Metals

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18 pages, 10433 KiB

Open AccessArticle

Microstructure and Mechanical Properties of Spark Plasma Sintered and Severely Deformed AA7075 Alloy

by Dariusz Garbiec, Volf Leshchynsky, Andrea García-Junceda, Radosław Swadźba, Piotr Siwak, Grzegorz Adamek and Krzysztof Radwański

Metals 2021, 11(9), 1433; https://doi.org/10.3390/met11091433 - 10 Sep 2021

Cited by 3 | Viewed by 1722

Abstract

In this paper, the microstructure and mechanical properties of AA7075 with a coarse-fine-grained laminated microstructure produced by spark plasma sintering (SPS) and the cyclic extrusion severe deformation (KOBO) technique were investigated. It was found that an inhomogeneous grain microstructure was formed from coarse [...] Read more.

In this paper, the microstructure and mechanical properties of AA7075 with a coarse-fine-grained laminated microstructure produced by spark plasma sintering (SPS) and the cyclic extrusion severe deformation (KOBO) technique were investigated. It was found that an inhomogeneous grain microstructure was formed from coarse and fine grains by the SPS process and then was transformed into a coarse-fine-grained laminated microstructure by means of KOBO extrusion at room temperature. The grain refinement during KOBO extrusion resulted in a fine grained laminated microstructure created due to the formation of low-angle grain boundaries (LAGBs), followed by dynamic recrystallization, leading to high-angle grain boundaries (HAGBs). The EBSD analysis results reveal the formation of a deformed and partially recrystallized ultrafine grain microstructure owing to the generation and development of shear bands during KOBO extrusion. The ultimate tensile strength (UTS) of the AA7075 alloy rose after SPS-KOBO severe deformation up to 422 MPa, with high strains of about 33%. The obtained results clearly show that the SPS-KOBO extrusion technique allows a bimodal laminated fine gradient grain microstructure to be obtained due to deformation and dynamic recrystallization, which result in both high strength and good ductility. The new heterogeneous AA7075 alloys obtained by the SPS-KOBO combined techniques demonstrate that microstructural heterogeneities can assist in overcoming the strength–ductility trade-off. Full article

(This article belongs to the Special Issue Spark Plasma Sintering of Metals and Metal Matrix Nanocomposites)

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15 pages, 7530 KiB

Open AccessArticle

Understanding the Links between the Composition-Processing-Properties in New Formulations of HEAs Sintered by SPS

by Paula Alvaredo-Olmos, Jon Molina-Aldareguía, Alvaro Vaz-Romero, Estela Prieto, Jesús González-Julián and Miguel Alberto Monclús

Metals 2021, 11(6), 888; https://doi.org/10.3390/met11060888 - 28 May 2021

Cited by 3 | Viewed by 2085

Abstract

This work presents two new compositions of high entropy alloys (HEAs) that were designed with the aim of obtaining a body-centered cubic (BCC) phase with high hardness values and a moderate density. Sintering was performed using Spark Plasma Sintering (SPS) with different heating [...] Read more.

This work presents two new compositions of high entropy alloys (HEAs) that were designed with the aim of obtaining a body-centered cubic (BCC) phase with high hardness values and a moderate density. Sintering was performed using Spark Plasma Sintering (SPS) with different heating rates to determine the influence of the processing parameters on the phase formation. The microstructural study revealed that the presence of Ni in the composition promoted phase separation, and the mechanical study confirmed a clear influence on the mechanical properties of both the composition and heating rate. The combination of microscopy with compression and nanoindentation tests at room and high temperature made it possible to advance our understanding of the relationships between the composition, processing, and properties of this emerging group of alloys. Full article

(This article belongs to the Special Issue Spark Plasma Sintering of Metals and Metal Matrix Nanocomposites)

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16 pages, 12179 KiB

Open AccessArticle

Microstructure Evolution in a Fast and Ultrafast Sintered Non-Equiatomic Al/Cu HEA

by Eduardo Reverte, Juan Cornide, Miguel A. Lagos, Mónica Campos and Paula Alvaredo

Metals 2021, 11(6), 848; https://doi.org/10.3390/met11060848 - 21 May 2021

Cited by 4 | Viewed by 1934

Abstract

One of the attractive characteristics of high entropy alloys (HEAs) is the ability to tailor their composition to obtain specific microstructures and properties by adjusting the stoichiometry to obtain a body-centered cubic (BCC) or face-centered cubic (FCC) structure. Thus, in this work, the [...] Read more.

One of the attractive characteristics of high entropy alloys (HEAs) is the ability to tailor their composition to obtain specific microstructures and properties by adjusting the stoichiometry to obtain a body-centered cubic (BCC) or face-centered cubic (FCC) structure. Thus, in this work, the target composition of an alloy of the FeCrCoNi family has been modified by adjusting the Al/Cu ratio in order to obtain a BCC crystalline structure. However, processing conditions always play a key role in the final microstructure and, therefore, in this work, the microstructure evolution of FeCrCoNiAl_1.8Cu_0.5 HEA sintered by different powder metallurgy (PM) techniques has been investigated. The techniques used range from the conventional PM sintering route, that uses high heating rates and sintering times, going through a fast sintering technique such as spark plasma sintering (SPS) to the novel and promising ultrafast sintering technique electrical resistance sintering (ERS). Results show that the increase in the processing time favours the separation of phases and the segregation of elements, which is reflected in a substantial change in the hardness of the alloy. In conclusion, the ERS technique is presented as a very promising consolidation technique for HEA. Full article

(This article belongs to the Special Issue Spark Plasma Sintering of Metals and Metal Matrix Nanocomposites)

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16 pages, 4622 KiB

Open AccessFeature PaperArticle

Magnetic Field Generated during Electric Current-Assisted Sintering: From Health and Safety Issues to Lorentz Force Effects

by Huaijiu Deng, Jian Dong, Filippo Boi, Theo Saunders, Chunfeng Hu and Salvatore Grasso

Metals 2020, 10(12), 1653; https://doi.org/10.3390/met10121653 - 8 Dec 2020

Cited by 7 | Viewed by 2788

Abstract

In the past decade, a renewed interest on electromagnetic processing of materials has motivated several investigations on the interaction between matter, electric and magnetic fields. These effects are primarily reconducted to the Joule heating and very little attention has been dedicated to the [...] Read more.

In the past decade, a renewed interest on electromagnetic processing of materials has motivated several investigations on the interaction between matter, electric and magnetic fields. These effects are primarily reconducted to the Joule heating and very little attention has been dedicated to the magnetic field contributions. The magnetic field generated during electric current-assisted sintering has not been widely investigated. Magnetism could have significant effects on sintering as it generates significant magnetic forces, resulting in inductive electrical loads and preferential heating induced by overlapping magnetic fields (i.e., proximity effect). This work summarizes the magnetic field effects in electric current-assisted processing; it focuses on health and safety issues associated with large currents (up to 0.4 MA); using FEM simulations, it computes the self-generated magnetic field during spark plasma sintering (SPS) to consolidate materials with variable magnetic permeability; and it quantifies the Lorentz force acting at interparticle contact points. The results encourage one to pay more attention to magnetic field-related effects in order to engineer and exploit their potentials. Full article

(This article belongs to the Special Issue Spark Plasma Sintering of Metals and Metal Matrix Nanocomposites)

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10 pages, 4325 KiB

Open AccessArticle

Microstructure Evolution and Mechanical Properties of Spark Plasma Sintered Manganese Addition on Ti-48Al-2Cr-2Nb Alloys

by A. Raja Annamalai, Muthe Srikanth, Raunak Varshney, Mehta Yash Ashokkumar, Swarup Kumar Patro and Chun-Ping Jen

Metals 2020, 10(12), 1577; https://doi.org/10.3390/met10121577 - 25 Nov 2020

Cited by 5 | Viewed by 2398

Abstract

Titanium aluminide (TiAl) is one of the most promising materials for aerospace applications. It is a suitable replacement for nickel-based superalloys predominantly used in these applications. Titanium aluminide with superior processability is the main task in carrying out this work. A less brittle [...] Read more.

Titanium aluminide (TiAl) is one of the most promising materials for aerospace applications. It is a suitable replacement for nickel-based superalloys predominantly used in these applications. Titanium aluminide with superior processability is the main task in carrying out this work. A less brittle TiAl alloy was fabricated using spark plasma sintering by adding the nominal composition (2.5, 5, and 7.5 wt.%) of manganese (Mn) to Ti-48Al-2Cr-2Nb. The samples were sintered at 1150 °C using spark plasma sintering (SPS), which helped produce highly dense models with fine grain sizes at the high heating rate (here, 100 °C per minute). The effects produced by Mn additions on the densification, mechanical properties (yield strength, hardness, and % elongation), and microstructure of the Ti aluminide alloys are studied. Scanning electron microscopy (SEM) has been used to explore the sintered samples’ microstructures. The alloyed materials are entirely dissolved in the gamma matrix due to the manganese approaching its melting point. XRD and SEM analysis confirmed the new intermetallic related to Mn neither with titanium nor aluminum. The enhancement of % elongation at break is evident for the little improvement in the ductility of TiAl by the addition of Mn. The samples’ tensile fracture nature is also evidence for enhancement in the alloy’s % elongation. Full article

(This article belongs to the Special Issue Spark Plasma Sintering of Metals and Metal Matrix Nanocomposites)

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16 pages, 4945 KiB

Open AccessArticle

Development of New 14 Cr ODS Steels by Using New Oxides Formers and B as an Inhibitor of the Grain Growth

by Alberto Meza, Eric Macía, Andrea García-Junceda, Luis Antonio Díaz, Paul Chekhonin, Eberhard Altstadt, Marta Serrano, María Eugenia Rabanal and Mónica Campos

Metals 2020, 10(10), 1344; https://doi.org/10.3390/met10101344 - 8 Oct 2020

Cited by 8 | Viewed by 2952

Abstract

In this work, new oxide dispersion strengthened (ODS) ferritic steels have been produced by powder metallurgy using an alternative processing route and characterized afterwards by comparing them with a base ODS steel with Y₂O₃ and Ti additions. Different alloying elements [...] Read more.

In this work, new oxide dispersion strengthened (ODS) ferritic steels have been produced by powder metallurgy using an alternative processing route and characterized afterwards by comparing them with a base ODS steel with Y₂O₃ and Ti additions. Different alloying elements like boron (B), which is known as an inhibitor of grain growth obtained by pinning grain boundaries, and complex oxide compounds (Y-Ti-Zr-O) have been introduced to the 14Cr prealloyed powder by using mechanical alloying (MA) and were further consolidated by spark employing plasma sintering (SPS). Techniques such as x-ray diffraction (XRD), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM) were used to study the obtained microstructures. Micro-tensile tests and microhardness measurements were carried out at room temperature to analyze the mechanical properties of the differently developed microstructures, which was considered to result in a better strength in the ODS steels containing the complex oxide Y-Ti-Zr-O. In addition, small punch (SP) tests were performed to evaluate the response of the material under high temperatures conditions, under which promising mechanical properties were attained by the materials containing Y-Ti-Zr-O (14Al-X-ODS and 14Al-X-ODS-B) in comparison with the other commercial steel, GETMAT. The differences in mechanical strength can be attributed to the precipitate’s density, nature, size, and to the density of dislocations in each ODS steel. Full article

(This article belongs to the Special Issue Spark Plasma Sintering of Metals and Metal Matrix Nanocomposites)

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12 pages, 13439 KiB

Open AccessArticle

Spark Plasma Sintering and Characterization of Al-TiB₂ Composites

by A. Raja Annamalai, Muthe Srikanth, A. Muthuchamy, Shashank Acharya, Anup Khisti, Dinesh K. Agrawal and Chun-Ping Jen

Metals 2020, 10(9), 1110; https://doi.org/10.3390/met10091110 - 19 Aug 2020

Cited by 9 | Viewed by 3194

Abstract

In this study, Al-TiB₂ compacts fabricated by spark plasma sintering methods at different temperatures were characterized for densification, microstructural development, and mechanical properties. Sintering parameters used were temperatures of 500 °C and 550 °C under the pressure of 30 MPa. A very [...] Read more.

In this study, Al-TiB₂ compacts fabricated by spark plasma sintering methods at different temperatures were characterized for densification, microstructural development, and mechanical properties. Sintering parameters used were temperatures of 500 °C and 550 °C under the pressure of 30 MPa. A very dense microstructure with uniform phase distribution and porosity was produced in the sample sintered at 550 °C with 2.5 wt% TiB₂. The same sample exhibited excellent hardness value, and a high-tensile strength attributed to full metallurgical bonding, presence of sub-micron sized grains, and their uniform distribution. These results show that the TiB₂ addition enhanced the composite’s hardness, sintered density, and tensile strength. In all the sintered samples, the fractographs revealed a mixed-mode fracture (ductile and brittle). Full article

(This article belongs to the Special Issue Spark Plasma Sintering of Metals and Metal Matrix Nanocomposites)

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25 pages, 9316 KiB

Open AccessArticle

The Effect of the Processing Parameters on the Properties of the Liquid Phase Spark Plasma Sintered 80Fe-20(Al + MWCNT) Magnetic Metal Matrix Nanocomposites

by Alexandre Tugirumubano, Sun Ho Go, Lee Ku Kwac, Hee Jae Shin and Hong Gun Kim

Metals 2020, 10(7), 962; https://doi.org/10.3390/met10070962 - 16 Jul 2020

Cited by 2 | Viewed by 2453

Abstract

In this paper, the liquid phase sintering was performed using spark plasma sintering to produce iron (Fe: 80 vol%)–aluminum (Al)–multi-walled carbon nanotubes (MWCNTs) magnetic hybrid metal matrix nanocomposites. The properties of the nanocomposites were investigated by considering different parameters of materials processing. The [...] Read more.

In this paper, the liquid phase sintering was performed using spark plasma sintering to produce iron (Fe: 80 vol%)–aluminum (Al)–multi-walled carbon nanotubes (MWCNTs) magnetic hybrid metal matrix nanocomposites. The properties of the nanocomposites were investigated by considering different parameters of materials processing. The reinforcement of MWCNT with a content of 0–2 vol% did not affect the saturation magnetization of the nanocomposites but increased the coercivity and reduced both the electrical resistivity and the mechanical transverse rupture strength. It was found that milling the powders for 24 h resulted in composite with high saturation magnetization (148.820 A·m²/kg) and high coercivity (2175.6 A/m) but further milling time had reduced the values of magnetic properties. The mixture of Fe nanoparticles and Fe microparticles in composites with a nanoparticles-to-microparticles volume ratio of 1:1 has led to the enhanced saturation magnetization up to 157.820 A·m²/kg and reduced the coercivity of 50.20% in comparison with the Fe nanoparticles based nanocomposites. That mixture exhibited good electrical resistivity but caused the reduction of mechanical strength. The post-sintering annealing has significantly improved the magnetic softness of the composites by reducing the coercivity up to 854.30 A/m and increased the saturation magnetization. Full article

(This article belongs to the Special Issue Spark Plasma Sintering of Metals and Metal Matrix Nanocomposites)

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13 pages, 6473 KiB

Open AccessArticle

Effect of Small Variations in Zr Content on the Microstructure and Properties of Ferritic ODS Steels Consolidated by SPS

by Andrea García-Junceda, Eric Macía, Dariusz Garbiec, Marta Serrano, José M. Torralba and Mónica Campos

Metals 2020, 10(3), 348; https://doi.org/10.3390/met10030348 - 6 Mar 2020

Cited by 17 | Viewed by 2514

Abstract

Two different zirconium contents (0.45 and 0.60 wt.%) have been incorporated into a Fe-14Cr-5Al-3W-0.4Ti-0.25Y₂O₃ oxide dispersion-strengthened (ODS) steel in order to evaluate their effect on the final microstructure and mechanical properties. The powders with the targeted compositions were obtained by [...] Read more.

Two different zirconium contents (0.45 and 0.60 wt.%) have been incorporated into a Fe-14Cr-5Al-3W-0.4Ti-0.25Y₂O₃ oxide dispersion-strengthened (ODS) steel in order to evaluate their effect on the final microstructure and mechanical properties. The powders with the targeted compositions were obtained by mechanical alloying (MA), and subsequently processed by spark plasma sintering (SPS) at two different heating rates: 100 and 400 °C·min⁻¹. Non-textured bimodal microstructures composed of micrometric and ultrafine grains were obtained. The increase in Zr content led to a higher percentage of Zr nano-oxides and larger regions of ultrafine grains. These ultrafine grains also seem to be promoted by higher heating rates. The effective pinning of the dislocations by the Zr dispersoids, and the refining of the microstructure, have significantly increased the strength exhibited by the ODS steels during the small punch tests, even at high temperatures (500 °C). Full article

(This article belongs to the Special Issue Spark Plasma Sintering of Metals and Metal Matrix Nanocomposites)

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