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Railway switch plates are important components in railroads, and copper-based graphite alloys have potential as substitutes for traditional materials. Graphite as an anti-friction phase could decrease both the friction coefficient and mechanical properties, with an increasing mass fraction for their poor interface bonding strength. Chromium, a multifunctional metal plated on the graphite (Cr@graphite), has solved this problem. Results have shown that a copper-based Cr@graphite alloy is composed of copper as a base, and graphite and Cr compound transition phase as reinforcements. The transition phase is made up of nano Cr3C2 and dispersed CrC, which offers a stable combination with both graphite and copper. The tribological property of copper-based graphite alloy exhibits a steadily decreasing slope with reinforcement content increasing, and the Cr@graphite samples show lower values than the alloy without any coating treatment. Both graphite and chromic oxide play role in antifriction, and are more efficient than graphite alone. Microcutting is the dominant wear method when copper-based Cr@graphite alloy has a 1~4 wt.% reinforcements content; additionally, adhesion wear and oxidation are also generated. When the anti-friction phase increases, the wear mechanism is affected, and fatigue deformation is the dominant wear method at 4~6 wt.% content. The formation of the chromic oxide phase, as well as the graphite phase, control the formation of an anti-friction layer. In that case, the tribological properties are dramatically improved with reinforcement content enhance. [ABSTRACT FROM AUTHOR]

Cu-coated graphite was applied to modify the interface of Cu-Ni-graphite composite used as switch slide baseplate. Up to now, interfacial characterization and modification mechanisms of Cu modified Cu-Ni-graphite composite are seldom researched. In this study, Cu-coated graphite was deposited by chemical plating, and Cu modified Cu-Ni-graphite composite was prepared by powder metallurgy. Both the microstructure characterizations of Cu-coated graphite and interfacial morphologies of the composite were investigated. Then, the comparison of mechanical properties of unmodified and Cu modified Cu-Ni-graphite composite was discussed. The results showed that the Cu coating was made of fine particles with uniform distribution and with the average thickness of 1.05 μm. The mutual diffusion was about 2.54 μm width at the interface. The interfacial modification mechanism of Cu coating in the composite was that the decreasing of diffusion activity both in the graphite and matrix; and the increase of diffusion driving force at the interface. The interfacial bonding method in the transition from mechanical bonding to the combination of mechanical bonding and diffusion bonding. Compared with the unmodified composite, the flexural strength raised 24.4%, and hardness increased by 9%. [ABSTRACT FROM AUTHOR]

Abstract: We developed a simple method to prepare individual nitrogen-containing carbon (CN x ) nanobells with high yield. A mass of nanobells were produced from polymerized CN x nanobells by in situ plasma etching inside a chemical vapor deposition chamber. Scanning electron microscopy and transmission electron microscopy characterization reveals that the polymerized nanobells have been totally separated into individual nanobells, where each nanobell keeps its structure as that before etched. The present method sheds a light in the large-scale production of size-controllable short nanotubes. [Copyright &y& Elsevier]

In this paper, the aging behavior of Cf(Ni)-ZrC/2024Al composites with a quasi-network structure was studied carefully. The microstructure observation exhibits that the ZrC particles, carbon fibers, and Al matrix form a good interface bonding. The interfacial phase between the carbon fiber and Al matrix exhibits good thermostability during solution and aging treatment. With the addition of carbon fibers and ZrC particles, the composites only take 8 h to reach peak-aged condition while in monolithic 2024Al alloy, it needs 12 h. The peak-aged hardness of the composites is 136.4 HV, having 15.2% increments than 2024Al (118.4 HV). The yield, tensile strength, and strain of the peak-aged composites are 350.5 MPa, 536.4 MPa, and 14.8% respectively, which are improved by 56.5%, 45.8%, and 52.6% compared with 2024Al. The yield and tensile strength of composites are increased with time going by until they reach a peak aging state, agreeing well with that of hardness. The TEM observations of precipitated phases demonstrate the size and number of Al 2 Cu and Al 2 CuMg present a similar variation tendency. The improved tensile property of the composites is mainly due to pulled-out carbon fibers, quasi-network structure, outstanding interface bond, and precipitate strengthening. • The Cf(Ni)-ZrC/2024Al composites only take 8 h to reach to peak-aged condition, while the 2024Al needs 12 h. • The yield, tensile strength and strain of the composites are significantly improved compared with the 2024Al. • The improved strength is due to pulled-out carbon fiber, quasi-network structure, good interface bond and fine precipitate. [ABSTRACT FROM AUTHOR]

In this study, the 2024Al alloy improved by the various fraction of ZrC particles (ZrC p /2024Al composites) were constructed and processed through the spark plasma sintering (SPS) combined with T6 heat treatment in order to improve the strength and toughness simultaneously. The microstructure observations revealed that the interfacial bond between the ZrC and aluminum matrix was satisfactory and the quasi-network distribution of ZrC particles was demonstrated. The precipitates of Al 2 Cu and Al 2 CuMg, dissolved out from the 2024Al and ZrC p /2024Al composite during ageing process, exhibited little different in size and shape. With the introduction of ZrC particles, the ageing behavior was expedited and the time to achieve the aged hardness was prominently shortened from 12 h to 6 h as 5.0 wt% ZrC particles were introduced. The accelerated aging process benefited from dislocations, caused by the mismatch of thermal expansion coefficients between the ZrC and matrix. The ultimate hardness, yield strength, tensile strength and strain were all enhanced with the addition of ZrC particles. When 4.0 wt% ZrC particles were applied to the composites, the highest yield strength, tensile strength with superior ductility (332 MPa, 495 MPa and 12.0%) was obtained, which were 48.2%, 34.5% and 23.7% higher than that of pure 2024Al respectively. The improved tensile strength and strain are contributed to the particularly inhomogeneous quasi-network structure, which made the matrix deformation blocked, dislocation motion impeded and crack propagation path increased. [ABSTRACT FROM AUTHOR]

In this study, chromium carbide-nickel composites were fabricated by mixing pure Cr 3 C 2 and Ni powders at 1250, 1275, 1300 and 1325 °C for 1 h. The effects of the Ni content on the microstructures and mechanical properties of these composites were researched. Both Cr 3 C 2 and Cr 7 C 3 showed a well-defined crystallographic orientation. Two groups: (002) Cr3C2 //(004) Cr7C3 and [ 2 ‾ 10 ] Cr 3 C 2 // [ 2 ‾ 10 ] Cr 7 C 3 were observed. The porosity of the specimens first declined and then risen slightly with an increase in the Ni content. The micro-hardness of the specimens showed an opposite trend. The bending strength and fracture toughness of the specimens first risen with an increase in the Ni content and then decreased, thus changing the fracture mechanism from inter-granular fracture to trans -granular fracture. The optimal temperature was 1300 °C and the composite with 20 wt% Ni showed the best mechanical properties. [ABSTRACT FROM AUTHOR]

Hybrid (Ti 5 Si 3 + TiC x) (x = 0.67) particles reinforced TC4 matrix composites were in-situ prepared by hot-press sintering, basing on the reactions between Ti 3 SiC 2 and Ti. To research the effects of Ti 3 SiC 2 content on the microstructures and mechanical properties, 1–10 wt% Ti 3 SiC 2 were selected. When Ti 3 SiC 2 content was less than 5 wt%, Si element dissolved in the matrix, and TiC x distributed in the matrix homogeneously. While the content exceeded 5 wt%, Si was precipitating as Ti 5 Si 3 attaching to TiC x particles, which resulted in the aggregations of reinforcements. The micro-hardness of matrix was improved with the solid solubility of Si increasing in matrix, and the compressive strength was improved with Ti 3 SiC 2 content increasing. The hardness was mainly affected by solid solution strengthening. The compressive strength was affected by the solid solution strengthening, fine-grain strengthening and the improvement effect of reinforcements. It was determined that solid solution strengthening played the major role by theoretical calculation. • In-situ preparing (Ti 5 Si 3 +TiC 0.67)/TC4 composites for the first time. • Ti 5 Si 3 particles is prone to attach the TiC 0.67 particles. • Solid solution strengthening dominate the improvement of mechanical properties. [ABSTRACT FROM AUTHOR]

Effect of Mo addition on the microstructure and mechanical properties of Cr3C2-20 wt. % Ni cermet was investigated. Three different phases can be seen in the microstructure after adding appropriate molybdenum. The completely undissolved (Cr, Mo)3C2 phase maintains the original grain size and effectively prevents the (Cr, Mo)7C3 grains from merging and growing. The relative densities of the sintered specimens decrease slightly, while the hardness and bending strength increase firstly and then decrease slightly with the increase of Mo content. The maximum values of the hardness (88·6 HRA) and bending strength (1200 MPa) are achieved with 1 wt. % Mo addition. [ABSTRACT FROM AUTHOR]

Nanostructural Y-Zr-O oxide dispersion-strengthened (ODS) Mo alloys were in-situ prepared based on the dissolution and re-precipitation strategy of oxides during mechanical alloying (MA) and spark plasma sintering (SPS). The effect of Zr addition on the microstructures and mechanical properties of Mo-1Y 2 O 3 -xZr alloy (x = 0.3, 0.6, 0.9, and 1.2 wt%) was investigated. The results show that both intragranular and intergranular Y-Zr-O particles are nanoscale and non-stoichiometric, possessing a different Y/Zr ratio. The Y-Zr-O particles and ultrafine grain structure jointly contribute to high strength (1.87 times over pure Mo) and simultaneously great elongation (2.98 times over pure Mo) of Mo-1Y 2 O 3 -0.3Zr alloy. The yield strength and elongation are reduced as Zr addition beyond 0.6 wt%, owing to the aggregation of Y-Zr-O particles at grain boundaries. The theoretical calculation indicates that the strength is mainly affected by grain refinement strengthening and Orowan precipitate strengthening. But the strength is less predicted due to a great amount of Y-Zr-O nanoclusters smaller than 5 nm cannot be considered in the statistical analysis by conventional TEM. • In-situ preparing nanostructural Y-Zr-O oxide dispersion-strengthened (ODS) Mo alloys byMA and SPS. • Nanoscale intragranular and intergranular Y-Zr-O oxides and ultra-grained structure jointly improved mechanical properties. • Grain refinement strengthening and Orowan precipitate strengthening dominate the improvement of strength. [ABSTRACT FROM AUTHOR]

The hot deformation behavior of nanostructural oxide dispersion-strengthened (ODS) Mo alloy was investigated in the temperature range of 1200–1500 °C and strain rate range of 0.001–1 s−1 with a constant strain of 0.50 by analyzing constitutive equations, hot processing maps, and microstructure evolution. The results show that the flow behavior is greatly affected by the deformation temperatures and strain rates, exhibiting typical hardening, softening, and steady stages. The constitutive equation is established, which can predict the flow stress precisely. The stress exponent n and the apparent activation energy Q are estimated to be 5.44 and 384.26 kJ·mol−1, respectively, revealing that the deformation mechanism is dominated by the dislocation climb. Furthermore, the hot processing maps of ODS Mo alloy are developed based on the dynamic materials model, presenting two stability zones of 1350–1450 °C/0.001 s−1 and 1450–1500 °C/0.1–1 s−1. By observing microstructures, dynamic recovery and dynamic recrystallization occur in the stability zone 1500 °C/1 s−1, and the mechanism of the stability zone 1400 °C/0.001 s−1 is dominated by dynamic recovery and grain growth. • The hot deformation behavior of nanostructural oxide dispersion-strengthened (ODS) Mo alloy was investigated in the temperature range of 1200–1500 °C and strain rate range of 0.001–1 s−1. • The constitutive equation and processing maps were established. • The microstructure evolution and deformation mechanism at instability and safety zones were clarified. [ABSTRACT FROM AUTHOR]

In this work, the effect of Sb addition on the microstructure and mechanical properties of Mg 2 Si phase in Mg 2 Si/AZ91 composites are investigated by experimental research and first-principles calculation. The experimental results show that the coarse dendritic shape is modified to blocky polygonal shape, and the size of primary Mg 2 Si, is successfully refined with the Sb addition. With enhancing Sb addition contents, the doping concentration of Sb in Mg 2 Si phase keeps increasing, which accounts for the morphology and size modification. Besides, nano-indentation tests reveal that the Young's modulus of Mg 2 Si phase exhibits less reduction, while the hardness is significantly improved when introducing 2.0 wt%Sb. The calculated results indicate that the structure stability of Mg 2 Si crystal is enhanced, and the mechanical modulus including bulk modulus, shear modulus and Young's modulus of Mg 2 Si are decreased with the increase of Sb concentration, agreeing well with experimental observation, but the hardness reduces, which is contrary to the experimental results. Mg 2 Si phase doping with Sb atoms, however, exhibits improved ductile behavior compared with undoped Mg 2 Si due to the increased Poisson's ratio and B/G ratio. In addition, Sb doping can weaken the bond strength and reduce the population of Mg-Si covalent bonds, as well as generate new Mg-Sb bonds with lower strength based on the electronic structure analysis, which contribute to the decrease of mechanical modulus. • The morphology of Mg 2 Si is modified with increasing Sb. • Sb doping reduces Young's modulus but enhances the hardness of Mg 2 Si. • The structure stability of Mg 2 Si crystal is enhanced by Sb doping. • Sb doped Mg 2 Si exhibits reduced mechanical modulus and improved ductility. • Newly formed Mg-Sb covalent bonds account for evolution of mechanical properties of Mg 2 Si. [ABSTRACT FROM AUTHOR]

To further improve the mechanical properties of titanium matrix composite containing relatively high fraction of TiC and Ti 5 Si 3 particles, (6.5 vol% TiC + 3.3 vol% Ti 5 Si 3)/Ti6Al4V composites were prepared at different sintering temperatures, and then were carried out heat treatments. The microstructure evolution and corresponding mechanical behavior of composites were investigated. It found that the aggregation of particles in composite was reduced with the sintering temperature increasing, while the size of particles was increased. During the quenching process, the Ti5Si3 particles dissolved into matrix and TiC particle played the role of preventing the growth of matrix. TEM and EBSD analyses revealed that the size of Ti5Si3 particles increased (from 50 nm to 300 nm) with the aging temperature increasing (from 700 °C to 900 °C), and growth mechanism of matrix transformed from boundary migration to grain coalescence, leading to the abnormal growth of matrix. 1200 °C sintered composite had the compressive yield strength of 1780 MPa and compressive strain of 21%. After 1200 °C solution treating followed by 800 °C aging treating, the yield strength increased to 1900 MPa without obvious decline of ductility. The improvement was attributed to the strengthening effect of particles. [ABSTRACT FROM AUTHOR]