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2339 KiB

Open AccessArticle

Structure Determination of Au on Pt(111) Surface: LEED, STM and DFT Study

by Katarzyna Krupski, Marco Moors, Paweł Jóźwik, Tomasz Kobiela and Aleksander Krupski

Materials 2015, 8(6), 2935-2952; https://doi.org/10.3390/ma8062935 - 27 May 2015

Cited by 46 | Viewed by 14683

Low-energy electron diffraction (LEED), scanning tunneling microscopy (STM) and density functional theory (DFT) calculations have been used to investigate the atomic and electronic structure of gold deposited (between 0.8 and 1.0 monolayer) on the Pt(111) face in ultrahigh vacuum at room temperature. The [...] Read more.

Low-energy electron diffraction (LEED), scanning tunneling microscopy (STM) and density functional theory (DFT) calculations have been used to investigate the atomic and electronic structure of gold deposited (between 0.8 and 1.0 monolayer) on the Pt(111) face in ultrahigh vacuum at room temperature. The analysis of LEED and STM measurements indicates two-dimensional growth of the first Au monolayer. Change of the measured surface lattice constant equal to 2.80 Å after Au adsorption was not observed. Based on DFT, the distance between the nearest atoms in the case of bare Pt(111) and Au/Pt(111) surface is equal to 2.83 Å, which gives 1% difference in comparison with STM values. The first and second interlayer spacing of the clean Pt(111) surface are expanded by +0.87% and contracted by −0.43%, respectively. The adsorption energy of the Au atom on the Pt(111) surface is dependent on the adsorption position, and there is a preference for a hollow fcc site. For the Au/Pt(111) surface, the top interlayer spacing is expanded by +2.16% with respect to the ideal bulk value. Changes in the electronic properties of the Au/Pt(111) system below the Fermi level connected to the interaction of Au atoms with Pt(111) surface are observed. Full article

(This article belongs to the Special Issue Intermetallic Alloys: Fabrication, Properties and Applications)

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7948 KiB

Open AccessArticle

Synthesis of Fe-Al-Ti Based Intermetallics with the Use of Laser Engineered Net Shaping (LENS)

by Monika Kwiatkowska, Dariusz Zasada, Jerzy Bystrzycki and Marek Polański

Materials 2015, 8(5), 2311-2331; https://doi.org/10.3390/ma8052311 - 29 Apr 2015

Cited by 20 | Viewed by 7289

Abstract

The Laser Engineered Net Shaping (LENS) technique was combined with direct synthesis to fabricate L2₁-ordered Fe-Al-Ti based intermetallic alloys. It was found that ternary Fe-Al-Ti alloys can be synthesized using the LENS technique from a feedstock composed of a pre-alloyed Fe-Al [...] Read more.

The Laser Engineered Net Shaping (LENS) technique was combined with direct synthesis to fabricate L2₁-ordered Fe-Al-Ti based intermetallic alloys. It was found that ternary Fe-Al-Ti alloys can be synthesized using the LENS technique from a feedstock composed of a pre-alloyed Fe-Al powder and elemental Ti powder. The obtained average compositions of the ternary alloys after the laser deposition and subsequent annealing were quite close to the nominal compositions, but the distributions of the elements in the annealed samples recorded over a large area were inhomogeneous. No traces of pure Ti were observed in the deposited alloys. Macroscopic cracking and porosity were observed in all investigated alloys. The amount of porosity in the samples was less than 1.2 vol. %. It seems that the porosity originates from the porous pre-alloyed Fe-Al powders. Single-phase (L2₁), two-phase (L2₁-C14) and multiphase (L2₁-A2-C14) Fe-Al-Ti intermetallic alloys were obtained from the direct laser synthesis and annealing process. The most prominent feature of the ternary Fe-Al-Ti intermetallics synthesized by the LENS method is their fine-grained structure. The grain size is in the range of 3–5 μm, indicating grain refinement effect through the highly rapid cooling of the LENS process. The Fe-Al-Ti alloys synthesized by LENS and annealed at 1000 °C in the single-phase B2 region were prone to an essential grain growth. In contrast, the alloys annealed at 1000 °C in the two-phase L2₁-C14 region exhibited almost constant grain size values after the high-temperature annealing. Full article

(This article belongs to the Special Issue Intermetallic Alloys: Fabrication, Properties and Applications)

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4106 KiB

Open AccessArticle

Fabrication of Fe-Al Intermetallic Foams via Organic Compounds Assisted Sintering

by Krzysztof Karczewski, Wojciech Jerzy Stępniowski, Piotr Kaczor and Stanisław Jóźwiak

Materials 2015, 8(5), 2217-2226; https://doi.org/10.3390/ma8052217 - 28 Apr 2015

Cited by 12 | Viewed by 5454

Abstract

The influence of the addition of organic compounds, such as palmitic acid and cholesteryl myristate, on the porous structure of Fe-Al intermetallics formation has been investigated in detail in this paper. It was found that additives have a significant effect on the final [...] Read more.

The influence of the addition of organic compounds, such as palmitic acid and cholesteryl myristate, on the porous structure of Fe-Al intermetallics formation has been investigated in detail in this paper. It was found that additives have a significant effect on the final porosity of the obtained sinters. Formed gaseous products from combustion play the role of the foaming agent during Fe-Al intermetallic alloy sintering. The influence of these additives is also clearly noticeable in chemical composition changes of the final products through the increase of carbon content in the porous structure. This is attributed to the thermal decomposition, namely combustion, of the organic additives. Full article

(This article belongs to the Special Issue Intermetallic Alloys: Fabrication, Properties and Applications)

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4834 KiB

Open AccessArticle

The Effect of Oxygen Partial Pressure on Microstructure and Properties of Fe40Al Alloy Sintered under Vacuum

by Dariusz Siemiaszko, Beata Kowalska, Paweł Jóźwik and Monika Kwiatkowska

Materials 2015, 8(4), 1513-1525; https://doi.org/10.3390/ma8041513 - 31 Mar 2015

Cited by 8 | Viewed by 4768

Abstract

This paper presents the results of studies on the influence of oxygen partial pressure (vacuum level in the chamber) on the properties of FeAl intermetallics. One of the problems in the application of classical methods of prepared Fe-Al intermetallic is the occurrence of [...] Read more.

This paper presents the results of studies on the influence of oxygen partial pressure (vacuum level in the chamber) on the properties of FeAl intermetallics. One of the problems in the application of classical methods of prepared Fe-Al intermetallic is the occurrence of oxides. Applying a vacuum during sintering should reduce this effect. In order to analyze the effect of oxygen partial pressure on sample properties, five samples were processed (by a pressure-assisted induction sintering—PAIS method) under the following pressures: 3, 8, 30, 80, and 300 mbar (corresponding to oxygen partial pressures of 0.63, 1.68, 6.3, 16.8, and 63 mbar, respectively). The chemical and phase composition, hardness, density, and microstructure observations indicate that applying a vacuum significantly impacts intermetallic samples. The compact sintered at pressure 3 mbar is characterized by the most homogeneous microstructure, the highest density, high hardness, and nearly homogeneous chemical composition. Full article

(This article belongs to the Special Issue Intermetallic Alloys: Fabrication, Properties and Applications)

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3636 KiB

Open AccessArticle

High-Temperature Oxidation of Fe₃Al Intermetallic Alloy Prepared by Additive Manufacturing LENS

by Radosław Łyszkowski

Materials 2015, 8(4), 1499-1512; https://doi.org/10.3390/ma8041499 - 30 Mar 2015

Cited by 18 | Viewed by 6694

Abstract

The isothermal oxidation of Fe-28Al-5Cr (at%) intermetallic alloy microalloyed with Zr and B (<0.08 at%) in air atmosphere, in the temperature range of 1000 to 1200 °C, was studied. The investigation was carried out on the thin-walled (<1 mm) elements prepared by Laser [...] Read more.

The isothermal oxidation of Fe-28Al-5Cr (at%) intermetallic alloy microalloyed with Zr and B (<0.08 at%) in air atmosphere, in the temperature range of 1000 to 1200 °C, was studied. The investigation was carried out on the thin-walled (<1 mm) elements prepared by Laser Engineered Net Shaping (LENS) from alloy powder of a given composition. Characterization of the specimens, after the oxidation, was conducted using X-ray diffraction (XRD) and scanning electron microscopy (SEM, with back-scatter detector (BSE) and energy-dispersive X-ray spectroscopy (EDS) attachments). The investigation has shown, that the oxidized samples were covered with a thin, homogeneous α-Al₂O₃ oxide layers. The intensity of their growth indicates that the material lost its resistance to oxidation at 1200 °C. Structural analysis of the thin-walled components’ has not shown intensification of the oxidation process at the joints of additive layers. Full article

(This article belongs to the Special Issue Intermetallic Alloys: Fabrication, Properties and Applications)

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4663 KiB

Open AccessArticle

Corrosion Behavior of Detonation Gun Sprayed Fe-Al Type Intermetallic Coating

by Cezary Senderowski, Michal Chodala and Zbigniew Bojar

Materials 2015, 8(3), 1108-1123; https://doi.org/10.3390/ma8031108 - 13 Mar 2015

Cited by 22 | Viewed by 6612

Abstract

The detonation gun sprayed Fe-Al type coatings as an alternative for austenitic valve steel, were investigated using two different methods of testing corrosion resistance. High temperature, 10-hour isothermal oxidation experiments at 550, 750, 950 and 1100 °C show differences in the oxidation behavior [...] Read more.

The detonation gun sprayed Fe-Al type coatings as an alternative for austenitic valve steel, were investigated using two different methods of testing corrosion resistance. High temperature, 10-hour isothermal oxidation experiments at 550, 750, 950 and 1100 °C show differences in the oxidation behavior of Fe-Al type coatings under air atmosphere. The oxide layer ensures satisfying oxidation resistance, even at 950 and 1100 °C. Hematite, α-Al₂O₃ and metastable alumina phases were noticed on the coatings top surface, which preserves its initial thickness providing protection to the underlying substrate. In general, only negligible changes of the phase composition of the coatings were noticed with simultaneous strengthening controlled in the micro-hardness measurements, even after 10-hours of heating at 1100 °C. On the other hand, the electrochemical corrosion tests, which were carried out in 200 ppm Cl⁻ (NaCl) and pH ~4 (H₂SO₄) solution to simulate the acid-rain environment, reveal higher values of the breakdown potential for D-gun sprayed Fe-Al type coatings than the ones for the bulk Fe-Al type alloy and Cr21Mn9Ni4 austenitic valve steel. This enables these materials to be used in structural and multifunctional applications in aggressive environments, including acidic ones. Full article

(This article belongs to the Special Issue Intermetallic Alloys: Fabrication, Properties and Applications)

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3025 KiB

Open AccessArticle

Characterization of Low-Symmetry Structures from Phase Equilibrium of Fe-Al System—Microstructures and Mechanical Properties

by Piotr Matysik, Stanisław Jóźwiak and Tomasz Czujko

Materials 2015, 8(3), 914-931; https://doi.org/10.3390/ma8030914 - 04 Mar 2015

Cited by 75 | Viewed by 11487

Abstract

Fe-Al intermetallic alloys with aluminum content over 60 at% are in the area of the phase equilibrium diagram that is considerably less investigated in comparison to the high-symmetry Fe₃Al and FeAl phases. Ambiguous crystallographic information and incoherent data referring to the [...] Read more.

Fe-Al intermetallic alloys with aluminum content over 60 at% are in the area of the phase equilibrium diagram that is considerably less investigated in comparison to the high-symmetry Fe₃Al and FeAl phases. Ambiguous crystallographic information and incoherent data referring to the phase equilibrium diagrams placed in a high-aluminum range have caused confusions and misinformation. Nowadays unequivocal material properties description of FeAl₂, Fe₂Al₅ and FeAl₃ intermetallic alloys is still incomplete. In this paper, the influence of aluminum content and processing parameters on phase composition is presented. The occurrence of low-symmetry FeAl₂, Fe₂Al₅ and FeAl₃ structures determined by chemical composition and phase transformations was defined by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) examinations. These results served to verify diffraction investigations (XRD) and to explain the mechanical properties of cast materials such as: hardness, Young’s modulus and fracture toughness evaluated using the nano-indentation technique. Full article

(This article belongs to the Special Issue Intermetallic Alloys: Fabrication, Properties and Applications)

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1757 KiB

Open AccessArticle

The Structure of FeAl Sinters Fabricated Using Cyclic Loading

by Tomasz Durejko, Michał Ziętala and Zbigniew Bojar

Materials 2015, 8(2), 575-585; https://doi.org/10.3390/ma8020575 - 09 Feb 2015

Cited by 6 | Viewed by 5058

Abstract

A two stage process including a sintering under a cyclic loading is proposed as an alternative fabrication method of dense FeAl intermetallics from elemental powder mixtures. The first stage (pre-sintering) is conducted at two temperature values (620 °C and 670 °C, respectively) under [...] Read more.

A two stage process including a sintering under a cyclic loading is proposed as an alternative fabrication method of dense FeAl intermetallics from elemental powder mixtures. The first stage (pre-sintering) is conducted at two temperature values (620 °C and 670 °C, respectively) under a static and a cyclic loading with a frequency of 20, 40 and 60 Hz. The second one includes a pressureless sintering at temperature of 1250 °C, under a protective argon atmosphere. A suitable selection of pre-sintering parameters (temperature, type and frequency of pressing) allows approximately five times grain size reduction of FeAl phase in comparison to particle size of raw Fe and Al powder material (40–60 µm), as well as induces an effective fragmentation of oxide layers. For the sinters obtained using 60 Hz loading frequency an oxide particle size of 4.0 or 4.5 µm (smaller for sintering with liquid phase) is observed. Material obtained after the full heat treatment are characterized by a fine-grained structure of chemically homogeneous FeAl phase with uniformly distributed Al₂O₃ spherical particles along grain boundaries. Moreover, it was found that temperature and frequency of loading during the presintering process also affect a consolidation level of the Fe-Al powder mixture, which increases with rising both temperature and frequency. Full article

(This article belongs to the Special Issue Intermetallic Alloys: Fabrication, Properties and Applications)

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Review

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8003 KiB

Open AccessReview

Applications of Ni₃Al Based Intermetallic Alloys—Current Stage and Potential Perceptivities

by Pawel Jozwik, Wojciech Polkowski and Zbigniew Bojar

Materials 2015, 8(5), 2537-2568; https://doi.org/10.3390/ma8052537 - 13 May 2015

Cited by 183 | Viewed by 14679

Abstract

The paper presents an overview of current and prospective applications of Ni₃Al based intermetallic alloys—modern engineering materials with special properties that are potentially useful for both structural and functional purposes. The bulk components manufactured from these materials are intended mainly for [...] Read more.

The paper presents an overview of current and prospective applications of Ni₃Al based intermetallic alloys—modern engineering materials with special properties that are potentially useful for both structural and functional purposes. The bulk components manufactured from these materials are intended mainly for forging dies, furnace assembly, turbocharger components, valves, and piston head of internal combustion engines. The Ni₃Al based alloys produced by a directional solidification are also considered as a material for the fabrication of jet engine turbine blades. Moreover, development of composite materials with Ni₃Al based alloys as a matrix hardened by, e.g., TiC, ZrO₂, WC, SiC and graphene, is also reported. Due to special physical and chemical properties; it is expected that these materials in the form of thin foils and strips should make a significant contribution to the production of high tech devices, e.g., Micro Electro-Mechanical Systems (MEMS) or Microtechnology-based Energy and Chemical Systems (MECS); as well as heat exchangers; microreactors; micro-actuators; components of combustion chambers and gasket of rocket and jet engines as well components of high specific strength systems. Additionally, their catalytic properties may find an application in catalytic converters, air purification systems from chemical and biological toxic agents or in a hydrogen “production” by a decomposition of hydrocarbons. Full article

(This article belongs to the Special Issue Intermetallic Alloys: Fabrication, Properties and Applications)

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