times. All of these characteristics are associated with Ti11Ni14 precipitates during the
ageing process. These aged Ti–Ni–Al alloys exhibit very good shape memory effects, in which the maximal shape recovery occurs
at the peak of hardness.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
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In the present work, effect of precipitation on two-way shape memory effect and deformation induced martensite stabilization of Ti50Ni25Cu25 ribbon was investigated. The two-way shape memory effect developed as a result of martensite deformation is affected by formation of precipitates. After straining martensite to 5.5%, a two-way shape memory strain of 1.25% was obtained in a sample annealed at 800 °C for 300 s that does not introduce B11 precipitates. Results also show that the deformed Ti50Ni25Cu25 ribbon containing precipitates has multiple-stage transformation characteristics during the first heating. 相似文献
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Sergey A. Egorov Margarita E. Evard Alexandre E. Volkov 《Computational Materials Science》2000,19(1-4):77-80
Simultaneous measurements of electrical resistivity and inelastic strain accumulation in Ti–49.5 at.% Ni undergoing a two-step B2→R→B19′ martensitic transformation were performed. To exclude the influence of specimen size changes during the deformation all experiments were made in torsion. It was detected that noticeable part of strain recovery after heating under a stress and active deformation in martensitic state takes place before the start of the reverse transformation and is obviously connected with twinning. At the same time the two-way shape memory effects are caused by the martensitic transformation. The obtained data may be useful for adequate modelling of mechanical properties of the shape memory alloys because allow to connect the macroscopic parameters with microscopic physical processes. 相似文献
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F. X. Gil J. M. Manero J. A. Planell 《Journal of materials science. Materials in medicine》1996,7(7):403-406
NiTi shape memory alloys showing pseudoelastic behaviour have great potential in dental and orthopaedic applications where constant correcting loads may be required. In most of the clinical applications the device may have been heat treated and during its life in service it will be cyclically deformed. It is therefore important to investigate the effect of cyclic straining and heat treatments upon the transformation stresses and temperatures of the material. The aim of this work is to study the thermal and mechanical ageing of a pseudoelastic NiTi shape memory alloy, as well as the environmental in vitro degradation of the alloy due to the effect of artificial saliva.This paper was accepted for publication after the 1995 Conference of the European Society of Biomaterials, Oporto, Portugal, 10–13 September. 相似文献