Deformation Mechanisms of a Micro-Sized Austenitic Stainless Steel with Fine Grains
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Deformation Mechanisms of A Micro-Sized Austenitic Stainless Steel with Fine Grains
G. P. Zhang, K. Takashima, M. Shimojo and Y. Higo Precision and Intelligence Laboratory, Tokyo Institute of Technology 4259 Nagatsuta-cho, Midori-ku, Yokohama, 226-8503, Japan ABSTRACT
In this study, deformation behavior of fine-grained austenitic stainless steel micro-cantilever beams was investigated using a newly developed testing machine for micro-sized specimens. The microbeams were deformed to different strain hardening stages of the material, and then the detailed deformation behavior on the specimen surface at the corresponding strain hardening stage was examined by scanning electron microscopy. Two deformation mechanisms corresponding to different strain hardening stages were found in the micro-sized austenitic stainless steel with fine grains. The dislocation slip mechanism characterized by the extensive dislocation slips and their interaction with grain boundaries resulted in the stage I strain hardening. With increasing deformation, the grain boundary sliding (GBS) mechanism at the stage II and subsequently intergranular cracking occurred. The differences in stress condition and work-hardening behavior on the top tension-side and rear compression-side surfaces of the micro-cantilever beam resulted in the different deformation behavior.
INTRODUCTION
With the demand for microelectromechanical systems (MEMS) and micromachines used in various fields, the research interest in micromaterials is now extending from silicon to non-silicon materials, such as metallic thin films. These thin films are usually of fine or ultra fine grains obtained from deposition process, such as sputtering. Just as in bulk materials, an understanding of mechanical properties of fine-grained micromaterials would play a key role in designing reliable microcomponents and securing their durable service [1-3]. The micro-cantilever beam is not only a common microcomponent widely used in micromachines but also a relatively simple specimen, which is easily micromachined to obtain mechanical properties of micro-sized materials [4-8]. According to the simple beam theory, deformation of a beam should occur initially at the fixed end, which is subjected to the maximum stress, and then spread out along the beam axis with increasing deformation. Thus, the surface of the microbeam deformed to a certain strain range is expected to reveal deformation behavior of micro-sized materials, especially for ductile micromaterials. In this study, the whole deformation behavior of micro-sized austenitic stainless steel with fine grains was examined to elucidate the basic deformation mechanism of the fine-grained material by microbeam bending tests. EXPERIMENTAL The material used in this study is a commercial 304 stainless steel sheet with fine grains (about 1-2 µm in diameter). The as-received sheet with 50 µm in thickness was firstly electropolished to about 25µm, and then fabricated to micro-cantilever beam type specimens by
EE5.10.1
focused ion beam (FIB) mac
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