Materials

2022

Jump to: 2021, 2020, 2019

20 pages, 8767 KiB

Open AccessArticle

Effect of Silicon Carbide Nanoparticles on the Friction-Wear Properties of Copper-Based Friction Discs

by Changsong Zheng, Zhiwei Ma, Liang Yu, Xu Wang, Liangjie Zheng and Li’an Zhu

Materials 2022, 15(2), 587; https://doi.org/10.3390/ma15020587 - 13 Jan 2022

Cited by 2 | Viewed by 1715

Abstract

To study the influence of nano-additives on the friction-wear characteristics of friction materials, the nano-sized silicon carbide particles which have excellent chemical and physical properties are considered to add in composite to form the modified friction material. The influence of the silicon carbide [...] Read more.

To study the influence of nano-additives on the friction-wear characteristics of friction materials, the nano-sized silicon carbide particles which have excellent chemical and physical properties are considered to add in composite to form the modified friction material. The influence of the silicon carbide nanoparticles (SCN) on the friction-wear characteristics of copper-based friction materials (CBFM) is investigated via the SAE#2 (made in Hangzhou, China) clutch bench test with the applied pressure, rotating speed, and automatic transmission fluid (ATF) temperature taken into account. Moreover, the variations of friction torque and temperature are considered to evaluate the friction performance, and the variable coefficient is employed to describe the friction stability. The wear characteristics of friction materials are investigated by the disc changes in thickness and micro-morphology. The results show that the CBFM with SCN can provide a higher friction torque, which increased by 30% to 50% compared with CBFM. The variable coefficient of CBFM with SCN changes from 674 to 52 with the rotating speed raised from 600 rpm to 3000 rpm, which shows that the friction stability is relatively worse. Furthermore, the micromorphology shows that the CBFM with SCN has lower porosity and surface roughness, which increases the microscopic contact area and the coefficient of friction (COF). Simultaneously, the reduction in porosity also leads to a decrease in the cooling quality, bringing about a rapid temperature rise. Thus, the wear amount of CBFM with SCN increases significantly, especially for the friction disc in the axial middle position. Full article

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2021

Jump to: 2022, 2020, 2019

12 pages, 4010 KiB

Open AccessArticle

Corrosion Properties of Mn-Based Alloys Obtained by Aluminothermic Reduction of Deep-Sea Nodules

by Šárka Msallamová, Pavel Novák, Pauline Miossec, Jaromír Kopeček, Alisa Tsepeleva, Darya Rudomilova and Jaroslav Fojt

Materials 2021, 14(18), 5211; https://doi.org/10.3390/ma14185211 - 10 Sep 2021

Cited by 6 | Viewed by 1548

Abstract

Deep-sea manganese nodules are polymetallic oxidic ores that can be found on a seabed. Aluminothermic reduction is one of the possibilities of manganese nodules processing. This process obtains the polymetallic alloy with a high content of Mn and a varying content of Al, [...] Read more.

Deep-sea manganese nodules are polymetallic oxidic ores that can be found on a seabed. Aluminothermic reduction is one of the possibilities of manganese nodules processing. This process obtains the polymetallic alloy with a high content of Mn and a varying content of Al, depending on the ratio between aluminum and nodules. The corrosion behaviors of three experimental Mn-based alloys produced by aluminothermic reduction with a content of Mn > 50 wt % were studied. The electrochemical testing in potable water and model seawater was used to explain the corrosion mechanism of Mn-based alloys. The results showed that the corrosion rate of experimental Mn-based alloy decreases with the increase in aluminum content in both potable water and model seawater. It was observed that the uniform corrosion of experimental Mn-based alloys is changed with an increase in aluminum content in alloy to localized corrosion, which was caused by microcells in an environment of model seawater. In contrast, the formation of a semi-protective layer of corrosion products was observed on the surface of Mn-based alloys with a higher content of aluminum in potable water. Moreover, the pitting corrosion of tested Mn-based alloys was observed neither in potable water nor in model seawater. Full article

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2020

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3 pages, 187 KiB

Open AccessEditorial

Advanced Powder Metallurgy Technologies

by Pavel Novák

Materials 2020, 13(7), 1742; https://doi.org/10.3390/ma13071742 - 08 Apr 2020

Cited by 13 | Viewed by 3678

Abstract

Powder metallurgy is a group of advanced processes for the synthesis, processing, and shaping of various kinds of materials. Initially inspired by ceramics processing, the methodology comprising of the production of a powder and its transformation to a compact solid product has attracted [...] Read more.

Powder metallurgy is a group of advanced processes for the synthesis, processing, and shaping of various kinds of materials. Initially inspired by ceramics processing, the methodology comprising of the production of a powder and its transformation to a compact solid product has attracted great attention since the end of World War II. At present, there are many technologies for powder production (e.g., gas atomization of the melt, chemical reduction, milling, and mechanical alloying) and its consolidation (e.g., pressing and sintering, hot isostatic pressing, and spark plasma sintering). The most promising ones can achieve an ultra-fine or nano-grained structure of the powder, and preserve it during consolidation. Among these methods, mechanical alloying and spark plasma sintering play a key role. This Special Issue gives special focus to the advancement of mechanical alloying, spark plasma sintering and self-propagating high-temperature synthesis methods, as well as to the role of these processes in the development of new materials. Full article

48 pages, 10878 KiB

Open AccessReview

The Critical Raw Materials in Cutting Tools for Machining Applications: A Review

by Antonella Rizzo, Saurav Goel, Maria Luisa Grilli, Roberto Iglesias, Lucyna Jaworska, Vjaceslavs Lapkovskis, Pavel Novak, Bogdan O. Postolnyi and Daniele Valerini

Materials 2020, 13(6), 1377; https://doi.org/10.3390/ma13061377 - 18 Mar 2020

Cited by 92 | Viewed by 14015

Abstract

A variety of cutting tool materials are used for the contact mode mechanical machining of components under extreme conditions of stress, temperature and/or corrosion, including operations such as drilling, milling turning and so on. These demanding conditions impose a seriously high strain rate [...] Read more.

A variety of cutting tool materials are used for the contact mode mechanical machining of components under extreme conditions of stress, temperature and/or corrosion, including operations such as drilling, milling turning and so on. These demanding conditions impose a seriously high strain rate (an order of magnitude higher than forming), and this limits the useful life of cutting tools, especially single-point cutting tools. Tungsten carbide is the most popularly used cutting tool material, and unfortunately its main ingredients of W and Co are at high risk in terms of material supply and are listed among critical raw materials (CRMs) for EU, for which sustainable use should be addressed. This paper highlights the evolution and the trend of use of CRMs) in cutting tools for mechanical machining through a timely review. The focus of this review and its motivation was driven by the four following themes: (i) the discussion of newly emerging hybrid machining processes offering performance enhancements and longevity in terms of tool life (laser and cryogenic incorporation); (ii) the development and synthesis of new CRM substitutes to minimise the use of tungsten; (iii) the improvement of the recycling of worn tools; and (iv) the accelerated use of modelling and simulation to design long-lasting tools in the Industry-4.0 framework, circular economy and cyber secure manufacturing. It may be noted that the scope of this paper is not to represent a completely exhaustive document concerning cutting tools for mechanical processing, but to raise awareness and pave the way for innovative thinking on the use of critical materials in mechanical processing tools with the aim of developing smart, timely control strategies and mitigation measures to suppress the use of CRMs. Full article

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18 pages, 7142 KiB

Open AccessArticle

Influence of Ti on the Tensile Properties of the High-Strength Powder Metallurgy High Entropy Alloys

by Igor Moravcik, Stepan Gamanov, Larissa Moravcikova-Gouvea, Zuzana Kovacova, Michael Kitzmantel, Erich Neubauer and Ivo Dlouhy

Materials 2020, 13(3), 578; https://doi.org/10.3390/ma13030578 - 26 Jan 2020

Cited by 10 | Viewed by 3719

Abstract

The focus of this study is the evaluation of the influence of Ti concentration on the tensile properties of powder metallurgy high entropy alloys. Three Ni_1.5Co_1.5CrFeTi_X alloys with X = 0.3; 0.5 and 0.7 were produced by mechanical [...] Read more.

The focus of this study is the evaluation of the influence of Ti concentration on the tensile properties of powder metallurgy high entropy alloys. Three Ni_1.5Co_1.5CrFeTi_X alloys with X = 0.3; 0.5 and 0.7 were produced by mechanical alloying and spark plasma sintering. Additional annealing heat treatment at 1100 °C was utilized to obtain homogenous single-phase face centered cubic (FCC) microstructures, with minor oxide inclusions. The results show that Ti increases the strength of the alloys by increasing the average atomic size misfit i.e., solid solution strengthening. An excellent combination of mechanical properties can be obtained by the proposed method. For instance, annealed Ni_1,5Co_1,5CrFeTi_0.7 alloy possessed the ultimate tensile strength as high as ~1600 MPa at a tensile ductility of ~9%, despite the oxide contamination. The presented results may serve as a guideline for future alloy design of novel, inclusion-tolerant materials for sustainable metallurgy. Full article

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17 pages, 7724 KiB

Open AccessArticle

Properties of FeAlSi-X-Y Alloys (X,Y=Ni, Mo) Prepared by Mechanical Alloying and Spark Plasma Sintering

by Filip Průša, Olga Proshchenko, Andrea Školáková, Vojtěch Kučera and František Laufek

Materials 2020, 13(2), 292; https://doi.org/10.3390/ma13020292 - 08 Jan 2020

Cited by 2 | Viewed by 2590

Abstract

Short-term mechanical alloying and compaction by spark plasma sintering was used for the production of FeAl20Si20Mo20-XNiX (X corresponds to 5–15 wt %) alloy, which showed an ultrafine-grained microstructure with dimensions of phases around 200 nm or smaller. It was found that the addition [...] Read more.

Short-term mechanical alloying and compaction by spark plasma sintering was used for the production of FeAl20Si20Mo20-XNiX (X corresponds to 5–15 wt %) alloy, which showed an ultrafine-grained microstructure with dimensions of phases around 200 nm or smaller. It was found that the addition of Mo and Ni to the FeAl20Si20 alloy results in the formation of the AlMoSi phase compared to the three-phase FeAl20Si20 alloy, which initially contained FeSi, Fe₃Si, and Fe₃Al₂Si₃ phases. All the investigated alloys increased their hardness, reaching up to 1401 HV 1 for the FeAl20Si20Mo5Ni15 alloy, which contained in total 58.5% of the FeSi and Fe₃Al₂Si₃ phases. As a result, all the prepared alloys showed one order magnitude lower wear rates ranging from 3.14 to 5.97·10⁻⁶ mm³·N⁻¹·m⁻¹ as well as significantly lower friction coefficients compared to two reference tool steels. The alloys achieved high compressive strengths (up to 2200 MPa); however, they also exhibited high brittleness even after long-term annealing, which reduced the strengths of all the alloys below approximately 1600 MPa. Furthermore, the alloys were showing ductile behavior when compressively tested at elevated temperature of 800 °C. The oxidation resistance of the alloys was superior due to the formation of a compact Al₂O₃ protective layer that did not delaminate. Full article

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2019

Jump to: 2022, 2021, 2020

10 pages, 2276 KiB

Open AccessArticle

Densification of Magnesium Aluminate Spinel Using Manganese and Cobalt Fluoride as Sintering Aids

by Ali Talimian, Vaclav Pouchly, Karel Maca and Dusan Galusek

Materials 2020, 13(1), 102; https://doi.org/10.3390/ma13010102 - 24 Dec 2019

Cited by 14 | Viewed by 3854

Abstract

Highly dense magnesium aluminate spinel bodies are usually fabricated using pressure-assisted methods, such as spark plasma sintering (SPS), in the presence of lithium fluoride as a sintering aid. The present work investigates whether the addition of transition metal fluorides promotes the sintering of [...] Read more.

Highly dense magnesium aluminate spinel bodies are usually fabricated using pressure-assisted methods, such as spark plasma sintering (SPS), in the presence of lithium fluoride as a sintering aid. The present work investigates whether the addition of transition metal fluorides promotes the sintering of MgAl₂O₄ bodies during SPS. At the same time, such fluorides can act as a source of optically active dopants. A commercial MgAl₂O₄ was mixed with 0.5 wt% of LiF, MnF₂, and CoF₂ and, afterwards, consolidated using SPS at 1400 °C. Although MnF₂ and CoF₂ promote the densification as effectively as LiF, they cause significant grain growth. Full article

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11 pages, 3474 KiB

Open AccessArticle

Application of a Dy₃Co_0.6Cu_0.4H_x Addition for Controlling the Microstructure and Magnetic Properties of Sintered Nd-Fe-B Magnets

by Katerina Skotnicova, Pavel A. Prokofev, Natalia B. Kolchugina, Gennady S. Burkhanov, Alexander A. Lukin, Yurii S. Koshkid’ko, Tomas Cegan, Henryk Drulis, Tatyana Romanova and Nikolay A. Dormidontov

Materials 2019, 12(24), 4235; https://doi.org/10.3390/ma12244235 - 17 Dec 2019

Cited by 4 | Viewed by 2317

Abstract

The focus of new technologies on the formation of inhomogeneous distributions of heavy rare-earth metals (REMs) in hard magnetic Nd–Fe–B materials is of scientific importance to increase their functional properties, along with preserving existing sources of heavy REMs. This paper focused on the [...] Read more.

The focus of new technologies on the formation of inhomogeneous distributions of heavy rare-earth metals (REMs) in hard magnetic Nd–Fe–B materials is of scientific importance to increase their functional properties, along with preserving existing sources of heavy REMs. This paper focused on the coercivity enhancement of Nd₂Fe₁₄B-based magnets by optimizing the microstructure, which includes the processes of grain boundary structuring via the application of a Dy₃Co_0.6Cu_0.4H_x alloy added to the initial Nd–Fe–B-based powder mixtures in the course of their mechanical activation. We have studied the role of alloying elements in the formation of phase composition, microstructure, the fine structure of grains, and the hysteretic properties of hard magnetic Nd(R)₂Fe₁₄B-based materials. It was shown that the Dy introduction via the two-component blending process (the hydrogenated Dy₃Co_0.6Cu_0.4 compound is added to a powder mixture) resulted in the formation of the core-shell structure of 2–14–1 phase grains. The efficient improvement of the coercivity of Nd(RE)–Fe–B magnets, with a slight sacrifice of remanence, was demonstrated. Full article

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9 pages, 4877 KiB

Open AccessArticle

Rapidly Solidified Aluminium Alloy Composite with Nickel Prepared by Powder Metallurgy: Microstructure and Self-Healing Behaviour

by Alena Michalcová, Anna Knaislová, Jiří Kubásek, Zdeněk Kačenka and Pavel Novák

Materials 2019, 12(24), 4193; https://doi.org/10.3390/ma12244193 - 13 Dec 2019

Cited by 3 | Viewed by 1975

Abstract

Composite material prepared by spark plasma sintering (SPS) from a powder mixture of AlCrFeSi rapidly solidified alloy and 5 wt. % of Ni particles was studied in this work. It was proven that during SPS compaction at 500 °C, no intermetallic phases formed [...] Read more.

Composite material prepared by spark plasma sintering (SPS) from a powder mixture of AlCrFeSi rapidly solidified alloy and 5 wt. % of Ni particles was studied in this work. It was proven that during SPS compaction at 500 °C, no intermetallic phases formed on the surface of Ni particles. The material exhibited sufficient mechanical properties obtained by tensile testing (ultimate tensile stress of 203 ± 4 MPa, ductility of 0.8% and 0.2% offset yield strength of 156 ± 2 MPa). Tensile samples were pre-stressed to 180 MPa and annealed at 450 and 550 °C for 1 h. Annealing at 450 °C did not lead to any recovery of the material. Annealing at 550 °C caused the full recovery of 0.2% offset yield strength, while the ductility was decreased. The self-healing behaviour originates from the growth of intermetallic phases between the Ni particle and the Al matrix. The sequence of NiAl, Ni₂Al₃ and NiAl₃ intermetallic phases formation was observed. In particular, the morphology of the NiAl₃ phase, growing in thin dendrites into the Al matrix, is suitable for the closing of cracks, which pass through the material. Full article

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10 pages, 4944 KiB

Open AccessFeature PaperArticle

High Strength X3NiCoMoTi 18-9-5 Maraging Steel Prepared by Selective Laser Melting from Atomized Powder

by Angelina Strakosova, Jiří Kubásek, Alena Michalcová, Filip Průša, Dalibor Vojtěch and Drahomír Dvorský

Materials 2019, 12(24), 4174; https://doi.org/10.3390/ma12244174 - 12 Dec 2019

Cited by 17 | Viewed by 3603

Abstract

Maraging steels are generally characterized by excellent mechanical properties, which make them ideal for various industrial applications. The application field can be further extended by using selective laser melting (SLM) for additive manufacturing of shape complicated products. However, the final mechanical properties are [...] Read more.

Maraging steels are generally characterized by excellent mechanical properties, which make them ideal for various industrial applications. The application field can be further extended by using selective laser melting (SLM) for additive manufacturing of shape complicated products. However, the final mechanical properties are strongly related to the microstructure conditions. The present work studies the effect of heat treatment on the microstructure and mechanical properties of 3D printed samples prepared from powder of high-strength X3NiCoMoTi 18-9-5 maraging steel. It was found that the as-printed material had quite low mechanical properties. After sufficient heat treatment, the hardness of the material increased from 350 to 620 HV0.1 and the tensile yield strength increased from 1000 MPa up to 2000 MPa. In addition, 3% ductility was maintained. This behavior was primarily affected by strong precipitation during processing. Full article

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17 pages, 9415 KiB

Open AccessArticle

Influence of Heat Treatment on Microstructure and Properties of NiTi46 Alloy Consolidated by Spark Plasma Sintering

by Pavel Salvetr, Jaromír Dlouhý, Andrea Školáková, Filip Průša, Pavel Novák, Miroslav Karlík and Petr Haušild

Materials 2019, 12(24), 4075; https://doi.org/10.3390/ma12244075 - 06 Dec 2019

Cited by 14 | Viewed by 2995

Abstract

Ni-Ti alloys are considered to be very important shape memory alloys with a wide application area including, e.g., biomaterials, actuators, couplings, and components in automotive, aerospace, and robotics industries. In this study, the NiTi46 (wt.%) alloy was prepared by a combination of self-propagating [...] Read more.

Ni-Ti alloys are considered to be very important shape memory alloys with a wide application area including, e.g., biomaterials, actuators, couplings, and components in automotive, aerospace, and robotics industries. In this study, the NiTi46 (wt.%) alloy was prepared by a combination of self-propagating high-temperature synthesis, milling, and spark plasma sintering consolidation at three various temperatures. The compacted samples were subsequently heat-treated at temperatures between 400 °C and 900 °C with the following quenching in water or slow cooling in a closed furnace. The influence of the consolidation temperature and regime of heat treatment on the microstructure, mechanical properties, and temperatures of phase transformation was evaluated. The results demonstrate the brittle behaviour of the samples directly after spark plasma sintering at all temperatures by the compressive test and no transformation temperatures at differential scanning calorimetry curves. The biggest improvement of mechanical properties, which was mainly a ductility enhancement, was achieved by heat treatment at 700 °C. Slow cooling has to be recommended in order to obtain the shape memory properties. Full article

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7 pages, 1549 KiB

Open AccessFeature PaperArticle

Zn-Mg Biodegradable Composite: Novel Material with Tailored Mechanical and Corrosion Properties

by Jiří Kubásek, Drahomír Dvorský, Jaroslav Čapek, Jan Pinc and Dalibor Vojtěch

Materials 2019, 12(23), 3930; https://doi.org/10.3390/ma12233930 - 27 Nov 2019

Cited by 19 | Viewed by 2935

Abstract

Zinc-based alloys represent one of the most highly developed areas regarding biodegradable materials. Despite this, some general deficiencies such as cytotoxicity and poor mechanical properties (especially elongation), are not properly solved. In this work, a Zn-5Mg (5 wt.% Mg) composite material with tailored [...] Read more.

Zinc-based alloys represent one of the most highly developed areas regarding biodegradable materials. Despite this, some general deficiencies such as cytotoxicity and poor mechanical properties (especially elongation), are not properly solved. In this work, a Zn-5Mg (5 wt.% Mg) composite material with tailored mechanical and superior corrosion properties is prepared by powder metallurgy techniques. Pure Zn and Mg are mixed and subsequently compacted by extrusion at 200 °C and an extrusion ratio of 10. The final product possesses appropriate mechanical properties (tensile yield strength = 148 MPa, ultimate tensile strength = 183 MPa, and elongation = 16%) and decreased by four times the release of Zn in the initial stage of degradation compared to pure Zn, which can highly decrease cytotoxicity effects and therefore positively affect the initial stage of the healing process. Full article

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16 pages, 4457 KiB

Open AccessArticle

Impact of the Morphology of Micro- and Nanosized Powder Mixtures on the Microstructure of Mg-Mg₂Si-CNT Composite Sinters

by Anita Olszówka-Myalska, Patryk Wrześniowski, Hanna Myalska, Marcin Godzierz and Dariusz Kuc

Materials 2019, 12(19), 3242; https://doi.org/10.3390/ma12193242 - 04 Oct 2019

Cited by 11 | Viewed by 2532

Abstract

The problem of preparing a ternary powder mixture, which was meant to fabricate sintered heterophase composite, and consisted of micro- and two nanosized powders, was analyzed. The microsized powder was a pure magnesium, and as nanocomponents, a silicon powder (nSi) and carbon nanotubes [...] Read more.

The problem of preparing a ternary powder mixture, which was meant to fabricate sintered heterophase composite, and consisted of micro- and two nanosized powders, was analyzed. The microsized powder was a pure magnesium, and as nanocomponents, a silicon powder (nSi) and carbon nanotubes (CNTs) with 2% and 1% volume fractions, respectively, were applied. The powder mixtures were prepared using ultrasonic and mechanical mixing in technological fluid, and four mixing variants were applied. The morphology of the powder mixtures was characterized with scanning electron microscopy (SEM), and then, composite sinters were fabricated in a vacuum with hot temperature pressing at 580 °C under 15 MPa pressure, using a Degussa press. The reaction between the nSi and the Mg matrix, which caused the creation of the Mg₂Si phase in the fabricated Mg-Mg₂Si-CNT composite, was confirmed with X-ray diffraction (XRD). The porosity and hardness of the composite sinters were examined, and optical microscopy (OM) and quantitative image analyses were carried out to characterize the microstructure of the composites. In the manufacturing process of the Mg-nSi-CNT mixtures, the best results were the following: first separate de-agglomeration of nanocomponents, then their common mixing, and finally, the deposition of nanocomponents at the surface of the microsized magnesium powder. The applied procedure ensured the uniform layer formation of de-agglomerated nanocomponents on the Mg powder, without re-agglomerated nSi and CNTs. Moreover, this type of powder mixture morphology allows to obtain sinters with lower porosity and higher hardness, which is accompanied by precipitation of a finer Mg₂Si phase. In the Mg-Mg₂Si-CNT composite, the carbon phase was present, and it was located in the magnesium matrix and in silicide. Full article

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19 pages, 18688 KiB

Open AccessArticle

Properties Comparison of Ti-Al-Si Alloys Produced by Various Metallurgy Methods

by Anna Knaislová, Pavel Novák, Jaromír Kopeček and Filip Průša

Materials 2019, 12(19), 3084; https://doi.org/10.3390/ma12193084 - 21 Sep 2019

Cited by 16 | Viewed by 2895

Abstract

Melting metallurgy is still the most frequently used and simplest method for the processing of metallic materials. Some of the materials (especially intermetallics) are very difficult to prepare by this method due to the high melting points, poor fluidity, or formation of cracks [...] Read more.

Melting metallurgy is still the most frequently used and simplest method for the processing of metallic materials. Some of the materials (especially intermetallics) are very difficult to prepare by this method due to the high melting points, poor fluidity, or formation of cracks and pores after casting. This article describes the processing of Ti-Al-Si alloys by arc melting, and shows the microstructure, phase composition, hardness, fracture toughness, and compression tests of these alloys. These results are compared with the same alloys prepared by powder metallurgy by the means of a combination of mechanical alloying and spark plasma sintering. Ti-Al-Si alloys processed by melting metallurgy are characterized by a very coarse structure with central porosity. The phase composition is formed by titanium aluminides and titanium silicides, which are full of cracks. Ti-Al-Si alloys processed by the powder metallurgy route have a relatively homogeneous fine-grained structure with higher hardness. However, these alloys are very brittle. On the other hand, the fracture toughness of arc-melted samples is immeasurable using Palmqvist’s method because the crack is stopped by a large area of titanium aluminide matrix. Full article

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16 pages, 6729 KiB

Open AccessArticle

Effect of Initial Powders on Properties of FeAlSi Intermetallics

by Jaroslav Čech, Petr Haušild, Miroslav Karlík, Václav Bouček, Kateřina Nová, Filip Průša, Pavel Novák and Jaromír Kopeček

Materials 2019, 12(18), 2846; https://doi.org/10.3390/ma12182846 - 04 Sep 2019

Cited by 3 | Viewed by 2387

Abstract

FeAlSi intermetallics are materials with promising high-temperature mechanical properties and oxidation resistance. Nevertheless, their production by standard metallurgical processes is complicated. In this study, preparation of powders by mechanical alloying and properties of the samples compacted by spark plasma sintering was studied. Various [...] Read more.

FeAlSi intermetallics are materials with promising high-temperature mechanical properties and oxidation resistance. Nevertheless, their production by standard metallurgical processes is complicated. In this study, preparation of powders by mechanical alloying and properties of the samples compacted by spark plasma sintering was studied. Various initial feedstock materials were mixed to prepare the material with the same chemical composition. Time of mechanical alloying leading to complete homogenization of powders was estimated based on the microstructure observations, results of XRD and indentation tests. Microstructure, phase composition, hardness and fracture toughness of sintered samples was studied and compared with the properties of powders before the sintering process. It was found that independently of initial feedstock powder, the resulting phase composition was the same (Fe₃Si + FeSi). The combination of hard initial powders required the longest milling time, but it led to the highest values of fracture toughness. Full article

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18 pages, 5683 KiB

Open AccessArticle

Structure and Properties of Fe–Al–Si Alloy Prepared by Mechanical Alloying

by Pavel Novák, Tomáš Vanka, Kateřina Nová, Jan Stoulil, Filip Průša, Jaromír Kopeček, Petr Haušild and František Laufek

Materials 2019, 12(15), 2463; https://doi.org/10.3390/ma12152463 - 02 Aug 2019

Cited by 16 | Viewed by 3029

Abstract

Fe–Al–Si alloys have been previously reported as an interesting alternative to common high-temperature materials. This work aimed to improve the properties of FeAl20Si20 alloy (in wt.%) by the application of powder metallurgy process consisting of ultrahigh-energy mechanical alloying and spark plasma sintering. The [...] Read more.

Fe–Al–Si alloys have been previously reported as an interesting alternative to common high-temperature materials. This work aimed to improve the properties of FeAl20Si20 alloy (in wt.%) by the application of powder metallurgy process consisting of ultrahigh-energy mechanical alloying and spark plasma sintering. The material consisted of Fe₃Si, FeSi, and Fe₃Al₂Si₃ phases. It was found that the alloy exhibits an anomalous behaviour of yield strength and ultimate compressive strength around 500 °C, reaching approximately 1100 and 1500 MPa, respectively. The results also demonstrated exceptional wear resistance, oxidation resistance, and corrosion resistance in water-based electrolytes. The tested manufacturing process enabled the fracture toughness to be increased ca. 10 times compared to the cast alloy of the same composition. Due to its unique properties, the material could be applicable in the automotive industry for the manufacture of exhaust valves, for wear parts, and probably as a material for selected aggressive chemical environments. Full article

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12 pages, 19679 KiB

Open AccessArticle

Mechanism of the Intermediary Phase Formation in Ti-20 wt. % Al Mixture during Pressureless Reactive Sintering

by Andrea Školáková, Pavel Salvetr, Pavel Novák, Jindřich Leitner and Davy Deduytsche

Materials 2019, 12(13), 2171; https://doi.org/10.3390/ma12132171 - 06 Jul 2019

Cited by 6 | Viewed by 2336

Abstract

This work aims to describe the mechanism of intermediary phases formation in TiAl20 (wt. %) alloy composition during reactive sintering. The reaction between titanium and aluminum powders was studied by in situ diffraction and the results were confirmed by annealing at various temperatures. [...] Read more.

This work aims to describe the mechanism of intermediary phases formation in TiAl20 (wt. %) alloy composition during reactive sintering. The reaction between titanium and aluminum powders was studied by in situ diffraction and the results were confirmed by annealing at various temperatures. It was found that the Ti₂Al₅ phase formed preferentially and its formation was detected at 400 °C. So far, this phase has never been found in this alloy composition during reactive sintering processes. Subsequently, the Ti₂Al₅ phase reacted with the titanium, and the formation of the major phase, Ti₃Al, was accompanied by the minor phase, TiAl. Equations of the proposed reactions are presented in this paper and their thermodynamic and kinetic feasibility are supported by Gibbs energies of reaction and reaction enthalpies. Full article

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