Production of a nanostructured copper by Spark Plasma Sintering (original) (raw)
Related papers
Synthesis and mechanical behavior of nanostructured materials via cryomilling
Progress in Materials Science, 2006
Cryomilling, the mechanical attrition of powders within a cryogenic medium, is a method of strengthening materials through grain size refinement and the dispersion of fine, nanometerscale particles. The technique was developed as a means to decrease both the size of these particles and their spacing within a metallic matrix to increase threshold creep stress and intermediate temperature performance. More recent work has been concerned with increasing the strength of lightweight structural materials. In this overview paper, the available literature is reviewed that covers the microstructural evolution during cryomilling, consolidation and processing, the thermal stability of the microstructure, and mechanical properties of consolidated materials. The properties of cryomilled materials are compared to those results for powders and consolidated materials generated by mechanical alloying, milling at ambient temperatures and other means to produce fine grained materials. Cryo Al-7.5Mg [40] Cryo Inconel 625 [39] Al [42] Al [29] AlRu [41] Fe [42] Ni [29]
Processing and behavior of nanostructured metallic alloys and composites by cryomilling
Journal of Materials Science, 2007
Recent interest in nanostructured materials stems, not only from their potential use in a variety of applications, but also from the reported discovery of novel fundamental phenomena. The consolidation of cryomilled powder provides a potential pathway towards large scale manufacturing of nanostructured metallic materials. This approach typically engenders the mechanical attrition of powders in liquid nitrogen, followed by consolidation, using established commercial techniques, such as isostatic pressing and extrusion. In this overview paper, published data are reviewed and discussed with particular emphasis on the following topics: nanostructure evolution mechanisms; primary consolidation and secondary processing methods; thermal stability of cryomilled materials; and mechanical behavior of consolidated materials. Recent mechanical behavior data and the associated mechanisms of cryomilled Al alloys are discussed in an effort to shed light into the fundamental behavior of ultrafine grained and nanostructured materials.
Cryomilled nanostructured materials: Processing and properties
Materials Science and Engineering: A, 2008
Nanostructured (i.e., 1-200 nm grain size) and ultrafine-grained (i.e., 200-500 nm grain size) metals are of interest, not only as a result of their unusual combinations of physical and mechanical properties, but also because they can be readily synthesized using well-developed synthesis techniques. Cryomilling, i.e., mechanical alloying in liquid nitrogen, is representative of a class of synthesis techniques that attain the nanostructured state via severe plastic deformation. In this overview, published data related to cryomilled materials are reviewed and discussed with particular emphasis on cryomilling mechanisms; microstructure and thermal stability of cryomilled powders; primary consolidation and secondary processing methods; microstructural evolution during consolidation; and mechanical response of consolidated materials. The deformation behavior and the underlying mechanisms that govern cryomilled materials are discussed and compared with those of nanostructured materials processed via other methods, in an effort to shed light into the fundamental behavior of ultrafine-grained and nanostructured materials. Published by Elsevier B.V.
Journal of Materials Science, 2011
It has been found difficult to fully densify some mechanically milled pure metal powders by spark plasma sintering (SPS). In this study, the densification behavior of cryomilled, nanostructured (NS) Cu powders during SPS was related to changes to the chemistry of the powders. The results showed that the presence of very small amounts of O and N in the powders, which were introduced during cryomilling and handling, significantly influenced the densification response. Moreover, reduction/removal of O/N via thermal annealing of the powders before SPS led to complete densification of the powders during subsequent SPS. The mechanisms responsible for this behavior were ascertained: O and N existed in the cryomilled powders in the form of thermally unstable compounds, and the subsequent thermal decomposition of these compounds during SPS generated the gaseous species, leading to porosity formation and incomplete densification; annealing of the powders before SPS removed the gases which resulted from thermal decomposition, thereby facilitating complete consolidation during subsequent SPS.
Nanometric grain formation in ductile powders by low-energy ball milling
Nanostructured Materials, 1999
Based on microstructural observations by TEM and in particle size distribution done by sedimentationphotometry, a new grain size refinement mechanism for ductile powders in mechanical alloying is proposed. A 90-95% of the particle population was of submicrometric fragmented particles. These were detected from the beginning of the milling process up to 90 ks. It seems that the fragmentation of the original particles occurred under dynamic conditions to generate those submicrometric ones. Under these conditions the original grain size (100 nm to 350 nm) was preserved and a low level of dislocations was observed at these submicrometric particles. Once these submicrometric particles were deformed, grains smaller than 20 nm were observed. It seems from TEM results that the submicrometric fragmented particles were also deformed under dynamic conditions. This could be a new grain size refinement mechanism present in ductile metallic powder systems where the fragmentation is the dominant stage from the beginning of the milling up to some intermediate milling time. In the Cu-20at%Ni, Cu and Ni systems where the particle coalescence process was the dominant stage during all the milling process, a derivation of the mechanism proposed by Hellstern [3] was identified. In our case, powders were mainly deformed by slip and not by shear. It recognizes that the way to refine the grain size in milled powders is influenced at least by the metallic system used as well as by the equipment and the process conditions employed.
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.
Localized Defects in Cold Die-Compacted Metal Powders
Journal of Manufacturing and Materials Processing
In powder metallurgy (PM), the compaction step is fundamental to determining the final properties of the sintered components. The deformation and defectiveness introduced in the powder material during uniaxial die compaction can be correlated to the activation and enhancement of the dislocation pipe diffusion, a lattice diffusion mechanism during the sintering process. Its coefficient depends on the dislocation density. The powder particles are mostly deformed along the direction of the compaction (longitudinal direction) rather than along the compaction plane; consequently, the contact areas perpendicular to the direction of the compaction present a higher density of dislocations and lattice defects. This high density intensifies the shrinkage along the direction of compaction. To demonstrate the influence of uniaxial cold compaction on the material’s stress state the powder particles and their contacts were modeled using spheres made of pure copper. These spheres are compacted in ...
Influence of Cryomilling on Crystallite Size of Aluminum Powder and Spark Plasma Sintered Component
Nanomaterials, 2022
The present investigation aims to develop nanocrystalline (NC) pure aluminum powders using cryomilling technique and manufacture bulk components using spark plasma sintering (SPS). The cryomilling was performed on pure Al powders for 2, 6, and 8 h. The cryomilled powders were then consolidated using SPS to produce bulk components. The particle morphology and crystallite size of the powders and the bulk SPS components were analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The results showed that the crystallite size of pure Al powders decreases with increased cryomilling time. The results also showed that the SPS at elevated temperatures resulted in a slight increase in crystallite size, however, the changes were insignificant. The mechanical properties of the bulk components were determined using a Vickers microhardness tester. The hardness of the cryomilled SPS component was determined to be three times higher th...