Advanced Materials Research Vols. 463-464

Abstract: Abstract. In this work, conventional and nanostructured Al₂O₃-13wt.%TiO₂ coatings were deposited by the plasma spraying technique. The microstructures of the two types of coatings were analyzed, and the solid particle erosion behaviors of the two coatings were comparatively researched in an erosion tester. Meanwhile, the erosion failure mechanisms of the coatings were discussed. The results show that the traditional coating has laminated structure and some pores. However, the nanostructured coating possesses a denser structure and not obviously lamellar-like structure, and exhibits a bimodal microstructure consisted of fully melted regions and partially melted regions. Owing to the compact microstructure and remained nano-particles, the nanostructured coating had a better erosion wear resistance than the conventional coating. Eroded morphology analysis indicates the main erosion mass loss of the coatings is attributed to lamellar spalling of the sprayed splats and fracture of brittle ceramic particles. In addition, the nanostructued coating has some impact craters and plough marks. In terms of the erosion mechanism, the conventional ceramic coating is dominated by brittle erosion, while the nanostructured ceramic coating is dominated by brittle erosion as well as ductile erosion to some extent.

Abstract: In this paper, the damage patterns of the hexagonal aluminum honeycomb sandwich plate subjected to normal and oblique impact by spherical, cylindrical and cubic fragments at different velocities are simulated using LS-DYNA code. The damage patterns of the sandwich plate and the energy loss ratio of fragment are acquired. In normal and oblique impact for different shapes of the fragment, the damage patterns of the sandwich plate include the plastic deformation, the fracture and the perforation of the face sheet and the tearing of the core or the combination of them. The curve of energy loss ratio waves with the velocity of fragment. And the peak point at the curve of energy loss ratio versus the velocity of fragment denotes the limit velocity of fragment. Furthermore, the energy loss ratios of fragments in oblique impact at the velocity of 500 m•s-1 with the angle of impact of 5°, 10°, 15° and 20° are obtained. The results denote that a fragment with large ratio of length to diameter is easy to perforate the sandwich plate both in normal and oblique impact.

Abstract: Hydrofluoric Acid (HF) and sand blasting have been incorporated together with chemical surface pretreatment (HF) for the surface pretreatment of the Al₂O₃ cutting tool. Amorphous graphite was deposited on the substrates by using PVD technique. Morphological observation by Scanning Electron Microscope (SEM), surface roughness and topography of the substrate by using Atomic Force Microscopy (AFM) was done in order to investigate the effect of surface pretreatment on the substrates. Critical load required in scratching the substrate’s surface after coating by different surface pretreatment was evaluated by microscratch testing. As-received micrograph has a continuous 45° direction based on horizontal line when the substrate was put in the chamber at the time the image was taken. Substrate with surface pretreatment shows non-uniform surface with peak and valley image. Coated surface micrograph shows amorphous graphite with cube in shape. Surface roughness and critical load for microscratch of sample was found increased with surface pretreatment both chemically and mechanically.

Abstract: Electroless Ni- P-coating of fly-ash cenosphere particles is demonstrated in the present investigation. The Electroless Ni- P-coating process is modified by replacing the conventional sensitization and activation steps with only using activation step with CuSO4 activator. The cenosphere particles are characterized by scanning electron microscope (SEM), energy dispersive spectroscopy (EDX), X-ray diffraction analysis (XRD) and X-ray photoelectron spectroscopy (XPS) during and after the coating process. Relatively uniform and continuous coating is obtained under the given coating conditions. The possible mechanism of electroless Ni-P-coating of cenosphere particles utilizing CuSO4 activator is suggested. The low density Ni-P coated cenosphere particles may be utilized for manufacturing conducting polymers for EMI-shielding application and microwave absorbing materials.

Abstract: By incorporating magnetism into semiconductors, it may possibly be viable to enhance the functionality of materials. An exceptionally important material in this context is GaAs, which can be doped with Mn atoms. (GaMn)As has fascinated research community as a promising candidate for spintronic application. It is quite appealing due to both its compatibility with existing III-V technology and great progress in improving its magnetic properties. Being fabricated by low temperature molecular beam epitaxy (LT-MBE), due to thermal instability at elevated temperatures, the material contains a high density of various defects compensating Mn acceptors. It is a well-established fact that the ferromagnetic state of (GaMn)As can be stabilized via post growth annealing. Nevertheless, in general, the annealed (GaMn)As layers do not remain useful for further epitaxial overgrowth that might be included in multilayer structure. We present a summary of our investigations regarding the synchrotron-based characterization of (GaMn)As layers grown via molecular beam epitaxy carried out at the Swedish National Facility of Synchrotron Radiation-the MAX-lab aiming at the reduction of the density of Mn interstitial and increase in the content of Mn.

Abstract: Vertical-aligned arrays of zinc oxide (ZnO) nanorod were grown on nickel-coated polyester s for future development of ZnO nanorod-based solar cells. ZnO nanorods with aspect ratio of three were deposited by chemical solution deposition (CBD). Besides, an underlying ZnO seed layer was introduced to grow large-area and continuous layer of ZnO nanorods using pulsed laser deposition (PLD). Structurally, dominating XRD diffraction of the ZnO nanorod arrays was occurred at lattice plane (002) and a specific Raman spectrum was also obtained. Optically, bandgap energy of the ZnO nanorods was 3.95 eV. The ZnO nanorods with full-width at half-maximun (FWHM) of about 16 nm were excited normally from ultraviolet laser source of λ=266 nm and released edge-emission of λ=383 nm. On the basis of our results, high quality ZnO nanorods have been successfully fabricated on nickel-coated polyester fibers.

Abstract: The casting WC particles reinforced steel matrix composite coatings on Cr15 steel substrate were fabricated using the vacuum infiltration casting technique, meanwhile, investigated the relationship between the structure, hardness and the volume fraction of tungsten-iron powder in the composite coatings. The fabricated composite coatings contained tungsten-iron powder of 4.96, 9.31, 17.15 and 23.64 vol%, respectively. The microstructures and phase of the composite coatings were analyzed using Optical Microscope (OM), Scanning Electron Microscope (SEM) and X-Ray Diffraction (XRD). The results shows that, with increase in volume fraction of tungsten-iron powder, the amount of martensite and in situ synthesized Fe3W3C have increased. The changes of the hardness in the composite coatings with the volume fraction of tungsten-iron powder, and the hardness has been improved greatly, the highest hardness value can reach HRC 65. In addition, the reacted layers have been formed around the WC particles and mainly consist of Fe3W3C, therefore, the interfacial strength is increased significantly. However, tungsten element in the matrix hampered the melting of the WC particles.

Abstract: In this study a single step of the chemical pre-treatment is implemented to tungsten carbide (WC 6 [%]) at the surface of the substrate in order to solve poor adhesion problem. During the pre-treatment process, numerous parameters such as etching time, acid temperature and concentration affect on the surface roughness and Cobalt content of WC-Co substrate are investigated. Optimal selection of these parameters is one of the significant issues to achieve high-quality work-piece in etching process. Thus, the statistical model based on nonlinear polynomial equations is developed for the different responses. Non-dominated Sorting Genetic Algorithm (NSGA-II) with the use of MATLAB Software codes is used to solve multi-objective optimization problem in order to provide a preferred solution for a process engineer in a short period of time.

Abstract: The paper reported the effect of zirconia incorporation on the oxide layer modification of the valve metal such as magnesium coated by plasma electrolytic oxidation (PEO). To incorporate zirconia particles into the oxide layer, PEO coatings were carried out under AC condition in electrolytes containing zirconia powder. After PEO coatings, structure observation revealed that a number of zirconia particles were distributed uniformly throughout the oxide layer while the size and distribution of pores remained unchanged as compared to the results coated by PEO without zirconia. It was found that fine zirconia particles incorporated into the oxide layers played an important role in enhancing the anti-corrosion properties of bare metal.

Abstract: A low-cost organic compound mainly comprising of polyarylate was selected as precursor and a chemical activation method was used to prepare an activated carbon material of large surface area, with which the activated carbon electrodes of high specific capacitance were fabricated for supercapacitor. Impact of activating temperature on the specific capacitance of activated carbon electrode was studied, the relationship between the pore structure, surface area and specific capacitance of activated carbon electrode were discussed. The specific capacitance and ESR (equivalent series resistance ) of the electrode fabricated with the activated carbon prepared at 700°C is 211F.g-1 and 0.2Ω/cm2 in hydrous electrolyte and the 122F/g and 1Ω/cm2 in orgnic electrolyte respectively. Because of the different ion diameter in orgnic and hydrous electrolyte, activated electrode show different electrochemical behavior in cyclic voltammetry examinations.