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4 pages, 190 KiB

Open AccessEditorial

Metallic Materials: Structure Transition, Processing, Characterization and Applications

by Jing Hu, Ze He and Xiliang Liu

Materials 2024, 17(5), 985; https://doi.org/10.3390/ma17050985 - 21 Feb 2024

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Abstract

This Special Issue provides readers with up-to-date information on the recent progress in the structure transition, processing, characterization, and applications of metals, including ferrous and nonferrous metals [...] Full article

(This article belongs to the Special Issue Metallic Materials: Structure Transition, Processing, Characterization and Applications)

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13 pages, 6201 KiB

Open AccessArticle

Mechanism Analysis for the Enhancement of Low-Temperature Impact Toughness of Nodular Cast Iron by Heat Treatment

by Huanyu Zhuang, Jiahui Shen, Minhua Yu, Xulong An and Jing Hu

Materials 2024, 17(2), 513; https://doi.org/10.3390/ma17020513 - 21 Jan 2024

Cited by 3 | Viewed by 1919

Abstract

The low-temperature impact toughness of nodular cast iron can be significantly enhanced by heat treatment, and thus meet the severe service requirements in the fields of high-speed rail and power generation, etc. In order to explore the enhancement mechanism, microstructure, hardness, composition and [...] Read more.

The low-temperature impact toughness of nodular cast iron can be significantly enhanced by heat treatment, and thus meet the severe service requirements in the fields of high-speed rail and power generation, etc. In order to explore the enhancement mechanism, microstructure, hardness, composition and other characteristics of as-cast and heat-treated nodular cast iron is systematically tested and compared by optical microscopy, microhardness tester, EBSD, SEM, electron probe, and impact toughness testing machine in this study. The results show that heat treatment has little effect on the morphology and size of graphite in nodular cast iron, ignores the effect on the grain size, morphology, and distribution of ferritic matrix, and has little effect on the hardness and exchange of elements, while it is meaningful to find that heat treatment brings about significant decrease in high-angle grain boundaries (HAGB) between 59° and 60°, decreasing from 10% to 3%. Therefore, the significant enhancement of low-temperature impact toughness of nodular cast iron by heat treatment may result from the obvious decrease in HAGB between 59° and 60°, instead of other reasons. From this perspective, the study can provide novel ideas for optimizing the heat treatment process of nodular cast iron. Full article

(This article belongs to the Special Issue Metallic Materials: Structure Transition, Processing, Characterization and Applications)

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8 pages, 1438 KiB

Open AccessCommunication

Improved Analytical Model for Thermal Softening in Aluminum Alloys Form Room Temperature to Solidus

by Gaoqiang Chen, Xin Liu, Junnan Qiao, Tianxiang Tang, Hua Zhang, Songling Xing, Gong Zhang and Qingyu Shi

Materials 2023, 16(23), 7358; https://doi.org/10.3390/ma16237358 - 26 Nov 2023

Cited by 1 | Viewed by 1515

Abstract

In advanced solid-state manufacturing processes such as friction stir welding, the metal’s temperature ranges from room temperature to the solidus temperature. The material strength in the temperature range is generally required for investigating the mechanical behaviors. In this communication paper, an analytical model [...] Read more.

In advanced solid-state manufacturing processes such as friction stir welding, the metal’s temperature ranges from room temperature to the solidus temperature. The material strength in the temperature range is generally required for investigating the mechanical behaviors. In this communication paper, an analytical model is proposed for describing the thermal softening of aluminum alloys for room temperature to solidus temperature, in which the concept of temperature-dependent transition between two thermal softening regimes is implemented. It is demonstrated that the proposed model compares favorably to the well-known Sellars–Tegart model and Johnson–Cook model. The constants of the proposed model for nine typical engineering commercial aluminum alloys are documented. Full article

(This article belongs to the Special Issue Metallic Materials: Structure Transition, Processing, Characterization and Applications)

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13 pages, 3240 KiB

Open AccessEditor’s ChoiceArticle

Effect of the Solid Solution and Aging Treatment on the Mechanical Properties and Microstructure of a Novel Al-Mg-Si Alloy

by Yan Chen, Wu Wei, Yu Zhao, Wei Shi, Xiaorong Zhou, Li Rong, Shengping Wen, Xiaolan Wu, Kunyuan Gao, Hui Huang and Zuoren Nie

Materials 2023, 16(21), 7036; https://doi.org/10.3390/ma16217036 - 4 Nov 2023

Cited by 10 | Viewed by 2552

Abstract

A novel Al-Mg-Si aluminum alloy with the addition of the micro-alloying element Er and Zr that was promptly quenched after extrusion has been studied. The solid solution and aging treatment of the novel alloy are studied by observing the microstructure, mechanical properties, and [...] Read more.

A novel Al-Mg-Si aluminum alloy with the addition of the micro-alloying element Er and Zr that was promptly quenched after extrusion has been studied. The solid solution and aging treatment of the novel alloy are studied by observing the microstructure, mechanical properties, and strengthening mechanism. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques are employed to examine the changes in the microstructure resulting from various solid solution treatments and aging treatments. The best strengthening effect can be achieved when the solubility of the MgSi phase and precipitate β″ (Mg₂Si phase) is at their maximum. The addition of Er and Zr elements promotes the precipitation of the β″ phase and makes the b″ phase more finely dispersed. The aging strengthening of alloys is a comprehensive effect of the dislocation cutting mechanism and bypass mechanism, the joint effect of diffusion strengthening of Al₃(Er,Zr) particles and the addition of Er and Zr elements promoting the precipitation strengthening of β″ phases. In this paper, by adding Er and Zr elements and exploring the optimal heat treatment system, the yield strength of the alloy reaches 437 MPa and the tensile strength reaches 453 MPa after solid solution treatment at 565 °C/30 min and aging at 175 °C/10 h. Full article

(This article belongs to the Special Issue Metallic Materials: Structure Transition, Processing, Characterization and Applications)

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9 pages, 1323 KiB

Open AccessArticle

Revisiting the High-Pressure Behaviors of Zirconium: Nonhydrostaticity Promoting the Phase Transitions and Absence of the Isostructural Phase Transition in β-Zirconium

by Lei Liu, Qiumin Jing, Hua Y. Geng, Yinghua Li, Yi Zhang, Jun Li, Shourui Li, Xiaohui Chen, Junjie Gao and Qiang Wu

Materials 2023, 16(14), 5157; https://doi.org/10.3390/ma16145157 - 21 Jul 2023

Cited by 5 | Viewed by 1447

Abstract

Zirconium (Zr) is an important industrial metal that is widely used in nuclear engineering, chemical engineering, and space and aeronautic engineering because of its unique properties. The high-pressure behaviors of Zr have been widely investigated in the past several decades. However, the controversies [...] Read more.

Zirconium (Zr) is an important industrial metal that is widely used in nuclear engineering, chemical engineering, and space and aeronautic engineering because of its unique properties. The high-pressure behaviors of Zr have been widely investigated in the past several decades. However, the controversies still remain in terms of the phase transition (PT) pressures and the isostructural PT in β-Zr: why the PT pressure in Zr is so scattered, and whether the β to β’ PT exists. In the present study, to address these two issues, the Zr sample with ultra-high purity (>99.99%) was quasi-hydrostatically compressed up to ~70 GPa. We discovered that both the purity and the stress state of the sample (the grade of hydrostaticity/nonhydrosaticity) affect the PT pressure of Zr, while the stress state is the dominant factor, the nonhydrostaticity significantly promotes the PT of Zr. We also propose two reasons why the β-β’ isostructural PT was absent in the subsequent and present experiments, which call for further investigation of Zr under quasi-compression up to 200 GPa or even higher pressures. Full article

(This article belongs to the Special Issue Metallic Materials: Structure Transition, Processing, Characterization and Applications)

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21 pages, 10860 KiB

Open AccessArticle

Friction Stir Welding of Dissimilar Al 6061-T6 to AISI 316 Stainless Steel: Microstructure and Mechanical Properties

by Mohamed Newishy, Matias Jaskari, Antti Järvenpää, Hidetoshi Fujii and Hamed Ahmed Abdel-Aleem

Materials 2023, 16(11), 4085; https://doi.org/10.3390/ma16114085 - 30 May 2023

Cited by 9 | Viewed by 3608

Abstract

The friction stir welding (FSW) process was recently developed to overcome the difficulty of welding non-ferrous alloys and steels. In this study, dissimilar butt joints between 6061-T6 aluminum alloy and AISI 316 stainless steel were welded by FSW using different processing parameters. The [...] Read more.

The friction stir welding (FSW) process was recently developed to overcome the difficulty of welding non-ferrous alloys and steels. In this study, dissimilar butt joints between 6061-T6 aluminum alloy and AISI 316 stainless steel were welded by FSW using different processing parameters. The grain structure and precipitates at the different welded zones of the various joints were intensively characterized by the electron backscattering diffraction technique (EBSD). Subsequently, the FSWed joints were tensile tested to examine the mechanical strength compared with that of the base metals. The micro-indentation hardness measurements were conducted to reveal the mechanical responses of the different zones in the joint. The EBSD results of the microstructural evolution showed that a significant continuous dynamic recrystallization (CDRX) occurred in the stir zone (SZ) of the Al side, which was mainly composed of the weak metal, Al, and fragmentations of the steel. However, the steel underwent severe deformation and discontinuous dynamic recrystallization (DDRX). The FSW rotation speed increased the ultimate tensile strength (UTS) from 126 MPa at a rotation speed of 300 RPM to 162 MPa at a rotation speed of 500 RPM. The tensile failure occurred at the SZ on the Al side for all specimens. The impact of the microstructure change in the FSW zones was significantly pronounced in the micro-indentation hardness measurements. This was presumably attributed to the promotion of various strengthening mechanisms, such as grain refinement due to DRX (CDRX or DDRX), the appearance of intermetallic compounds, and strain hardening. The aluminum side underwent recrystallization as a result of the heat input in the SZ, but the stainless steel side did not experience recrystallization due to inadequate heat input, resulting in grain deformation instead. Full article

(This article belongs to the Special Issue Metallic Materials: Structure Transition, Processing, Characterization and Applications)

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13 pages, 4012 KiB

Open AccessArticle

Towards an Optimized Artificial Neural Network for Predicting Flow Stress of In718 Alloys at High Temperatures

by Chunbo Zhang, Qingyu Shi, Yihe Wang, Junnan Qiao, Tianxiang Tang, Jun Zhou, Wu Liang and Gaoqiang Chen

Materials 2023, 16(7), 2663; https://doi.org/10.3390/ma16072663 - 27 Mar 2023

Cited by 4 | Viewed by 1915

Abstract

Artificial neural networks (ANNs) have been an important approach for predicting the value of flow stress, which is dependent on temperature, strain, and strain rate. However, there is still a lack of sufficient knowledge regarding what structure of ANN should be used for [...] Read more.

Artificial neural networks (ANNs) have been an important approach for predicting the value of flow stress, which is dependent on temperature, strain, and strain rate. However, there is still a lack of sufficient knowledge regarding what structure of ANN should be used for predicting metal flow stress. In this paper, we train an ANN for predicting flow stress of In718 alloys at high temperatures using our experimental data, and the structure of the ANN is optimized by comparing the performance of four ANNs in predicting the flow stress of In718 alloy. It is found that, as the size of the ANN increases, the ability of the ANN to retrieve the flow stress results from a training dataset is significantly enhanced; however, the ability to predict the flow stress results absent from the training does not monotonically increase with the size of the ANN. It is concluded that the ANN with one hidden layer and four nodes possesses optimized performance for predicting the flow stress of In718 alloys in this study. The reason why there exists an optimized ANN size is discussed. When the ANN size is less than the optimized size, the prediction, especially the strain dependency, falls into underfitting and fails to predict the curve. When the ANN size is less than the optimized size, the predicted flow stress curves with the temperature, strain, and strain rate will contain non-physical fluctuations, thus reducing their prediction accuracy of extrapolation. For metals similar to the In718 alloy, ANNs with very few nodes in the hidden layer are preferred rather than the large ANNs with tens or hundreds of nodes in the hidden layers. Full article

(This article belongs to the Special Issue Metallic Materials: Structure Transition, Processing, Characterization and Applications)

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12 pages, 5031 KiB

Open AccessArticle

Microstructure and High-Temperature Ablation Behaviour of Hafnium-Doped Tungsten-Yttrium Alloys

by Rui Wu, Chuanbing Huang, Huifeng Zhang, Haozhong Lv, Xiaoming Sun, Hao Lan and Weigang Zhang

Materials 2023, 16(6), 2529; https://doi.org/10.3390/ma16062529 - 22 Mar 2023

Cited by 3 | Viewed by 1732

Abstract

W is a widely used refractory metal with ultra-high melting point up to 3410 °C. However, its applications are limited by poor ablation resistance under high-temperature flame and air flow, which is crucial for aerospace vehicles. To improve the ablation resistance of W [...] Read more.

W is a widely used refractory metal with ultra-high melting point up to 3410 °C. However, its applications are limited by poor ablation resistance under high-temperature flame and air flow, which is crucial for aerospace vehicles. To improve the ablation resistance of W under extreme conditions, W-Y alloys doped with different Hf mass fractions (0, 10, 20, and 30) were prepared using the fast hot pressing sintering method. Microstructure and ablation behaviours at 2000 °C were investigated. Results showed that adding an appropriate amount of Hf improved the properties of the W-Y alloy evidently. In particular, the hardness of the alloy increased with the increased content of Hf. The formation of the HfO₂ layer on the surface during ablation decreased the mass and linear ablation rates, indicating enhanced ablation resistance. However, excessive Hf addition will result in crack behaviour during ablation. With a Hf content of 20 wt.%, the alloy exhibited high stability and an excellent ablation resistance. Full article

(This article belongs to the Special Issue Metallic Materials: Structure Transition, Processing, Characterization and Applications)

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10 pages, 5143 KiB

Open AccessArticle

The Effect of Novel Complex Treatment of Annealing and Sandblasting on the Microstructure and Performance of Welded TA1 Titanium Plate

by Yanbin Xu, Dayue Wang, Mingyen Li, Jing Hu, Xulong An and Wei Wei

Materials 2023, 16(6), 2149; https://doi.org/10.3390/ma16062149 - 7 Mar 2023

Cited by 6 | Viewed by 1546

Abstract

The welding titanium cathode roller has the obvious advantages of low cost, high efficiency, and no diameter restriction. Unfortunately, the longitudinal weld on the cathode roller adversely impacts the quality of the electrolytic copper foil due to the great difference between the microstructure [...] Read more.

The welding titanium cathode roller has the obvious advantages of low cost, high efficiency, and no diameter restriction. Unfortunately, the longitudinal weld on the cathode roller adversely impacts the quality of the electrolytic copper foil due to the great difference between the microstructure of the weld zone and the base metal. Thus, it is crucial to reduce their difference by regulating the microstructure of the weld zone. In this study, a novel complex treatment of heat treatment and sandblasting is primarily developed for regulating the microstructure of the weld zone. The results show that the novel complex treatment has an efficient effect on regulating the microstructure of the weld zone and making the microstructure in the weld zone close to that of the base metal. During vacuum annealing, the microstructure of the weld zone is refined to some degree, and 650 °C annealing has the optimal effect, which can effectively reduce the ratio of α phase’s length to width and reduce the microstructure difference between the weld zone and the base metal. At the same time, with an increase in the annealing temperature, the tensile strength and yield strength decreased by about 10 MPa; the elongation after fracture increased by 20%; the average microhardness of the WZ and the HAZ decreased by about 10 HV_0.10; and that of the BM decreased by about 3 HV_0.10. The heat treatment after welding can effectively adjust the properties of the weld zone, reduce the hardness and strength, and improve the toughness. The subsequent sandblasting after annealing can further refine the grain size in the weld zone and make the microstructure in the weld zone close to that of the base metal. Sandblasting after annealing can further refine the grain in the weld zone and make the microstructure in the weld zone close to that of base metal. Meanwhile, an application test confirmed that the adverse impact of a longitudinal weld on the quality of electrolytic copper foil could be resolved by adopting this novel complex treatment. Therefore, this study provides valuable technical support for the “welding” manufacturing of the titanium sleeves of the cathode roller. Full article

(This article belongs to the Special Issue Metallic Materials: Structure Transition, Processing, Characterization and Applications)

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10 pages, 3940 KiB

Open AccessArticle

Effect of Pulsed Magnetic Field on the Microstructure of QAl9-4 Aluminium Bronze and Its Mechanism

by Yujun Hu, Hongjin Zhao, Junwei Li, Kefu Hu and Jing Qin

Materials 2022, 15(23), 8336; https://doi.org/10.3390/ma15238336 - 23 Nov 2022

Cited by 6 | Viewed by 1831

Abstract

The effect of a pulsed magnetic field on the microstructure of a QAl9-4 aluminium bronze alloy was studied in this work. It was found that the dislocation density, grain boundary angle, and microhardness of the alloy significantly changed after the magnetic field treatment [...] Read more.

The effect of a pulsed magnetic field on the microstructure of a QAl9-4 aluminium bronze alloy was studied in this work. It was found that the dislocation density, grain boundary angle, and microhardness of the alloy significantly changed after the magnetic field treatment with a peak magnetic induction intensity of 3T, pulse duration of about 100 us, pulse interval of 10 s, and pulse time of 360. EBSD was used to test the KAM maps of the alloy microzone. It was found that the alloy’s dislocation density decreased by 10.88% after the pulsed magnetic field treatment; in particular, the dislocation in the deformed grains decreased significantly. The quantity of dislocation pile-up and the degree of distortion around the dislocation were reduced, which decreased the residual compressive stress on the alloy. Dislocation motion caused LAGB rotation, which reduced the misorientation of adjacent points inside the grain. The magnetic field induced the disappearance of deformation twins and weakened the strengthening effect of twins. The microhardness test results show that the alloy’s microhardness decreased by 8.06% after pulsed magnetic field treatment. The possible reasons for the magnetic field effect on dislocation were briefly discussed. The pulsed magnetic field might have caused the transition to the electronic energy state at the site of dislocation pinning, which led to free movement of the vacancy or impurity atom. The dislocation was easier to depin under the action of internal stress in the alloy, changing the dislocation distribution and alloy microstructure. Full article

(This article belongs to the Special Issue Metallic Materials: Structure Transition, Processing, Characterization and Applications)

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13 pages, 11768 KiB

Open AccessArticle

Characterization of Carbide Precipitation during Tempering for Quenched Dievar Steel

by Yixin Xie, Xiaonong Cheng, Jiabo Wei and Rui Luo

Materials 2022, 15(18), 6448; https://doi.org/10.3390/ma15186448 - 16 Sep 2022

Cited by 19 | Viewed by 3042

Abstract

Carbide precipitation and coarsening are investigated for quenched Dievar steel during tempering. Lath/lenticular martensite, retained austenite, lower bainite, auto-tempered, and larger spherical carbides are all observed in the as-quenched condition. The carbide precipitation sequence on tempering is ascertained to be: M₈C [...] Read more.

Carbide precipitation and coarsening are investigated for quenched Dievar steel during tempering. Lath/lenticular martensite, retained austenite, lower bainite, auto-tempered, and larger spherical carbides are all observed in the as-quenched condition. The carbide precipitation sequence on tempering is ascertained to be: M₈C₇ + cementite → M₈C₇ + M₂C + M₇C₃ → M₈C₇ + M₇C₃ + M₂₃C₆ → M₈C₇ + M₇C₃ + M₂₃C₆ + M₆C; carbides become coarser on tempering, and the sizes for inter-lath carbides increase noticeably with increasing tempering temperatures due to the faster grain boundary diffusion, whereas the sizes for intra-lath carbides remain nearly constant. The rate of coarsening for carbides by tempering at 650 °C is much higher than those by tempering at 550 °C and 600 °C, due to the faster diffusion of alloying elements at higher temperatures. Full article

(This article belongs to the Special Issue Metallic Materials: Structure Transition, Processing, Characterization and Applications)

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10 pages, 4820 KiB

Open AccessArticle

The Local Structure and Metal-Insulator Transition in a Ba₃Nb_5−xTi_xO₁₅ System

by G. M. Pugliese, F. G. Capone, L. Tortora, F. Stramaglia, L. Simonelli, C. Marini, Y. Kondoh, T. Kajita, T. Katsufuji, T. Mizokawa and N. L. Saini

Materials 2022, 15(13), 4402; https://doi.org/10.3390/ma15134402 - 22 Jun 2022

Cited by 4 | Viewed by 1893

Abstract

The local structure of the filled tetragonal tungsten bronze (TTB) niobate Ba

_{3}

Nb

_{5 - x}

Ti

_{x}

O

_{15}

(x = 0, 0.1, 0.7, 1.0), showing a metal-insulator transition with Ti substitution, has been studied by Nb K-edge extended X-ray [...] Read more.

The local structure of the filled tetragonal tungsten bronze (TTB) niobate Ba

_{3}

Nb

_{5 - x}

Ti

_{x}

O

_{15}

(x = 0, 0.1, 0.7, 1.0), showing a metal-insulator transition with Ti substitution, has been studied by Nb K-edge extended X-ray absorption fine structure (EXAFS) measurements as a function of temperature. The Ti substitution has been found to have a substantial effect on the local structure, that remains largely temperature independent in the studied temperature range of 80–400 K. The Nb-O bonds distribution shows an increased octahedral distortion induced by Ti substitution, while Nb-Ba distances are marginally affected. The Nb-O bonds are stiffer in the Ti substituted samples, which is revealed by the temperature dependent mean square relative displacements (MSRDs). Furthermore, there is an overall increase in the configurational disorder while the system with Nb 4d electrons turns insulating. The results underline a clear relationship between the local structure and the electronic transport properties suggesting that the metal-insulator transition and possible thermoelectric properties of TTB structured niobates can be tuned by disorder. Full article

(This article belongs to the Special Issue Metallic Materials: Structure Transition, Processing, Characterization and Applications)

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11 pages, 6785 KiB

Open AccessArticle

Development of Y₂O₃ Dispersion-Strengthened Copper Alloy by Sol-Gel Method

by Jiangang Ke, Zhuoming Xie, Rui Liu, Ke Jing, Xiang Cheng, Hui Wang, Xianping Wang, Xuebang Wu, Qianfeng Fang and Changsong Liu

Materials 2022, 15(7), 2416; https://doi.org/10.3390/ma15072416 - 25 Mar 2022

Cited by 15 | Viewed by 2806

Abstract

In this study, oxide dispersion-strengthened Cu alloy with a Y₂O₃ content of 1 wt.% was fabricated through citric acid sol-gel synthesis and spark plasma sintering (SPS). The citric acid sol-gel method provides molecular mixing for the preparation of precursor powders, [...] Read more.

In this study, oxide dispersion-strengthened Cu alloy with a Y₂O₃ content of 1 wt.% was fabricated through citric acid sol-gel synthesis and spark plasma sintering (SPS). The citric acid sol-gel method provides molecular mixing for the preparation of precursor powders, which produces nanoscale and uniformly distributed Y₂O₃ particles in an ultrafine-grained Cu matrix. The effects of nanoscale Y₂O₃ particles on the microstructure, mechanical properties and thermal conductivity of the Cu-1wt.%Y₂O₃ alloy were investigated. The average grain size of the Cu-1wt.%Y₂O₃ alloy is 0.42 μm, while the average particle size of Y₂O₃ is 16.4 nm. The unique microstructure provides excellent mechanical properties with a tensile strength of 572 MPa and a total elongation of 6.4%. After annealing at 800 °C for 1 h, the strength of the alloy does not decrease obviously, showing excellent thermal stability. The thermal conductivity of Cu-1wt.%Y₂O₃ alloy is about 308 Wm⁻¹K⁻¹ at room temperature and it decreases with increasing temperature. The refined grain size, high strength and excellent thermal stability of Cu-1wt.%Y₂O₃ alloys can be ascribed to the pinning effects of nanoscale Y₂O₃ particles dispersed in the Cu matrix. The Cu-Y₂O₃ alloys with high strength and high thermal conductivity have potential applications in high thermal load components of fusion reactors. Full article

(This article belongs to the Special Issue Metallic Materials: Structure Transition, Processing, Characterization and Applications)

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