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Metals
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Alloy Design and Microstructural Control of Structural Intermetallic Alloys
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Alloy Design and Microstructural Control of Structural Intermetallic Alloys

A special issue of Metals (ISSN 2075-4701). This special issue belongs to the section "Metal Casting, Forming and Heat Treatment".

Deadline for manuscript submissions: closed (30 September 2021) | Viewed by 12539

Special Issue Editor

Prof. Dr. Takayuki Takasugi

E-Mail Website1 Website2
Guest Editor
Department of Materials Science, Osaka Prefecture University, Gakuen-cho 1-1, Naka-ku, Sakai, Osaka 599-8531, Japan
Interests: intermetallic compounds; heat-resistant materials; microstructural control; mechanical properties; materials processing; hydrogen embrittlement
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Structural intermetallic alloys have high potential for use as high-temperature structural materials that are both wear- and corrosion-resistant, which makes them suitable for use as components of gas turbine engines or high-temperature tools working in severely oxidizing or corrosive environments. However, the structural intermetallic alloys that have been successfully applied to engineering materials so far are limited to a few alloy systems, e.g., titanium aluminides used as gas turbine blades. The properties and performance of structural intermetallic alloys as well as many other alloys are strongly correlated with received processing, designed alloy composition, and created microstructure. For processing, approaches involving additive manufacturing, powder metallurgy, and laser- or electron-deposition have recently been applied. For alloy design, simulated phase diagrams and phase field calculations have recently been used to explore novel intermetallic alloys. Regarding the microstructure, attempts have been made to be develop multiphase, nano-structured, harmonized, and multiscale microstructures. Enhancement of the performance of structural intermetallic alloys or the development of novel structural intermetallic alloys cannot be achieved without appropriate design and control of the processing, composition, and microstructure.

In this Special issue, we will cover the subjects of processing, alloy design, phase relation, microstructure, relationship between (micro)structure and (mechanical) properties, and development to advanced applications, among others. Moreover, articles dealing functional intermetallic alloys whose performance is directly or indirectly associated with mechanical properties are broadly solicited. It is hoped that this issue will serve as a platform for everyone—not only those who are currently developing advanced intermetallic alloys based on new concepts but also who are interested in this field.

Prof. Dr. Takayuki Takasugi
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

  • generic melting and casting
  • powder metallurgy
  • additive manufacturing
  • laser-, electron-, and arc-deposition processing
  • thermomechanical fabrication
  • titanium-, nickel-, cobalt-, iron-, and refractory metal-based intermetallic alloys
  • aluminides, silicides
  • phase diagram and phase stability
  • monolithic, multiphase, nano-structured and multiscaled microstructures
  • heat-treatment, strengthening, and hardening
  • ductility and fracture toughening
  • oxidation and corrosion resistance
  • wear and friction resistance

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Published Papers (4 papers)

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Research

15 pages, 9280 KiB  
Article
High Nb–TiAl Intermetallic Blades Fabricated by Isothermal Die Forging Process at Low Temperature
by Xiaopeng Wang, Wenchen Xu, Peng Xu, Haitao Zhou, Fantao Kong and Yuyong Chen
Metals 2020, 10(6), 757; https://doi.org/10.3390/met10060757 - 6 Jun 2020
Cited by 8 | Viewed by 3097
Abstract
In this study, the isothermal die forging process of high Nb–TiAl (Ti-44Al-8Nb-0.2W-0.2B-Y, at.%) alloy blades was simulated using the ABAQUS V6.11 software and the blades were fabricated successfully. The influence of a low forging temperature (lower than 1000 °C) and strain rate on [...] Read more.
In this study, the isothermal die forging process of high Nb–TiAl (Ti-44Al-8Nb-0.2W-0.2B-Y, at.%) alloy blades was simulated using the ABAQUS V6.11 software and the blades were fabricated successfully. The influence of a low forging temperature (lower than 1000 °C) and strain rate on the distributions of effective strain and stress were analyzed. The results indicate that the effective strain exhibits negative temperature sensitivity and positive strain rate sensitivity. The stress exponent (n = 3.02) and the apparent activation energy (Q = 293.381 kJ/mol) of the present alloy suggests that this as-forged high Nb–TiAl alloy exhibits good deformability at low temperatures. With the reduction in strain rate and the increase in forging temperature, the effective stress decreases. Finally, high-quality high Nb–TiAl alloy blades were fabricated using an isothermal die forging technology at a rate of 0.01 mm/s and temperature of 950 °C, chosen on the basis of the simulations results. Scanning electron microscopy (SEM) and electron back scatter diffraction (EBSD) results indicated that the center of the TiAl alloy blade possessed a duplex microstructure, consisting of remnant lamellar colonies and recrystallized γ/B2 grains. The refined α2 laths showed a typical forging flow line feature in the edge position, whereas the γ laths had broken down and recrystallized. Full article
(This article belongs to the Special Issue Alloy Design and Microstructural Control of Structural Intermetallic Alloys)
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12 pages, 9136 KiB  
Article
Effect of Boron Content and Cooling Rate on the Microstructure and Boride Formation of β-Solidifying γ-TiAl TNM Alloy
by Daniel Bernal, Xabier Chamorro, Iñaki Hurtado and Iñaki Madariaga
Metals 2020, 10(5), 698; https://doi.org/10.3390/met10050698 - 25 May 2020
Cited by 5 | Viewed by 3319
Abstract
Boron is a unique and popular grain refiner element in cast titanium aluminide (TiAl) alloys, as it helps to improve mechanical properties if properly alloyed. However, the formation mechanism of different types of borides in cast TiAl alloys is not yet clearly understood. [...] Read more.
Boron is a unique and popular grain refiner element in cast titanium aluminide (TiAl) alloys, as it helps to improve mechanical properties if properly alloyed. However, the formation mechanism of different types of borides in cast TiAl alloys is not yet clearly understood. This study seeks to correlate the chemical composition and cooling rate during solidification of cast TiAl alloys, with the type of boride precipitated and the resulting microstructure. Several β-solidifying γ-TiAl alloys of the TNM family were cast, alloying boron to a starting Ti-44.5Al-4Nb-1Mo-0.1B (at.%) alloy. The alloys were manufactured with an induction skull melting furnace and poured into a stepped 2, 4, 8 and 16 mm thickness mold to achieve different cooling rates. On one hand, the results reveal that boron contents below 0.5 at.% and cooling rates during solidification above 10 K/s promote the formation of detrimental ribbon borides. On the other hand, boron contents above 0.5 at.% and cooling rates during solidification below 10 K/s promote the formation of a refined microstructure with blocky borides. Finally, the formation mechanisms of both ribbon and blocky borides are proposed. Full article
(This article belongs to the Special Issue Alloy Design and Microstructural Control of Structural Intermetallic Alloys)
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10 pages, 8055 KiB  
Article
Multi-Refinement Effect of Rare Earth Lanthanum on α-Al and Eutectic Si Phase in Hypoeutectic Al-7Si Alloy
by Xiaoyan Wu, Huarui Zhang, Haitao Jiang, Zhenli Mi and Hu Zhang
Metals 2020, 10(5), 621; https://doi.org/10.3390/met10050621 - 9 May 2020
Cited by 10 | Viewed by 2743
Abstract
The effect of La addition on primary α-Al and the eutectic Si phase of Al-7Si alloy is investigated systematically in this work. The results indicate that La addition causes a multi-refining efficiency on the microstructure of Al-7Si alloy, including refinement of α-Al grains [...] Read more.
The effect of La addition on primary α-Al and the eutectic Si phase of Al-7Si alloy is investigated systematically in this work. The results indicate that La addition causes a multi-refining efficiency on the microstructure of Al-7Si alloy, including refinement of α-Al grains and secondary dendrite arm spacing as well as eutectic Si particles. The grain size, secondary dendrite arm spacing and area of eutectic Si particles are decreased by 26.8%, 7.7% and 26.7%, respectively, with the addition of 0.1 wt.% La. It is also found that La-rich phases of Al2Si2La form and distribute in the vicinity of the eutectic Si phase. The crystal structure and lattice parameter of Al2Si2La phase are determined to be hexagonal (a = b = 0.405 nm, c = 6.944 nm) based on the TEM analysis results. The multi-refinement effects are mainly attributed to the increased constitutional undercooling caused by the low solubility of La in Al alloy and the growth-restricting factor caused by the Al2Si2La phase. Full article
(This article belongs to the Special Issue Alloy Design and Microstructural Control of Structural Intermetallic Alloys)
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8 pages, 2806 KiB  
Article
Effect of Nb on the Microstructure and Mechanical Properties of Ti2Cu Intermetallic through the First-Principle Calculations and Experimental Investigation
by Jialin Cheng, Yeling Yun, Jingjing Wang, Jiaxin Rui, Shun Wang and Yulei Du
Metals 2020, 10(4), 547; https://doi.org/10.3390/met10040547 - 23 Apr 2020
Cited by 6 | Viewed by 2621
Abstract
Through the first-principle calculations based on density functional theory and experimental investigation, the structural stability elastic properties and mechanical properties of Ti2Cu and Ti18Cu5Nb1 intermetallics were studied. The first-principle calculations showed that the ratio of bulk [...] Read more.
Through the first-principle calculations based on density functional theory and experimental investigation, the structural stability elastic properties and mechanical properties of Ti2Cu and Ti18Cu5Nb1 intermetallics were studied. The first-principle calculations showed that the ratio of bulk modulus to shear modulus (B/G) and Poisson’s ratio (ν) of Ti2Cu and Ti18Cu5Nb1 intermetallics were 2.03, 0.288, and 2.22, 0.304, respectively, indicating that the two intermetallics were ductile. This was confirmed by the compression tests, which showed that the plastic strain of both intermetallics was beyond 25%. In addition, the yield strength increased from the 416 to 710 MPa with the addition of Nb. The increase in strength is the result of three factors, namely covalent bond tendency, fine grain strengthening, and solid solution strengthening. This finding gives clues to design novel intermetallics with excellent mechanical properties by first-principle calculations and alloying. Full article
(This article belongs to the Special Issue Alloy Design and Microstructural Control of Structural Intermetallic Alloys)
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