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17 pages, 15291 KiB

Open AccessArticle

Design and Production of a New FeCoNiCrAlCu High-Entropy Alloy: Influence of Powder Production Method on Sintering

by Eduardo Reverte, Monique Calvo-Dahlborg, Ulf Dahlborg, Monica Campos, Paula Alvaredo, Pablo Martin-Rodriguez, Elena Gordo and Juan Cornide

Materials 2021, 14(15), 4342; https://doi.org/10.3390/ma14154342 - 03 Aug 2021

Cited by 3 | Viewed by 2298

Abstract

The structure of FeCoNiCrAl1.8Cu0.5 high-entropy alloys (HEA) obtained by two different routes has been studied. The selection of the composition has followed the Hume–Rothery approach in terms of number of itinerant electrons (e/a) and average atomic radius to control the formation of specific [...] Read more.

The structure of FeCoNiCrAl1.8Cu0.5 high-entropy alloys (HEA) obtained by two different routes has been studied. The selection of the composition has followed the Hume–Rothery approach in terms of number of itinerant electrons (e/a) and average atomic radius to control the formation of specific phases. The alloys were obtained either from a mixture of elemental powders or from gas-atomised powders, being consolidated in both cases by uniaxial pressing and vacuum sintering at temperatures of 1200 °C and 1300 °C. The characterization performed in the sintered samples from both types of powder includes scanning electron microscopy, X-ray diffraction, differential thermal analysis, and density measurements. It was found that the powder production techniques give similar phases content. However, the sintering at 1300 °C destroys the achieved phase stability of the samples. The phases identified by all techniques and confirmed by Thermo-Calc calculations are the following: a major Co-Ni-Al-rich (P1) BCC phase, which stays stable after 1300 °C sintering and homogenising TT treatments; a complex Cr-Fe-rich (P2) B2 type phase, which transforms into a sigma phase after the 1300 °C sintering and homogenising TT treatments; and a very minor Al-Cu-rich (P3) FCC phase, which also transforms into Domain II and Domain III phases during the heating at 1300 °C and homogenising TT treatments. Full article

(This article belongs to the Special Issue Materials Sintering)

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15 pages, 4198 KiB

Open AccessArticle

Properties of WCCo Composites Produced by the SPS Method Intended for Cutting Tools for Machining of Wood-Based Materials

by Joanna Wachowicz, Tomasz Dembiczak, Grzegorz Stradomski, Zbigniew Bałaga, Marcin Dyner and Jacek Wilkowski

Materials 2021, 14(10), 2618; https://doi.org/10.3390/ma14102618 - 17 May 2021

Cited by 9 | Viewed by 1926

Abstract

This paper presents the possibility of using the Spark Plasma Sintering (SPS) method to obtain WCCo composite materials. Such materials are used as cutting blades for machining wood-based materials. Two series of composites, different in grain size and cobalt content, were analyzed in [...] Read more.

This paper presents the possibility of using the Spark Plasma Sintering (SPS) method to obtain WCCo composite materials. Such materials are used as cutting blades for machining wood-based materials. Two series of composites, different in grain size and cobalt content, were analyzed in the paper. The produced materials were characterized using Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), and tribological properties were determined. In addition, preliminary tests were carried out on the durability of the blades made of sintered WCCo composites while machining three-layer chipboard. The results of the microstructure analysis proved that the SPS method makes it possible to obtain solid composites. Phase analysis showed the occurrence of the following phases: WC, Co, and Co₃W₉C₄. The lowest friction coefficient value was found in samples sintered using powder with an average primary particle size of 400 nm (ultrafine). Full article

(This article belongs to the Special Issue Materials Sintering)

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17 pages, 4292 KiB

Open AccessArticle

Particle Characteristics’ Influence on FLASH Sintering of Potassium Sodium Niobate: A Relationship with Conduction Mechanisms

by Ricardo Serrazina, Camila Ribeiro, Maria Elisabete Costa, Luis Pereira, Paula M. Vilarinho and Ana M. O. R. Senos

Materials 2021, 14(5), 1321; https://doi.org/10.3390/ma14051321 - 09 Mar 2021

Cited by 7 | Viewed by 2516

Abstract

The considerable decrease in temperature and time makes FLASH sintering a more sustainable alternative for materials processing. FLASH also becomes relevant if volatile elements are part of the material to be processed, as in alkali-based piezoelectrics like the promising lead-free K_0.5Na [...] Read more.

The considerable decrease in temperature and time makes FLASH sintering a more sustainable alternative for materials processing. FLASH also becomes relevant if volatile elements are part of the material to be processed, as in alkali-based piezoelectrics like the promising lead-free K_0.5Na_0.5NbO₃ (KNN). Due to the volatile nature of K and Na, KNN is difficult to process by conventional sintering. Although some studies have been undertaken, much remains to be understood to properly engineer the FLASH sintering process of KNN. In this work, the effect of FLASH temperature, T_F, is studied as a function of the particle size and impurity content of KNN powders. Differences are demonstrated: while the particle size and impurity degree markedly influence T_F, they do not significantly affect the densification and grain growth processes. The conductivity of KNN FLASH-sintered ceramics and KNN single crystals (SCs) is compared to elucidate the role of particles’ surface conduction. When particles’ surfaces are not present, as in the case of SCs, the FLASH process requires higher temperatures and conductivity values. These results have implications in understanding FLASH sintering towards a more sustainable processing of lead-free piezoelectrics. Full article

(This article belongs to the Special Issue Materials Sintering)

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21 pages, 8624 KiB

Open AccessArticle

Strength Properties of a Porous Titanium Alloy Ti6Al4V with Diamond Structure Obtained by Laser Power Bed Fusion (LPBF)

by Anna Falkowska, Andrzej Seweryn and Marcin Skrodzki

Materials 2020, 13(22), 5138; https://doi.org/10.3390/ma13225138 - 14 Nov 2020

Cited by 21 | Viewed by 3158

Abstract

This paper presents the results of experimental research on the strength properties of porous structures with different degrees of density manufactured of Ti6Al4V titanium alloy by Laser Power Bed Fusion. In the experiment, samples with diamond structure of porosity: 34%, 50%, 73% and [...] Read more.

This paper presents the results of experimental research on the strength properties of porous structures with different degrees of density manufactured of Ti6Al4V titanium alloy by Laser Power Bed Fusion. In the experiment, samples with diamond structure of porosity: 34%, 50%, 73% and 81% were used, as well as samples with near-zero porosity. Monotonic tensile tests were carried out to determine the effective values of axial modulus of elasticity, ultimate tensile strength, offset yield strength, ultimate elongation and Poisson ratio for titanium alloys with different porosities. The paper also proposes relationships that can be easily used to estimate the strength and rigidity of a porous material manufactured by 3D printing. They were obtained by the approximation of two quotients. The first one refers to the relationship between the tensile strength of a material with a defined porosity to the strength of full-filled material. The second similarly determines the change in the value of the axial modulus of elasticity. The analysis of microscopic observations of fracture surfaces and also microtomography visualization of the material structure are also presented. Full article

(This article belongs to the Special Issue Materials Sintering)

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14 pages, 9448 KiB

Open AccessArticle

Spark Plasma Sintering of Copper Matrix Composites Reinforced with TiB₂ Particles

by Massimo Pellizzari and Giulia Cipolloni

Materials 2020, 13(11), 2602; https://doi.org/10.3390/ma13112602 - 07 Jun 2020

Cited by 13 | Viewed by 2147

Abstract

The aim of this study is to fabricate a Cu-0.5wt%TiB₂ composite by mechanical alloying (MA) and spark plasma sintering (SPS). Increasing the milling time, the powders are subjected firstly to a severe flattening process and then to intense welding, which promotes the [...] Read more.

The aim of this study is to fabricate a Cu-0.5wt%TiB₂ composite by mechanical alloying (MA) and spark plasma sintering (SPS). Increasing the milling time, the powders are subjected firstly to a severe flattening process and then to intense welding, which promotes the refinement of TiB₂ particles, their uniform dispersion in the metal matrix, and the adhesion between the two constituents. Sintered metal matrix composites (MMC) exhibit density values between 99 and 96%, which are generally decreased by increasing milling time in view of the stronger strain hardening. On the other side, the hardness increases with milling time due to the refinement of TiB₂ particles and their improved distribution. The hardness of MMC is three times higher (225 HV0.05) than the starting hardness of atomized copper (90 HV0.05). Tensile tests show a loss of ductility, but ultimate tensile strength has been increased from 276 MPa of atomized copper to 489 MPa of MMC milled for 240 min. The thermal conductivity of MMC is comparable to that of atomized copper (300 W/mK), i.e., much higher than that of the commercial Cu-Be alloy (Uddeholm Moldmax HH, 106 W/mK) typically used for tooling applications. Full article

(This article belongs to the Special Issue Materials Sintering)

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12 pages, 4517 KiB

Open AccessArticle

In Situ Formation of TiB₂ in Fe-B System with Titanium Addition and Its Influence on Phase Composition, Sintering Process and Mechanical Properties

by Mateusz Skałoń, Marek Hebda, Benedikt Schrode, Roland Resel, Jan Kazior and Christof Sommitsch

Materials 2019, 12(24), 4188; https://doi.org/10.3390/ma12244188 - 13 Dec 2019

Cited by 1 | Viewed by 1999

Abstract

Interaction of iron and boron at elevated temperatures results in the formation of an E (Fe + Fe₂B) eutectic phase that plays a great role in enhancing mass transport phenomena during thermal annealing and therefore in the densification of sintered compacts. [...] Read more.

Interaction of iron and boron at elevated temperatures results in the formation of an E (Fe + Fe₂B) eutectic phase that plays a great role in enhancing mass transport phenomena during thermal annealing and therefore in the densification of sintered compacts. When cooled down, this phase solidifies as interconnected hard and brittle material consisting of a continuous network of Fe₂B borides formed at the grain boundaries. To increase ductile behaviour, a change in precipitates’ stoichiometry was investigated by partially replacing iron borides by titanium borides. The powder of elemental titanium was introduced to blend of iron and boron powders in order to induce TiB₂ in situ formation. Titanium addition influence on microstructure, phase composition, density and mechanical properties was investigated. The observations were supported with thermodynamic calculations. The change in phase composition was analysed by means of dilatometry and X-ray diffraction (XRD) coupled with thermodynamic calculations. Full article

(This article belongs to the Special Issue Materials Sintering)

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Review

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20 pages, 7918 KiB

Open AccessReview

Effect of Rare Earth Metals (Y, La) and Refractory Metals (Mo, Ta, Re) to Improve the Mechanical Properties of W–Ni–Fe Alloy—A Review

by Senthilnathan Natarajan, Venkatachalam Gopalan, Raja Annamalai Arunjunai Rajan and Chun-Ping Jen

Materials 2021, 14(7), 1660; https://doi.org/10.3390/ma14071660 - 28 Mar 2021

Cited by 18 | Viewed by 3139

Abstract

Tungsten heavy alloys are two-phase metal matrix composites that include W–Ni–Fe and W–Ni–Cu. The significant feature of these alloys is their ability to acquire both strength and ductility. In order to improve the mechanical properties of the basic alloy and to limit or [...] Read more.

Tungsten heavy alloys are two-phase metal matrix composites that include W–Ni–Fe and W–Ni–Cu. The significant feature of these alloys is their ability to acquire both strength and ductility. In order to improve the mechanical properties of the basic alloy and to limit or avoid the need for post-processing techniques, other elements are doped with the alloy and performance studies are carried out. This work focuses on the developments through the years in improving the performance of the classical tungsten heavy alloy of W–Ni–Fe through doping of other elements. The influence of the percentage addition of rare earth elements of yttrium, lanthanum, and their oxides and refractory metals such as rhenium, tantalum, and molybdenum on the mechanical properties of the heavy alloy is critically analyzed. Based on the microstructural and property evaluation, the effects of adding the elements at various proportions are discussed. The addition of molybdenum and rhenium to the heavy alloy gives good strength and ductility. The oxides of yttrium, when added in a small quantity, help to reduce the tungsten’s grain size and obtain good tensile and compressive strengths at high temperatures. Full article

(This article belongs to the Special Issue Materials Sintering)

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9 pages, 1956 KiB

Open AccessReview

What We Should Consider for Full Densification when Sintering

by Suk-Joong L. Kang

Materials 2020, 13(16), 3578; https://doi.org/10.3390/ma13163578 - 13 Aug 2020

Cited by 16 | Viewed by 2695

Abstract

To fully densify a powder compact, we should avoid two things: (i) entrapment of insoluble gases within pores and (ii) entrapment of isolated pores within grains. This paper describes general directions for promoting full densification in view of the above two points. Emphasis [...] Read more.

To fully densify a powder compact, we should avoid two things: (i) entrapment of insoluble gases within pores and (ii) entrapment of isolated pores within grains. This paper describes general directions for promoting full densification in view of the above two points. Emphasis is placed on ways to potentially prevent pore entrapment in terms of grain growth control. Currently available techniques that can enhance densification while suppressing grain growth are briefly described, and their major mechanisms are discussed. Full article

(This article belongs to the Special Issue Materials Sintering)

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