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A ZrB2–copper–graphite composite was produced through powder metallurgy and was tested as a new electric brush material. The aim of this paper was to study the effect of ZrB2 addition on the composite's properties. Besides its physical properties such as density and resistivity, its mechanical properties, such as hardness, bending strength and wear resistance, were studied. A scanning electron microscope (SEM) was used to study the morphology of the wear surface, and a configured energy-dispersive spectrometer (EDS) was used to research the chemical composition of the samples. The results showed that, with the addition of ZrB2, the composite's properties such as density, resistivity, hardness, and bending strength improved significantly. Compared with samples without ZrB2, samples with the addition of 4% ZrB2 achieved a hardness of 87.5 HRA, which was improved by 45.8%, and a bending strength of 53.1 MPa, which was increased by nearly 50.0%. Composites with 1% content of ZrB2 showed the best wear resistance under non-conductive friction; however, under conductive friction, composites with 4% content of ZrB2 showed better wear resistance. [ABSTRACT FROM AUTHOR]

Abstract: The Red River fault is an important plate‐boundary fault that has played a significant role in the tectonic evolution of northern Southeast Asia. Nonetheless, its millennial slip rate and earthquake recurrence behavior are poorly constrained. Analysis of 5‐ and 30‐m‐resolution topography reveals right‐lateral offsets that range from 60 m to 24 km along its “mid‐valley” trace but none along its “range‐front” trace. This strongly implies that the range‐front fault has experienced very little lateral slip for millions of years, even though it is the geologically more significant fault. Stratigraphic and geomorphologic investigation of the mid‐valley fault within a small channel near Gasa yields a 14C‐based slip rate of 1.1 ± 0.4 mm/year, averaged over the last 30,000–50,000 years. Three‐dimensional paleoseismic excavation of colluvial wedges produced by collapse of shutter ridges into the channel shows that sudden dextral ruptures of the fault have occurred every 6,000 ± 1,000 years over the past 30,000 years. Two and possibly three large surface ruptures occurred in the past 13,500 years, and two previous ones occurred at 18,500 and 24,500 calendar years before present (cal yr BP). The oldest one in the section likely occurred at or a few 1,000 years before 29,800 ± 2,000 cal yr BP. The 3‐D extent of the colluvial wedges implies dextral offsets of ≥4.5 m, amounts that are consistent with the slip rate and recurrence interval. The evidence for low slip rate and rare large seismic events is consistent with the lack of large historical earthquakes along the fault and the low Global Positioning System (GPS)‐derived slip rate, but is much lower than widely cited geological slip rates. [ABSTRACT FROM AUTHOR]

To meet the requirements of structural and functional integration, machinability and workability of engineering materials, continuous mesophase pitch-based carbon fiber (MPCF) reinforced 2024 aluminum (Al) matrix composites with 20–50 vol % MPCF were fabricated by vacuum hot pressing method. The effects of MPCF volume fraction and T6 heat treatment on microstructure, thermal and mechanical properties of MPCF/2024Al composites were investigated. The results show that the interface of the as-sintered composite was well bonded. After T6 heat treatment, the amorphous layer at the interface changed from continuous to discontinuous and the interfacial bonding was further improved, but there was no interfacial reaction. The increase of MPCF volume fraction was beneficial to improve the thermal conductivity (TC) and elastic modulus (E) of the as-sintered composites, up to 258.3 W/(m⋅K) and 343.5 GPa respectively, while the composites with 30 vol % and 40 vol % MPCF respectively had the highest ultimate tensile strength (UTS) and a coefficient of thermal expansion (CTE) close to zero. After heat treatment, the TC and E were slightly changed, while the CTE was further reduced and UTS was significantly improved. In this work, the heat-treated composite with 30 vol % MPCF had the highest UTS of 499.3 MPa and good thermal properties, and the TC of this composite may be further improved by using MPCFs with higher TC. Therefore, this composite is expected to become a promising engineering material integrating structure and function. [ABSTRACT FROM AUTHOR]

Continuous mesophase pitch-based carbon fiber (MPCF) reinforced aluminum (Al) matrix composites were fabricated by vacuum hot pressing to meet the requirements of good thermal conductivity (TC), low coefficient of thermal expansion (CTE) and resistance to deformation for thermal management materials. The effect of process parameters on the microstructures and TC of 40 vol % MPCF/Al composites and the influence of MPCF volume fraction on the thermal-mechanical properties of MPCF/Al composites were studied. The results reveal that the composites with 20–50 vol % MPCF fabricated at 650 °C/45 MPa/60 min have longitudinal TC of 230.3–288.3 W/(m⋅K), over 90% of the predictions by rule of mixture, longitudinal CTE of 2.28−-0.22 ppm/K and elastic modulus of 147.5–324 GPa. The interface is mainly composed of an amorphous interface layer of 2–5 nm and a very small amount of carbide crystals. Furthermore, these composites have moderate TC, lower CTE and higher specific modulus compared with other Al matrix composites and Al alloys, which indicates they are expected to become unidirectional thermal management materials with integrated structure and function. [ABSTRACT FROM AUTHOR]

Continuous carbon fiber (CF) reinforced aluminum (Al) matrix composites have become a potential lightweight material in aerospace and commercial applications. In this work, the alumina (Al 2 O 3) coating was uniformly synthesized on the surface of CF by the sol-gel method for improving the wettability and reducing the interfacial reaction between molten Al alloy and CF, while the Al 2 O 3 -coated CF was subsequently used to fabricate CF/Al composites via pressure infiltration technique. Effects of heat treatment temperature, immersion time, and immersion-drying cycle on the surface morphologies and mechanical properties of Al 2 O 3 -coated CF were studied, and the influences of the coating thickness on the infiltration quality and the mechanical properties of composites were also investigated by means of the microstructural analysis, interfacial characterizations and tensile property tests. The results show that the Al 2 O 3 -coated CF with excellent integrity and mechanical properties was obtained at 500 °C for 2 immersion-drying cycles by the immersion time of 5 min per cycle. The Al 2 O 3 coating can effectively improve pressure infiltration quality and mechanical properties based on the suitable interfacial bonding strength and good wettability. The optimized Al 2 O 3 coating thickness is 100 nm for better improving the mechanical properties of CF/Al composites. [ABSTRACT FROM AUTHOR]

Micro-sized silicon carbide particles (SiCp) reinforced aluminum (Al) matrix composites have been widely used in the aerospace, electronics and transportation applications. However, due to the easily formed stress concentration in the SiCp/Al interfacial micro-zones, the large-sized SiCp may cause serious plastic loss of SiCp/Al composites that have limited their applications. In this study, the 14.5 μm SiCp was selected to prepare the SiCp(CNT) hybrid reinforcement, and then the 15 wt. % SiCp/Al and SiCp(CNT)/Al composites were fabricated by the vacuum hot-pressing sintering, respectively. Compared to the SiCp/Al composite, the SiCp(CNT)/Al composites own the larger mechanical properties such as the Young's modulus, the yield strength and the tensile strength. Among these composites, the SiCp(0.5CNT)/Al composite presents the best matching of strength and plasticity as a result of the existence of CNTs in the SiCp/Al interfacial micro-zones. Strengthening and toughening effects of CNTs in the SiCp/Al interfacial micro-zones can contribute to: 1) increasing the punched zone size around the SiCp; 2) increasing the dislocation density in the SiCp/Al interfacial micro-zones; 3) changing the dislocation distributions in the SiCp/Al interfacial micro-zones; 4) pinning the dislocation movements by CNTs in the SiCp/Al interfacial micro-zones. From the analysis above, the strengthening and toughening mechanism of the CNTs introduced in the SiCp/Al interfacial micro-zones of SiCp(CNT)/Al composites can be revealed, which can be further developed to guide and prepare the hybrid particles reinforced metal matrix composites. [Display omitted] • The strength-plasticity matching relationship of SiCp/Al composites can be improved by the presence of CNTs at the interface micro-zones. • Compared with SiCp/Al composites, the introduction of CNTs can increase the dislocation density at the interface micro-zones and pin the dislocation movement. • The existence of CNTs can change the dislocation distribution of SiCp/Al interface micro-zones. [ABSTRACT FROM AUTHOR]

In the trend of integration of structure and function, novel thermal management materials are urgent to be developed owning good mechanical properties as well as excellent thermal properties. In this work, a complete and dense copper (Cu) coating with a thickness of 400 nm was deposited on the surfaces of graphite films (GFs) by ultrasonic-assisted electroless plating, which can improve the surface roughness of GFs and interfacial bonding between GFs and Cu foils. Cu-coated and uncoated GFs reinforced copper matrix laminated composites (noted as GFs(Cu)/Cu and GFs/Cu) were fabricated by optimized vacuum hot-pressing sintering. Based on the scratch test and microstructures of GFs(Cu) and GFs(Cu)/Cu composites, addition of Cu coating can improve the interfacial adhesion and element diffusion behavior, and intuitively explains the mechanical interlocking effect at the C–Cu interface. On basis of the nanoindentation mechanical properties across GFs(Cu)/Cu and GFs/Cu interfaces, the interfacial transition region with Cu coating of ~3 μm is three times of that without Cu coating. Flexural strength of 27.6 vol% GFs(Cu)/Cu laminated composite is 45.9 MPa, which is 56% higher than that of the corresponding GFs/Cu laminated composite. In-plane thermal conductivity (TC) and out-of-plane coefficient of thermal expansion (CTE) of 69.4 vol % GFs(Cu)/Cu laminated composite are 1177.8 W/m·K and −2.5 ppm/K respectively, which could be explained on the theoretical calculations and interfacial structures. In conclusion, the Cu coating on surfaces of GFs can generally improve the interfacial bonding, mechanical properties and thermal properties of GFs(Cu)/Cu laminated composites. It provides an effective way to develop novel structural and functional materials for thermal management. [ABSTRACT FROM AUTHOR]