Nanomechanical investigations of plasticity in topologically close-packed phases at high temperatures

该项目的科学目标是全面表征金属间，拓扑紧密堆积的沉淀（TCP相）的可塑性，例如，在高合金化的高温合金中形成。它们在蠕变过程中影响漂流，并与裂纹的产生和重要合金元素的提取使基体软化而导致的寿命缩短有关。本项目第一期采用显微力学测试方法，结合扫描电镜和（高分辨率）透射电镜对微相Fe7Mo6的力学性能、变形机制和缺陷结构进行了研究。对σ相的初步研究揭示了其变形的化学计量关系。在这项工作的范围内，已经开发并实施了复杂晶体中未知滑动面的计算机辅助分析，该分析加速并扩展了对压痕周围形成的滑动痕迹的识别。此外，纳米压痕方法已经扩展到现在达到高温合金的工作温度为1000℃。基于这些结果，计划对技术相关的Fe-Mo体系中的µ、σ和Laves TCP相的变形机制、热活化和化学计量学依赖性进行完整的确定。为此，将采用纳米压痕、高温纳米压痕、纳米压痕-应变速率跳变测试、微柱压缩等微力学测试方法，并结合后续的原子尺度分析。本文将重点比较纯Laves相和μ相内Laves相层的变形机制和位错结构。已有的结果表明，在室温下，Laves三层上的微相发生了同步剪切变形。考虑复杂晶体的变形，不是基于完整的单元胞，而是基于其组成的子胞，将使分类和识别适合特定应用的复杂金属间相变得容易得多。因此，我们期望计划中的研究将影响对复杂金属间相的未来适用性和合金元素的影响的评估，例如在高温应用或作为高强度材料的增强相。

The scientific aim of this project is the comprehensive characterisation of plasticity in the intermetallic, topologically close packed precipitates (TCP phases) which form, for example, in the highly alloyed superalloys. They affect rafting during creep and are associated with a reduction in lifetime by the initiation of cracks and the softening of the matrix by extraction of important alloying elements.In the first phase of this project, the mechanical properties, deformation mechanisms and defect structure of the µ-phase Fe7Mo6 have been investigated using micromechanical test methods in combination with scanning and (high resolution) transmission electron microscopy. First investigations of the σ-phase revealed a stoichiometry dependence of its deformation. Within the scope of this work, a computer-assisted analysis for unknown glide planes in complex crystals has been developed and implemented which has accelerated and expanded the identification of slip traces formed around indentation. In addition, the nanoindentation methods was expanded to now reach the operating temperature of superalloys at 1000 °C.Based on these results, a complete determination of the deformation mechanisms, their thermal activation and dependence on stoichiometry is planned for the µ, σ und Laves TCP phases in the technically relevant Fe-Mo system. To this end, micromechanical test methods, such as nanoindentation, high temperature nanoindentation, nanoindentation-strain rate jump testing and micropillar compression will be used and combined with subsequent analysis to the atomic scale. Here, the focus will be laid on the comparison of the deformation mechanisms and dislocation structures in the pure Laves phase and the Laves phase layers within the µ-phase. The existing results have shown that at room temperature deformation of the µ-phase occurs by synchroshear on the Laves triple layers. Consideration of deformation of complex crystals based not on a complete unit cell, but rather its constituent sub-cells, would make the categorisation and identification of suitable complex intermetallic phases for defined applications much easier. We therefore expect that the planned investigations will affect the evaluation of future applicability of complex intermetallic phases and the effects of alloying elements, for example in high temperature applications or as reinforcement phases in high strength materials.