Advanced Materials Research Vols. 538-541

Abstract: TiC reinforced Ni-based composite coating added with 10% TiC and 20% TiC particles were prepared on the surface of Q235 steel by plasma cladding, respectively. SEM as well as EDS and XRD were used to investigate the microstructure and formation mechanism of composite coating. The results show that between composite coating and substrate is metallurgical combination, and the microstructure of composite coating is composed of basic microstructure dendrite γ-Ni, interdendritic eutectic structure (α-Fe+Cr23C6+CrB) and dispersed TiC particle. Part of TiC particles melt when the composite coating added with 10% TiC particles, in the composite coating added with 20% TiC particles, part of TiC particles precipitate after dissolution. TiC particles have a uniform distribution with the size 3~5µm. The maximum value of micro-hardness of composite coating added with 10% TiC and 20% TiC particle is 460 HV0.2 and 620 HV0.2, respectively.

Abstract: Gypsum and slurry with high content of Cl- lead to the damage of desulfurization pump caused by erosion and corrosion. Gas tungsten arc welding (GTAW) and shield metal arc welding (SMAW) were employed to develop weld repairing technology. High-velocity oxygen fuel (HVOF) spraying was employed to prepare NiCr cermet coating and WC cermet coating against erosion and corrosion. Microstructures and mechanical properties of the weld and the protective coatings were tested. The mechanical properties of the weld joints with duplex microstructure were in accordance with related standards. The technology of HVOF sprayed NiCr cermet coating was selected to prolong the service lifetime and was applied on the pump casing and impeller repaired by using the weld repairing procedures developed in this study. The integrity of the pump parts after 30 months in-field service confirmed the reliability of the repairing technology and the protection technology.

Abstract: The Cu-Ce infiltration layer was formed on 304 Stainless Steel surface by double glow plasma surface metallurgy technology. The effects of source voltage and cathode voltage on surface alloying concentration, surface hardness and infiltration layer depth were analyzed by comparative test. The results showed: In the experimental range, the contents of Cu and Ce, surface hardness, deposition layer depth increase with the source voltage increasing, which is contrary to the cathode voltage; the diffusion layer depth increases with either voltage increasing in a certain range.

Abstract: Surface composite layer was fabricated on the cast steel matrix using the evaporative pattern casting (EPC) technology. The pre-coating with WC and Cr-Fe particles as raw reinforcements was reacted with matrix and formed the composite layer. Then, the microstructure and hardness of surface composite layer were investigated by Scanning Electron Microscope (SEM), Olympus Microscope (OM), Energy Dispersive X-ray Spectroscopy (EDAX) and Rockwell Apparatus. The results show that the composite layer can be divided into transitive layer and penetrated layer, and the component analysis shows that the microstructure distribution of the penetrated layer is homogeneous.

Abstract: The hybrid effect of Al and Cr in zinc bath on galvanizing coatings were studied by means of scanning electron microscope (SEM) and energy dispersive X-ray spectroscope (EDS), coupled with hot-dip galvanizing experiments. A new phase T1 was found in the coating, and the ζ phase was absent when hot-dip galvanizing at 480 °C. When Cr added zinc bath were alloyed with 0.1 wt.% Al, coating was composed of δ, ζ, η and T1 phases; when Cr added zinc bath were alloyed with 0.2 wt.% Al, δ phase layer became thinner, ζ changed from even layer to blocky crystals, and diffuse-Δ coexisted with the ζ phase. The morphology evolution of galvanizing coating was analyzed and the hybrid effect of Al and Cr were discussed with diffusion path theory.

Abstract: It takes advantages of non-abrasive cryogenic polishing to polish the metal cylindrical surfaces in the paper. In cryogenic condition, the ice tool is produced by deionized water. The feed apparatus of the ice tool is also designed and produced. It is analyzed the influence of the ice tool material, metal material, rotate speed, polishing time and other parameters in the experiments.

Abstract: In this paper, the electromagnetic shielding fabric with Ni-Cu-Ni three layers and colorized appearance was prepared by the electroless plating and colorized electroplating. The current density was distributed unevenly in the course of colorized electroplating, which resulted in the nonuniform color of the electroplated fabric. In this paper, this problem was solved by improving the electroplating fixture. The adhesion strength and the conductivity of the coating were measured respectively. The results showed that the Ni-Cu- Ni multilayered coating possessed stronger adhesion strength to the fabric substrate than single layered coating, and the conductivity of coating was better than that of pure metal.

Abstract: Grain growth simulations considering heat treatment process were carried and the change in microstructure on the surface was regenerated. Stress-dependency of the phase transformation from original phase to precipitate was introduced into the conventional multi-phase-field model, and stress distributions were calculated. Volumetric dilatation was considered as a source of the stress generation, and a slight variation in the dilatation coefficient was applied for each grain. As a result, a mosaic pattern in the stress distribution correlated to the polycrystalline microstructure was obtained. The residual stress distribution was also calculated under three different conditions, and revealed to vary depending on the microstructure obtained.

Abstract: α-SiC particles have been processed with surface treatment of high-temperature calcination and water washing technology. SiCp/Al-30Si composite has been prepared in the vacuum hot extrusion process. The powder morphology and specimens microstructure have been observed using scanning electron microscopy, the phase of SiC has been analyzed using the X-ray diffraction. Meanwhile, the tensile strength and thermal expansion coefficient of the composite have been tested. The effects of the morphology of the SiC particles, tensile strength and thermal expansion coefficient have been studied on composite microstructure. The consequences show that, after the surface treatment SiCp/Al-30Si composite，the interfaces combined with matrix are in a better condition and less holes, the tensile strength of composite materials has been improved significantly, the coefficient of thermal expansion becomes lower than before.

Abstract: The metal and nano-ceramic nanocomposite coatings were prepared on gray cast iron surface by electrodepositon. The nickel and cobalt were used as metal matrix of coating, and the nano-Al2O3 was chosen as second-phase particulates, which had good chemical stability, high microhardness and good wear resistance. The morphology of composite coatings was flatter and microstructure was denser than pure nickel and cobalt coatings. The composite coatings were fabricated by different dispersion methods such as high speed mechanical stir, ultrasonic vibration and ultrasonic vibration together with mechanical stir. The result indicated the nano-Al2O3/Ni+Co composite coating with fine and compact microstructure are obtained compared with pure Ni-Co coating. The nanoparticles were dispersion evenly when dispersion style was ultrasonic vibration together with mechanical stir according to composite coatings SEM images of different dispersion style. The concentration of nanoparticulates reached a maximum value when the dispersion style was ultrasonic vibration together with mechanical stir, at the same time the mechanical property such as microhardness reached a maximum value also. The reason was that nano-Al2O3 caused dispersive strengthening and grain refining.