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

TP 2项目的科学目标是解释高温形状记忆合金（HT SMA）中微观结构与马氏体相变之间的关系。将使用透射电子显微镜（TEM）研究局部合金化学和晶体学（包括点缺陷、位错和沉淀物）的影响。研究将首先集中在有前途的多晶钛基合金Ti 80 Ta 20和Ti 75 Ta 20 Al 5（演员合金）以及Co-Ni-Ga（演员合金和伪弹性SMA）。稍后的研究还将解决优化的三元和四元Ti-Ta（-X-Y）合金。TP 2使用先进的TEM研究元素转变和变形过程。将记录加工过程中的微观结构演变（锭冶金：熔化和成型，薄膜技术：溅射和热处理）。特别强调将放在微观结构的演变过程中的机械和热形状记忆效应（功能疲劳）的重复利用。TP 2项目具有科学目标。首先，它旨在帮助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，位错塑性和马氏体相变的相互作用将被研究。第三，将研究沉淀过程对随后的马氏体相变的影响。高温氧化作为一个新的课题将得到解决。这包括氧化物层的形成和靠近氧化物的合金表面区域的演变。不断变化的表面层合金成分对马氏体相变的作用也将受到关注。这些方面对于HT SMA的薄膜应用特别重要，其中高温氧化可以抑制形状记忆效应。TP 2的结果将直接有助于发展强大的和损伤容限HT SMA。

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.