纳米多孔金属变形中的表面-晶界协同作用

表面与晶界间交互作用，特别是表面-晶界截交线邻近区域材料力学行为，对工程合金诸多表面相关使役行为至关重要。但如何研究该微观区域力学响应是一个极具挑战的难题。本项目拟利用脱合金腐蚀制备纳米晶纳米多孔金属，构筑一种含有大量表面与晶界以及表面-晶界截交线的宏观材料；以此为模型材料，系统研究表面、晶界及其截交线对力学性能的影响。在宏观尺度，将利用申请人发展的两个新方法，一方面精确表征晶界的引入对纳米多孔金属强度的影响规律，另一方面研究表面状态对强度等力学性能的影响并阐明表面与晶界作用。在微观尺度，将研究晶界-表面-位错间交互作用微观机制及其与材料宏观性能的关联。本项目将力学性能研究与电化学表面控制相结合，旨在深刻理解纳米尺度晶体塑性变形中的尺寸效应、表面效应、晶界效应及其间耦合关系。该研究将为理解表面敏感的工程合金使役性能提供重要信息。将表面与晶界优化结合，也有望发展出力学性能优异的新型纳米材料。

Understandings of the interactions between free surface and grain boundary, and particularly the mechanical response of the material in the vicinity of grain boundary-free surface triple junctions are vital to the understanding of many properties (such as stress corrosion cracking) of engineering materials. But it is still a challenge to experimentally study the local mechanical response in this small region. In this project, we propose to develop the nanocrystalline nanoporous metals by dealloying. This is a macroscopic material that consists of large areas of free surface and grain boundaries, and large quantity of grain boundary –free surface triple junctions. With this model material, the contribution of surface, grain boundary and the triple junctions to the mechanical properties such as strength will be systematically studied. At microscopic scale, by using two new methods developed recently by the applicant’s group, we will clarify whether and how the presence of grain boundary affect the strength of the nanoporous metals and the metal nano-ligaments, and whether and how the grain boundary affect the surface-controlled strength changes in nanoporous metals. The latter will be studied by in situ mechanical tests under electrochemical controls. At microscopic scale, the deformation mechanism of nanocrystalline nanoporous metals, particularly the grain boundary activities, the interaction of dislocations with surface and grain boundaries will be studied by structural characterizations, aiming at establishing a correlation between macroscopic mechanical response and the microscopic deformation mechanism. This study is an interdisciplinary study, which combines the mechanical studies and electrochemical surface modifications. The goal of this study is to clarify the contribution of size effect, surface effect and the grain boundary to the deformation of nanoscale crystals. It will provide clues to the understanding of a variety of mechanical properties of engineering materials. Furthermore, it is expected that by combining free surfaces and grain boundaries, this study will lead to new nanostructured materials with exceptional high strength and novel functionalities.