Abstract
In the present investigation, an aluminum powder of 99.7% purity with particle size of ~45 µm was cryomilled for 7 hours. The produced powder as characterized by scanning, transmission electron microscopy, and X-ray diffraction gave a particle size of ~1 µm and grain (crystallite) size of23±6 nm. This powder, after degassing process, was consolidated using high-frequency induction heat sintering (HFIHS) at various temperatures for short periods of time of 1 to 3 minutes. The present sintering conditions resulted in solid compact with nanoscale grain size (<100 nm) and high compact density. The mechanical properties of a sample sintered at 773 K for 3 minutes gave a compressive yield and ultimate strength of 270 and 390 MPa, respectively. The thermal stability of grain size nanostructured compacts is in agreement with the kinetics models based on the thermodynamics effects.
Highlights
Interest in the field of nanocrystalline materials has grown tremendously in recent years
The major problem with such route was the relatively prolonged time exposure at elevated temperature to achieve an acceptable level of densification, which would be accompanied by a considerable grain growth bringing the bulk material out of the nanocrystalline range (>100 nm) [2, 3]
The introduction of cryogenic liquid media during milling effectively eliminates these problems, demonstrating that cryomilling is capable of producing nanometer scaled microstructures in powders with a uniform particle size distribution
Summary
Interest in the field of nanocrystalline (nc) materials has grown tremendously in recent years. The origin of the exceptional grain size stability of milled aluminum powders has been attributed to pinning effects arising from aluminum oxide/nitride/carbide dispersoids as well as segregation of solute atoms to grain boundaries It was demonstrated by He et al [9] that mechanical milling can alter the expected deformation mechanism in high stacking fault energy (SFE) FCC materials. The aim of this work is to study the cryomilling of 99.7% purity aluminum powder at various milling times and evaluate the crystal size achieved The selection of this powder is based on twofold: (i) this alloy is the base material for various commercial Al alloys and (ii) to compare cryomilling to other sever-plastic deformation techniques used to produce ultrafine grain size in the present alloy. This sintering technique was selected to examine the possibility of minimizing grain growth in consolidated powders
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