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17 pages, 5901 KiB

Open AccessFeature PaperArticle

Medium-Frequency Electrical Resistance Sintering of Soft Magnetic Powder Metallurgy Iron Parts

by Raquel Astacio, Fátima Ternero, Jesús Cintas, Francisco G. Cuevas and Juan Manuel Montes

Metals 2021, 11(6), 994; https://doi.org/10.3390/met11060994 - 21 Jun 2021

Cited by 1 | Viewed by 2059

The fabrication of soft magnetic Fe parts by the medium-frequency electrical resistance sintering (MF-ERS) technique is studied in this paper. This consolidation technique involves the simultaneous application to metallic powders of pressure and heat, the latter coming from the Joule effect of a [...] Read more.

The fabrication of soft magnetic Fe parts by the medium-frequency electrical resistance sintering (MF-ERS) technique is studied in this paper. This consolidation technique involves the simultaneous application to metallic powders of pressure and heat, the latter coming from the Joule effect of a low-voltage and high-intensity electric current. Commercially pure iron powder was used in the consolidation experiences. The porosity distribution, microhardness, electrical resistivity and hysteresis curves of the final compacts were determined and analysed. The results obtained were compared both with those of compacts consolidated by the conventional powder metallurgy (PM) route of cold pressing and vacuum furnace sintering, and with fully dense compacts obtained by double cycle of cold pressing and furnace sintering in hydrogen atmosphere. Full article

(This article belongs to the Special Issue Metals Powders 2021: Synthesis and Processing)

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13 pages, 7289 KiB

Open AccessArticle

Carbide Nanoparticle Dispersion Techniques for Metal Powder Metallurgy

by Bahrum Prang Rocky, Christopher R. Weinberger, Steven R. Daniewicz and Gregory B. Thompson

Metals 2021, 11(6), 871; https://doi.org/10.3390/met11060871 - 26 May 2021

Cited by 5 | Viewed by 2936

Abstract

Nanoparticles (NP) embedded into a matrix material have been shown to improve mechanical properties such as strength, hardness, and wear-resistance. However, the tendency of NPs to agglomerate in the powder mixing process is a major concern. This study investigates five different mechanochemical processing [...] Read more.

Nanoparticles (NP) embedded into a matrix material have been shown to improve mechanical properties such as strength, hardness, and wear-resistance. However, the tendency of NPs to agglomerate in the powder mixing process is a major concern. This study investigates five different mechanochemical processing (MCP) routes to mitigate agglomeration to achieve a uniform dispersion of ZrC NPs in an Fe-based metal matrix composite. Our results suggest that MCP with only process controlling agents is ineffective in avoiding aggregation of these NPs. Instead, the uniformity of the carbide NP dispersion is achieved by pre-dispersing the NPs under ultrasonication using suitable surfactants followed by mechanically mixing of the NPs with iron powders in an alcohol solvent which is then dried. High-energy MCP is then used to embed the NPs within the powders. These collective steps resulted in a uniform dispersion of ZrC in the sintered (consolidated) Fe sample. Full article

(This article belongs to the Special Issue Metals Powders 2021: Synthesis and Processing)

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14 pages, 53985 KiB

Open AccessArticle

Electrical Explosion Synthesis, Oxidation and Sintering Behavior of Ti-Al Intermetallide Powders

by Marat Lerner, Alexandr Pervikov, Elena Glazkova, Nikolay Rodkevich and Nikita Toropkov

Metals 2021, 11(5), 760; https://doi.org/10.3390/met11050760 - 05 May 2021

Cited by 5 | Viewed by 1789

Abstract

In this research, Ti-Al powders were produced by electrical explosion of twisted titanium and aluminum wires. The resulting powders were pressed and sintered in a vacuum to obtain bulk composites. Transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), and [...] Read more.

In this research, Ti-Al powders were produced by electrical explosion of twisted titanium and aluminum wires. The resulting powders were pressed and sintered in a vacuum to obtain bulk composites. Transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), and X-ray diffraction (XRD) studies were performed to analyze synthesized powders and bulk composites. The studies carried out showed the presence of α-Ti, α₂-Ti₃Al, and γ-TiAl phases, which are formed by coalescence of Ti and Al clusters formed in the process of non-synchronous electrical explosion of twisted wires. Furthermore, an increase in the energy injected into the wires leads to a decrease in the content of micron particles in the powder. During sintering of pressed Ti-Al powder in the range 800–1250 °C, phase transformations occur due to the diffusion of aluminum atoms towards Ti compounds. The research findings can be used to obtain Ti-Al particles and bulk composites with a controllable phase composition. Full article

(This article belongs to the Special Issue Metals Powders 2021: Synthesis and Processing)

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19 pages, 14589 KiB

Open AccessFeature PaperArticle

Novel Characterization Techniques for Additive Manufacturing Powder Feedstock

by Benjamin Young, Joseph Heelan, Sean Langan, Matthew Siopis, Caitlin Walde and Aaron Birt

Metals 2021, 11(5), 720; https://doi.org/10.3390/met11050720 - 27 Apr 2021

Cited by 7 | Viewed by 2730

Abstract

Additive manufacturing is a rapidly expanding field, encompassing many methods to manufacture parts and coatings with a wide variety of feedstock. Metal powders are one such feedstock, with a range of compositions and morphologies. Understanding subtle changes in the feedstock is critical to [...] Read more.

Additive manufacturing is a rapidly expanding field, encompassing many methods to manufacture parts and coatings with a wide variety of feedstock. Metal powders are one such feedstock, with a range of compositions and morphologies. Understanding subtle changes in the feedstock is critical to ensure successful consolidation and quality control of both the feedstock and manufactured part. Current standards lack the ability to finely distinguish almost acceptable powders from barely acceptable ones. Here, novel means of powder feedstock characterization for quality control are demonstrated for the solid-state AM process of cold spray, though similar methods may be extrapolated to other additive methods as well. These characterization methods aim to capture the physics of the process, which in cold spray consists of high strain rate deformation of solid-state feedstock. To capture this, in this effort powder compaction was evaluated via rapidly applied loads, flowability of otherwise non-flowable powders was evaluated with the addition of vibration, and powder electrical resistivity was evaluated through compaction between two electrodes. Several powders, including aluminum alloys, chromium, and cermet composites, were evaluated in this effort, with each case study demonstrating the need for non-traditional characterization metrics as a means of quality control and classification of these materials. Full article

(This article belongs to the Special Issue Metals Powders 2021: Synthesis and Processing)

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10 pages, 6289 KiB

Open AccessArticle

Interaction between WC and Inconel 625 under Solid and Liquid State Sintering Conditions

by Lorena Emanuelli, Alberto Molinari and Massimo Pellizzari

Metals 2021, 11(4), 666; https://doi.org/10.3390/met11040666 - 19 Apr 2021

Cited by 4 | Viewed by 2199

Abstract

Cobalt is the most used metal binder in hard metals since its extraordinary wetting, adhesion and mechanical properties. Nevertheless, it has been recognized genotoxic and cancerogenic with higher toxicity in combination with WC. To substitute Co with an alternative binder, the interaction between [...] Read more.

Cobalt is the most used metal binder in hard metals since its extraordinary wetting, adhesion and mechanical properties. Nevertheless, it has been recognized genotoxic and cancerogenic with higher toxicity in combination with WC. To substitute Co with an alternative binder, the interaction between the binder and WC must be taken into account. In this work, IN625 is considered as a binder alternative due to its desirable combination of high-temperature strength and corrosion/oxidation resistance. A characterization of the interaction between WC and IN625 was carried out by means of Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDXS) and X-Ray Diffraction (XRD). Depending on the sintering temperatures, different phases were evidenced at the WC–IN625 superalloy interface. From 1250 °C to 1300 °C, where solid-state sintering takes place, (Cr,Mo)₂₃C₆, W₂C and (Cr,W) solid solutions were detected. At a sintering temperature of 1350 °C, IN625 melts and the formation of additional phases, such as an intermetallic Ni₄W phase and (Mo,W) and (Mo,Nb) solid solutions, were observed. The precipitation of NbC and (Mo,Cr)₂₃C₆ carbides in IN625 was also detected. Full article

(This article belongs to the Special Issue Metals Powders 2021: Synthesis and Processing)

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14 pages, 5871 KiB

Open AccessFeature PaperArticle

Influence of Processing Parameters on the Conduct of Electrical Resistance Sintering of Iron Powders

by Fátima Ternero, Raquel Astacio, Eduardo S. Caballero, Francisco G. Cuevas and Juan M. Montes

Metals 2020, 10(4), 540; https://doi.org/10.3390/met10040540 - 22 Apr 2020

Cited by 3 | Viewed by 2422

Abstract

The influence of the applied pressure and electrical parameters on the macrostructure of specimens consolidated by the medium-frequency electrical resistance sintering technique (MF-ERS) is analysed in this work. This technique is based on the application of pressure to a mass of conductive powder [...] Read more.

The influence of the applied pressure and electrical parameters on the macrostructure of specimens consolidated by the medium-frequency electrical resistance sintering technique (MF-ERS) is analysed in this work. This technique is based on the application of pressure to a mass of conductive powder that, simultaneously, is being crossed by a high intensity and low voltage electric current. The simultaneous action of the pressure and the heat released by the Joule effect causes the densification and consolidation of the powder mass in a very short time. The effect of the current intensity and heating time on the global porosity, the porosity distribution, and the microhardness of sintered compacts is studied for two applied pressures (100 and 150 MPa). For the different experiments of electrical consolidation, a commercially available pure iron powder was chosen. For comparison purposes, the properties of the compacts consolidated by MF-ERS are compared with the results obtained by the conventional powder metallurgy route (cold pressing and furnace sintering). Results show that, as expected, higher current intensities and dwelling times, as well as higher pressures and the consolidation of compacts with lower aspects ratios, produce denser materials. Full article

(This article belongs to the Special Issue Metals Powders 2021: Synthesis and Processing)

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Review

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21 pages, 2277 KiB

Open AccessReview

Influence of the Total Porosity on the Properties of Sintered Materials—A Review

by Fátima Ternero, Luís Guerra Rosa, Petr Urban, Juan Manuel Montes and Francisco G. Cuevas

Metals 2021, 11(5), 730; https://doi.org/10.3390/met11050730 - 28 Apr 2021

Cited by 54 | Viewed by 5346

Abstract

Porosity is a characteristic present in most sintered materials, full densification only being achieved in special cases. For some sintered materials, porosity is indeed a desired characteristic, serving for the intended application of the material. In any case, the porosity present in materials [...] Read more.

Porosity is a characteristic present in most sintered materials, full densification only being achieved in special cases. For some sintered materials, porosity is indeed a desired characteristic, serving for the intended application of the material. In any case, the porosity present in materials can have a strong effect on some of their properties, both structural and functional. In this paper, some of the expressions proposed to describe the influence of the total porosity on the effective properties of sintered materials are examined. Moreover, a universal expression (with two fitting parameters) valid to satisfactorily represent all the analysed behaviours is proposed. One of these parameters can be assimilated to the tap porosity of the powders used to manufacture the material. The properties examined were elastic moduli, ultimate strength, thermal and electrical conductivities, magnetic characteristics, and other properties directly related to these ones. The study is valid for sintered materials, both metallic and ceramic, with a homogeneous and non-texturised microstructure. Full article

(This article belongs to the Special Issue Metals Powders 2021: Synthesis and Processing)

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35 pages, 6662 KiB

Open AccessReview

Capacitor Electrical Discharge Consolidation of Metallic Powders—A Review

by Rosa María Aranda, Fátima Ternero, Sergio Lozano-Pérez, Juan Manuel Montes and Francisco G. Cuevas

Metals 2021, 11(4), 616; https://doi.org/10.3390/met11040616 - 11 Apr 2021

Cited by 11 | Viewed by 2620

Abstract

Manufacturing metallic materials from elemental or alloyed powders is an option in many industrial processes. Nevertheless, the traditional powder metallurgy processing including furnace sintering is at times detrimental for the microstructure attained in the powders. Alternative sintering processes based on the use of [...] Read more.

Manufacturing metallic materials from elemental or alloyed powders is an option in many industrial processes. Nevertheless, the traditional powder metallurgy processing including furnace sintering is at times detrimental for the microstructure attained in the powders. Alternative sintering processes based on the use of electricity and the energy obtained by the Joule effect in powder particles can be quick enough to avoid microstructural changes. In particular, when the energy is stored in a capacitor and then discharged, the heating process is extremely quick, lasting milliseconds or even microseconds. This process, generally known as electrical discharge consolidation, has been applied to a wide variety of metallic materials, easily preserving the original microstructure of the powders. Both porous or homogeneous and highly densified material can be obtained, and without losing the desired properties of the consolidated material. A general overview of the process and applications, as well as the results obtained by different research groups around the world, have been reviewed in this manuscript. Full article

(This article belongs to the Special Issue Metals Powders 2021: Synthesis and Processing)

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