On the role of precipitates and lattice defects in the martensitic transformation of high temperature shape memory alloys (HT SMAs)

TP2项目的科学目标是解释高温形状记忆合金（HT SMAs）的显微组织与马氏体相变之间的关系。利用透射电子显微镜（TEM）研究局部合金化学和晶体学的影响，包括点缺陷、位错和析出物。研究将首先集中在有前途的多晶ti基合金Ti80Ta20和Ti75Ta20Al5（行为体合金）以及Co-Ni-Ga（行为体合金和伪弹性SMA）。随后的研究还将涉及优化的三元和四元Ti-Ta（-X-Y）合金。TP2采用先进的瞬变电磁法研究初等相变和变形过程。加工过程中的显微组织演变将被记录（铸锭冶金：熔化和成型，薄膜技术：溅射和热处理）。特别强调的是在机械和热形状记忆效应（功能疲劳）的反复利用过程中微观结构的演变。TP2项目已达到科学目标。首先，它的目的是有助于更好地理解合金化学和晶体学的作用，包括点缺陷的重要性。其次，研究位错塑性与马氏体相变的相互作用。第三，研究沉淀过程对后续马氏体相变的影响。高温氧化是一个新兴的研究课题。这包括氧化层的形成和合金靠近氧化物的表面区域的演变。表面层合金成分的变化对马氏体相变的影响也将受到关注。这些方面对于高温sma的薄膜应用特别重要，高温氧化可以抑制形状记忆效应。TP2的研究结果将直接促进强健和耐损伤的HT sma的发展。

The scientific objective of project TP2 is to explain the relation between microstructure and martensitic phase transformations in high temperature shape memory alloys (HT SMAs). The effects of local alloy chemistry and crystallography including point defects, dislocations and precipitates will be studied using transmission electron microscopy (TEM). Research will first focus on the promising polycrystalline Ti-based alloys Ti80Ta20 and Ti75Ta20Al5 (actor alloys) as well as on Co-Ni-Ga (actor alloy and pseudoelastic SMA). Later the investigations will also address optimized ternary and quarternary Ti-Ta(-X-Y) alloys. TP2 uses advanced TEM to study elementary transformation and deformation processes. The microstructural evolution during processing will be documented (ingot metallurgy: melting and forming, thin film technology: sputtering and heat treatment). Special emphasis will be placed on the evolution of the microstructure during the repeated exploitation of the mechanical and thermal shape memory effects (functional fatigue). Project TP2 has for scientific objectives. First, it aims at contributing to a better understanding of the role of alloy chemistry and crystallography including the importance of point defects. Second, the interaction of dislocation plasticity and martensitic transformations will be studied. Third, the influence of precipitation processes on subsequent martensitic transformations will be investigated. As a new topic, high temperature oxidation will be addressed. This includes the formation of oxide layers and the evolution of surface zones of the alloy next to the oxide. The role of the evolving surface layer alloy compositions on the martensitic transformations will also receive attention. These aspects are of particular importance for thin film applications of HT SMAs, where high temperature oxidation can suppress the shape memory effects. TP2 results will directly contribute to the development of robust and damage tolerant HT SMAs.