Structure and Mechanical Properties of Bulk Nanocrystalline Aluminium by Cryomilling
Bulk nanocrystalline Al were fabricated by cryomilling,compacting, vacuum sintering and extrusion with hard particle addition to improve the strength and hardness of the material. Microstructures of the materials were observed and analyzed by TEM and XRD. Density, microhardness and tensile property of the materials were measured. Experiment results demonstrate that grain size of the aluminum powder is reduced from 55 to 43 nm, and microstrain of the crystalline materials is increased from 0. 027 2 to 0.075 9% when the cryomilling time is increaseed from 8 to 14 h. Grain sizes of the bulk nanocrystalline Al is reduced from 115 to 71 nm. The maximum microhardness of the bulk of nano Al and A1-A12O3 are 1. 02 and 1. 22 GPa. The maximum yield stress of the bulk nano Al and Al-Al2O3reach 165 and 243 MPa, while the bulk nano Al-Al2O3has a 47% stress increase compared with the bulk nano Al under the same processing condition. When the grain size is below 223 nm, the relationship between yield stress and grain size of the bulk nano Al material is expressed as σ1 — 71.8 + 1.8D-1/2.
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