Ni-Mn-In-Al合金的马氏体相变及预相变研究

发布时间：2018-10-10 11:04

【摘要】：Ni-Mn-Z(Z=In,Sn,Sb)是一类新型的铁磁形状记忆合金,近年来备受关注。和传统的Ni-Mn-Ga合金相比,该类合金高温奥氏体相和低温马氏体相之间具有较大的磁矩差,表现出较强的磁弹耦合和磁场驱动逆马氏体相变特性,因此在其马氏体相变温度附近呈现出有趣的物理效应,如形状记忆效应,磁电阻效应和磁卡效应等。通过施加压力改变Mn-Mn间距是调节合金马氏体相变温度的一种有效方法,这里的压力可以是外压力也可以通过小半径元素替代实现。本文中,我们通过利用小半径的Al替代Ni50Mn34In16合金中的In,制备了Ni50Mn34In16-xAlx(x=0.5,1)系类合金。研究结果表明替代之后马氏体相变温度逐渐升高,同时由于磁弹耦合作用的增强,在Ni50Mn34In15.5Al0.5合金马氏体相变温度之前,观察到预马氏体相变行为。具体研究内容如下:1)Ni50Mn34In15.5AI0.5合金的预马氏体相变研究预马氏体相是存在于奥氏体和马氏体相之间的中间相,它具有近立方结构,可以视为奥氏体相的微调制结构,该现象在Ni-Mn-Ga合金中已经被广泛研究。大量研究表明,其来源于磁弹耦合作用。然而由于预马氏体相变过程温度范围较窄,磁矩差较小,有关于其物理效应很少被报道。近期研究表明,热压合成的Ni43Mn41Co5Sn11具有中间相变行为。在Ni50Mn34In15.5Al0.5合金中,A1的掺杂产生内压力,也将大大提高了合金的磁弹耦合作用。电输运,热学和磁性测量表明,样品表现出两步连续的结构/磁相变,即在马氏体相变之前,出现明显的中间相变行为,其一级相变行为可以由热滞和磁滞体现。我们利用光学显微镜对其微结构进行变温原位观察,进一步证实了低温马氏体条纹出现之前的微结构调制,即预马氏体相的存在。Ni50Mn34In15.5Al0.5合金预马氏体相变过程具有较大的磁矩差,因此施加外磁场可以降低预马氏体相变温度,说明预马氏体相的出现可以归结于磁弹耦合作用。磁场驱动逆预马氏体相变将产生较大的磁电阻,同时也会通过提高磁熵峰值和宽度来提高磁卡效应。2)Ni50Mn34In15Al合金中近室温的磁电阻和磁卡效应目前较少的Ni-Mn基合金在室温附近同时具有大的磁电阻和磁卡效应。Ni50Mn34In16Al合金在室温附近具有一级马氏体相变和奥氏体相的二级磁相变,且马氏体相变过程中具有大的磁矩差和较小的热滞。测量结果表明,50 kOe磁场作用下,Ni50Mn34In16Al合金在室温附近不仅具有较大的磁电阻(峰值为-58%),而且具有大的连续磁熵变,对应一级相变和二级相变的峰值分别为21 J/Kg K和-8.2 J/Kg K。同时,由于较小的磁滞损失,一级相变具有和二级相变数值相当的有效制冷能力,达到150 J/Kg。
[Abstract]:Ni-Mn-Z is a new type of ferromagnetic shape memory alloy, which has attracted much attention in recent years. Compared with the traditional Ni-Mn-Ga alloy, the magnetic moment difference between the austenitic phase at high temperature and the martensite phase at low temperature in this kind of alloy shows strong magnetoelastic coupling and magnetic field driven inverse martensite transformation. Therefore, there are some interesting physical effects near the martensitic transformation temperature, such as shape memory effect, magnetoresistance effect and magnetic card effect. Changing the Mn-Mn spacing by applying pressure is an effective method to adjust the martensitic transformation temperature of the alloy. The pressure can be either external pressure or small radius element substitution. In this paper, we have prepared Ni50Mn34In16-xAlx (x0. 5)-like alloys by using small radius Al instead of In, in Ni50Mn34In16 alloys. The results show that the martensite transformation temperature increases gradually after substitution and the pre-martensite transformation behavior is observed before the martensite transformation temperature of Ni50Mn34In15.5Al0.5 alloy due to the enhancement of magnetoelastic coupling. Study on Premartensite Transformation of Ni50Mn34In15.5AI0.5 Alloy; the premartensite phase is a mesophase between austenite and martensite, which has a near-cubic structure and can be regarded as a micromodulation structure of the austenitic phase. This phenomenon has been widely studied in Ni-Mn-Ga alloys. A large number of studies show that it comes from magnetoelastic coupling. However, due to the narrower temperature range and the smaller magnetic moment difference in the premartensite transformation process, the physical effects of premartensite transformation are rarely reported. Recent studies have shown that Ni43Mn41Co5Sn11 synthesized by hot pressing has intermediate phase transition behavior. The magnetoelastic coupling of Ni50Mn34In15.5Al0.5 alloy is also greatly enhanced by the internal pressure produced by doping of Al in the alloy. Electrical transport, thermal and magnetic measurements show that the sample exhibits a two-step continuous structural / magnetic phase transition, i.e., the intermediate phase transition behavior is obvious before martensitic transformation, and the first-order transformation behavior can be reflected by thermal hysteresis and magnetic hysteresis. The microstructure of the alloy was observed by optical microscope at varying temperature in situ. It is further proved that the microstructure modulation before the appearance of martensite stripe at low temperature, that is, the existence of premartensite phase. Ni50Mn34In15.5Al0.5 alloy has great magnetic moment difference in the process of pre-martensite transformation. Therefore, the temperature of premartensite transformation can be reduced by applying external magnetic field, which indicates that the appearance of premartensite phase can be attributed to the magnetoelastic coupling. The magnetic field drive inverse martensite transformation will produce larger magnetoresistance. At the same time, the magnetoresistance and magnetic card effect near room temperature in Ni50Mn34In15Al alloy will be increased by increasing the peak and width of magnetic entropy.) the magnetoresistance and magnetic card effect of Ni-Mn base alloy near room temperature will also be increased. Ni50Mn34In16Al alloy has high magnetoresistance and magnetic card effect near room temperature. There are first order martensite transformation and secondary magnetic transformation of austenite phase near room temperature. In the process of martensitic transformation, the magnetic moment difference and the thermal lag are large. The measured results show that the Ni _ (50) mn _ (34) in _ (16) Al alloy has not only a large magnetoresistance (peak value of -58%) but also a large continuous magnetic entropy change at room temperature under the action of a magnetic field of 50 kOe. The corresponding peak values of first-order and second-order phase transitions are 21 J/Kg K and -8.2 J/Kg K, respectively. At the same time, due to the small hysteresis loss, the first-order phase transition has the same effective refrigeration capacity as the second-order phase transition value, reaching 150 J / Kg.
【学位授予单位】：湖北大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TG139.6

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