Materials

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14 pages, 7096 KiB

Open AccessFeature PaperArticle

Structure and Properties of Cast Ti-Al-Si Alloys

by Anna Knaislová, Pavel Novák, Jiří Linhart, Ivo Szurman, Kateřina Skotnicová, Jan Juřica and Tomáš Čegan

Materials 2021, 14(4), 813; https://doi.org/10.3390/ma14040813 - 8 Feb 2021

Cited by 4 | Viewed by 1908

Abstract

Intermetallic compounds based on Ti-Al- (Si) are attractive materials with good thermal stability and low density. However, the production of these materials is quite complicated. Partially modified conventional methods of melting metallurgy are most often used due to availability, possible high productivity, and [...] Read more.

Intermetallic compounds based on Ti-Al- (Si) are attractive materials with good thermal stability and low density. However, the production of these materials is quite complicated. Partially modified conventional methods of melting metallurgy are most often used due to availability, possible high productivity, and relatively low production costs. Therefore, some technologies for the production of intermetallics based on Ti-Al are currently available, but with certain disadvantages, which are caused by poor casting properties or extreme reactivity of the melt with crucibles. Some shortcomings can be eliminated by modifying the melting technology, which contributes to increasing the cost of the process. The work deals with the preparation of Ti-Al-Si intermetallic compounds with different contents of aluminum and silicon, which were produced by centrifugal casting in an induction vacuum furnace Linn Supercast-Titan. This process could contribute to the commercial use of these alloys in the future. For this research, the TiAl15Si15(in wt.%) alloy was selected, which represents a balanced ratio of aluminides and silicides in its structure, and the TiAl35Si5 alloy, which due to the lower silicon content allows better melting conditions, especially with regard to the melting temperature. This alloy was also investigated after HIP (“Hot Isostatic Pressing”) treatment. Full article

(This article belongs to the Special Issue High Temperature Alloys and Intermetallic Materials)

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13 pages, 3046 KiB

Open AccessArticle

Thermal Expansion of a Multiphase Intermetallic Ti-Al-Nb-Mo Alloy Studied by High-Energy X-ray Diffraction

by Peter Staron, Andreas Stark, Norbert Schell, Petra Spoerk-Erdely and Helmut Clemens

Materials 2021, 14(4), 727; https://doi.org/10.3390/ma14040727 - 4 Feb 2021

Cited by 8 | Viewed by 2367

Abstract

Intermetallic γ-TiAl-based alloys are lightweight materials for high-temperature applications, e.g., in the aerospace and automotive industries. They can replace much heavier Ni-based alloys at operating temperatures up to 750 °C. Advanced variants of this alloy class enable processing routes that include hot forming. [...] Read more.

Intermetallic γ-TiAl-based alloys are lightweight materials for high-temperature applications, e.g., in the aerospace and automotive industries. They can replace much heavier Ni-based alloys at operating temperatures up to 750 °C. Advanced variants of this alloy class enable processing routes that include hot forming. These alloys consist of three relevant crystallographic phases (γ-TiAl, α₂-Ti₃Al, β_o-TiAl) that transform into each other at different temperatures. For thermo-mechanical treatments as well as for adjusting alloy properties required under service conditions, the knowledge of the thermal expansion behavior of these phases is important. Therefore, thermal expansion coefficients were determined for the relevant phases in a Ti-Al-Nb-Mo alloy for temperatures up to 1100 °C using high-energy X-ray diffraction. Full article

(This article belongs to the Special Issue High Temperature Alloys and Intermetallic Materials)

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13 pages, 2962 KiB

Open AccessArticle

Recovery and Characterization Studies of Post-Production Alloy Waste from the Automotive Industry

by Sylwester Żelazny, Witold Żukowski, Dariusz Bogdał, Szczepan Bednarz, Wiktor Kasprzyk and Tomasz Świergosz

Materials 2020, 13(24), 5600; https://doi.org/10.3390/ma13245600 - 8 Dec 2020

Cited by 3 | Viewed by 2157

Abstract

Superalloys provide high corrosion resistance and are widely used as high-performance materials in aerospace, automotive, chemical, and other industries. Herein, the investigation into the characteristics and properties of alloy waste; Inconel 625, Inconel 718, and Titanium Grade 5, from the automotive industry, was [...] Read more.

Superalloys provide high corrosion resistance and are widely used as high-performance materials in aerospace, automotive, chemical, and other industries. Herein, the investigation into the characteristics and properties of alloy waste; Inconel 625, Inconel 718, and Titanium Grade 5, from the automotive industry, was introduced as a result of a recovery in various processes. For this reason, the following procedures were carried as follows; the washing process to remove oil from the swarf was evaluated using several commercial agents and for the process of thermal disposal of processing fluids, a temperature of 900 °C was used in a muffle furnace without air access. The presented studies show that the commercially available series of washing agents did not modify the composition of the surface. However, the high temperatures during the calcination of oil residues are affecting the elemental composition of the alloys. According to the results of the analyses, it is not possible to remove 100% of the oil residues from alloy waste using washing agents based on light organic fractions; however, the effectiveness of this method reaches 99%. In this report, accurate SEM-EDS analyses show changes that occur on the surface after machining and removal of processing fluids. The NMR and GC/MS investigations indicate contaminants as a mixture of aliphatic and cycloaliphatic hydrocarbons with carbon numbers from C8–C30. Full article

(This article belongs to the Special Issue High Temperature Alloys and Intermetallic Materials)

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14 pages, 3282 KiB

Open AccessFeature PaperArticle

An Advanced TiAl Alloy for High-Performance Racing Applications

by Michael Burtscher, Thomas Klein, Janny Lindemann, Oliver Lehmann, Holger Fellmann, Volker Güther, Helmut Clemens and Svea Mayer

Materials 2020, 13(21), 4720; https://doi.org/10.3390/ma13214720 - 22 Oct 2020

Cited by 41 | Viewed by 2705

Abstract

Requirements and strict regulations for high-performance racing applications involve the use of new and innovative lightweight structural materials. Therefore, intermetallic γ-TiAl-based alloys enable new opportunities in the field due to their lower density compared to commonly used Ni-base superalloys. In this study, a [...] Read more.

Requirements and strict regulations for high-performance racing applications involve the use of new and innovative lightweight structural materials. Therefore, intermetallic γ-TiAl-based alloys enable new opportunities in the field due to their lower density compared to commonly used Ni-base superalloys. In this study, a β-solidifying TiAl alloy was examined toward its use as structural material for inlet and outlet valves. The nominal composition of the investigated TNM alloy is Ti–43.5Al–4Nb–1Mo–0.1B (in at%), which enables an excellent formability at elevated temperatures due to the presence of bcc β-phase. Different hot-extrusion tests on an industrial scale were conducted on the cast and hot isostatic pressed material to determine the ideal microstructure for the respective racing application. To simulate these operation conditions, hot tensile tests, as well as rotational bending tests, at room temperature were conducted. With a higher degree of deformation, an increasing strength and fatigue limit was obtained, as well as a significant increment of ductility. The fracture surfaces of the rotational bending test specimens were analyzed using scanning electron microscopy, revealing the relationship between crack initiation and microstructural constituents. The results of this study show that the mechanical performance of extruded TiAl material can be tailored via optimizing the degree of hot-extrusion. Full article

(This article belongs to the Special Issue High Temperature Alloys and Intermetallic Materials)

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7 pages, 6717 KiB

Open AccessCommunication

Coating Reactions on Vanadium and V-Si-B Alloys during Powder Pack-Cementation

by Georg Hasemann, Chad Harris, Manja Krüger and John H. Perepezko

Materials 2020, 13(18), 4099; https://doi.org/10.3390/ma13184099 - 15 Sep 2020

Cited by 5 | Viewed by 2476

Abstract

Alloys in the V-Si-B system are a new and promising class of light-weight refractory metal materials for high temperature applications. Presently, the main attention is focused on three-phase alloy compositions that consist of a vanadium solid solution phase and the two intermetallic phases [...] Read more.

Alloys in the V-Si-B system are a new and promising class of light-weight refractory metal materials for high temperature applications. Presently, the main attention is focused on three-phase alloy compositions that consist of a vanadium solid solution phase and the two intermetallic phases V₃Si and V₅SiB₂. Similar to other refractory metal alloys, a major drawback is the poor oxidation resistance. In this study, initial pack-cementation experiments were performed on commercially available pure vanadium and a three-phase alloy V-9Si-5B to achieve an oxidation protection for this new type of high temperature material. This advance in oxidation resistance now enables the attractive mechanical properties of V-Si-B alloys to be used for high temperature structural applications. Full article

(This article belongs to the Special Issue High Temperature Alloys and Intermetallic Materials)

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12 pages, 8985 KiB

Open AccessArticle

Microstructure and Compression Properties of V_SS-V₃B₂ Eutectic Alloys in the V-Si-B System

by Christopher Müller, Georg Hasemann, Maximilian Regenberg, Ulf Betke and Manja Krüger

Materials 2020, 13(9), 2100; https://doi.org/10.3390/ma13092100 - 1 May 2020

Cited by 2 | Viewed by 3691

Abstract

The present study reports on the microstructural evolution and room temperature plasticity of V(-Si)-B alloys with respect to the V solid solution (V_SS)-V₃B₂ phase region. To investigate the occurring effects systematically, different binary V-B and ternary V-Si-B alloys [...] Read more.

The present study reports on the microstructural evolution and room temperature plasticity of V(-Si)-B alloys with respect to the V solid solution (V_SS)-V₃B₂ phase region. To investigate the occurring effects systematically, different binary V-B and ternary V-Si-B alloys were produced by conventional arc melting. Scanning electron microscope (SEM) analyses and X-ray diffraction (XRD) measurements were used to characterize the resulting as-cast microstructures. For the first time, the eutectic composition was systematically traced from the binary V-B domain to the ternary V-Si-B system. The observations discover that the binary eutectic trough (V_SS-V₃B₂) seems to reach into the ternary system up to an alloy composition of V-5Si-9B. Room temperature compression tests were carried out in order to study the impact of single-phase and multi-phase microstructures on the strength and plasticity of binary and ternary alloys. The results indicate that the V_SS phase controls the plastic deformability in the V_SS-V₃B₂ eutectic microstructure whereas the intermetallic V₃B₂ acts as a strong hardening phase. Full article

(This article belongs to the Special Issue High Temperature Alloys and Intermetallic Materials)

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11 pages, 1934 KiB

Open AccessArticle

Effects of Cr, W, and Mo on the High Temperature Oxidation of Ni-Based Superalloys

by Si-Jun Park, Seong-Moon Seo, Young-Soo Yoo, Hi-Won Jeong and HeeJin Jang

Materials 2019, 12(18), 2934; https://doi.org/10.3390/ma12182934 - 11 Sep 2019

Cited by 39 | Viewed by 3209

Abstract

The oxidation behavior of Ni–9.5Co–(8~12)Cr–(2.5~5.5)Mo–(4~8)W–3Al–5Ti–3Ta–0.1C–0.01B alloys was investigated at 850 °C and 1000 °C The mass change, the phase of oxides, and the cross-sectional structure of specimens were analyzed after cyclic oxidation tests. The oxide scale was composed mainly of Cr₂O [...] Read more.

The oxidation behavior of Ni–9.5Co–(8~12)Cr–(2.5~5.5)Mo–(4~8)W–3Al–5Ti–3Ta–0.1C–0.01B alloys was investigated at 850 °C and 1000 °C The mass change, the phase of oxides, and the cross-sectional structure of specimens were analyzed after cyclic oxidation tests. The oxide scale was composed mainly of Cr₂O₃ and NiCr₂O₄, but NiO, TiO₂, and CrTaO₄ were also found. Al₂O₃ was formed beneath the Cr oxide layer. The Cr oxide layer and internal Al oxide acted as barriers to oxidation at 850 °C, while Al oxide was predominantly protective at 1000 °C. Cr increased the mass gain after oxidation test at both temperatures. Mo increased the oxidation rate at 850 °C but decreased the oxidation rate at 1000 °C. W slightly increased the mass gain at 850 °C but did not produce a significant effect at 1000 °C. The effects of Cr, Mo, W, and the temperature were discussed as well as the volatilization of oxides, the valence number of elements, and diffusion retardation. Full article

(This article belongs to the Special Issue High Temperature Alloys and Intermetallic Materials)

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13 pages, 3628 KiB

Open AccessFeature PaperArticle

Microstructural Evolution of Post-Processed Hastelloy X Alloy Fabricated by Laser Powder Bed Fusion

by Giulio Marchese, Emilio Bassini, Alberta Aversa, Mariangela Lombardi, Daniele Ugues, Paolo Fino and Sara Biamino

Materials 2019, 12(3), 486; https://doi.org/10.3390/ma12030486 - 5 Feb 2019

Cited by 55 | Viewed by 6027

Abstract

Hastelloy X (HX) is a Ni-based superalloy which is employed to produce gas turbine and gas-cooled reactor sectors due to its outstanding oxidation resistance and high tensile strength at high temperatures. This alloy can be processed by laser powder bed fusion (LPBF) fabricating [...] Read more.

Hastelloy X (HX) is a Ni-based superalloy which is employed to produce gas turbine and gas-cooled reactor sectors due to its outstanding oxidation resistance and high tensile strength at high temperatures. This alloy can be processed by laser powder bed fusion (LPBF) fabricating complex geometries in a single step. However, post-processing thermal treatments must be applied to generate a suitable microstructure for high-temperature applications. The investigation reports the microstructure evolution of LPBF HX samples under specific post-processing treatments. A hot isostatic pressing (HIP) treatment can close the internal cracks and reduce the residual porosity (less than 0.1%). Moreover, the HIP-triggered recrystallization generated equiaxed grains, while the slow cooling rate generated a film of intergranular carbides (Mo-rich M₆C and Cr-rich M₂₃C₆) and intragranular carbides (Mo-rich M₆C carbides). Therefore, a solution annealing was performed to dissolve the film of carbides which may reduce the ductility. The post solution annealed material consisted of equiaxed grains with ASTM grain size number mainly 4.5-5.5 and inter/intragranular Mo-rich M₆C carbides. The microstructure is highly comparable with solution annealed wrought HX alloy. Finally, after simulating short thermal exposure at 745 °C for 6 h, a significant formation of Cr-rich M₂₃C₆ carbides was observed strengthening the LPBF HX alloy. Full article

(This article belongs to the Special Issue High Temperature Alloys and Intermetallic Materials)

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