Advanced Materials Research Vol. 75

Abstract: Electrophoretic deposition (EPD) allows the fabrication of ceramic coatings at lower cost and higher speed than most other deposition techniques. The processing consists of powder deposition from a suspension under the influence of an electric field and subsequent consolidation of the coating by sintering. Adherent zirconia coatings with coating thicknesses up to 0.1 mm were obtained from different suspensions, one methyl-ethyl-ketone and the other ethanol based. The standard sintering temperature is 1200°C, which easily may damage or change the substrate and also means high production costs. In order to reduce the sintering temperature, suspensions with the addition of ZrN were investigated. Due to reaction bonding, sintering in air at a remarkable low temperature of 1000°C was successful. The elastic modulus of the EPD coatings has been derived from impulse excitation experiments and the thermal conductivity from laser flash analysis. The elastic modulus was about 22 GPa and the thermal conductivity between 0.4 and 0.6 W/(m•K) at room temperature, both decreasing slightly with temperature. Especially the exceptionally low thermal conductivity makes EPD coatings a promising candidate for thermal barrier coatings.

Abstract: Electroless Ni-Co-P coatings have been deposited on sintered Nd-Fe-B permanent magnets by optimizing the bath composition and operating conditions. The corrosion resistance of coated Nd-Fe-B magnets was significantly improved and corresponding corrosion current density Icorr in 3.5 wt. % NaCl solution decreased by two orders of magnitude. Coated with 12μm-thick Ni-Co-P, Nd-Fe-B magnets possessed slight reduction in magnetic properties, with a modest loss of remanence (Br) by 3.9 % and coercivity (iHC) by 4.5 %.

Abstract: Pretreatment process for electroless nickel coating on ultrafine glass microspheres with an average diameter smaller than 10μm was studied. Through comparative experiments, three-step pretreatment process including washing, coupling and activating was selected to pretreat ultrafine glass microspheres with supersonic. Then the amount and distribution of palladium activate sites absorbed on the surface of microspheres were measured by energy-dispersive X-ray spectroscopy (EDX). It was found that the content of palladium was increased obviously because of addition of coupling treatment and optimization of pretreatment parameters such as agitation method and loading weight, meanwhile palladium was distributed more uniformly due to the action of supersonic. In addition, pretreated microspheres were placed in an alkaline plating solution with supersonic and nickel coated microspheres were obtained. Then morphology and composition of the coating were characterized by scanning electron microscopy (SEM) and EDX. The results proved that EDX results of palladium could characterize the result of pretreatment effectively. The low density Ni coated microspheres may be utilized for manufacturing conducting materials for EMI shielding applications.

Abstract: In this paper, the anodic oxidation film was prepared in the 1~3mol/L NaAlO2 solution with and without silicon sol added. The film thickness, high temperature oxidation resistance, corrosion resistance, and SEM image, element composition in the film were investigated. The results show that there were obvious improvement in high temperature oxidation resistance and corrosion resistance of the film on titanium alloys after adding silicon sol into the NaAlO2 solution, and with the sol percentage in the solution increased, the foregoing protection abilities of the anodic oxidation film became better, while the film thickness was little affected with the sol percentage difference. The reason was discussed and the effective factor was the silicon composition and more even and compact image in the film.

Abstract: Titanium alloys has been widely used in many fields, while in high temperature and rigorous corrosive environment, it is very necessary to do some work on the surface of titanium alloys to satisfy with application purpose. In this paper, four kinds of sol film were prepared on titanium alloys with and without anodic oxidation film. The prepared sol included Al2O3, Al2O3-ZrO2 and doped sol by adding additive into them respectively. The film thickness, high temperature oxidation resistance and corrosion resistance after high temperature oxidation for some time were investigated. The results show that the sol film obtained on the anodic oxidation film of titanium alloys is thicker than that without anodic oxidation film. Compared with the other three kinds of film, the doped Al2O3-ZrO2 sol film has the best high temperature oxidation resistance and corrosion resistance due to insulation effect of the sol film, and the composition of additive and zirconic.