Bulk nanocrystalline Al prepared by cryomilling

Junsheng Cheng1), Hua Cui2), Hanbin Chen1), Bin Yang1), Jianzhong Fan3), and Jishan Zhang1) 1) State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China 2) Materials Science and Engineering School, University of Science and Technology Beijing, Beijing 100083, China 3) Beijing General Research Institute for Nonferrous Metals, Beijing 100088, China

摘 要：Bulk nanocrystalline Al was fabricated by mechanically milling at cryogenic temperature （cryomilling） and then by hot pressing in vacuum. By using X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and transmission electron microscopy （TEM）, the microstructure evolution of the material during cryomilling and consolidation was investigated. With increasing the mill- ing time, the grain size decreased sharply and reduced to 42 nm when cryomilled for 12 h. The grains had grown up, and the colum- nar grain was formed under the hot pressing and extrusion compared with the cryomilled powders. The grain size of as-extruded specimen was approximately 300-500 nm. The reason of high thermal stability of this bulk was attributed primarily to the Zener pin- ning from the grain boundary of the AlN arising from cryomilling and the solute drag of the impurity. Tensile tests show that the strength of nanocrystalline Al is enhanced with decreasing grain size. The ultimate tensile strength and tensile elongation were 173 MPa and 17.5%, respectively. It appears that the measured high strength in the cryomilled Al is related to a grain-size effect, disper- sion strengthening, and dislocation strengthening.

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