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A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Crystalline Metals and Alloys".

Deadline for manuscript submissions: closed (31 May 2023) | Viewed by 18109

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Dr. Li-Wei Tseng

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Department of Mechatronics Engineering, National Changhua University of Education, Kaohsiung 50007, Taiwan
Interests: shape memory alloys; metallurgy; microstructure; mechanics of materials; mechanical properties; materials processing
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Dr. Yu-Chih Tzeng

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Department of Power Vehicle and Systems Engineering, Chung Cheng Institute of Technology, National Defense University, Taoyuan 334, Taiwan
Interests: microstructure; metal; steel foam; materials engineering

Prof. Dr. Yeong-Lin Lai

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Department of Mechatronics Engineering, National Changhua University of Education, Kaohsiung 50007, Taiwan
Interests: Internet of Things (IoT); intelligent systems; artificial intelligence (AI); integrated circuit design; opto-electronic materials and devices
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

High-performance alloys such as shape memory alloys, high entropy alloys, and aluminium alloys can be used in different industrial applications. Their properties are required to customize material processing and microstructure. As a result, it is important to investigate how the thermomechanical processing conditions affect the microstructure and property profile of high performance alloys. This investigation is important to developing and optimizing new alloys for different thermomechanical processing, as well as in the transfer to industrial processes. Therefore, the purpose of this Special Issue is the correlations between thermomechanical processes, microstructure, and mechanical properties of high-performance alloys. Contributions are intended to show the influence of the thermomechanical process, e.g., casting, hot or cold rolling, heat treatment, sintering, and extrusion on the property profile. In addition to experimental approaches, the development methods of modelling and simulation approaches are useful to predict composition–microstructure–property relations for high-performance alloy development and thermomechanical process design. The editors therefore welcome all contributions that add knowledge to this scientific field.

We look forward to receiving your submissions.

Dr. Li-Wei Tseng
Dr. Yu-Chih Tzeng
Prof. Dr. Yeong-Lin Lai
Guest Editors

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Keywords

smart materials
high-performance alloys
shape memory alloys
high entropy alloys
high strength aluminium alloys
mechanical property
microstructure characterization

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Published Papers (11 papers)

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13 pages, 31963 KiB

Open AccessArticle

Microstructures and Mechanical Properties of Annealed Ti₅₀Ni₄₇Fe₃ Shape Memory Alloy

by Shuwei Liu, Yanfeng Li, Xiaoyun Song, Yang Yu, Wenjun Ye and Songxiao Hui

Crystals 2023, 13(4), 706; https://doi.org/10.3390/cryst13040706 - 21 Apr 2023

Cited by 3 | Viewed by 1471

Abstract

The effect of annealing temperature on the microstructures and mechanical properties of Ti₅₀Ni₄₇Fe₃ (at. %) shape memory alloy was investigated by using a cold-rolled alloy sheet. For this purpose, a scanning electron microscope, electron backscatter diffraction, a transmission electron microscope, X-ray diffraction, tensile tests and Vickers hardness tests were used. The evolution of the microstructures, mechanical properties and fracture morphology of Ti₅₀Ni₄₇Fe₃ alloy was studied. The results show that the recovery occurs at an annealing temperature of 500 °C, and the recrystallization occurs at 600 °C. Because of the recrystallization at 600 °C, the <110>//RD texture disappears, and the intensity of the <111>//RD texture decreases; the alloy reaches its maximum elongation while maintaining a high strength, and at this annealing temperature, the alloy has excellent comprehensive mechanical properties. After the temperature exceeds 600 °C, the mechanical properties of the alloy decrease sharply. With the increase of the annealing temperature, the quantity and distribution of elliptical Ti₂Ni-phase particles show almost no specific changes. Additionally, with the increase of annealing temperatures to 600 °C, the fracture surface of Ti₅₀Ni₄₇Fe₃ alloys becomes flatter. Full article

(This article belongs to the Special Issue Emerging Topics on High Performance Alloys)

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13 pages, 3695 KiB

Open AccessArticle

Creep Behavior of Squeeze-Cast Mg–15Gd Alloy

by Ferdinand Dobeš and Petr Dymáček

Crystals 2023, 13(3), 374; https://doi.org/10.3390/cryst13030374 - 22 Feb 2023

Viewed by 1191

Abstract

The creep behavior of a binary Mg-15 wt.% Gd alloy was investigated over the temperature range from 523 K to 743 K, i.e., in both the single-phase region (the hexagonal close-packed solid solution of Gd in Mg) and the two-phase region (the solid solution plus Mg₅Gd precipitates). The alloy was prepared by the squeeze casting technique. In the higher temperature range, at 723 and 743 K, the specimens were solution treated by in situ annealing prior to testing. At the temperature of 673 K and below, the alloy was tested in the cast state. In the higher temperature range, the behavior was interpreted in terms of the viscous glide, where the dislocation motion was constrained by the presence of solute atmospheres. The dislocation motion was controlled by the rate of the cross slip from the basal to the prismatic planes. At the temperatures of 623 K and 673 K, the creep behavior was rationalized by introducing the threshold stress concept. At the temperatures of 523 K and 573 K, the stresses required to achieve experimentally measurable creep rates were such that dislocations broke away from the atmospheres of foreign atoms. Comparison with a series of magnesium alloys prepared by squeeze casting and creep-tested by the same technique showed that gadolinium can be a favorable creep-resistance enhancing element. Full article

(This article belongs to the Special Issue Emerging Topics on High Performance Alloys)

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16 pages, 9979 KiB

Open AccessArticle

Determining Localized Necking in Polycrystalline Sheet Metals Using the Bifurcation Phenomenon in Strain Evolution

by Ji He and Yishuang Feng

Crystals 2023, 13(2), 272; https://doi.org/10.3390/cryst13020272 - 4 Feb 2023

Cited by 5 | Viewed by 1616

Abstract

The forming limit is an important failure criterion for polycrystalline sheet metals when approving the forming process. Recent developments in strain measurement technology, e.g., digital image correlation (DIC), enable the strain evolution to be captured continuously and accurately. This new technology would improve the forming limit measurements if the onset of the necking detection method was developed accordingly. This paper proposes a new method based on the bifurcation phenomenon in strain evolution to detect the onset of localized necking through DIC measurements. This detection method was inspired by a physical understanding and experimental observations of the necking phenomenon. The method eliminates the derivative calculation from the traditional method, while it can directly determine the onset of localized necking through strain evolution curves. The robustness and accuracy of the method are also investigated through experiments. Imperfection and non-defect analyses, based on non-associated and associated flow rules, were utilized and compared to the determined results. The detection method provides satisfactory forming limit results and can be used as an alternative method to determine the forming limit diagram (FLD). Full article

(This article belongs to the Special Issue Emerging Topics on High Performance Alloys)

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10 pages, 1467 KiB

Open AccessArticle

Quantification of Modifiers Fading during Melt Holding in the Aluminum Casting Furnace

by Mile Djurdjevic, Srecko Manasijevic, Slavko Smiljanic and Marko Ristic

Crystals 2023, 13(2), 191; https://doi.org/10.3390/cryst13020191 - 21 Jan 2023

Viewed by 1872

Abstract

Strontium (Sr) and sodium (Na) are the most used modifiers in the aluminum casting industry. Both lose their concentration (fade) during holding in the melting furnace. Three types of chemical reactions in the melt may cause modifier fading: vaporizing, oxidizing, or reacting with some other elements from the melt. Due to Na and Sr’s very low vapor pressure, their vaporization from the aluminum melt was excluded as a reason for the modifiers’ fading. Oxidation looks like the major chemical reaction that causes the fading of Na and Sr from an aluminum melt. The present paper aimed to quantify the fading of Na and Sr in an Al–Si–Cu–Mg alloy. The loss of modifiers (Na and Sr) during melt holding in a furnace can be analytically quantified using equations taken from the literature. The calculated surface reaction rate constant (k_s) can estimate the modifier’s loss during melt holding in industrial and laboratory furnaces. Full article

(This article belongs to the Special Issue Emerging Topics on High Performance Alloys)

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11 pages, 11751 KiB

Open AccessArticle

Design of Porous Shape Memory Alloys with Small Mechanical Hysteresis

by Zheng Wu, Baosheng Liu, Jiali Wei, Yuanxi Yang, Xudong Zhang and Junkai Deng

Crystals 2023, 13(1), 34; https://doi.org/10.3390/cryst13010034 - 25 Dec 2022

Cited by 4 | Viewed by 1600

Abstract

The mechanical hysteresis loop behavior always limits the applicability of shape memory alloys (SMAs) in mechanical devices requiring high sensitivity, durability and energy conversion efficiency. In this study, through experiments and finite element simulations, we systematically investigated the effects of porosity and pore distribution on the mechanical hysteresis behavior of porous Ti_49.2Ni_50.8 SMAs. Inspired by atomic crystal structures, some porous SMAs with ordered void distributions were investigated to compare them with SMAs with random pore distributions. Our results show that the hysteresis reduces with increasing porosity in porous SMAs. The designed BCC-type ordered porous SMAs possess a narrower hysteresis loop with less energy dissipation at the same porosity. The gradual and homogenous martensitic-phase transformations are responsible for this characteristic. The present work provides an effective way to design porous SMAs with narrow hysteresis, which is promising in applications for mechanical sensors or actuators. Full article

(This article belongs to the Special Issue Emerging Topics on High Performance Alloys)

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18 pages, 9001 KiB

Open AccessArticle

Preventing Crack in an Aluminum Alloy Complex Structure during Welding Process Based on Numerical Simulation Technology

by Yuelai Zhang, Wenze Luo, Jiongmeng Zeng, Xixian Li, Long Hu and Dean Deng

Crystals 2022, 12(12), 1742; https://doi.org/10.3390/cryst12121742 - 1 Dec 2022

Cited by 6 | Viewed by 1502

Abstract

Aluminum alloy structures are widely used for weight reduction in aviation, shipbuilding, rail vehicles and automotive industries. Fusion welding technology is one of the most important joining methods for lightweight structure assembly due to its advantages such as flexibility in design, high production efficiency, and low cost. However, the local centralized heating during fusion welding inevitably produces residual stress and welding deformation. For actual engineering structures, if the product design is unreasonable or the external restraint is inappropriate, the transient stress or residual stress become a key factor resulting in cracking during the assembly process. In the current study, an effective computational approach was developed based on the MSC Marc software to simulate transient and residual stress fields for complex aluminum alloy structures during the welding process. In the developed computational approach, according to the location and arrangement of welding lines, an instantaneous heat source model was used to replace the traditional moving heat source model, and as a result significanlty improved the calculation efficiency to meet actual engineering needs. The welding stresses, including transient and residual stress, of an A6061 aluminum alloy complex structure were calculated by the developed numerical simulation technology. The simulation results indicated that the cracking was produced by excessive transient stress during welding process. Subsequently, the effect of external restraint intensity on welding stress at the key location was examined numerically. Based on the simulation results, measures to reduce welding stress and cracking risk were put forward based on adjusting the external restraint intensity. Full article

(This article belongs to the Special Issue Emerging Topics on High Performance Alloys)

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8 pages, 1800 KiB

Open AccessArticle

Enhanced Fracture Toughness and High-Temperature Strength of Directionally Solidified Mo-XC Alloys

by Julia Becker, Danio Breuer, Iurii Bogomol and Manja Krüger

Crystals 2022, 12(11), 1534; https://doi.org/10.3390/cryst12111534 - 28 Oct 2022

Cited by 2 | Viewed by 1299

Abstract

The present article focuses on refractory metals strengthened by ceramic phases to improve the mechanical properties at ambient temperatures as well as at high temperatures. In this work, near-eutectic, directionally solidified (DS) Mo-34TiC and Mo-27ZrC alloys are investigated with regard to their microstructures, fracture toughness at room temperature and compressive strength at high temperatures. Superior fracture toughness as well as competitive strength compared with other Mo-XC composites are achieved. Compressive tests up to 1000 °C on longitudinal and transversal specimens show the significant impact of the anisotropy on the strength. Full article

(This article belongs to the Special Issue Emerging Topics on High Performance Alloys)

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11 pages, 1806 KiB

Open AccessArticle

The Influence of Internal Stress on the Nanocrystal Formation of Amorphous Fe_73.8Si₁₃B_9.1Cu₁Nb_3.1 Microwires and Ribbons

by Artem Fuks, Galina Abrosimova, Oleg Aksenov, Margarita Churyukanova and Alexandr Aronin

Crystals 2022, 12(10), 1494; https://doi.org/10.3390/cryst12101494 - 21 Oct 2022

Cited by 4 | Viewed by 1394

Abstract

The early stages of nanocrystallization in amorphous Fe_73.8Si₁₃B_9.1Cu₁Nb_3.1 ribbons and microwires were compared in terms of their internal stress effects. The microstructure was investigated by the X-ray diffraction method. Classical expressions of crystal nucleation and growth were modified for microwires while accounting for the internal stress distribution, in order to justify the XRD data. It was assumed that, due to the strong compressive stresses on the surface part and tensile stresses on the central part, crystallization on the surface part of the microwire proceeded faster than in the central part. The results revealed more rapid nanocrystallization in microwires compared to that in ribbons. During the initial period of annealing, the compressive surface stress of a microwire caused the formation of a predominantly crystallized surface layer. The results obtained open up new possibilities for varying the high-frequency properties of microwires and their application in modern sensorics. Full article

(This article belongs to the Special Issue Emerging Topics on High Performance Alloys)

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13 pages, 3646 KiB

Open AccessArticle

Study of the Microstructural, Thermal, and Magnetic Properties of High-Energy Ball-Milled Nanocrystalline Fe(Al)

by Hana Ibn Gharsallah, Myriam Azabou, Mohamed Khitouni, Jason Daza and Joan-Josep Suñol

Crystals 2022, 12(10), 1430; https://doi.org/10.3390/cryst12101430 - 10 Oct 2022

Cited by 2 | Viewed by 1364

Abstract

In this work, structural, microstructural, thermal, and magnetic properties of a Fe-25at%Al alloy produced by high-energy mechanical milling were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and vibrating sample magnetometry (VSM) techniques. At the early stage of the milling process, three phases, namely, Fe, Al, and Fe(Al), coexist in the milled powder. After 20 h of milling, the results of the refinement of the XRD pattern reveal the formation of the supersaturated bcc-Fe(Al) solid solution with a crystallite size of 10 nm. The DSC curves show several overlapped exothermic peaks associated with the relaxation of the deformed structure and various phase transitions, such as the formation of Al₁₃Fe₄ and Fe₃Al intermetallic. During milling times, the alloyed samples have a hard-ferromagnetic behavior, where Hc varies from 628 Oe to 746 Oe when the milling time increases from 4 to 40 h. The magnetic properties were related to the microstructural changes. Full article

(This article belongs to the Special Issue Emerging Topics on High Performance Alloys)

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9 pages, 3940 KiB

Open AccessEditor’s ChoiceArticle

Characterization of ZTA Composite Ceramic/Ti6Al4V Alloy Joints Brazed by AgCu Filler Alloy Reinforced with One-Dimensional Al₁₈B₄O₃₃ Single Crystal

by Yifeng Wang, Zhouxin Jin, Guangjie Feng, Jian Cao, Hao Zhang and Dean Deng

Crystals 2022, 12(7), 933; https://doi.org/10.3390/cryst12070933 - 30 Jun 2022

Cited by 2 | Viewed by 2028

Abstract

Al₁₈B₄O₃₃ whiskers were used as a reinforcer to study the effect of one-dimensional single crystal on the quality improvement of ZTA composite ceramic/Ti6Al4V alloy joints brazed by AgCu alloy. The microstructure of the joint with whisker additions was characterized in detail. The effects of brazing temperature on the microstructure and shear strength of the brazed joints were investigated. The results showed that the whiskers reacted with the liquid alloy during the brazing process and continuous (Cu,Al)₃Ti₃O layers were formed in contact with the residual whiskers. The addition of 2 wt.% Al₁₈B₄O₃₃ whiskers into AgCu filler alloy can delay the growth of the (Cu,Al)₃Ti₃O layer on the ZTA side, and can significantly restrain the growth of the Ti-Cu compound region over a brazing temperature range of 800~875 °C. Because of the one-dimensional reinforcement, the temperature window for obtaining ZTA/Ti6Al4V joints with shear strength values higher than 50 MPa was extended, and the maximum shear strength of the joints reached 56 MPa. Full article

(This article belongs to the Special Issue Emerging Topics on High Performance Alloys)

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11 pages, 2381 KiB

Open AccessReview

Microstructure and Mechanical Properties of Ni-Based Complex Concentrated Alloys under Radiation Environment

by Qiuwei Xing, Xu Zhu, Guoju Li, Xinzhe Zhang, Xinfang Zhang and Zhanxing Chen

Crystals 2022, 12(9), 1322; https://doi.org/10.3390/cryst12091322 - 19 Sep 2022

Cited by 2 | Viewed by 2032

Abstract

The rapid development of fusion-reactor technology calls for excellent anti-irradiation materials. Complex concentrated alloy (CCA) is a newly proposed alloy concept which is a promising candidate of nuclear fusion materials by virtue of its great phase stability under irradiation. This article summarizes anti-radiation mechanism and the microstructure evolution in HEAs. The effective factors on irradiation behavior of HEAs, including entropy, sample size and temperature, are discussed. Finally, the article introduces the potential ways to solve the economic and environmental problems which the HEAs faced for their applications in the future. In summary, the HEAs usually show better irradiation resistance than traditional alloys, such as less swelling, smaller size of defects, and more stable mechanical properties. One possible reason for the irradiation resistance of HEA is the self-healing effect induced by the high-entropy and atomic-level stress among the metal atoms. The activation of the principal element should be considered when selecting components of HEA, and the high throughput technique is a potential way to reduce the design and fabrication cost of HEAs. It is reasonable to expect that coming years will see the application of novel HEAs in fusion reactors. Full article

(This article belongs to the Special Issue Emerging Topics on High Performance Alloys)

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