DSC ANALYSIS OF A CuZnAl TWO WAY SHAPE MEMORY ALLOY DURING AGEING

ＤＳＣＡＮＡＬＹＳＩＳＯＦＡＣｕＺｎＡｌＴＷＯＷＡＹＳＨＡＰＥＭＥＭＯＲＹＡＬＬＯＹＤＵＲＩＮＧＡＧＥＩＮＧ①ＺｈａｎｇＪｉａｎｘｉｎ，ＣａｉＷｅｉ，ＺｈａｏＬｉａｎｃｈｅｎｇＳｃｈｏｏｌｏｆＭａｔｅｒｉａｌｓＳｃｉｅｎｃｅａｎｄＥｎｇｉｎｅｒｉｎｇ...     

Ti-Ni-Cu形状记忆合金的温度记忆效应

采用差示扫描量热仪研究了Ti50Ni35Cu15以及Ti50Ni45Cu5(摩尔分数,%)形状记忆合金的温度记忆效应.结果表明:温度记忆效应仅在Ti-Ni-Cu合金的逆转变加热过程出现,在单斜结构马氏体与母相逆相变(B19'→B2)及正交结构马氏体与母相逆相变(B19→B2)过程中均能发生温度记忆效应;在随后的完全循环过程中,温度记忆记忆效应不再出现,DSC相变曲线又"恢复"到其原始形态;而在马氏体相变冷却过程中未发现温度记忆效应.分析表明,不完全相变过程中的弹性能再分布是可能的温度记忆效应机制.     

Twice reverse shape memory effect in CuZnAl shape memory alloy

The variations of the shape memory effects in the Cu-13Zn-15Al(mole fraction, %) alloy upon successive heating (the rate of heating is 5℃/min) have been studied by means of ρ-T curve , shape memory effect measurement, optical metallographical observation and X-ray diffraction. The first abnormal reverse shape memory effect occurs when the tested alloy is heated to the temperature below 320℃ ; when it is heated to the temperature between 320℃ and 450℃, the forward shape memory effect occurs; in the two stages, the shape of the sample remains the same as that in the furnace when it is taken out from the furnace and air-cooled; when the tested alloy is heated to the temperature above 450℃, the shape of the sample remains unchanged during heating, but the second reverse shape memory effect occurs after it is air-quenched.     

Effect of chemical component on shape memory effect of Fe-Mn-Si-Ni-C-RE shape memory alloy

Effect of chemical component on shape memory effect (SME) of Fe-Mn-Si-Ni-C-RE shape memory alloys was studied by bent measurement, thermal cycle training, SEM etc. Results of study indicate that the alloys with high Mn content (25%) appeare better SME, especially in lower strain. SME improves evidently when Si is higher content, especially it's range from 3% up to 4%. But brittleness of Fe-Mn-Si-Ni-C-RE alloy increases by increasing the Si content. SME of the alloy is weakening gradually as carbon content increases under small strain (3%). But in the condition of large strain (above 6%), SME of the alloy whose carbon content ranges from 0.1 % to 0.12% shows small decreasing range, especially of alloy with the addition of compound RE.     

应力制约双程形状记忆材料的相交特性

利用应力对双程形状记忆(TWSM)材料相变的制约作用,在NiTi合金TWSM材料中实现速动相变和速动TWSM效应。研究了应力场的形式、大小对热滞回线的影响;计算了相变驱动力ΔG_c随温度变化的关系并给出速动相变的热力学解释。     

DSC study on temperature memory effect of NiTi shape memory alloy

A systematic study on the temperature memory effect （TME） in a polycrystalline NiTi shape memory alloy was presented. The investigation was carded out through a series of differential scanning calorimeter （DSC） tests. Two types of tests were conducted, namely single-step test and multi-step test. The influence of the step temperature on the peak/trough temperatures in the subsequent heating process and the associated energy absorption/release in the phase transformations was investigated. Using a simple theoretical model, the exact mechanism behind TME was studied.     

Cu-11.19Al-6.43Mn合金的形状记忆效应

测试了Ｃｕ－１１．１９Ａｌ－６．４３Ｍｎ合金的形状记忆效应,研究了预变形程度、恢复温度和训练次数对该合金的单向和双向形状记忆效应的影响。结果表明：该合金有一个能完全恢复的最大预变形程度εｍ,它随恢复温度的提高而增大,其最大值约为４．５％;合金的双向记忆效应随训练次数增加而增大。在适当的训练次数和训练温度下,其最大的冷却和加热时的开头恢复量之比值约为３０％。     

Two-way shape memory effect and its stability in Ti-Ni-Hf high temperature shape memory alloy

The two-way shape memory effect(TWSME) in a Ti36 Ni49 Hf15 high temperature shape memory alloy (SMA) was systematically studied by bending tests. In the TiNiHf alloy, the martensite deformation is an effective method to get two-way shape memory effect even with a small deformation strain. The results indicate that the internal stress field formed by the bending deformation is in the direction of the preferentially oriented martensite variants formed during the bending deformation. Upon cooling the preferentially oriented martensite variants form under such an oriented stress field, which should be responsible for the generation of the two-way shape memory effect.Proper training process benefits the formation of the oriented stress field, resulting in the improvement of the twoway shape memory effect. A maximum TWSME of 0.88% is obtained in the present alloy.     

单向,双向记忆合金的相变热测定

用ＤＳＣ－７研究了ＣｕＺｎＡｌ单向，双向记忆合金相变潜热，发现：单向，双向记忆合金相变过程的ＤＳＣ曲线形状各异，单向记忆合金的ＤＳＣ曲线为犬牙状，有多个峰；而双向记忆合金的ＤＳＣ曲线只有一个峰。在相变大小上，单向记忆合金的相变热比双向记忆合金约大１／４。     

热处理及训练对NiTi形状记忆合金弹簧双向记忆效应的影响

形状记忆合金作为双驱动元件时通常是与一偏压元件同时使用来实现双程驱动。本文通过不同热处理制度对TiNi形状记忆合金的弹簧相变点和形状恢复率的影响以及训练次数对形状恢复率的影响研究，以期获得性能良好的双向记忆合金弹簧单独作为双向驱动元件的最佳处理条件。结果表明在450℃热处理并经过20次训练得到的TiNi形状记忆合金弹簧是最优的。     

Factors affecting the generation of stress-assisted two-way memory effect in NiTi shape memory alloy

The combined effects of martensite pre-deformation and constrained stress on the generation of stress-assisted two-way memory effect (SATWME) were studied. Particular attention was paid to the generation of internal stress during thermal cycling under constant stress. The result highlights that the maximum SATWME is not determined solely by the maximum internal stress developed. The SATWME strain when subjected to 18% martensite pre-strain coincides, independently of constrained stress applied and internal stress developed. This study also provides experimental evidence that when under 400 MPa constrained stress the maximum SATWME shifts toward higher pre-deformation amplitude and this phenomenon is comparable to the increased cold-work. The results further suggest that the mechanism that associates with the change of M_s temperature plays critical role in determining the SATWME.     

热循环对Fe-Mn-Si-Cr-Ni合金形状记忆效应的影响

采用电阻法和OM等手段研究了不同温度区间的热循环对Fe-14Mn-5.5Si-8Cr-5Ni合金微观组织和形状记忆效应的影响。结果表明:298 K～353 K、520 K、773 K和77 K～773 K热循环1次后,合金形状回复率均大幅度提高;298～773 K循环5次后的形状回复率提高了26%,77～773 K热循环5次后的形状回复率提高了36%。热循环显著减少了因淬火热应力导致的热诱发ε马氏体量,并且热诱发ε马氏体的逆转变向基体引入了大量的堆垛层错。与固溶态相比,热循环后再变形不仅使α’马氏体的数量显著减少,而且应力诱发ε马氏体以区域化的方式形成,因而合金的形状记忆效应显著提高。77～773 K的热循环比298～773 K的热循环更能显著提高合金形状记忆效应的原因是由于其引入了更多的堆垛层错。     

退火温度对淬火态Fe-Mn-Si-Cr-Ni合金记忆效应的影响

研究了退火温度对淬火态预先存在热诱发ε马氏体的Fe-14Mn-5.5Si-8.0Cr-5.0Ni合金和无热诱发ε马氏体的Fe-19Mn-5.0Si-8.0Cr-6.0Ni合金记忆效应的影响。结果表明:预先存在热马氏体合金的形状回复率随退火温度的升高,先上升后下降,在500℃附近达到最大值。但无热马氏体存在合金的形状回复率随退火温度的变化却相反,在500℃附近达到最小值;两种合金的Ms温度都随退火温度的升高而下降,在500℃附近达到最低。预先存在热马氏体的合金由于退火后Ms温度的降低,减少了热诱发的马氏体量,因而形状记忆效应得到了提高;而无热马氏体存在的合金由于退火后Ms温度的进一步下降,使得应力诱发马氏体转变更不容易发生,因此形状记忆效应反而下降。     

Influence of process factors on shape memory effect of CuZnAl alloys

1Introduction CuZnAl shape memory alloy(SMA),characterized by low cost and high processing performance,has been studied comprehensively and has developed rapidly in recent years.Since the fundamental problems of large grain and martensitic stabilization w…     

TRANSFORMATION CHARACTERISTIC OF TWO WAY SHAPE MEMORY MATERIAL CONSTRAINED BY STRESS

The snap-acting transition and two way shape memory (TWSM) effect have been obtainedin a TWSM spring made of Ni51Ti49 alloy using the constrained effect of stress on drivingforce of TWSM material.When the snap-acting transition has been realized:M_s= M_f andA_s=A_f;hysteresis is rectangular,the height (TWSM effect) and width (hysteresis) of therectangle can be readjusted by means of constrained stress.The results of resistancemeasurments show that,the snap-acting TWSM effect mentioned above was supplied mainlyfrom the transformation of P←→R.The thermodynamic model has also been proposed to ac-count for the snap-acting transformation.     

深冷处理对Ni-Ti合金形状记忆效应的影响

用退火、DSC、XRD、深冷处理及机械训练等方法,对Ni(50.62%)Ti(49.38%)合金的显微组织、相变温度、相组成、形状回复率进行研究,探索提高该合金形状记忆效应的新方法。结果表明,该合金Ms点为-2℃,As点为22℃;退火态Ni-Ti合金主要由奥氏体及少量粒状的Ti3Ni4相组成;用液氮与乙醇经不同比例混合配制成的介质进行深冷处理,随着深冷温度的降低,合金的形状回复率增大;随着训练次数的增加,其回复率曲线呈抛物线状;该合金在3次机械训练-196℃深冷时回复率最好,为51.27%。     

Effect of heat treatment on the transformation behavior and temperature memory effect in TiNiCu wires

The effect of heat treatment on the phase transformation behavior of TiNiCu shape memory alloy wires and the temperature memory effect in this alloy were investigated by the resistance method. These results showed that with increasing annealing temperature and annealing time, the phase transformation temperatures of TiNiCu wires were shifted to higher temperatures in the heating and cooling process. It was also found that incomplete thermal cycles, upon heating the TiNiCu wires, which were arrested at a temperature between the start and finish tem-peratures of the reverse martensite transformation, could induce a kinetic stop in the next complete thermal cycle. The kinetic stop tempera-ture was closely related to the previous arrested temperature. This phenomenon was defined as the temperature memory effect. The result of this study was consistent with the previous report on the phenomenon obtained using the differential scanning calorimetry method, indicating that temperature memory effect was a common phenomenon in shape memory alloys.     

Martensitic transition and shape memory effect of Ti-Zr-Mo series alloys

Development of shape memory alloys is always one of the most important directions for functional Ti alloys. The Ti-Zr-Mo series alloys with various Mo contents were prepared. The main aim of the current work is to investigate the effects of Mo on martensitic transition and shape memory effect of Ti-Zr alloy. The X-ray diffraction and transmission electron microscope results indicate that the phase constitution of the examined alloys is greatly dependent on Mo content. The Ti-Zr-Mo alloy with 2 wt% Mo is composed mainly of α′ martensite and a few β phase. As the Mo content increased to 4 wt%, the Ti-50Zr-4Mo alloy consists of α″ martensite and β phase. As the Mo content further increased to 8 wt%, the alloy consists mainly β phase and a barely detectable amount of α″ martensite. Thermal analysis shows that the reverse martensitic transition temperature of the examined alloys decreases with the increasing of Mo. The reverse martensitic transition start, A_s, temperature is approximately 584 °C for Ti-50Zr-2Mo alloy and 519 °C for Ti-50Zr-4Mo, respectively. And the martensitic transition start, M_s, temperature is approximately 553 °C and 501 °C for that two alloys, respectively. But no obvious exothermic and/or endothermic peak can be observed in DSC curve of Ti-50Zr-8Mo alloy. Furthermore, the effect of Mo content on shape memory recovery ratio, η, of the examined alloys was also investigated. Results show that the η first increases and then decreases with the increasing of Mo. The alloy with 4 wt% Mo has the maximum η approximately 13.8%. The influencing mechanism of Mo content on shape memory effect of the examined alloys was also discussed. This findings not only supplied a series of shape memory TiZr-based alloys, but also enriched and deepened the theory of shape memory effect.     

激冷Ti-46Ni合金薄带的组织、相变和形状记忆效应

用激冷甩带法制备了Ti-46Ni合金薄带,用扫描电子显微镜、X射线衍射仪、示差扫描热分析仪和弯曲试验研究了合金薄带的组织特征、相变行为和形状记忆效应。结果表明,铸态及400~600℃退火态Ti-46Ni合金薄带的显微组织形态呈树枝状,晶粒细小,由B19?马氏体和B2母相组成;在冷却、加热过程中,该合金薄带发生一阶段马氏体相变;铸态和退火态Ti-46Ni合金薄带均具有良好的形状记忆效应。