Key Engineering Materials Vol. 693

Abstract: The load transfer of CNT films under tensile loading at different scales was studied by using in situ Raman spectroscopy. The single-point and plane mapping Raman spectrum data was collected during the film tension to monitor the load transfer process of CNTs and CNT bundle network, respectively. The reason why the CNT film had well strength and ductility and low Young's modulus was revealed.

Abstract: A good dispersion of powders is crucial to obtain the sintered materials with superior properties. In this paper, the application of different dispersants in fabricating Ti (C,N)-based cermets was investigated. The effect of dispersant on the microstructure and mechanical properties of cermet materials was studied by observing the microstructure, indention cracks and fracture morphology using scanning electron microscope (SEM), and by measuring the transverse rupture strength (TRS), Vickers hardness (HV) and fracture toughness (K_IC). The results reveal that the dispersant oleic acid is helpful for the dispersion of Ti (C,N)-based cermet powders, and can contribute to the homogeneous microstructure and stable mechanical properties of the cermet materials. Compared with the cermets fabricated with polyethylene glycol (PEG), the microstructure of cermets fabricated with oleic acid shows more homogeneously distributed Ti (C,N) particles embedded into more evenly spread binder phases without agglomerations of Ti (C,N) grains. The cermets fabricated with oleic acid possess better comprehensive mechanical properties, with higher transverse rupture strength, hardness and a bit lower fracture toughness than the cermets fabricated with PEG.

Abstract: The carbon nanotubes (CNTs) modified by the carbon particles with diameter of 120-180 nm are prepared by using hydrocarbon ion deposition techniques. Based on the investigation of scanning electron microscopy and transmission electron microscopy, the CNTs are decorated by some nanospheres with size of 120-180 nm randomly, and the full CNTs surface besides the area of nanosphere is coated by the graphene stacks with size of 10-15 nm. The nanospheres are composed of several nanoparticles of graphene stacks and are seamless connected with graphene stacks. The sparse distribution CNTs on Si substrate is crucial for the formation of carbon nanospheres. The formation of carbon nanospheres proceeds through the following three stages: the formation of graphene nanoparticle on CNTs surface and silicon substrate – the migration of active hydrocarbon groups towards the surface of the CNTs deposition zone at high temperature – the formation of carbon nanospheres by the aggregating hydrocarbon active groups.

Abstract: Based on the theoretical model and physical mechanism of dynamic recrystallization (DRX) in metal materials, the dislocation density change, nucleation and grain growth model during the process of DRX are taken into account. And according to the nucleation driven by dislocation and grain growth kinetic, transformation rules are made. A modeling methodology coupling fundamental metallurgical principles based on amended nucleation rate with the cellular automaton (CA) technique is here derived to simulate the 316LN.The two-dimensional CA model uses quadrilateral element and periodic boundary condition and Von-Neumann neighbor type. The influence of strain, strain rate and deformation temperature on dynamic recrystallization volume fraction and average grain size are analyzed on the basis of established CA model.

Abstract: The diamond coating can improve the performance and durability of cutting tool. To obtain the structure of nano/micro CVD diamond coating, the finite element analysis of nano/micro composite CVD diamond coating on boronized cemented carbide was carried on using ANSYS. The relationship between nanoand micron diamond layer thickness and coating fall off stress was simulated. The thickness of nanodiamond and the micron diamond layer was suggested for the nano/micro CVD diamond coating on boronized cemented carbide cutting tool.

Abstract: In this paper, the drawing die of cemented carbide WC-Co (Wolfram Carbide-Cobalt) was taken as the substrate which was preprocessed by Murakami solution and aqua regia. DCS (Direct Current Magnetron Sputtering) was adopted to sputter the Nb interlayer in the bore of the drawing die. By using EACVD (Electron Assisted Chemical Vapor Deposition), micro-nanocomposite coating was deposited. Then, specimens were characterized through methods like SEM (scanning electron microscope) and Raman etc. Results indicated that the drawing die showed very smooth coating surface and a compact, uniform structure; the grain size < 50 nm and surface roughness < 10 nm. It can be inferred from the indentation experiment that there was satisfactory adhesion force between coating and the substrate. So, the drawing die can satisfy the working requirement of drawing wires.

Abstract: The admixture of graphene oxide (GO) sheets and chloroacetic acid were ultrasonic treated. As a result, epoxy and hydroxyl groups which existed onto GO sheets were transformed into carboxyl groups. Then, the carboxyl-GO sheets were assembled on silicon substrate by taking use of 3-aminopropyltriethoxysilane (APS) as an intermediate coupling agent (marked as APS-GO). Furthermore, La elements were deposited on the APS-GO by means of chemisorption to form multilayer film (APS-GO-La). Chemical compositions, surface morphologies, and microstructures were investigated by using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and water contact angle (WCA). Experimental results suggested that carboxyl-GO sheets distributed homogeneously on Si substrate. Results also indicated that lanthanum elements can react with the-COOH functional groups of GO film and be adsorbed on the APS-GO film surface. The prepared APS-GO-La multilayer film showed low surface free energy, which has potential applications in nano/micro electro-mechanical systems (N/MEMS).

Abstract: Poly (diallyl dimethylammonium chloride)-graphene oxide multilayer film (PDDA/GO) was successfully fabricated onto a silicon substrate by a layer-by-layer self-assembly technology. Subsequently, PDDA/GO were thermally reduced to be PDDA/RGO in a vacuum. X-ray photoelectron spectroscopy (XPS) was carried out to investigate the formation and microstructure of multilayer samples, as well as by water contacted angle (WCA). Results indicates that the multilayer film was prepared successfully, and the surface energy of PDDA/RGO is lower than PDDA/GO. nanotribological properties was investigated by an atomic force microscopy (AFM). It was found that the frictional coefficients of PDDA/RGO is better than PDDA/GO. To investigate the micro-tribological behaviors, a ball-on-plate tribometer was adopted. Results show that the layer-by-layer self-assembled multilayer thin film possesses good frictional and anti-wear properties. Therefore, both nanoand micro friction performance of PDDA/RGO behaves better than PDDA/GO. The obtained samples make the further application to be more possible.

Abstract: The chemical compositions and microstructures of several different cemented carbides were checked by XRD, XRF, SEM, metallographic microscope and stereomicroscope. The influences of phase compositions and microstructures on mechanical properties were investigated. The results show that improving the Co content and refining WC grain properly are effective means to acquire the excellent mechanical properties of cemented carbide. A series of friction and wear tests were carried out in a high-speed tribometer to explore the tribological behavior of three cemented carbides with different Co content and WC grain size against aluminum alloy 7050-T7451. It was found that the tribological behaviors of cemented carbides are largely dependent on their microstructures and mechanical properties. The enhancement of flexural strength and fracture toughness can be ascribed to deformation buffering effects of Co binder, but the improved hardness depends on the rigid skeleton of WC-WC grains.

Abstract: Oxygen-enriched Combustion behavior of indigenous lignite was investigated by using thermo gravimetric analyzer (TG). Combustion tests were carried out in six different atmospheres. The experiment results showed the oxygen–enriched atmosphere can improve the combustion rate of the lignite and expand the application scope of the lignite. Determine the Combustibility index to reveal the oxygen-enriched combustion process in detail.