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10 pages, 3390 KiB

Open AccessArticle

Enhanced Reversible Magnetic-Field-Induced Strain in Ni-Mn-Ga Alloy

by Pingping Wu and Yongfeng Liang

Metals 2021, 11(12), 2017; https://doi.org/10.3390/met11122017 - 13 Dec 2021

Cited by 2 | Viewed by 1917

A phase-field model was developed to simulate the ferromagnetic domain structure and martensite variant microstructure of Ni-Mn-Ga shape-memory alloy. The evolution of reversible magnetic-field-induced strain (MFIS) and associated magnetic domain/martensite variant structure were modeled under an external magnetic field. It was found that [...] Read more.

A phase-field model was developed to simulate the ferromagnetic domain structure and martensite variant microstructure of Ni-Mn-Ga shape-memory alloy. The evolution of reversible magnetic-field-induced strain (MFIS) and associated magnetic domain/martensite variant structure were modeled under an external magnetic field. It was found that MFIS increased significantly from 0.2% to 0.28% as the temperature increased from 265 K to 285 K. In addition, compressive pre-stress efficiently enhanced the MFIS of the alloy, while tensile stress reduced MFIS. Furthermore, it was proved that there was possibility of achieving similar enhancement of MFIS by replacing compressive stress with perpendicular biaxial tensile stress. The results revealed that the residual variant induced by stress plays an important role in the reversible MFIS effect. Full article

(This article belongs to the Special Issue Microstructure and Properties of High Temperature Intermetallic)

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12 pages, 2854 KiB

Open AccessArticle

Effects of Al and Mo on Microstructure and Hardness of As-Cast TNM TiAl Alloys

by Gang Yang, Xiangjun Xu, Yongfeng Liang, Yongsheng Wang, Guojian Hao, Yuewen Zhai and Junpin Lin

Metals 2021, 11(11), 1849; https://doi.org/10.3390/met11111849 - 17 Nov 2021

Cited by 1 | Viewed by 1576

Abstract

The effects of Al and Mo elements on the microstructure and hardness of TNM TiAl alloys (Ti-43.5Al-4Nb-1Mo-0.1B) were studied by decreasing 0.5 at.% Mo and/or increasing 1.5 at.% Al. The results showed that the changed composition of the alloy had a slight influence [...] Read more.

The effects of Al and Mo elements on the microstructure and hardness of TNM TiAl alloys (Ti-43.5Al-4Nb-1Mo-0.1B) were studied by decreasing 0.5 at.% Mo and/or increasing 1.5 at.% Al. The results showed that the changed composition of the alloy had a slight influence on the morphology, but had important effects on the volume fraction, size, and composition of each phase. All the alloys had nearly full lamellar (NL) microstructures, with a few β_o phases at the boundaries of the colony or in the lamellar colony. The lamellar colony size and the lamellar spacing increased with the decrease in Mo and the increase in Al. The reduction in Mo content reduced the content of each phase in proportion, but the increase in Al content in the alloys led to the corresponding increase in Al content in the α₂ and γ phases. The hardness of the alloys decreased with the increase in Al content and the decrease in Mo content. This is mainly due to the increase in lamellar spacing caused by the change in composition. Therefore, the increased content of Al and decreased Mo content are unbeneficial for the microstructure. The relationship between the Vickers hardness and the lamellar spacing obeyed the Hall–Petch relationship. Full article

(This article belongs to the Special Issue Microstructure and Properties of High Temperature Intermetallic)

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10 pages, 2689 KiB

Open AccessArticle

Microstructural Characterization and Crack Propagation Behavior of a Novel β-Solidifying TiAl Alloy

by Shuling Zhang, Ning Cui, Wei Sun and Qiucheng Li

Metals 2021, 11(8), 1231; https://doi.org/10.3390/met11081231 - 02 Aug 2021

Cited by 2 | Viewed by 1642

Abstract

Novel β-solidifying TiAl alloys have great potential for engineering applications in the aerospace and automotive industries. The introduction of the β₀ phase will inevitably affect crack propagation. However, the related mechanism is unclear. In this study, the crack propagation behavior of different [...] Read more.

Novel β-solidifying TiAl alloys have great potential for engineering applications in the aerospace and automotive industries. The introduction of the β₀ phase will inevitably affect crack propagation. However, the related mechanism is unclear. In this study, the crack propagation behavior of different β₀-containing microstructures was systematically investigated by three-point bending tests. The results show that the coarse γ/α₂ lamellar microstructure exhibits better fracture toughness than the fine-grain microstructure because large numbers of γ/α₂ lamellar boundaries can effectively hinder crack propagation. The propagation direction depends largely on the orientation of the γ/α₂ lamellae. When the angle between the crack propagation direction and the γ/α₂ lamellar boundary is small, the crack tends to propagate along γ/α₂ lamellae. When the angle is close to 90°, the crack generally propagates by the trans-lamellar mode. Moreover, the crack tends to traverse across the fine β₀/γ duplex region due to the low resistance of fine grains in the crack propagation. The transgranular and intergranular modes are the main fracture mechanisms in the microstructure of the fine β₀/γ grains. Some shear ligaments can also be identified in the lamellar microstructure and these can consume propagation energy. The enlarged image shows that the crack propagation direction can be changed by the β₀ phase, owing to its high hardness. The crack tends to stop at the β₀ phase region. Full article

(This article belongs to the Special Issue Microstructure and Properties of High Temperature Intermetallic)

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14 pages, 4739 KiB

Open AccessArticle

Experimental Phase Equilibria and Isopleth Section of 8Nb-TiAl Alloys

by Yong Xu, Yongfeng Liang, Lin Song, Guojian Hao, Bin Tian, Rongfu Xu and Junpin Lin

Metals 2021, 11(8), 1229; https://doi.org/10.3390/met11081229 - 01 Aug 2021

Cited by 6 | Viewed by 1842

Abstract

The 8Nb isopleth section of a Ti-Al-Nb system is experimentally determined based on thermal analysis and thermodynamic calculation methods to obtain the phase transformation and equilibrium relations required for material design and fabrication. The phase transus and relations for the 8Nb-TiAl system show [...] Read more.

The 8Nb isopleth section of a Ti-Al-Nb system is experimentally determined based on thermal analysis and thermodynamic calculation methods to obtain the phase transformation and equilibrium relations required for material design and fabrication. The phase transus and relations for the 8Nb-TiAl system show some deviations from the calculated thermodynamic results. The ordered β_o phase transforms from the disordered β/α phases at 1200–1400 °C over a large Al concentration range, and this transformation is considered to be an intermediate type between the first- and second-order phase transitions. Moreover, the β_o phases are retained at the ambient temperature in the 8Nb-TiAl microstructures. The ω_o phase transforms from the highly ordered β_o phase, rather than from α₂ or β_o with a low degree of atom ordering B2 (LOB2) structure, with Al concentration of 32–43 at% at approximately 850 °C. From the experimental detection, the transition of the ω_o phase from the β_o phase is considered to be a further ordering process. Full article

(This article belongs to the Special Issue Microstructure and Properties of High Temperature Intermetallic)

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9 pages, 27582 KiB

Open AccessFeature PaperArticle

Microstructure Characterization and Properties of Graphene Oxide-Reinforced TiAl Matrix Composites

by Zhiyu Sun, Langping Zhu, Xiaofei Mo, Hai Nan and Xianfei Ding

Metals 2021, 11(6), 883; https://doi.org/10.3390/met11060883 - 28 May 2021

Cited by 19 | Viewed by 1678

Abstract

TiAl matrix composites reinforced with graphene oxide (GO) were prepared by powder metallurgy technology. The graphene oxide plates were added into TiAl powder by ultrasonic dispersion and milling, and then, shaped by Hot Isostatic Pressing (HIPing). Microstructures of the composites were characterized by [...] Read more.

TiAl matrix composites reinforced with graphene oxide (GO) were prepared by powder metallurgy technology. The graphene oxide plates were added into TiAl powder by ultrasonic dispersion and milling, and then, shaped by Hot Isostatic Pressing (HIPing). Microstructures of the composites were characterized by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). X-ray photoelectron spectroscopy (XPS) as well as Raman spectrum were conducted on the composite powder. The thermal and mechanical properties were tested on the TiAl matrix composites. The results show that the compression strength and heat conductivity of the composites can be improved distinctly at both room temperature and high temperature. The heat conductivity coefficient can reach to above 23 W/m K, and the compressive strength can reach to 1700 MPa at room temperature. GO was homogeneously dispersed into TiAl matrix in the form of random film with the diameter less than 10 μm. The minimum thickness of the GO film is about 5 nm. However, The GO does not well represent thermodynamically stable reinforcement at high temperatures, GO existed not only in the form of graphene but also a certain amount of Ti₃AlC, and its size is about 2 μm rather than nanoscale, which can decrease the ductile reinforcement of GO in the TiAl matrix. Full article

(This article belongs to the Special Issue Microstructure and Properties of High Temperature Intermetallic)

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Review

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17 pages, 8088 KiB

Open AccessReview

Microstructure and Mechanical Properties of TiAl Matrix Composites Reinforced by Carbides

by Ying Yang, Yongfeng Liang, Chan Li and Junpin Lin

Metals 2022, 12(5), 790; https://doi.org/10.3390/met12050790 - 04 May 2022

Cited by 5 | Viewed by 1980

Abstract

TiAl alloys have the potential to become a new generation of high-temperature materials due to their lightweight and high-strength properties, while the brittleness at room temperature and microstructure stability at elevated temperature are the key problems. The preparation of composite materials is an [...] Read more.

TiAl alloys have the potential to become a new generation of high-temperature materials due to their lightweight and high-strength properties, while the brittleness at room temperature and microstructure stability at elevated temperature are the key problems. The preparation of composite materials is an effective way to solve these problems, because the mechanical properties of TiAl matrix composites can be improved by the close combination of the reinforced phase and matrix. The preparation methods, microstructure, and mechanical properties of TiAl matrix composites reinforced by carbides are reviewed from the literature in this paper. A comprehensive summary of the effect of C on TiAl alloys can reveal the relationship between the microstructure and mechanical properties and provide guidance for subsequent experimental works. Two forms of C in TiAl matrix composites are reviewed: solid solutions in matrix and carbide precipitations. For TiAl alloys, the minimum carbon content for the carbide precipitation is about 0.5 at.% for low-Nb-containing TiAl alloys and about 0.8 at.% for high-Nb-TiAl alloys. An appropriate amount of C can improve the tensile properties and flexural strength of TiAl alloys. The hardness of the composites is higher than that of pure TiAl due to solution strengthening when the carbon content is low. The minimum creep rate of TiAl alloys can be reduced by one order of magnitude by adding C at the amount near the solubility limit. Full article

(This article belongs to the Special Issue Microstructure and Properties of High Temperature Intermetallic)

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18 pages, 7084 KiB

Open AccessReview

En-Garde! A Review of Fencing Blade Material Development

by Haocheng Jiang, Jingfang Shen, Xingyu Yao, Constance Van Horne, Xianhui Lu, Yong Xiong and Limei Cha

Metals 2022, 12(2), 236; https://doi.org/10.3390/met12020236 - 26 Jan 2022

Cited by 1 | Viewed by 7146

Abstract

Using two fencing swords manufactured in Europe and China, we investigated the typical materials used for fencing blades and compared the experimental results with the nominal compositions of a variety of steels. We found that spring steels and maraging steels were the primary [...] Read more.

Using two fencing swords manufactured in Europe and China, we investigated the typical materials used for fencing blades and compared the experimental results with the nominal compositions of a variety of steels. We found that spring steels and maraging steels were the primary metals used in fencing blades. The review then provides an overview of the chemical compositions, heat treatment processes, microstructures and associated mechanical properties of these materials. By combining the requirements for the safety of athletes, mechanical behaviors of different steels, and production costs for industry, we introduced possible directions for the heat treatments and processing methods that have the potential to enhance performance and overcome the limitations of previous materials. In addition, an ultra-strong steel, Fe-9.95Mn-0.44C-1.87Al-0.67V which could be a promising new candidate in this area, was recommended. Finally, we suggested that successful cooperation between manufacturers and researchers is necessary to reach the various requirements of fencing blades to meet the growing popularity of fencing in China. Full article

(This article belongs to the Special Issue Microstructure and Properties of High Temperature Intermetallic)

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23 pages, 4627 KiB

Open AccessReview

Microstructure Design and Its Effect on Mechanical Properties in Gamma Titanium Aluminides

by Xuqi Liu, Qia Lin, Wenjing Zhang, Constance Van Horne and Limei Cha

Metals 2021, 11(10), 1644; https://doi.org/10.3390/met11101644 - 16 Oct 2021

Cited by 9 | Viewed by 3571

Abstract

Intermetallic gamma titanium aluminides display attractive engineering properties at high temperatures of up to 750 °C. To date, they have been used in low-pressure turbine blades and turbocharger rotors in advanced aircraft and automotive engines. This review summarizes the fundamental information of the [...] Read more.

Intermetallic gamma titanium aluminides display attractive engineering properties at high temperatures of up to 750 °C. To date, they have been used in low-pressure turbine blades and turbocharger rotors in advanced aircraft and automotive engines. This review summarizes the fundamental information of the Ti–Al system. After providing the development of

γ

TiAl alloys, typical phases, microstructures and their characteristics in TiAl alloys, the paper focuses on the effects of alloying elements on the phase boundary shifting, stabilizing effects and strengthening mechanism. The relationships between chemical additions, microstructure evolution and mechanical properties of the alloy are discussed. In parallel, the processing technologies and the common heat treatment methods are described in detail, both of which are applied to optimize the mechanical properties via adjusting microstructures. On this basis, the effects from chemical composition, processing technologies and heat treatments on microstructure, which controls the mechanical properties, can be obtained. It has a certain guiding significance for tailoring the microstructures to gain desired mechanical properties. Full article

(This article belongs to the Special Issue Microstructure and Properties of High Temperature Intermetallic)

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