Advanced Materials Research Vols. 785-786

Abstract: Carbon nanotubes (CNTs) was introduced into Ni60/Al₂O₃ coating by flame spraying. The effect of adding CNTs on the tribological properties of the coating was studied by varying the CNTs content as 0.0, 1.5, 3.0 and 4.5 wt% in the Ni60/Al₂O₃ powders. The microhardness tester was used to measure the microhardness of the coating. Wear tests were performed on a pin-on-disk tribometer, to evaluate the tribological properties of the Ni60/Al₂O₃/CNTs coatings. Microstructural characterization was performed using scanning and transmission electron microscopy. Ni60/Al₂O₃/CNTs coatings revealed a lower wear rate and friction coefficient compared with the original coating, and their wear rates and friction coefficients showed a decreasing trend with increasing mass fraction of CNTs within the range from 0 to 3.0 wt% due to the effects of the reinforcement and reduced friction of CNTs. The results showed that the CNTs played dual roles in improving the tribological performance of the coating, indirectly by influencing the microstructure and mechanical properties of the coating and directly by acting as a lubricating medium.

Abstract: This work elucidated corrosion resistance of the electrodeposited MgO/calcium phosphate (Ca-P/MgO) films on titanium (Ti). The microstructure, phase composition, and corrosion resistance of the films were studied. Results revealed that The Ca-P/MgO composite coatings were rough and inhomogeneous, the upper layer was floral-like crystals or flakes agglomerates morphology, and the lower layer was needle-like crystals which were mutually cross linked. The coating was very dense, and the content of Mg was about 0.3 wt%. Potentiodynamic polarization test manifested that the Ca-P/MgO-coated surface exhibited superior corrosion resistance than the bare titanium.

Abstract: Using solvothermal method to modify the surface of polymethyl methacrylate (PMMA), the silica films were prepared on it via sol solution and solvothermal treatment. Silica-based hybrid sol solutions were synthesized from tetraethoxysilane (TEOS) and methyltrimethoxysilane (MTMS). The obtained silica-based hybrid films consisted of the uniform particles around 40 nm in diameter observed by atomic force microscopy (AFM). The optical property was evaluated by the UV-Vis absorption spectra. The silica hybrid films prepared through this process showed good optical transmittance.

Abstract: The corrosion resistance of chromium-free passivation film with single chromate-free passivation solution to deal with galvanized steel still has a gap compared to chromate passivation. In this experiment, the passivation solution consisting of the inorganic salt as corrosion inhibitor, silane as sealer, water-based epoxy resin and additives which formed a layer of inorganic and organic composite passivation film on galvanized steel through the synergistic effect between inorganic and organic. The morphology and elements of the passivation film was analyzed by scanning electron microscopy (SEM) and the corrosion resistance of the composite film was tested by neutral salt spray test (NSS), lead acetate spot test (ASS), tafel polarization curves and AC impedance spectroscopy (EIS). The results show that the composite film has a good adhesion and an excellent corrosion resistance, the corrosion area is only 3% after 72h NSS.

Abstract: The types and addition dose of zinc in the zinc-rich coating have a significant impact on the character of coating. Two types of the zinc powders and the amount of zinc were researched in this paper. It reveals that flaky zinc coating is better than the spherical zinc coating on corrosion performance, and the performance of the coating will be the best only when the solid content of zinc is reasonable. The results also show that optimal solid content of flaky zinc are 62.5%, 60% and 60.5% in the inorganic zinc-rich coating, epoxy zinc-rich coating and vinyl resin zinc-rich coating, respectively.

Abstract: Bisphenol A based epoxy acrylate (BABEA), a commercial ultraviolet (UV)-curiable material, was introduced as a new manufacturing material for facile fabrication of epoxy-functionalized films through UV-initiated copolymerization using glycidyl methacrylate (GMA) as the functional monomer. X-ray photoelectron spectroscope (XPS) results indicated the existence of epoxy groups on the surface of the poly (BABEA-co-GMA), which allowed for binding protein through an epoxy-amino group reaction. The contact angel results indicated the poly (BABEA-co-MMA) is hydrophilic, which avoided nonspecific adsorption of biological species. Bovine serum albumin (BSA) was successfully immobilized on the poly (BABEA-co-GMA) films by using the introduced epoxy groups effectively. This makes it possible to extend the application of such films in the fields of bio-separations and bio-recognitions.

Abstract: In this study, the 300 µm width micro-channel was manufactured by spray etching method. The surface roughness was analyzed by Laser scanning con-focal microscope. The relationship of the surface roughness and etching factor such as spray etching pressure, mask gap and time had been studied. The results show that the surface roughness increases initially, and then reduces with the size of mask gap. While the roughness increases as the spraying pressure increases. The etching time plays slightly effect on roughness for it has no impact on the etch uniformity as mask gap and spray pressure do.

Abstract: In this study, thick ceramic coatings were fabricated by laser multi-layer cladding with Al₂O₃-13%TiO₂ nanostructured agglomerated powders based on series of crack control of clad layer. The microstructural characteristics and microhardness of the coating were investigated by using scanning electron microscopy (SEM) and microhardness measurement. The results show that the laser-clad thick ceramic coating has no obvious interface between the layers with dense, continuous structure, and almost no pores and free of large penetrating cracks. The ceramic layer is composed of fully melted regions (fine equiaxed grains) and partially melted regions (remained nanoparticles). In addition, the most microcracks in the coating are focus on the partially melted region. The grain size of ceramic coating in the depth direction is gradually increased, while the hardness along depth direction is gradually decreased.

Abstract: The formation of cracks is one of the key problems which restricts the development and application of laser-clad ceramic coating technique on metal surface, especially during laser multi-layer cladding process because of stress superposition effect. In this study, a thick ceramic coating was fabricated by laser multi-layer cladding based on series of crack control methods. The crack of clad layer was controlled by preheating and slow cooling rate of sample with incubator, applying the ultrasonic vibration and adopting closed-loop controlling temperature of molten pool during laser cladding process. In addition, the crack of layer was controlled by the strengthening and toughening effect of remained nanoparticles in the laser-clad coating. Moreover, the use of a transition layer is also help to reduce layer cracks. The results show that the laser-clad ceramic coating is free of macroscopic cracks and the mcirocrack density is significantly reduced.

Abstract: The spherical casting WC powder is a kind of new potential wear-resistance ceramic material. In this paper, its chemical composition, surface morphology, microstructure, phase, microhardness and some powder characteristics were investigated, and then the powders were applied in laser surface alloying treatment on medium carbon steel. The results indicate that the spherical WC powder consists of (wt.%) 94.06 W, 4.03 C and 1.91 other elements including Fe, V, Cr and Nb. Most of powder particles have regular spherical shape and smooth surface, and the microstructure is acicular eutectic of WC and W₂C, which leads to high microhardness of 2812 HV. The fluidity of powders is 5.97 s/50g, and the apparent density of powders is 10.1 g/cm³. The laser alloyed layer is characterized by dendritic primary phase, ledeburite microstructure and some residual WC particles. The laser surface alloying treatment with adding material of spherical casting WC powder can enhanc the abrasive wear resistance of medium carbon steel by over 200%.