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Metals
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Intermetallics for Structural Applications
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Intermetallics for Structural Applications

A special issue of Metals (ISSN 2075-4701). This special issue belongs to the section "Structural Integrity of Metals".

Deadline for manuscript submissions: closed (31 July 2023) | Viewed by 7345

Special Issue Editor

Prof. Dr. Florian Pyczak

E-Mail Website
Guest Editor
Helmholtz Zentrum Hereon, Inst Materials Physics, Max Planck Str 1, D-21502 Geesthacht, Germany
Interests: intermetallics; TiAl; superalloys; characterization at synchrotron sources; electron microscopy

Special Issue Information

Dear Colleagues,

Intermetallic compounds can exhibit properties vastly different from those of the pure metals or alloys of them. Therefore, they can compete with and surpass conventional metallic materials in high demanding structural applications in such key fields as aeronautics, energy, and transport. The impact of intermetallics for structural applications is even higher if we consider that they also play a key role in hardening conventional metallic matrix materials but also high-entropy alloys. A prime example are the extremely successful Ni-base superalloys for high-temperature applications. Those can contain a higher fraction of the intermetallic hardening phase than Ni solid solution matrix itself. In a future with the necessity to build stronger aircraft fuselages, lighter car chassis and more efficient engines, the importance of intermetallics for structural applications will further increase.

For this Special Issue, we invite contributions on the topic of intermetallics for structural applications. These can either be fully intermetallic materials or metals and alloys where intermetallic phases play a significant role to enhance the properties as hardening phases. Contributions can cover the whole range starting from fundamental properties and features of intermetallic phases and their deformation mechanisms over processing with formation of the microstructure up to the mechanical behavior of whole parts relating the mechanical strength to the properties and structure of the intermetallics present in the material.

Prof. Dr. Florian Pyczak
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Metals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • intermetallics
  • mechanical properties
  • structural application
  • microstructure formation
  • microstructure–property relationships

Published Papers (4 papers)

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Research

23 pages, 4649 KiB  
Article
Laser Powder Bed Fusion of Intermetallic Titanium Aluminide Alloys Using a Novel Process Chamber Heating System: A Study on Feasibility and Microstructural Optimization for Creep Performance
by Reinhold Wartbichler, Tobias Maiwald-Immer, Fabian Pürstl and Helmut Clemens
Metals 2022, 12(12), 2087; https://doi.org/10.3390/met12122087 - 05 Dec 2022
Cited by 1 | Viewed by 1814
Abstract
A laser powder bed fusion process operating at elevated temperatures is introduced capable of fabricating crack-free and dense intermetallic titanium aluminide alloy specimens as well as demonstrator components using a base plate heating up to 900 °C and a unique heating system of [...] Read more.
A laser powder bed fusion process operating at elevated temperatures is introduced capable of fabricating crack-free and dense intermetallic titanium aluminide alloy specimens as well as demonstrator components using a base plate heating up to 900 °C and a unique heating system of the uppermost powder bed layer up to 1200 °C. Two so-called 4th generation alloys, TNM and TNM+, were used for this study. The microstructure and its evolution during subsequent heat treatments were investigated and explained by employing scanning electron microscopy, hardness testing, X-ray diffraction, differential scanning calorimetry and thermodynamic equilibrium calculation. Selected specimens were subjected to creep tests at 750 °C. The microstructures after processing consist of extraordinarily fine lamellar γ-TiAl/α2-Ti3Al-colonies with globular γ and βo-TiAl grains for both the TNM and TNM+ alloy, exhibiting a microstructure gradient from the last consolidated powder layer down to the starting layer due to cellular reaction, which increases the amount of globular γ and βo at the boundaries of the γ/α2-colonies. During annealing in proximity to the γ-solvus temperature, banded microstructures might form, as the α-grain size is only partially controlled by heterogeneously distributed γ/β-phase, which stems from the process-related Al loss. Additionally, the occurrence of thermally-induced porosity is investigated. Optimizing the microstructure to a homogenized, almost fully lamellar microstructure, involved annealing in the β-single phase field region and led to improved creep properties. Finally, TNM demonstrator components with complex geometries, such as aero engine blades and turbocharger turbine wheels, are fabricated by employing the novel laser powder bed fusion process. Full article
(This article belongs to the Special Issue Intermetallics for Structural Applications)
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22 pages, 5404 KiB  
Article
Microstructure, Plasticity and Ductility of a TNM+ Alloy Densified by Spark Plasma Sintering
by Michael Musi, Christophe Deshayes, Guy Molénat, Louise Toualbi, Benjamin Galy, Petra Spoerk-Erdely, Muriel Hantcherli, Jean-Philippe Monchoux, Marc Thomas, Helmut Clemens and Alain Couret
Metals 2022, 12(11), 1915; https://doi.org/10.3390/met12111915 - 08 Nov 2022
Cited by 1 | Viewed by 1131
Abstract
This work presents a study of the microstructure and mechanical properties of a TNM+ alloy (Ti-43.5Al-4Nb-1Mo-0.1B-0.3C-0.3Si, in at.%) densified by Spark Plasma Sintering (SPS), in comparison to the as-SPSed TNM alloy, which contains neither carbon nor silicon. Tensile tests at room temperature [...] Read more.
This work presents a study of the microstructure and mechanical properties of a TNM+ alloy (Ti-43.5Al-4Nb-1Mo-0.1B-0.3C-0.3Si, in at.%) densified by Spark Plasma Sintering (SPS), in comparison to the as-SPSed TNM alloy, which contains neither carbon nor silicon. Tensile tests at room temperature and 800 °C, as well as creep tests at 800 °C and 200 MPa, were performed. The microstructures and the fracture surfaces of deformed samples were studied by scanning and transmission electron microscopies, as well as by X-ray diffraction. The deformation mechanisms were investigated by means of in situ straining experiments and post-mortem analyses of deformed samples, both performed by transmission electron microscopy. Contrary to the TNM alloy, the as-SPSed microstructure of the TNM+ alloy does not contain β/βo phase due to the incorporation of carbon. At room temperature, the TNM+ alloy exhibits a yield stress of 520 MPa but a poor ductility of less than 0.1% of plastic strain. The incorporation of carbon and silicon leads to an increase in the creep resistance of the alloy at 800 °C. Despite the fact that iron inclusions are responsible for the premature failure of some samples during tensile tests, the TNM+ alloy is found to be able to deform plastically at room temperature by the glide of ordinary dislocations and by twinning. Full article
(This article belongs to the Special Issue Intermetallics for Structural Applications)
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16 pages, 5250 KiB  
Article
Microstructure Evolution of a New Precipitation-Strengthened Fe–Al–Ni–Ti Alloy down to Atomic Scale
by Flora Godor, Martin Palm, Christian H. Liebscher, Frank Stein, Christoph Turk, Katharina Leitner, Boryana Rashkova and Helmut Clemens
Metals 2022, 12(6), 906; https://doi.org/10.3390/met12060906 - 26 May 2022
Cited by 1 | Viewed by 1768
Abstract
Ferritic materials consisting of a disordered matrix and a significant volume fraction of ordered intermetallic precipitates have recently gained attention due to their favorable properties regarding high-temperature applicability. Alloys strengthened by Heusler-type precipitates turned out to show promising properties at elevated temperatures, e.g., [...] Read more.
Ferritic materials consisting of a disordered matrix and a significant volume fraction of ordered intermetallic precipitates have recently gained attention due to their favorable properties regarding high-temperature applicability. Alloys strengthened by Heusler-type precipitates turned out to show promising properties at elevated temperatures, e.g., creep resistance. The present work aims at developing a fundamental understanding of the microstructure of an alloy with a nominal composition of 60Fe–20Al–10Ni–10Ti (in at. %). In order to determine the microstructural evolution, prevailing phases and corresponding phase transformation temperatures are investigated. Differential thermal analysis, high-temperature X-ray diffraction, and special heat treatments were performed. The final microstructures are characterized by means of scanning and transmission electron microscopy along with hardness measurements. Atom probe tomography conducted on alloys of selected heat-treated conditions allows for evaluating the chemical composition and spatial arrangement of the constituent phases. All investigated sample conditions showed microstructures consisting of two phases with crystal structures A2 and L21. The L21 precipitates grew within a continuous A2 matrix. Due to a rather small lattice mismatch, matrix–precipitate interfaces are either coherent or semicoherent depending on the cooling condition after heat treatment. Full article
(This article belongs to the Special Issue Intermetallics for Structural Applications)
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12 pages, 3465 KiB  
Article
Influence of Nb, Ta and Zr on the Interdiffusion Coefficients and Solid Solution Strengthening of γ-TiAl Single Phase Alloys
by Lukas Haußmann, Steffen Neumeier, Johannes Bresler, Simon Keim, Florian Pyczak and Mathias Göken
Metals 2022, 12(5), 752; https://doi.org/10.3390/met12050752 - 28 Apr 2022
Cited by 2 | Viewed by 1907
Abstract
The alloying elements Nb, Ta and Zr improve the creep properties of fully lamellar γ/α2 titanium aluminides significantly. Since high temperature deformation mainly occurs in the γ-phase of γ/α2 titanium aluminides, the diffusivity and the solid solution hardening effect of these [...] Read more.
The alloying elements Nb, Ta and Zr improve the creep properties of fully lamellar γ/α2 titanium aluminides significantly. Since high temperature deformation mainly occurs in the γ-phase of γ/α2 titanium aluminides, the diffusivity and the solid solution hardening effect of these three elements in the γ-phase is studied by analyzing the concentration gradients of the alloying elements and the resulting hardness across the interdiffusion zone of diffusion couples by energy dispersive X-ray diffraction and nanoindentation. The results reveal that Zr has the highest interdiffusion coefficient but also the largest solid solution hardening coefficient. The mechanical properties of single γ-phase Ti-54Al-5X alloys were investigated by strain rate jump tests. The addition of 5 at.% Nb or Ta lead to an increased strength compared to a binary γ-Ti-54Al alloy. The Zr-containing γ-TiAl alloy reveals the highest strength at 750 °C and 900 °C, which is discussed to be due to the strong solid solution hardening effect of Zr. However, in comparison to the other alloys, Ti-54Al-5Zr shows quite brittle behavior up to 900 °C. The lower diffusivity of Ta compared to Nb leads to a higher strength of the Ta-modified alloy at 900 °C. Full article
(This article belongs to the Special Issue Intermetallics for Structural Applications)
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