六角Ni2In型MM'X合金的负热膨胀效应和因瓦效应
毕业论文关键词：成分，粘接，磁性转变，马氏体结构相变，负热膨胀
Title Negative Thermal Expansion and Invar Effect in Compounds with Ni2In-Type Hexagonal Structure
Abstract MnNiGe-based compounds undergo a giant negative thermal expansion (NTE) during the martensitic structural transition from Ni2In-type hexagonal to TiNiSi-type orthorhombic structure. The optimized compositions with concurrent magnetic and structural transitions have been studied for magnetocaloric effect. However, these materials have not been considered as NTE materials partially due to the limited temperature window of phase transition. The as-cast MnNiGe-based compounds are quite brittle and naturally collapse into powders. By using a few percents(3−4%) of epoxy to bond the powders, we introduced residual stress in the bonded samples and thus realized the broadening of structural transition by utilizing the specific characteristics of lattice softening enforced by the stress.Then we studied their properties by differential scanning calorimetry (DSC),vibrating sample magnetometry (VSM), X-ray diffraction (XRD), scanning electron microscope(SEM) and thermomechanical analysis (TMA).As a result, giant NTE has been achieved. For example, the average α as much as −432×10-6 /K with an operating temperature window as wide as 109 K from 153 to 262 K has been observed in a bonded MnNiGe compound. These novel NTE behaviors exceed the performance of most other materials reported previously. In the future, we should make more research about these materials.
Keywords： component， bonded,the change of magnetic entropy， structural trasition， negative thermal expansion.
目次
1引言（或绪论）2
1.1MM'X合金2
1.2MnNiGe基合金简介3
2热膨胀4
2.1热膨胀简介4
2.2热膨胀的本质4
2.3热膨胀系数6
2.4热料膨胀材的分类6
3负热膨胀8
3.1负热膨胀效应的机理8
3.2负膨胀材料的发展及应用10
3.3本课题的研究的内容10
4实验11
4.1实验方案11
4.2实验化学药品11
4.3实验样品的制备11
4.4实验样品的研究方法12
5实验数据及分析16
5.1实验样品的XRD图像及结果分析16
5.2实验样品的DSC曲线及结果分析17
5.3实验样品的M-T曲线及结果分析18
5.4实验样品的SEM图像及结果分析19
5.5实验样品的热膨胀曲线20
结论21
致谢22
参考文献23
1 绪论 1.1 MM'X合金 1.1.1 MM'X合金的简介 1953年,L.Castelliz 发现了一类三元金属间化合物，这类化合物都含有 3d过渡族的磁性相关元素［1］ ，而且其晶体结构均是六角 Ni2In 型。随着后来研究的不断深入，此种相关的三元金属间化合物的种类不断增加，而最终自成为一个大的体系。现在人们把相关的三元金属间化合物均称为 MM'X合金。在研究的初级阶段，研究人员主要研究了此类合金的结构和磁性等相关问题，并使用了一系列的研究方法进行表征。随着研究的不断深入，以及 Heusler合金中的形状记忆效应研究新方向的出现，研究人员对这种材料的磁相变耦合的兴趣也日益浓厚。结合以前所做的相关研究，以及使用新的仪器和研究方法的研究和表征，目前，研究人员主要针对该类材料的磁相变和磁热效应进行深入研究，从而不断挖掘该类材料在磁制冷等相关应用的潜力。 1.1.2 MM'X合金体系的晶体结构 在 MM'X 合金体系中，其结构通常为稳定的六角 Ni2In 型晶体结构。一般在所研究的体系中此三种元素配比为