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Graphene oxide nanosheets reinforced Cu matrix composites were prepared using ball milling process and spark plasma sintering (SPS). Effects of ball milling times on morphology of composites powders were studied. Furthermore, microstructure evolution and properties of sintered composites were investigated. Results show that the size and shape of the composites gradually transformed from regular sphericity to flake with the increase in ball milling times. Correspondingly, the average flake diameter of Cu alloy powders increased gradually from 7.2 ± 0.5 to 25.0 ± 1.0 μm. Compared with the matrix alloy, the tensile strength of the composites increases significantly and the elongation decreases gradually. For 20 h of ball milling, the yield strength of composites increased by 35% from 126 to 170 MPa, and elongation decreases from 44 to 31%. However, for 60 h of ball milling, the tensile strength and yield strength increased to 290 and 211 MPa, respectively, while the elongation significantly descends. Besides, during the ball milling, the conductivity of composite gets a slight decrease owing to the increasing degree of powder defects. [ABSTRACT FROM AUTHOR]

The effects of carbon nanotube (CNT) inclusion on the microstructure and performance of a TiC coating on a Ti-6Al-4V substrate brought about by laser cladding were studied. Mixing produced TiC+CNT powders with CNT concentrations of 2.5% CNTs, 5.0% CNTs and 7.5% CNTs. The microstructure and phase compositions were identified by scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS) and X-Ray diffraction (XRD). The wear resistance was indicated by the friction wear testing machine. The results showed that the binding interfaces of the substrate and the laser clad coating were all combined closely and there was no euphotic zone. The main microstructure of the coating was dendritic and rod-like or granuliform structures. The XRD pattern showed that the coatings which mainly consisted of TiC, VC and a-Ti, some of the Ti3AlC2 phase was found in the 5.0% CNTs addition coating. The wear mechanism of the coatings was abrasive wear and oxidation and the wear mechanism of substrate was plastic deformation, ploughing grooves and oxidation. The wear rates of the coatings were 3.9 × 10-7 mm3/Nm for the TiC+2.5% CNT addition, 5.92 × 10-7 mm3/Nm for the TiC+5.0% CNT addition and 4.57 × 10-7 mm3/Nm, for the TiC+7.5% CNT addition, which were smaller than that of the Ti-6Al-4V substrate at 7.83 × 10-7 mm³/Nm. [ABSTRACT FROM AUTHOR]

This study investigated the high-temperature tensile properties and deformation mechanisms of a solution treated Ni–Fe-based alloy ranging from 600 to 750 °C. The solution treated GH4070P (HT700P) alloy exhibits superior yield strength of 490 MPa and ultimate strength of 593 MPa at 700 °C. The major carbides in the alloy are the blocky MC and discrete-distributed M 23 C 6. The MC and M 23 C 6 carbides at the grain boundaries (GBs) can impede crack propagation, yet concurrently intensify the stress concentration. The transgranular and intergranular fractures are observed. Above 700 °C, micro-cracks emerge around M 23 C 6 carbides at GBs and then are interlinked to form lengthy secondary micro-cracks, resulting in the intergranular fracture. The precipitation of γ′ precipitates during tension at 700 and 750 °C confers the alloy to a higher strength. [ABSTRACT FROM AUTHOR]

We report that β-relaxation of amorphous NiW alloy film was effectively enhanced by adding two thin crystalline layers into the amorphous layer. Correspondingly, more bright bands, i.e., nano shear bands, were captured in the amorphous layer, which experienced more pronounced β-relaxations. Based on the potential energy landscape theory, the bright band was proposed to be the localized percolation of flow units corresponding to β-relaxation. Our findings may help connecting experimentally β-relaxation with flow units and shed light on the microstructure origin of β-relaxation. [ABSTRACT FROM AUTHOR]

Local elastic and thermal behaviors of dielectric breakdown regions in BaTiO3 based multilayer ceramic capacitors were investigated by acoustic and thermal mode scanning probe microscopy. Nanoscale elastic microstructures closely related to the dielectric breakdown-induced stress release was found to develop in the BaTiO3 ceramic grains adjacent to the dielectric breakdown region. Such nanostructures could be supposed to be the origin of the elementary structures for the failure of MLCC. The breakdown region exhibits very lower thermal conductivity due to the possible glass phase formation. Such new findings provide a new clue to further understand the breakdown mechanism of multilayer ceramic capacitors. [ABSTRACT FROM AUTHOR]

The microstructures, mechanical properties and electrical resistivity have been evaluated for deformation processed Al-20 vol % Mg and Al-13 vol % Mg composites. The Mg second phase adopts a convoluted, ribbon shape filamentary morphology after deformation. Both the size and spacing of these filaments decreases with deformation. The strength of these composites increases exponentially with reduced spacing of Mg filaments. The electrical resistivity of these Al-Mg composites is slightly higher than that of pure Al. [ABSTRACT FROM AUTHOR]

Fivefold annealing twin has been observed in nanocrystalline Cu at zero external stress. The microstructure of the multifold twins at various annealing temperatures has been examined by transmission electron microscopic in detail. Contrary to the well known sequential twinning mechanism, coherent twin boundaries formed via migration of grain boundary segment were proposed to be the dominant mechanism of fivefold annealing twin, which associated with grain growth during annealing. Moreover, the possibilities of the proposed mechanism may operate in forming fivefold deformation twin were discussed. [ABSTRACT FROM AUTHOR]

Owing to great hardness and low friction coefficients on steel, AlMgB 14 has several potential applications in the fields of cutting tools and wear-resistant materials. In the current work, the effect of Y 2 O 3 addition on the mechanical properties and microstructure of spark plasma sintered AlMgB 14 and AlMgB 14 -TiB 2 has been investigated. An increase in the amount of Y 2 O 3 led to an increase in the number of secondary phases including MgAl 2 O 4 and Y 2 O 3 in AlMgB 14 matrix. The addition of Y 2 O 3 led to a refinement in the grain size of AlMgB 14 and AlMgB 14 -TiB 2 ; however, simultaneously increased the porosity. With the addition of 3 wt% Y 2 O 3 , both AlMgB 14 and AlMgB 14 -TiB 2 reached the finest grain size and the highest hardness while maintaining a low porosity. [ABSTRACT FROM AUTHOR]

Scale-dependent microstructure and electronic transportation of Ni/Al-type nanomultilayers as a function of the bilayers number, the modulated ratio, and the periodicity were investigated. The deposited multilayers have anisotropic nanocrystalline structure and asymmetrical interfaces. This special interfacial feature is the result of asymmetrical diffusion of Ni to Al lattice near the Ni-Al interface. Anomalous resistivity enhancement increases with decreasing both the periodicity and the modulated ratio, but is insensitive to the number of bilayers. Accounting for the effects of grain boundary and interface boundary, the dominative mechanism at distinct length scales can be interpreted with the modified model of those of Fuchs-Sondheimer and Mayadas-Shatzkes. Especially for the thinnest film with smallest modulated ratio, the intermixing effect turns out to be the crucial mechanism in the electronic transportation of metallic nanomultilayers. [ABSTRACT FROM AUTHOR]

In present study, the Inconel 718 alloys fabricated by selective laser melting (SLM) were subjected to traditional homogenization plus double aging heat treatment (HT1), and a novel heat treatment (HT2). The effect of heat treatment on the anisotropic microstructure and the small punch creep (SPC) property of Inconel 718 samples was investigated. The experimental results show that the general high-angle grain boundaries with stress concentration, and the equiaxed and columnar grains are observed in the HT1 samples. Compared with the traditional solution treatment at 1065 °C for the HT1 samples, a higher solution performed at 1150 °C can efficiently eliminate the stress concentration and lead to the transformation of columnar grains to equiaxed grains in the HT2 samples by introducing complete recrystallization. The recrystallization is accompanied by the formation of annealing twins with high proportion Σ3n (n = 1, 2, 3) twin boundaries. The larger γ″ phases, less grain boundaries perpendicular to the load direction and smaller Laves phases in the HT1-Z (Z represents parallel to the building direction) sample result in a longer creep life. Microcracks distributed along the general high-angle grain boundaries rather than twin boundaries promote the final intergranular fracture. The anisotropy in creep rupture time of SLMed Inconel 718 alloy can be obviously alleviated by applying higher temperature solution treatment. [ABSTRACT FROM AUTHOR]

Highlights • The buffer layer grown at 1350 °C by HVPE is recognized to be single crystal. • The buffer layers grown at 1050 °C by MOCVD or HVPE have columnar structures. • High temperature improved the in-plane misorientation of buffer layers. • AlN films on 1350 °C buffer layers have the best crystal quality. Abstract The microstructures of AlN films grown by high-temperature hydride vapor phase epitaxy (HT-HVPE) on (0 0 0 1) sapphires with three different kind of buffer layers (BLs) were investigated by plan-view and cross-sectional transmission electron microscopy (TEM). The buffer layers were grown by HVPE at 1350 °C, MOCVD 1050 °C and HVPE at 1050 °C. The microstructures and in-plane misorientation of buffer layers are related to the crystal quality of the AlN films and dislocation evolution. The misorientation angles and average grain sizes of buffer layers were analyzed quantitatively using Moire fringe method. The buffer layer grown at 1350 °C by HVPE was recognized to be single crystalline, but buffer layers with mosaic-structure are formed at 1050 °C either by MOCVD or HVPE. High growth temperature of 1350 °C significantly reduced the in-plane misorientation of the buffer layer and the dislocation density was greatly reduced. AlN films on high-temperature growth buffer layers (∼1350 °C) have the lowest treading dislocation density ∼3 × 108 cm−2 determined using a combination of X-ray rocking curve measurement and plan-view transmission electron microscopy. [ABSTRACT FROM AUTHOR]