Abstract
Micro-forming with ultrafine-grained (UFG) materials is a promising direction for the fabrication of micro-electro-mechanical systems (MEMS) components due to the improved formability, good surface quality, and excellent mechanical properties it provides. In this paper, micro-compression tests were performed using UFG pure aluminum processed by equal-channel angular pressing (ECAP) with subsequent annealing treatment. Microstructural evolution was investigated by electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM). The results show that microstructural evolutions during compression tests at the micro/meso-scale in UFG pure Al are absolutely different from the coarse-grained (CG) materials. A lot of low-angle grain boundaries (LAGBs) and recrystallized fine grains are formed inside of the original large grains in CG pure aluminum after micro-compression. By contrast, ultrafine grains are kept with few sub-grain boundaries inside the grains in UFG pure aluminum, which are similar to the original microstructure before micro-compression. The surface roughness and coordinated deformation ability can be significantly improved with UFG pure aluminum, which demonstrates that the UFG materials have a strong potential application in micro/meso-forming.
Highlights
With the rapid development of micro-electro-mechanical systems (MEMS), a lot of miniaturized components are widely used for electronics, automobiles, aerospace, and biomedical devices [1,2]
There is a way to solve grain size effects in micro/meso-forming by applying ultrafine-grained (UFG) materials with sub-micrometer or even nano-scale grain sizes produced by severe plastic deformation (SPD) [16,17,18,19], because ultrafine grains can improve the formability, surface quality, and high mechanical properties of MEMS components [20,21,22]
Yu et al [23] studied deformation behavior in UFG pure aluminum processed by equal-channel angular pressing (ECAP) and post-annealed specimens at room temperature (RT), and the results show that different work hardening behavior were observed during a macro-compression test when the grain size increased from 0.35 μm to 45 μm
Summary
With the rapid development of micro-electro-mechanical systems (MEMS), a lot of miniaturized components are widely used for electronics, automobiles, aerospace, and biomedical devices [1,2]. There is a way to solve grain size effects in micro/meso-forming by applying ultrafine-grained (UFG) materials with sub-micrometer or even nano-scale grain sizes produced by severe plastic deformation (SPD) [16,17,18,19], because ultrafine grains can improve the formability, surface quality, and high mechanical properties of MEMS components [20,21,22]. Micro/meso-deformation behavior of the sample with different grain sizes was investigated, and microstructural evolution of compressive samples was analyzed by electron back-scattered diffraction. Microstructural evolution after micro-compression was investigated by EBSD using the Quanta 200FEG FESEM with a working distance of ~13 mm and the data were analyzed with a TSL orientation imaging microscopy (OIM) software contained in the SEM. A field emission TEM (Tecnai G2 F30, FEI Instruments Co., Ltd., Hillsboro, OR, USA) was used for selected-area electron diffraction (SAED) analysis of microstructure observations at an operating voltage of 30 kV
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