Morphology of WC grains in WC–Co alloys

In two alloys WC–(24 wt.%) Co containing a C and W excess respectively, sintered at 1450 °C (10 h) the shape of the larger WC grains that is a prism with a truncated triangle base is studied by transmission electron microscopy. The truncation that is the ratio of the short/long triangle sides and the elongation that is the ratio of the prism/triangle heights are quantified. The grains are less truncated and flatter in the C rich alloy. In equilibrium condition the ratio of the interface energies of the prismatic facets determine the truncation. The ratio of the energies of the basal and prismatic planes determines the elongation. The measured truncation confirms the ratio of the interface energies predicted from atomistic calculation for the prismatic facets. The experimental elongation is of the same range as the ratio between the calculated energies in the W rich alloy but much smaller in the C rich alloy. The possible origins of the discrepancy – departure from the equilibrium WC grain shape, model of the WC–Co interfaces used to calculate the interface energies – are discussed.     

Fabrication and properties of WC–10Co cemented carbide reinforced by multi-walled carbon nanotubes

High-velocity parting-off has been applied to 80 mm bars of pearlitic 100CrMn6, resulting in shear localisation and white-etching bands in a severely deformed region below the fracture surface. Electron microscopy showed that going from the bulk material towards the fracture surface the grains become elongated and refined. The region below the fracture surface can be divided into three subzones: 50–100 μm below the surface grains are elongated, cementite lamellae are distorted, break up and the lamellar spacing decreases. <50 μm below the fracture surface the microstructure becomes a mix of cementite lamellae and carbides in a ferrite matrix. Within the white-etching band the microstructure consists of equiaxed ferrite refined to a grain size of 50–150 nm. Several twinned regions caused by the deformation can be observed. Selected area electron diffraction and low angle convergent beam electron diffraction indicate nanocrystalline cementite dispersed in the ferrite matrix.     

Formation of metal–TiN/TiC nanocomposite powders by mechanical alloying and their consolidation

Fe–TiN, Ni–TiN, and SUS316–TiC nanocomposite powders were prepared by ball-milling Fe–Ti, Ni–Ti, and SUS316–TiC powder mixtures in a nitrogen or argon gas atmosphere. Fe–63vol.% TiN and Ni–44–64vol.% TiN milled powders were dynamically compacted by use of a propellant gun to produce bulk materials of nanocrystalline structure and having grain sizes between about 5 and 400 nm. SUS316–2.8–5.6vol.% TiC milled powders were consolidated by hot isostatic pressing (HIP) to produce bulk materials having grain sizes between about 100 and 400 nm. The possibility of using fine-dispersed TiN/TiC particles to pin grain boundaries and thereby maintain ultra-fine grained structures of grain sizes down to the nanocrystalline scale has been discussed.     

Convenient near-field optical measurement and analysis of polystyrene spheres

The modification of a commercial tapping mode atomic force microscope (AFM) into a transmission mode near-field scanning optical microscope (NSOM) is presented and polystyrene spheres in the diameter of 100 nm are used in this experiment. The detection of near-field signals is based on photodiodes with lock-in technique, and resolutions of topography and near-field signals obtained are about 10 and 20 nm, respectively. Furthermore, it is discovered that the computer-simulated near-field energy distribution profile, obtained by scanning over polystyrene spheres under illumination mode, falls within 5% range as compared with experimental values. The near-field absorption coefficient can be determined by this way. This will be a useful theoretical model to analyze the near-field transmission effect from others.     

TriSilanolPhenyl POSS–polyimide nanocomposites: Structure–properties relationship

Polyhedral Oligomeric Silsesquioxane (POSS)–polyimide (PI) thin films were synthesized from pre-mixed solution of oxydianiline–pyromellitic dianhydryde (ODA–PMDA) and TriSilanolPhenyl (TSP) POSS. POSS–PI polymerization reaction kinetics was studied using Fourier Transform Infrared (FTIR) spectroscopy. The POSS–PI films were then investigated by tensile tests, followed by surface morphology examination using Atomic Force Microscopy (AFM) and Environmental Scanning Electron Microscopy (ESEM). An interdisciplinary approach was applied for establishing a relation between POSS–PI composites chemical microstructure properties and failure mechanisms. Inter molecular POSS–POSS interaction by either phase separation, or chemical POSS–POSS condensation reaction were observed as key factors, affecting the nanocomposite mechanical properties via formation of aggregates. The amount and density of these aggregates were shown to be composition dependent. A model based on formation and coalescence of voids during tensile tests was suggested for understanding the effect of the POSS content on the POSS–PI mechanical response.     

Influence of the processing conditions on charge transfer and transport properties in poly(2-methoxy-5-(2′-ethylhexyloxy)1-4-phenylenevinylene):C60 composites for photovoltaics

Polymer-based photovoltaic devices have been elaborated by blending the conjugated polymer, poly(2-methoxy-5-(2′-ethylhexyloxy)1-4-phenylenevinylene) (MEH-PPV) with the buckminsterfullerene, C₆₀. The solvent used has a main influence on the optical and electrical properties of the photoactive layers. This could be attributed to different dispersion abilities of C₆₀ in the polymer layers shown by Atomic Force Microscopy and Scanning Electron Microscopy. Its effect on the transfer and transport properties has been studied. Thin film processing conditions have been modified by the preparation of blends of solutions of the polymer in Tetrahydrofuran and fullerene in Ortho-dichlorobenzene. The resulting spin casted layers show improved morphologies implying better dispersion of the fullerenes and increased short circuit currents. A decrease in the fullerene critical concentration to form percolation paths has been demonstrated. The improvement of the photovoltaic properties of the MEH-PPV/C₆₀ composites has been attributed to the nanosized fullerene domains formed upon phase separation. We used optical spectroscopy to study the charge transfer efficiency and electrical measurements to investigate charge transport properties in MEH-PPV:C₆₀.     

纳米样板的制备及其精度分析

介绍了纳米样板的研究现状及制备工艺，特别对扫描探针显微镜(SPM)表面局域氧化反应工艺进行了详述；分析了原子力显微镜(AFM)探针诱导局域氧化工艺的原理及其影响参数，原理为高度局域化的电化学反应，影响参数包括探针上所施加的电压、扫描速度、探针曲率半径、相对湿度以及氧化物厚度等；用该方法分别制备了5条栅线和7条栅线的一维纳米结构样板，并对7条栅线的纳米结构样板的精度和不确定度影响因素进行了分析。     

Controlled growth and investigations on the morphology and mechanical properties of hydroxyapatite/titania nanocomposite thin films

In this paper, the focus is on understanding the properties of nanocomposite hydroxyapatite (HAp)/titania (TiO₂) thin films with respect to TiO₂ concentration. HAp/TiO₂ nanostructured composite thin films with different TiO₂ concentrations were successfully fabricated by a simple sol–gel dip coating method. Highly stable HAp and TiO₂ sols were prepared prior to the formation of nanocomposite thin films. The coatings were performed under controlled dipping and heat treatment processes. Phase pure HAp and TiO₂ were well developed in the nanocomposite after the heat treatment and this was confirmed by XRD. The SEM and AFM analyses of HAp/TiO₂ nanocomposite coatings show the variation in the morphology as a consequence different TiO₂ concentration. This shows a reduction in the particle size to nanoscale due to the addition of TiO₂. The mechanical strength of the coating also increased upon the addition of TiO₂ as determined by nanoindentation. The composite thin films with 50 and 80 vol.% of TiO₂ show good mechanical strength when compared to other concentrations of TiO₂.