Research

17 pages, 29214 KiB

Open AccessArticle

Orthogonal Experimental Optimization of Preparation and Microstructural Properties of a Diffusion Barrier for Tantalum-Based Silicide Coatings

by Lairong Xiao, Jiawei Xu, Xiaojun Zhou, Yafang Zhang, Guanzhi Deng, Hongtai Shen, Wei Li, Xiaojun Zhao and Zhenyang Cai

Materials 2023, 16(11), 4097; https://doi.org/10.3390/ma16114097 - 31 May 2023

Cited by 1 | Viewed by 787

Abstract

To solve the problem of silicide coatings on tantalum substrates failing due to elemental diffusion under high-temperature oxidation environments and to find diffusion barrier materials with excellent effects of impeding Si elemental spreading, TaB₂ and TaC coatings were prepared on tantalum substrates [...] Read more.

To solve the problem of silicide coatings on tantalum substrates failing due to elemental diffusion under high-temperature oxidation environments and to find diffusion barrier materials with excellent effects of impeding Si elemental spreading, TaB₂ and TaC coatings were prepared on tantalum substrates by the encapsulation and infiltration methods, respectively. Through orthogonal experimental analysis of the raw material powder ratio and pack cementation temperature, the best experimental parameters for the preparation of TaB₂ coatings were selected: powder ratio (NaF:B:Al₂O₃ = 2.5:1:96.5 (wt.%)) and pack cementation temperature (1050 °C). After diffusion treatment at 1200 °C for 2 h, the thickness change rate of the Si diffusion layer prepared using this process was 30.48%, which is lower than that of non-diffusion coating (36.39%). In addition, the physical and tissue morphological changes of TaC and TaB₂ coatings after siliconizing treatment and thermal diffusion treatment were compared. The results prove that TaB₂ is a more suitable candidate material for the diffusion barrier layer of silicide coatings on tantalum substrates. Full article

(This article belongs to the Special Issue Study on Advanced Metal Matrix Composites)

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11 pages, 5193 KiB

Open AccessArticle

Effect of Temperatures and Graphene on the Mechanical Properties of the Aluminum Matrix: A Molecular Dynamics Study

by Jingtao Huang, Mingwei Li, Jiaying Chen, Yuan Cheng, Zhonghong Lai, Jin Hu, Fei Zhou, Nan Qu, Yong Liu and Jingchuan Zhu

Materials 2023, 16(7), 2722; https://doi.org/10.3390/ma16072722 - 29 Mar 2023

Cited by 3 | Viewed by 996

Abstract

Graphene has become an ideal reinforcement for reinforced metal matrix composites due to its excellent mechanical properties. However, the theory of graphene reinforcement in graphene/aluminum matrix composites is not yet well developed. In this paper, the effect of different temperatures on the mechanical [...] Read more.

Graphene has become an ideal reinforcement for reinforced metal matrix composites due to its excellent mechanical properties. However, the theory of graphene reinforcement in graphene/aluminum matrix composites is not yet well developed. In this paper, the effect of different temperatures on the mechanical properties of the metal matrix is investigated using a classical molecular dynamics approach, and the effects of the configuration and distribution of graphene in the metal matrix on the mechanical properties of the composites are also described in detail. It is shown that in the case of a monolayer graphene-reinforced aluminum matrix, the simulated stretching process does not break the graphene as the strain increases, but rather, the graphene and the aluminum matrix have a shearing behavior, and thus, the graphene “pulls out" from the aluminum matrix. In the parallel stretching direction, the tensile stress tends to increase with the increase of the graphene area ratio. In the vertical stretching direction, the tensile stress tends to decrease as the percentage of graphene area increases. In the parallel stretching direction, the tensile stress of the system tends to decrease as the angle between graphene and the stretching direction increases. It is important to investigate the effect of a different graphene distribution in the aluminum matrix on the mechanical properties of the composites for the design of high-strength graphene/metal matrix composites. Full article

(This article belongs to the Special Issue Study on Advanced Metal Matrix Composites)

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11 pages, 2736 KiB

Open AccessArticle

Accelerating Density Functional Calculation of Adatom Adsorption on Graphene via Machine Learning

by Nan Qu, Mo Chen, Mingqing Liao, Yuan Cheng, Zhonghong Lai, Fei Zhou, Jingchuan Zhu, Yong Liu and Lin Zhang

Materials 2023, 16(7), 2633; https://doi.org/10.3390/ma16072633 - 26 Mar 2023

Cited by 3 | Viewed by 1569

Abstract

Graphene has attracted significant interest due to its unique properties. Herein, we built an adsorption structure selection workflow based on a density functional theory (DFT) calculation and machine learning to provide a guide for the interfacial properties of graphene. There are two main [...] Read more.

Graphene has attracted significant interest due to its unique properties. Herein, we built an adsorption structure selection workflow based on a density functional theory (DFT) calculation and machine learning to provide a guide for the interfacial properties of graphene. There are two main parts in our workflow. One main part is a DFT calculation routine to generate a dataset automatically. This part includes adatom random selection, modeling adsorption structures automatically, and a calculation of adsorption properties. It provides the dataset for the second main part in our workflow, which is a machine learning model. The inputs are atomic characteristics selected by feature engineering, and the network features are optimized by a genetic algorithm. The mean percentage error of our model was below 35%. Our routine is a general DFT calculation accelerating routine, which could be applied to many other problems. An attempt on graphene/magnesium composites design was carried out. Our predicting results match well with the interfacial properties calculated by DFT. This indicated that our routine presents an option for quick-design graphene-reinforced metal matrix composites. Full article

(This article belongs to the Special Issue Study on Advanced Metal Matrix Composites)

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12 pages, 5780 KiB

Open AccessArticle

The Effects of Microstructure on the Dynamic Mechanical Response and Adiabatic Shearing Behaviors of a Near-α Ti-6Al-3Nb-2Zr-1Mo Alloy

by Haisheng Chen, Fang Hao, Shixing Huang, Jing Yang, Shaoqiang Li, Kaixuan Wang, Yuxuan Du, Xianghong Liu and Xiaotong Yu

Materials 2023, 16(4), 1406; https://doi.org/10.3390/ma16041406 - 07 Feb 2023

Cited by 1 | Viewed by 1096

Abstract

The formation and evolution of adiabatic shear behaviors, as well as the corresponding mechanical properties of a near-Ti-6Al-3Nb-2Zr-1Mo (Ti-6321) alloy during dynamic compression process, were systematically investigated by the split Hopkinson pressure bar (SHPB) compression tests in this paper. Ti-6321 samples containing three [...] Read more.

The formation and evolution of adiabatic shear behaviors, as well as the corresponding mechanical properties of a near-Ti-6Al-3Nb-2Zr-1Mo (Ti-6321) alloy during dynamic compression process, were systematically investigated by the split Hopkinson pressure bar (SHPB) compression tests in this paper. Ti-6321 samples containing three types of microstructures, i.e., equiaxed microstructure, duplex microstructure and Widmanstätten microstructure, were prepared to investigate the relationship between microstructures and dynamic mechanical behaviors under different strain rates in a range from 1000 s⁻¹ to 3000 s⁻¹. It was found by the dynamic strain–stress relation that the Ti-6321 alloys containing equiaxed microstructure, duplex microstructure and Widmanstätten microstructure all exhibited a strong strain-hardening effect. The samples containing equiaxed microstructure exhibited a larger flow stress than samples containing duplex microstructure and Widmanstätten microstructure. The adiabatic shearing behaviors in Ti-6321 alloy are significantly influenced by different types of microstructures. The formation of adiabatic shearing bands occurs in equiaxed microstructure when the strain rate is increased to 2000 s⁻¹. The adiabatic shear bands are formed in duplex microstructure when the strain rate reaches 3000 s⁻¹. However, the initiation of adiabatic shear bands is found in Widmanstätten microstructure under the strain rate of 1000 s⁻¹. The Widmanstätten microstructure shows a larger sensitivity to adiabatic shearing than the equiaxed microstructure and duplex microstructure samples. Full article

(This article belongs to the Special Issue Study on Advanced Metal Matrix Composites)

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16 pages, 6558 KiB

Open AccessArticle

Effect of Interfacial Strength on Mechanical Behavior of Be/2024Al Composites by Pressure Infiltration

by Zeyang Kuang, Yixiao Xia, Guoqin Chen, Dongli Sun, Boyu Ju, Ping Wu, Wenshu Yang and Gaohui Wu

Materials 2023, 16(2), 752; https://doi.org/10.3390/ma16020752 - 12 Jan 2023

Cited by 2 | Viewed by 1366

Abstract

In this paper, two kinds of Be/2024Al composites were prepared by the pressure infiltration method using two different beryllium powders as reinforcements and 2024Al as a matrix. The effect of interfacial strength on the mechanical behavior of Be/2024Al composites was studied. Firstly, the [...] Read more.

In this paper, two kinds of Be/2024Al composites were prepared by the pressure infiltration method using two different beryllium powders as reinforcements and 2024Al as a matrix. The effect of interfacial strength on the mechanical behavior of Be/2024Al composites was studied. Firstly, the microstructure and mechanical properties of the two composites were characterized, and then the finite element analysis (FEA) simulation was used to further illustrate the influence of interfacial strength on the mechanical properties of the two Be/2024Al composites. The mechanical tensile test results show that the tensile strength and elongation of the beryllium/2024Al composite prepared by the blocky impact grinding beryllium powder (blocky-Be/2024Al composite) are 405 MPa and 1.58%, respectively, which is superior to that of the beryllium/2024Al composite prepared by the spherical atomization beryllium powder (spherical-Be/2024Al composite), as its strength and elongation are 331 MPa and 0.38%, respectively. Meanwhile, the fracture of the former shows brittle fracture of beryllium particles and ductile fracture of aluminum, while the latter shows interface debonding. Further FEA simulation illustrates that the interfacial strength of the blocky-Be/2024Al composite is 600 MPa, which is higher than that of the spherical-Be/2024Al composite (330 MPa). Therefore, it can be concluded that the better mechanical properties of the blocky-Be/2024Al composite contribute to its stronger beryllium/aluminum interfacial strength, and the better interfacial strength might be due to the rough surface and microcrack morphology of blocky beryllium particles. These research results provide effective experimental and simulation support for the selection of beryllium powder and the design and preparation of high-performance beryllium/aluminum composites. Full article

(This article belongs to the Special Issue Study on Advanced Metal Matrix Composites)

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14 pages, 6173 KiB

Open AccessArticle

Effect of Volume Fraction of Reinforcement on Microstructure and Mechanical Properties of In Situ (Ti, Nb)B/Ti₂AlNb Composites with Tailored Three-Dimensional Network Architecture

by Ningbo Zhang, Boyu Ju, Taiqing Deng, Sen Fu, Cungao Duan, Yiwei Song, Yijun Jiang, Qin Shen, Caogen Yao, Mingda Liu, Ping Wu, Ziyang Xiu and Wenshu Yang

Materials 2022, 15(24), 9070; https://doi.org/10.3390/ma15249070 - 19 Dec 2022

Cited by 2 | Viewed by 1741

Abstract

The mechanical properties of (Ti, Nb)B/Ti₂AlNb composites were expected to improve further by utilizing spark plasma sintering (SPS) and inducing the novel three-dimensional network architecture. In this study, (Ti, Nb)B/Ti₂AlNb composites with the novel architecture were successfully fabricated by [...] Read more.

The mechanical properties of (Ti, Nb)B/Ti₂AlNb composites were expected to improve further by utilizing spark plasma sintering (SPS) and inducing the novel three-dimensional network architecture. In this study, (Ti, Nb)B/Ti₂AlNb composites with the novel architecture were successfully fabricated by ball milling the LaB₆ and Ti₂AlNb mixed powders and subsequent SPS consolidation. The influence of the (Ti, Nb)B content on the microstructure and mechanical properties of the composites was revealed by using the scanning electron microscope (SEM), transmission electron microscopy (TEM) and electronic universal testing machine. The microstructural characterization demonstrated that the boride crystallized into a B27 structure and the α₂-precipitated amount increased with the (Ti, Nb)B increasing. When the (Ti, Nb)B content reached 4.9 vol%, both the α₂ and reinforcement exhibited a continuous distribution along the prior particle boundaries (PPBs). The tensile test displayed that the tensile strength of the composites presented an increasing trend with the increasing (Ti, Nb)B content followed by a decreasing trend. The composite with a 3.2 vol% reinforcement had the optimal mechanical properties; the yield strengths of the composite at 25 and 650 °C were 998.3 and 774.9 MPa, showing an 11.8% and 9.2% improvement when compared with the Ti₂AlNb-based alloy. Overall, (Ti, Nb)B possessed an excellent strengthening effect and inhibited the strength weakening of the PPBs area at high temperatures; the reinforcement content mainly affected the mechanical properties of the (Ti, Nb)B/Ti₂AlNb composites by altering the α₂-precipitated amount and the morphology of (Ti, Nb)B in the PPBs area. Both the continuous precipitation of the brittle α₂ phase and the agglomeration of the (Ti, Nb)B reinforcement dramatically deteriorated the mechanical properties. Full article

(This article belongs to the Special Issue Study on Advanced Metal Matrix Composites)

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13 pages, 4173 KiB

Open AccessArticle

Thin-Copper-Layer-Induced Early Fracture in Graphene-Nanosheets (GNSs)-Reinforced Copper-Matrix-Laminated Composites

by Hailong Shi, Xiaojun Wang, Xuejian Li, Xiaoshi Hu, Weimin Gan, Chao Xu and Guochao Wang

Materials 2022, 15(21), 7677; https://doi.org/10.3390/ma15217677 - 01 Nov 2022

Viewed by 1063

Abstract

The strength–ductility trade-off has been a long-standing challenge when designing and fabricating a novel metal matrix composite. In this study, graphene-nanosheets (GNSs)-reinforced copper (Cu)-matrix-laminated composites were fabricated through two methods, i.e., the alternating electrodeposition technique followed by spark plasma sintering (SPS) and direct [...] Read more.

The strength–ductility trade-off has been a long-standing challenge when designing and fabricating a novel metal matrix composite. In this study, graphene-nanosheets (GNSs)-reinforced copper (Cu)-matrix-laminated composites were fabricated through two methods, i.e., the alternating electrodeposition technique followed by spark plasma sintering (SPS) and direct electrodeposition followed by hot-press sintering. As a result, a Cu-GNS-Cu layered structure formed in the composites with various Cu layer thicknesses. Compared with the pure Cu, the yield strength of the GNS/Cu composites increased. However, the mechanical performance of the GNS/Cu composites was strongly Cu-layer-thickness-dependent, and the GNS/Cu composite possessed a brittle fracture mode when the Cu layer was thin (

\leq

10 μm). The fracture mechanism of the GNS/Cu composites was thoroughly investigated and the results showed that the premature failure of the GNS/Cu composites with a thin Cu layer may be due to the lack of Cu matrix, which can relax the excessive stress intensity triggered by GNSs and delay the crack connection between neighboring GNS layers. This study highlights the soft Cu matrix in balancing the strength and ductility of the GNS/Cu-laminated composites and provides new technical and theoretical support for the preparation and optimization of other laminated metal matrix composites. Full article

(This article belongs to the Special Issue Study on Advanced Metal Matrix Composites)

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21 pages, 11630 KiB

Open AccessArticle

Mechanism Analysis of Nanosecond Pulse Laser Etching of SiC_p/Mg Composites

by Zhe Wu, Jianyang Song, Yang Zhang, Bo Xue and Sijia Wang

Materials 2022, 15(21), 7654; https://doi.org/10.3390/ma15217654 - 31 Oct 2022

Cited by 1 | Viewed by 1199

Abstract

Due to the introduction of silicon carbide reinforcement, the physical and cutting properties of SiC_p/Mg composites are very different from those of metal composites. Nanosecond pulse laser processing is more efficient than traditional processing for SiC_p/Mg composites. A low-power [...] Read more.

Due to the introduction of silicon carbide reinforcement, the physical and cutting properties of SiC_p/Mg composites are very different from those of metal composites. Nanosecond pulse laser processing is more efficient than traditional processing for SiC_p/Mg composites. A low-power pulsed fiber laser was used to etch 3.0 mm thick SiC_p/Mg composites. The effect of low laser power (0~50 W) on the morphology and heat-affected zone of the SiC_p/Mg composite after etching was studied. The results show that when the laser power increases, the material accumulation at the ablation end of the machining surface becomes more and more serious. With the increase in power, the differences in ablation width and ablation depth on the surface of composite materials do not increase proportionally. When the laser power increases gradually, the width of the heat-affected zone increases in the direction of the perpendicular laser beam and reaches the maximum value at the etched end. Full article

(This article belongs to the Special Issue Study on Advanced Metal Matrix Composites)

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18 pages, 8054 KiB

Open AccessArticle

Effect of Laser Welding Parameters on Joint Structure of AZ31B Magnesium Alloy and 304 Stainless Steel

by Zhe Wu, Jiaqi Wan, Yang Zhang, Bo Xue, Ruizhi Wu and Chunmei Yang

Materials 2022, 15(20), 7114; https://doi.org/10.3390/ma15207114 - 13 Oct 2022

Cited by 1 | Viewed by 1286

Abstract

The effects of laser welding parameters on the interface microstructure of AZ31B magnesium alloy and 304 stainless steel were investigated. After welding, a scanning electron microscope and ultra-depth of field microscope were used to observe the microstructure of the welded material, to analyze [...] Read more.

The effects of laser welding parameters on the interface microstructure of AZ31B magnesium alloy and 304 stainless steel were investigated. After welding, a scanning electron microscope and ultra-depth of field microscope were used to observe the microstructure of the welded material, to analyze the effects of power on the interface morphology. The simulation of laser welding of magnesium and steel was carried out by the COMSOL software. The results showed that when the power was 15 W–20 W, the temperature did not reach the melting point of magnesium alloy, there was MgO at the welding, and the interface had poor connection strength. When the power was 35 W–50 W, the temperature reached or even exceeded the boiling point of magnesium alloy, and the interface formed hot cracks, pores, and oxides and had poor joint strength. When the power was 25 W–30 W, the temperature was between the melting point and boiling point of magnesium, and the interface had excellent connection strength. Full article

(This article belongs to the Special Issue Study on Advanced Metal Matrix Composites)

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10 pages, 1218 KiB

Open AccessArticle

Electrical Properties of In Situ Synthesized Ag-Graphene/Ni Composites

by Jingqin Wang, Dekao Hu, Yancai Zhu and Peijian Guo

Materials 2022, 15(18), 6423; https://doi.org/10.3390/ma15186423 - 16 Sep 2022

Cited by 6 | Viewed by 1485

Abstract

Ag/Ni composite contact materials are widely used in low-voltage switches, appliances, instruments, and high-precision contacts due to their good electrical conductivity and processing properties. The addition of small amounts of additives can effectively improve the overall performance of Ag/Ni contact materials. Graphene has [...] Read more.

Ag/Ni composite contact materials are widely used in low-voltage switches, appliances, instruments, and high-precision contacts due to their good electrical conductivity and processing properties. The addition of small amounts of additives can effectively improve the overall performance of Ag/Ni contact materials. Graphene has good applications in semiconductors, thermal materials, and metal matrix materials due to its good electrical and thermal conductivity and mechanical properties. In this paper, Ag-graphene composites with different added graphene contents were prepared by in situ synthesis of graphene oxide (GO) and AgNO₃ by reduction at room temperature using ascorbic acid as a reducing agent. The Ag-graphene composites and nickel powder were ball-milled and mixed in a mass ratio of 85:15. The Ag-graphene/Ni was tested as an electrical contact material after the pressing, initial firing, repressing, and refiring processes. Its fusion welding force and arc energy were measured. The results show a 12% improvement in electrical conductivity with a graphene doping content of approximately 0.3 wt% compared to undoped contacts, resulting in 33.8 IACS%. The average contact fusion welding force was 49.49 cN, with an average reduction in the fusion welding force of approximately 8.04%. The average arc ignition energy was approximately 176.77 mJ, with an average decrease of 13.06%. The trace addition of graphene can improve the overall performance of Ag/Ni contacts and can promote the application of graphene in electrical contact materials. Full article

(This article belongs to the Special Issue Study on Advanced Metal Matrix Composites)

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13 pages, 5492 KiB

Open AccessArticle

TiO₂ Thickness-Dependent Charge Transfer in an Ordered Ag/TiO₂/Ni Nanopillar Arrays Based on Surface-Enhanced Raman Scattering

by Cai Wang, Xufeng Guo and Qun Fu

Materials 2022, 15(10), 3716; https://doi.org/10.3390/ma15103716 - 22 May 2022

Cited by 5 | Viewed by 1873

Abstract

In this study, an ordered Ag/TiO₂/Ni nanopillar arrays hybrid substrate was designed, and the charge transfer (CT) process at the metal–semiconductor and substrate–molecule interface was investigated based on the surface-enhanced Raman scattering (SERS) spectra of 4-Aminothiophenol (PATP) absorbed on the composite [...] Read more.

In this study, an ordered Ag/TiO₂/Ni nanopillar arrays hybrid substrate was designed, and the charge transfer (CT) process at the metal–semiconductor and substrate–molecule interface was investigated based on the surface-enhanced Raman scattering (SERS) spectra of 4-Aminothiophenol (PATP) absorbed on the composite system. The surface plasmon resonance (SPR) absorption of Ag changes due to the regulation of TiO₂ thickness, which leads to different degrees of CT enhancement in the system. The CT degree of SERS spectra obtained at different excitation wavelengths was calculated to study the contribution of CT enhancement to SERS, and a TiO₂ thickness-dependent CT enhancement mechanism was proposed. Furthermore, Ag/TiO₂/Ni nanopillar arrays possessed favorable detection ability and uniformity, which has potential as a SERS-active substrate. Full article

(This article belongs to the Special Issue Study on Advanced Metal Matrix Composites)

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19 pages, 9744 KiB

Open AccessArticle

Synergistic Strengthening of Mechanical Properties and Electromagnetic Interference Shielding Performance of Carbon Nanotubes (CNTs) Reinforced Magnesium Matrix Composites by CNTs Induced Laminated Structure

by Zhenming Sun, Hailong Shi, Xiaoshi Hu, Mufu Yan and Xiaojun Wang

Materials 2022, 15(1), 300; https://doi.org/10.3390/ma15010300 - 31 Dec 2021

Cited by 6 | Viewed by 1886

Abstract

In this study, we reported a laminated CNTs/Mg composite fabricated by spray-deposition and subsequent hot-press sintering, which realized simultaneous enhancement effects on strength and electromagnetic interference (EMI) shielding effectiveness (SE) by the introduced CNTs and CNT induced laminated ‘Mg-CNT-Mg’ structure. It was found [...] Read more.

In this study, we reported a laminated CNTs/Mg composite fabricated by spray-deposition and subsequent hot-press sintering, which realized simultaneous enhancement effects on strength and electromagnetic interference (EMI) shielding effectiveness (SE) by the introduced CNTs and CNT induced laminated ‘Mg-CNT-Mg’ structure. It was found that the CNTs/Mg composite with 0.5 wt.% CNTs not only exhibited excellent strength-toughness combination but also achieved a high EMI SE of 58 dB. The CNTs increased the strength of the composites mainly by the thermal expansion mismatch strengthening and blocking dislocation movements. As for toughness enhancement, CNTs induced laminated structure redistributes the local strain effectively and alleviates the strain localization during the deformation process. Moreover, it could also hinder the crack propagation and cause crack deflection, which resulted in an increment of the required energy for the failure of CNTs/Mg composites. Surprisingly, because of the laminated structure induced by introducing CNTs, the composite also exhibited an outperforming EMI SE in the X band (8.2–12.4 GHz). The strong interactions between the laminated ‘Mg-CNT-Mg’ structure and the incident electromagnetic waves are responsible for the increased absorption of the electromagnetic radiation. The lightweight CNTs/Mg composite with outstanding mechanical properties and simultaneously increased EMI performance could be employed as shell materials for electronic packaging components or electromagnetic absorbers. Full article

(This article belongs to the Special Issue Study on Advanced Metal Matrix Composites)

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15 pages, 5954 KiB

Open AccessArticle

Study on the Evolution of Graphene Defects and the Mechanical and Thermal Properties of GNPs/Cu during CVD Repair Process

by Ziyang Xiu, Boyu Ju, Cungao Duan, Sen Fu, Ningbo Zhang, Yong Mei, Jinming Liu, Yuhan Feng, Wenshu Yang and Pengchao Kang

Materials 2022, 15(1), 130; https://doi.org/10.3390/ma15010130 - 24 Dec 2021

Cited by 1 | Viewed by 1954

Abstract

Graphene has extremely high theoretical strength and electrothermal properties, and its application to Cu-based composites is expected to achieve a breakthrough in the performance of existing composites. As a nano-reinforced body, graphene often needs a long time of ball milling to make it [...] Read more.

Graphene has extremely high theoretical strength and electrothermal properties, and its application to Cu-based composites is expected to achieve a breakthrough in the performance of existing composites. As a nano-reinforced body, graphene often needs a long time of ball milling to make it uniformly dispersed, but the ball milling process inevitably brings damage to the graphene, causing the performance of the composite to deviate from expectations. Therefore, this paper uses CH₄ as a carbon source to repair graphene through a CVD process to prepare low-damage graphene/Cu composites. The process of graphene defect generation was studied through the ball milling process. The effects of defect content and temperature on the graphene repair process were studied separately. The study found that the graphene defect repair process, the decomposition process of oxygen-containing functional groups, and the deposition process of active C atoms existed simultaneously in the CVD process. When the repair temperature was low, the C atom deposition process and the oxygen-containing functional group decomposition process dominated. In addition, when the repair temperature is high, the graphene defect repair process dominated. 3 wt% graphene/Cu composites were prepared by pressure infiltration, and it was found that the bending strength was increased by 48%, the plasticity was also slightly increased, and the thermal conductivity was increased by 10–40%. This research will help reduce graphene defects, improve the intrinsic properties of graphene, and provide theoretical guidance for the regulation of C defects in composites. Full article

(This article belongs to the Special Issue Study on Advanced Metal Matrix Composites)

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12 pages, 2099 KiB

Open AccessFeature PaperArticle

Analysis of Causes of Porosity Change of Castings under the Influence of Variable Biscuit Height in the Filling Chamber

by Štefan Gašpár, Ján Majerník and Jan Kolínský

Materials 2021, 14(22), 6827; https://doi.org/10.3390/ma14226827 - 12 Nov 2021

Cited by 3 | Viewed by 1486

Abstract

Quality properties of castings produced in a die casting process correlate with porosity that is conditioned by a number of factors, which range from input melt quality to setup of technological factors of the die casting, and through structural design of the gating [...] Read more.

Quality properties of castings produced in a die casting process correlate with porosity that is conditioned by a number of factors, which range from input melt quality to setup of technological factors of the die casting, and through structural design of the gating system. One of the primary parameters conditioning the inner soundness of the casting is the liquid metal dose per single operation of die casting. This paper examines the issue of metal dose. The experiments are performed with casting a gate system of an electromotor flange. The gating system examined was die cast with a variable volume of metal dose per single operation. The metal dose was adjusted to reach the height of a biscuit of 10, 20, and 30 mm. The examination of the inner homogeneity of the castings of the individual variants of gating systems with variable height of the biscuit proved that decreasing biscuit height results in an increase of porosity share in the casting volume. The programme MagmaSoft 5.4 revealed the main causes of changes in porosity share. The simulations detected that the change in biscuit height and volume of liquid metal directly influence thermal conditions of the melt in the filling chamber, and in the mould by means of the period in which the holding pressure action is influenced. Simultaneously, the melt flow mode in the sprues and gas entrapment in the melt volume are affected as well. Correlation of the factors consequently influences the final porosity of castings. Full article

(This article belongs to the Special Issue Study on Advanced Metal Matrix Composites)

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12 pages, 3074 KiB

Open AccessArticle

Microstructure Evolution Mechanism of W_f/Cu₈₂Al₁₀Fe₄Ni₄ Composites under Dynamic Compression at Different Temperatures and Strain Rates

by Zhe Wu, Yang Zhang, Haifeng Jiang, Shuai Zhao and Qingnan Wang

Materials 2021, 14(19), 5563; https://doi.org/10.3390/ma14195563 - 25 Sep 2021

Viewed by 1298

Abstract

W_f/Cu₈₂Al₁₀Fe₄Ni₄ composites were fabricated by the pressure infiltration method. The composites were compressed by means of a split Hopkinson pressure bar (SHPB) with strain rates of 800 and 1600 s⁻¹ at different temperatures. [...] Read more.

W_f/Cu₈₂Al₁₀Fe₄Ni₄ composites were fabricated by the pressure infiltration method. The composites were compressed by means of a split Hopkinson pressure bar (SHPB) with strain rates of 800 and 1600 s⁻¹ at different temperatures. The microstructure of the composites after dynamic compressing was analyzed by transmission electron microscopy (TEM). Observation revealed that there were high-density dislocations, stacking faults, twins, and recrystallization existing in the copper alloy matrix of the composites. High-density dislocations, stacking faults, and twins were generated due to the significant plastic deformation of the copper alloy matrix under dynamic load impact. We also found that the precipitated phase of the matrix played a role in the second phase strengthening; recrystallized microstructures of copper alloy were generated due to dynamic recrystallization of the copper alloy matrix under dynamic compression at high temperatures. Full article

(This article belongs to the Special Issue Study on Advanced Metal Matrix Composites)

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10 pages, 4188 KiB

Open AccessArticle

Microstructures and Properties of Cu-rGO Composites Prepared by Microwave Sintering

by Xuebin Chen, Lei Zhao, Liwu Jiang and Haizhou Wang

Materials 2021, 14(17), 4899; https://doi.org/10.3390/ma14174899 - 28 Aug 2021

Cited by 6 | Viewed by 1584

Abstract

This study investigated the effects of microwave sintering on the microstructures and properties of copper-rGO composites. Graphene oxide was coated onto copper particles by wet ball milling, and copper-rGO composites were formed upon microwave sintering in an argon atmosphere. Scanning electron microscopy was [...] Read more.

This study investigated the effects of microwave sintering on the microstructures and properties of copper-rGO composites. Graphene oxide was coated onto copper particles by wet ball milling, and copper-rGO composites were formed upon microwave sintering in an argon atmosphere. Scanning electron microscopy was then used to observe the mixing in the ball-milled composite powder, and the morphology of the bulk composite after microwave sintering. Raman spectra revealed how graphene oxide changed with ball milling and with microwave sintering. The microhardness, electrical conductivity, and thermal conductivity of the composite were also measured. The results showed that graphene oxide and copper particles were well combined and uniformly distributed after wet ball milling. The overall microhardness of microwave-sintered samples was 81.1 HV, which was 14.2% greater than that of pure copper (71 HV). After microwave sintering, the microhardness of the samples in areas showing copper oxide precipitates with eutectic structures was 89.5 HV, whereas the microhardness of the precipitate-free areas was 70.6 HV. The electrical conductivity of the samples was 87.10 IACS%, and their thermal conductivity was 391.62 W·m⁻¹·K⁻¹. Full article

(This article belongs to the Special Issue Study on Advanced Metal Matrix Composites)

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14 pages, 43459 KiB

Open AccessArticle

Effect of Microstructure on the Dimensional Stability of Extruded Pure Aluminum

by Linlin Fu, Gaohui Wu, Chang Zhou, Ziyang Xiu, Wenshu Yang and Jing Qiao

Materials 2021, 14(17), 4797; https://doi.org/10.3390/ma14174797 - 24 Aug 2021

Cited by 10 | Viewed by 2196

Abstract

High-performance extruded aluminum alloys with complex textures suffer significant dimension variation under environmental temperature fluctuations, dramatically decreasing the precision of navigation systems. This research mainly focuses on the effect of the texture of extruded pure aluminum on its dimensional stability after various annealing [...] Read more.

High-performance extruded aluminum alloys with complex textures suffer significant dimension variation under environmental temperature fluctuations, dramatically decreasing the precision of navigation systems. This research mainly focuses on the effect of the texture of extruded pure aluminum on its dimensional stability after various annealing processes. The result reveals that a significant increment in the area fraction of recrystallized grains with <100> orientation and a decrement in the area fraction of grains with <111> orientation were found with increasing annealing temperature. Moreover, with the annealing temperature increasing from 150 °C to 400 °C, the residual plastic strain after twelve thermal cycles with a temperature range of 120 °C was changed from −1.6 × 10⁻⁵ to −4.5 × 10⁻⁵. The large amount of equiaxed grains with <100> orientation was formed in the microstructure of the extruded pure aluminum and the average grain size was decreased during thermal cycling. The area fraction of grain with <100> crystallographic orientation of the sample annealed at 400 °C after thermal cycling was 30.9% higher than annealed at 350 °C (23.7%) or at 150 °C (18.7%). It is attributed to the increase in the proportion of recrystallization grains with <100> direction as the annealing temperature increases, provided more nucleation sites for the formation of fine equiaxed grains with <100> orientation. The main orientation of the texture was rotated from parallel to <111> to parallel to <100> after thermal cycling. The change in the orientation of grains contributed to a change in interplanar spacing, which explains the change in the dimension along the extrusion direction during thermal cycling. Full article

(This article belongs to the Special Issue Study on Advanced Metal Matrix Composites)

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