Influence of microstructure on the flow behaviour of metallic materials inside micro- and nanocavities - Nanoimprinting

本课题研究了金属在微、纳米空腔内的塑性流动行为。该提案的概念是基于纳米压印方法，在这里应用于金属。在纳米压印过程中，一个带空腔的平面冲孔金刚石被压在金属上，空腔内的塑性流动过程导致表面结构。该科学项目关注的是在印记过程中单个或多个颗粒如何在小尺度腔内流动。我们的目标是使用基于实验和模拟的多长度尺度方法来研究流动过程如何依赖于成形工具的尺寸以及材料的晶粒尺寸。通过系统地利用材料的晶粒尺寸、膜厚和加工硬化行为的变化以及不同的空腔刀具尺寸，为控制不同长度尺度下的流动行为奠定科学基础。从纳米晶薄涂层到细晶大块金属，广泛的晶粒尺寸和薄膜厚度正在被考虑。利用电镜分析了导致挤压材料形成的变形机制（位错运动、亚晶形成、应变梯度、晶界滑动、晶粒旋转）以及挤压高度。电镜内的原位变形实验与有限元模拟相结合，将为塑性机理的研究提供新的思路。对不同长度尺度和不同晶粒尺寸与空腔尺寸比例下的变形机制进行详细分析，将用于开发微流过程的变形机制图。研究结果可以为金属成形工艺在表面结构或微部件成形领域的应用提供重要的新见解。

Within this project the plastic flow behavior of metals inside micro- and nanocavities is studied. The concept of the proposal is based on nanoimprinting methods, which are applied here to metals. During nanoimprinting a flat punch diamond with cavities is pressed onto the metal and plastic flow processes inside the cavities lead to surface structuring. The scientific program is concerned with how single or multiple grains flow inside small scale cavities during an imprinting process. We aim to use a multiple length scale approach, based on both experiments and simulations to study how the flow process depends on the size of the forming tool with respect to the grain size of the material. By using a systematic variation of grain size, film thickness and work hardening behavior of the material together with various cavity tool dimensions, it is envisaged to lay the scientific basis for controlling the flow behavior at different length scales. Starting from nanocrystalline thin coatings up to fine grained bulk metals, a wide range of grain sizes and film thicknesses is being considered. The deformation mechanism (dislocation motion, subgrain formation, strain gradients, grain boundary sliding, grain rotation) leading to the formation of the extruded material as well as the extrusion height will be analyzed by means of electron microscopy. In-situ deformation experiments inside the electron microscope together with finite element modelling will lead to new insights into the plasticity mechanism. The detailed analysis of the deformation mechanism at different length scales and for various ratios of grain size to cavity size, will be used to develop a deformation mechanism map for microflow processes. The results can give important new insights for applications in the field of surface structuring or the forming of microparts, using metal forming processes.