Manufacturing Bulk Nanocrystalline Al-3Mg Components Using Cryomilling and Spark Plasma Sintering (original) (raw)
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Influence of Cryomilling on Crystallite Size of Aluminum Powder and Spark Plasma Sintered Component
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In this study, nanostructured Al 5083 powders, which were prepared via cryomilling, were consolidated using spark plasma sintering (SPS). The influence of processing conditions, e.g., the loading mode, starting microstructure (i.e., atomized vs cryomilled powders), sintering pressure, sintering temperature, and powder particle size on the consolidation response and associated mechanical properties were studied. Additionally, the mechanisms that govern densification during SPS were discussed also. The results reported herein suggest that the morphology and microstructure of the cryomilled powder resulted in an enhanced densification rate compared with that of atomized powder. The pressure-loading mode had a significant effect on the mechanical properties of the samples consolidated by SPS. The consolidated compact revealed differences in mechanical response when tested along the SPS loading axis and radial directions. Higher sintering pressures improved both the strength and ductility of the samples. The influence of grain size on diffusion was considered on the basis of available diffusion equations, and the results show that densification was attributed primarily to a plastic flow mechanism during the loading pressure period. Once the final pressure was applied, power law creep became the dominant densification mechanism. Higher sintering temperature improved the ductility of the consolidated compact at the expense of strength, whereas samples sintered at lower temperature exhibited brittle behavior. Finally, densification rate was found to be inversely proportional to the particle size.
Spark Plasma Sintering of Cryomilled Nanocrystalline Al Alloy - Part I: Microstructure Evolution
Metallurgical and Materials Transactions A, 2012
Aluminum alloys are widely used because they are lightweight and exhibit high strength. In recent years, spark plasma sintering (SPS) technology has emerged as a viable approach to sinter materials due to its application of rapid heating and high pressure. In this study, SPS was chosen to consolidate dense ultrafine-grained (UFG) bulk samples using cryomilled nanostructured Al 5083 alloy (Al-4.5Mg-0.57Mn-0.25Fe, wt pct) powder. Both bimodal microstructure and banded structure were observed through transmission electron microscopy (TEM) investigation. The evolution of such microstructures can be attributed to the starting powder and the process conditions, which are associated with the thermal, electrical, and pressure fields present during SPS. A finite element method (FEM) was also applied to investigate distributions in temperature, current, and stress between metallic powder particles. The FEM results reveal that the localized heating, deformation, and thermal activation occurring at interparticle regions are associated with the formation of the special microstructure.
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Advances in Materials Science and Engineering, 2013
In the present investigation, an aluminum powder of 99.7% purity with particle size of ∼45 m 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 m and grain (crystallite) size of 23 ± 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.
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The aim of this paper focuses on presenting a recent study that describes the fundamental steps needed to effectively scale-up from lab to mass production parts produced from Al powders reinforced with 0.5 wt% of industrial multiwalled carbon nanotubes (MWCNTs), with mechanical and electrical conductivity properties higher that those measured at the lab scale. The produced material samples were produced via a Spark Plasma Sintering (SPS) process using nanocomposite aluminum powders elaborated with a planetary ball-mill at the lab scale, and high-volume attrition milling equipment in combination with controlled atmosphere sinter hardening furnace equipment, which were used to consolidate the material at the industrial level. Surprisingly, the electrical conductivity and mechanical properties of the samples produced with the reinforced nanocomposite Al powders were made with mass production equipment and were similar or higher than those samples fabricated using metallic powders prepa...
How to cite this article Rounaghi S. A, Esmaeil E. A Comparative Study of the Synthesis and Thermal Stability of Nanostrucrured Al and Al-Mg Powders Fabricated by Mechanical Alloying Technique. Nanostructured Al and Al-Mg (Mg 30 wt. %) powders with the mean crystallite sizes of 42 and 11 nm were prepared through the solid state ball milling technique. The milling process was performed for various times up to 12 h in argon atmosphere and the synthesized powders were in detail characterized by different techniques. The effect of milling time and Mg addition on the size, morphology, chemical composition, phase structure and crystallite size of the powder particles were thoroughly investigated and the results were compared with the non-alloyed Al system. Two distinct particle morphologies comprising lamellar flakes and solid granules were obtained as final milling products in Al and Al-Mg systems, respectively. It was revealed that Mg atoms gradually diffuse into the Al lattice during milling and form a supersaturated Al-Mg solid solution (α phase). Thermal analyses of the powders revealed that metastable nanostructures formed during the milling transform into the equilibrium and stable phases such as Al 4 C 3 and Al 2 Mg 3 (β) upon the heating.
Journal of Nanostructures, 2017
Nanostructured Al and Al-Mg (Mg 30 wt. %) powders with the mean crystallite sizes of 42 and 11 nm were prepared through the solid state ball milling technique. The milling process was performed for various times up to 12 h in argon atmosphere and the synthesized powders were in detail characterized by different techniques. The effect of milling time and Mg addition on the size, morphology, chemical composition, phase structure and crystallite size of the powder particles were thoroughly investigated and the results were compared with the non-alloyed Al system. Two distinct particle morphologies comprising lamellar flakes and solid granules were obtained as final milling products in Al and Al-Mg systems, respectively. It was revealed that Mg atoms gradually diffuse into the Al lattice during milling and form a supersaturated Al-Mg solid solution (α phase). Thermal analyses of the powders revealed that metastable nanostructures formed during the milling transform into the equilibrium ...