Experimental and theoretical investigations of the structure and the properties of Ti-Ta-X-Y and Co-Ni-Ga-X high-temperature shape Memory alloys: Syncrotron and Neutron diffraction and atomistic modelling

Ti-Ta-X-Y 和 Co-Ni-Ga-X 高温形状记忆合金的结构和性能的实验和理论研究：同步加速器和中子衍射和原子建模

• 批准号: 222155296
• 负责人: Privatdozentin Dr. Jutta Rogal
• 金额: --
• 依托单位: Arbeitsgebiet für anorganische und biogene Geomaterialien
• 依托单位国家: 德国
• 项目类别: Research Units
• 财政年份: 2012
• 资助国家: 德国
• 起止时间: 2011-12-31 至 2019-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/222155296?language=en
• 关键词: Experimental; theoretical; investigations; structure; properties

In Subproject 3 the structure and stability of Ti-Ta based HT-SMA is investigated on an atomistic level and combined with the study of crystallographic mechanisms of the shape memory effect in Ti-Ta- and Co-Ni-Ga alloys. The obtained insights are used to identify i) Ti-Ta-based alloys and appropriate thermomechanical treatments providing stable shape memory behaviour at high Ms temperatures and ii) Co-Ni-Ga alloys with cyclic stability of superelastic strain at high temperatures. For this we combine density-functional theory calculations with high-resolution diffraction methods. Essential aspects of the 2nd funding period are the extension of the theoretical methods to ternary systems Ti-Ta-X (X=Al, Sn, Zr), a consistent treatment of finite temperatures and disordered systems, and the investigation of diffusion processes. The envisaged approaches to disordered systems and diffusion are the Special Quasirandom Structures method and the Nudged Elastic Band method, respectively. Phonon contributions to the free energy will be calculated - depending on the system - by ab initio quasiharmonic approximation or molecular dynamics simulation. The diffraction experiments determine structural parameters and phase formation processes with neutron- and synchrotron-radiation. In the 2nd funding period the experiments are expanded to cover ternary and quaternary alloys Ti-Ta-(X-Y), with X,Y = Al, Sn, Zr, according to alloy development in TP1. Combining simulations and experiment the function of alloying elements in modifying the structure and thermodynamic properties of stable or metastable phases and the kinetics of phase formation (or inhibition, respectively) is addressed. In the Ti-Ta-(X-Y)-system this relates to (i) the newly discovered nano-beta-phase and its relationship to the other beta-phases forming in the system, (ii) the omega-phase and the influence of alloying elements X,Y on its structure, stability and kinetics of its formation, and (iii) the formation of alpha-Ti coexisting with several beta-phases of different Ta-contents, which are observed in Ti-rich systems (Ti-20Ta-5Al) and in the creep experiments of TP2. Furthermore, investigations of the crystallographic characteristics of the martensitic twinning and transformation behaviour in the Ti-Ta and Co-Ni-Ga-system are performed. By diffraction we investigate the effect of advantageous microstructures for improved shape memory behaviour on the martensite variant formation and residual strain. Here, the Bamboo-structure of Co-Ni-Ga bicrystals (produced in TP5) and thermomechanical treatments of the Ti-Ta-X-Y alloys (from TP1/TP4) and Co-Ni-Ga systems (from TP5) are of special interest. TP2 carries out complementary TEM-investigations on phases and microstructures and will be supported by the theoretical insights and diffraction experiments.

在第3个中，研究了基于Ti-Ta的HT-SMA的结构和稳定性在原子水平上研究，并与Ti-Ta-和Co-Ni-GA合金中形状记忆效应的晶体学机理进行研究。所获得的见解用于识别I）基于Ti-Ta的合金和适当的热机械处理，可在高MS温度下提供稳定的形状记忆行为，ii）高温下超弹性应变的循环稳定性的Co-Ni-GA合金。为此，我们将密度功能理论计算与高分辨率衍射方法相结合。第二资金期间的基本方面是将理论方法扩展到三元系统Ti-Ta-X（X = AL，SN，ZR），对有限温度和无序系统的一致处理以及扩散过程的研究。所设想的无序系统和扩散方法分别是特殊的Quasirandom结构方法和轻度的弹性带方法。根据系统的Quasiharmonic近似或分子动力学模拟，将计算出对自由能的贡献 - 取决于系统。衍射实验确定了结构参数和相位形成过程，并具有中子和同步辐射。根据TP1的合金开发，在第二筹时期，实验扩展到覆盖三元和第四纪合金Ti-Ta-（X-Y），X，Y = Al，Sn，Zr。解决了模拟和实验在修改稳定或可稳态相的结构和热力学特性中的合金元素的功能以及相位形成的动力学（或分别抑制）。在Ti-ta-（X-Y）系统中，这与（i）新发现的纳米β相及其与系统中其他β强调的关系，（ii）omega-phase及其影响合金元素x，y在其形成的结构，稳定性和动力学上，以及（iii）α-Ti的形成，并在富含Ti-20ta中观察到不同ta的β-ti型的几个β- -5AL）和TP2的蠕变实验。此外，对Ti-Ta和Co-Ni-GA系统中马氏体孪生和转化行为的晶体学特征进行了研究。通过衍射，我们研究了有利的微观结构对改善形状记忆行为对马氏体变体形成和残余应变的影响。在这里，Co-Ni-GA双晶（在TP5中生产）和Ti-Ta-X-Y合金（来自TP1/TP4）和Co-Ni-GA系统的竹结构（来自TP5）具有特殊利益。 TP2对阶段和微观结构进行了互补的温度研究，并将得到理论见解和衍射实验的支持。