Editorial

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3 pages, 180 KiB

Open AccessEditorial

Metals Powders: Synthesis and Processing

by Francisco Paula Gómez Cuevas

Metals 2019, 9(12), 1358; https://doi.org/10.3390/met9121358 - 17 Dec 2019

Cited by 3 | Viewed by 1711

Abstract

Metallic parts can be obtained by a wide variety of techniques [...] Full article

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

Research

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13 pages, 4937 KiB

Open AccessArticle

Mechanical Properties of Some Metallic Powder Alloys and Their Contribution to the Performance of Diamond Tools Used for Cutting Granite

by Luís Guerra Rosa, Carlos A. Anjinho, Pedro M. Amaral and Jorge Cruz Fernandes

Metals 2019, 9(11), 1219; https://doi.org/10.3390/met9111219 - 13 Nov 2019

Cited by 2 | Viewed by 2782

Abstract

This work examined some pre-alloyed cobalt-, iron-, and copper-based powder binder systems—such as those launched commercially under the brand names of Cobalite and Next—in terms of their as-sintered physical-mechanical properties, namely, apparent density, Young´s modulus, yield strength, rupture strength, rupture strain, toughness modulus, [...] Read more.

This work examined some pre-alloyed cobalt-, iron-, and copper-based powder binder systems—such as those launched commercially under the brand names of Cobalite and Next—in terms of their as-sintered physical-mechanical properties, namely, apparent density, Young´s modulus, yield strength, rupture strength, rupture strain, toughness modulus, and Vickers hardness. These types of sintered products are traditionally used in the fabrication of diamond impregnated tools for cutting granite stones. The following powder binder systems were evaluated: Cobalite HDR pre-alloyed powder, Next 300 pre-alloyed powder, and four other mixtures of these with Cu and Fe powders: Cobalite HDR + 20 wt% Cu; Cobalite HDR + 20 wt% Fe; Next 300 + 20 wt% Cu; Next 300 + 20 wt% Fe. The evaluation methodology aimed to establish criteria for developing new diamond tools and, therefore, it included the measurement of several technological parameters directly related to the cutting performance of the tools (e.g., energy consumption measurements made exclusively in the tool drive motor, forces generated in the tool, tool consumption per unit weight of stone removed by the cutting). The results show the adequacy of the methodology for the optimisation of diamond retention capacity of these types of metal matrices and for improving the working performance of the diamond tools. Full article

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

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14 pages, 6426 KiB

Open AccessArticle

Amorphous Al-Ti Powders Prepared by Mechanical Alloying and Consolidated by Electrical Resistance Sintering

by Petr Urban, Fátima Ternero, Eduardo S. Caballero, Sooraj Nandyala, Juan Manuel Montes and Francisco G. Cuevas

Metals 2019, 9(11), 1140; https://doi.org/10.3390/met9111140 - 24 Oct 2019

Cited by 11 | Viewed by 2895

Abstract

A novel processing method for amorphous Al₅₀Ti₅₀ alloy, obtained by mechanical alloying and subsequently consolidated by electrical resistance sintering, has been investigated. The characterisation of the powders and the confirmation of the presence of amorphous phase have been carried out [...] Read more.

A novel processing method for amorphous Al₅₀Ti₅₀ alloy, obtained by mechanical alloying and subsequently consolidated by electrical resistance sintering, has been investigated. The characterisation of the powders and the confirmation of the presence of amorphous phase have been carried out by laser diffraction, scanning electron microscopy, X-ray diffraction, differential scanning calorimetry and transmission electron microscopy. The amorphous Al₅₀Ti₅₀ powders, milled for 75 h, have a high hardness and small plastic deformation capacity, not being possible to achieve green compacts for conventional sintering. Moreover, conventional sintering takes a long time, being not possible to avoid crystallisation. Amorphous powders have been consolidated by electrical resistance sintering. Electrically sintered compacts with different current intensities (7–8 kA) and processing times (0.8–1.6 s) show a porosity between 16.5 and 20%. The highest Vickers hardness of 662 HV is reached in the centre of an electrically sintered compact with 8 kA and 1.2 s from amorphous Al₅₀Ti₅₀ powder. The hardness results are compared with the values found in the literature. Full article

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

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16 pages, 6034 KiB

Open AccessArticle

Balancing Porosity and Mechanical Properties of Titanium Samples to Favor Cellular Growth against Bacteria

by Ana Civantos, Ana M. Beltrán, Cristina Domínguez-Trujillo, Maria D. Garvi, Julián Lebrato, Jose A. Rodríguez-Ortiz, Francisco García-Moreno, Juan V. Cauich-Rodriguez, Julio J. Guzman and Yadir Torres

Metals 2019, 9(10), 1039; https://doi.org/10.3390/met9101039 - 24 Sep 2019

Cited by 23 | Viewed by 2574

Abstract

Two main problems limit the success of titanium implants: bacterial infection, which restricts their osseointegration capacity; and the stiffness mismatch between the implant and the host cortical bone, which promotes bone resorption and risk of fracture. Porosity incorporation may reduce this difference in [...] Read more.

Two main problems limit the success of titanium implants: bacterial infection, which restricts their osseointegration capacity; and the stiffness mismatch between the implant and the host cortical bone, which promotes bone resorption and risk of fracture. Porosity incorporation may reduce this difference in stiffness but compromise biomechanical behavior. In this work, the relationship between the microstructure (content, size, and shape of pores) and the antibacterial and cellular behavior of samples fabricated by the space-holder technique (50 vol % NH₄HCO₃ and three ranges of particle sizes) is established. Results are discussed in terms of the best biomechanical properties and biofunctional activity balance (cell biocompatibility and antibacterial behavior). All substrates achieved suitable cell biocompatibility of premioblast and osteoblast in adhesion and proliferation processes. It is worth to highlighting that samples fabricated with the 100–200 μm space-holder present better mechanical behavior—in terms of stiffness, microhardness, and yield strength—which make them a very suitable material to replace cortical bone tissues. Those results exposed the relationship between the surface properties and the race of bacteria and mammalian cells for the surface with the aim to promote cellular growth over bacteria. Full article

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

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10 pages, 4686 KiB

Open AccessArticle

Microstructure of a V-Containing Cobalt Based Alloy Prepared by Mechanical Alloying and Hot Pressed Sintering

by Niannian Li, Fengshi Yin and Liu Feng

Metals 2019, 9(4), 464; https://doi.org/10.3390/met9040464 - 22 Apr 2019

Cited by 5 | Viewed by 3259

Abstract

In this paper, a bulk V-containing cobalt-based alloy with high chromium and tungsten contents was prepared by mechanical alloying and hot pressed sintering using Co, Cr, W, Ni, V and C pure element powders. XRD, SEM, TEM and Vickers hardness tests were employed [...] Read more.

In this paper, a bulk V-containing cobalt-based alloy with high chromium and tungsten contents was prepared by mechanical alloying and hot pressed sintering using Co, Cr, W, Ni, V and C pure element powders. XRD, SEM, TEM and Vickers hardness tests were employed to characterize the microstructure and mechanical properties of the mechanical alloyed powders and hot pressed bulk cobalt-based alloy. The results show that all elements can be mixed uniformly and that the Co, Cr, and Ni elements were made into an amorphous state after 10 h ball milling in a high energy ball miller. The microstructure of the prepared bulk alloy was composed of a γ-Co matrix with a large number of nano-twins and fine M₂₃C₆ and M₁₂C carbide particles well-distributed in the alloy. The V element was mainly distributed in M₂₃C₆-type carbide and no V-rich MC-type carbide was found in the microstructure. The prepared alloy had a high hardness of 960 ± 9.2 HV and good a fracture toughness K_Ic of about 10.5 ± 0.46 MPa·m^1/2. The microstructure formation and strengthening mechanisms of the prepared cobalt-based alloy are discussed. Full article

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

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9 pages, 3545 KiB

Open AccessArticle

Microstructure and Magnetic Properties of Mn₅₅Bi₄₅ Powders Obtained by Different Ball Milling Processes

by Xiang Li, Dong Pan, Zhen Xiang, Wei Lu and Dan Batalu

Metals 2019, 9(4), 441; https://doi.org/10.3390/met9040441 - 15 Apr 2019

Cited by 6 | Viewed by 2731

Abstract

Low-temperature phase (LTP) MnBi is considered as a promising rare-earth-free permanent magnetic material with high coercivity and unique positive temperature coefficient of coercivity. Mn₅₅Bi₄₅ ribbons with high purity of LTP MnBi phase were prepared by melt spinning. Then, Mn₅₅ [...] Read more.

Low-temperature phase (LTP) MnBi is considered as a promising rare-earth-free permanent magnetic material with high coercivity and unique positive temperature coefficient of coercivity. Mn₅₅Bi₄₅ ribbons with high purity of LTP MnBi phase were prepared by melt spinning. Then, Mn₅₅Bi₄₅ powders with different particle size were obtained by low-energy ball milling (LEBM) with and without added surfactant. The coercivity is enhanced in both cases. Microstructure characterization reveals that Mn₅₅Bi₄₅ powders obtained by surfactant assisted low-energy ball milling (SALEBM) have better particle size uniformity and show higher decomposition of LTP MnBi. Coercivity can achieve a value of 17.2 kOe and the saturation magnetization (M_s) is 16 emu/g when Mn₅₅Bi₄₅ powders milled about 10 h by SALEBM. Coercivity has achieved a maximum value of 18.2 kOe at room temperature, and 23.5 kOe at 380 K after 14 h of LEBM. Furthermore, Mn₅₅Bi₄₅ powders obtained by LEBM have better magnetic properties. Full article

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

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9 pages, 16425 KiB

Open AccessArticle

Strategy to Enhance Magnetic Properties of Fe₇₈Si₉B₁₃ Amorphous Powder Cores in the Industrial Condition

by Haibo Sun, Ce Wang, Weihong Chen and Jiexin Lin

Metals 2019, 9(3), 381; https://doi.org/10.3390/met9030381 - 26 Mar 2019

Cited by 7 | Viewed by 3327

Abstract

In this study, the soft magnetic properties of Fe₇₈Si₉B₁₃ amorphous magnetic powder cores (AMPCs) were enhanced by coordinately adjusting the technological parameters, including the particle size distribution, molding pressure, and coating agent content, in the industrial condition. The [...] Read more.

In this study, the soft magnetic properties of Fe₇₈Si₉B₁₃ amorphous magnetic powder cores (AMPCs) were enhanced by coordinately adjusting the technological parameters, including the particle size distribution, molding pressure, and coating agent content, in the industrial condition. The results show that the optimized comprehensive soft magnetic properties of the Fe₇₈Si₉B₁₃ AMPCs could be obtained under the following process conditions: (1) the distribution of particle size is 20 wt.% for 140–170 mesh, 70 wt.% for 170–270 mesh, and 10 wt.% for 270–400 mesh; (2) the molding pressure is in the range of 2.35–2.45 GPa; and (3) the additive amount of sodium silicate is 1.5 wt.%. After the collaborative optimization, the AMPCs’ compact density, ρ, the effective permeability, μ_e, and the residual effective permeability at the applied magnetizing field of 7.96 kA/m, μ_e@7.96 kA/m, increased from 5.61 g/cm³ to 5.86 g/cm³, from 58.13 to 77.01, and from 40.36 to 49.57, respectively. The attenuation ratio of the effective permeability, when in the frequency band of 20–100 kHz, was less than 0.85%. The core loss at the 50 kHz for the maximum magnetic flux density of 0.1 T reduced from 380.85 mW/cm³ to 335.23 mW/cm³. This work will encourage the further application of Fe-based AMPCs in the fields of electronics and telecommunication. Full article

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

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13 pages, 4319 KiB

Open AccessArticle

Fabrication of Functionally Graded Materials Using Aluminum Alloys via Hot Extrusion

by Dasom Kim, Kwangjae Park, Minwoo Chang, Sungwook Joo, Sanghwui Hong, Seungchan Cho and Hansang Kwon

Metals 2019, 9(2), 210; https://doi.org/10.3390/met9020210 - 11 Feb 2019

Cited by 9 | Viewed by 4400

Abstract

In this study, we have attempted to manufacture functionally graded materials (FGMs) using aluminum alloys 3003 and 6063 via a hot extrusion process to realize multifunctionality through achieving high strength and low weight. The FGMs were fabricated using Al3003 powder and Al6063 bulk [...] Read more.

In this study, we have attempted to manufacture functionally graded materials (FGMs) using aluminum alloys 3003 and 6063 via a hot extrusion process to realize multifunctionality through achieving high strength and low weight. The FGMs were fabricated using Al3003 powder and Al6063 bulk to improve the interfacial properties. Particle size analysis and X-ray fluorescence of the Al3003 powder were used to analyze the composition of general Al3003; microstructure analysis revealed improved hardness with almost no defects, such as cracks at the interface between the two materials. The experimentally determined tensile strength of the composite was observed to be higher than the theoretical value calculated using the rule of mixtures; the strengthening mechanisms considered for the calculations were grain size reduction and precipitation hardening. In particular, we attempted to predict the strengthening effect resulting from the fine grain size of the powder and grain size reduction due to the extrusion process using the Hall–Petch equation. The Kelly–Tyson equation was also used to calculate the theoretical strength in the presence of the strengthening phases. Based on these results, it was confirmed that FGMs can be successfully produced using the hot extrusion process. Full article

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

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9 pages, 2808 KiB

Open AccessArticle

Extraction of Tantalum Powder via the Magnesium Reduction of Tantalum Pentoxide

by Seon-Min Hwang, Jei-Pil Wang and Dong-Won Lee

Metals 2019, 9(2), 205; https://doi.org/10.3390/met9020205 - 09 Feb 2019

Cited by 16 | Viewed by 5006

Abstract

The metallic tantalum powder was successfully synthesized via reduction of tantalum pentoxide (Ta₂O₅) with magnesium gas at 1073~1223 K for 10 h inside the chamber held under an argon atmosphere. The powder obtained after reduction shows the Ta–MgO mixed [...] Read more.

The metallic tantalum powder was successfully synthesized via reduction of tantalum pentoxide (Ta₂O₅) with magnesium gas at 1073~1223 K for 10 h inside the chamber held under an argon atmosphere. The powder obtained after reduction shows the Ta–MgO mixed structure and that the MgO component was dissolved and removed fully via stirring in a water-based HCl solution. The particle size in the tantalum powder obtained after acid leaching was shown to be in a range of 50~300 nm, and the mean internal crystallite sizes measured by the Scherrer equation varied from 11.5 to 24.7 nm according to the increase in reduction temperatures. The temperature satisfactory for a maximal reduction effect was found to be 1173 K because the oxygen content was minimally saturated to about 1.3 wt %. Full article

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

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11 pages, 3883 KiB

Open AccessArticle

Removal of Mg and MgO By-Products through Magnesiothermic Reduction of Ti Powder in Self-Propagating High-Temperature Synthesis

by Sang Hoon Choi, Jae Jin Sim, Jae Hong Lim, Seok-Jun Seo, Dong-Wook Kim, Soong-Keun Hyun and Kyoung-Tae Park

Metals 2019, 9(2), 169; https://doi.org/10.3390/met9020169 - 01 Feb 2019

Cited by 4 | Viewed by 5734

Abstract

Commercial production of titanium involves chlorination using chlorine gas that can be converted to hydrochloric acid by atmospheric moisture and is hazardous to human health. In the titanium production process, self-propagating high-temperature synthesis is one of the process to directly reduce titanium dioxide. [...] Read more.

Commercial production of titanium involves chlorination using chlorine gas that can be converted to hydrochloric acid by atmospheric moisture and is hazardous to human health. In the titanium production process, self-propagating high-temperature synthesis is one of the process to directly reduce titanium dioxide. In this work, titanium powder was prepared by self-propagating high-temperature synthesis using titanium dioxide as the starting material and magnesium powder as a reducing agent. After the reaction, magnesium and magnesium oxide by-products were then removed by acid leaching under different leaching conditions, leaving behind pure Ti. During each leaching condition, the temperature of the leaching solution was carefully monitored. After leaching, the recovered titanium in the form of a powder was collected, washed with water and dried in a vacuum oven. Detailed compositional, structural, and morphological analyses were performed to determine the presence of residual reaction by-products. It was found that leaching in 0.4 M hydrochloric acid followed by second leaching in 7.5 M hydrochloric acid is the optimum leaching condition. Furthermore, it was also noticed that total volume of solution in 0.4 M hydrochloric acid leaching condition is advantageous to maintain uniform temperature during the process. Full article

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

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9 pages, 2408 KiB

Open AccessArticle

Production of Ultrafine Grained Hardmetals by Electrical Resistance Sintering

by Jesús Cintas, Raquel Astacio, Francisco G. Cuevas, Juan Manuel Montes, Thomas Weissgaerber, Miguel Ángel Lagos, Yadir Torres and José María Gallardo

Metals 2019, 9(2), 159; https://doi.org/10.3390/met9020159 - 01 Feb 2019

Cited by 9 | Viewed by 2716

Abstract

In this work, powders of cemented ultrafine WC-6 wt.% Co were consolidated. The feasibility of the medium frequency electrical resistance sintering (MF-ERS) technique were studied to prevent WC grain growth during consolidation. Porosity and hardness were measured at different zones of the MF-ERS [...] Read more.

In this work, powders of cemented ultrafine WC-6 wt.% Co were consolidated. The feasibility of the medium frequency electrical resistance sintering (MF-ERS) technique were studied to prevent WC grain growth during consolidation. Porosity and hardness were measured at different zones of the MF-ERS compacts. The compacts showed a slight inhomogeneity in their properties across their section, but it was controlled by choosing suitable values of the processing parameters. The optimal values for the material studied were current intensities between 7 and 8 kA and sintering times between 600 and 800 ms. The main achievement using this consolidation method was that sintered compacts essentially maintained the initial WC grain size. This was attained to processing times of less than 2 s, and without the need for using protective atmospheres. Full article

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

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