Advanced Materials Research Vols. 314-316

Abstract: In this paper, dense AZ91D/SiC composite coatings were fabricated by cold spraying. The microstructure and microhardness of the as-sprayed coatings were investigated. The results show that the content of SiC particles in the composite coating was 23.6 ± 7.5 vol.%. The microhardness of the composite coating was improved to 140 HV0.3 due to the enhancement of SiC particles, compared to 98 HV0.3 for the pure AZ91D coating. The wear behavior of the composite coating in an ambient condition was studied through a ball-on-disc dry sliding test system. The composite coating showed higher friction coefficient and lower wear rate than the pure AZ91D coating. The wear mechanism of the composite coating was discussed.

Abstract: By electron energy spectrometer,X-ray diffractometer,transmission elec-tron microscopy andmicro-hardometer,the depositing speed of electrolessNi-Co-P plating baths,chemical composition,crystal structure and microhardness of the alloy coatings were inspected and analyzed with ultrasonic and rare earth metalcerium intervening in electroless Ni-Co-P plating•The results show that the depositing speed of electroless Ni-Co-P plating isobviously increased under the effect of ultrasonic.The chemical compositions of electroless Ni-Co-P plating are changed，The XRD of coating has a diffuse sexual diffraction peak closing to typical amorphous structure.the obtained Ni-Co-P coating has more fine crystal grain, even and dense surface morphology. Its wear resistance and hardness have been improved obviously.

Abstract: This research is to investigate tribological properties of thermal diffusion (TD) treated D2 steels against aluminum (Al 6061) counterface material for its potential applications in dry machining/forming of aluminum composite materials. A hard vanadium carbide (VC) layer was formed on the tool steels by the TD process. Original D2, thermal treatment hardened D2 and TiN coating on hardened D2 were used as references. Pin-on-disc tribo-tests were performed on those samples against Al pins under a dry sliding condition. Wyko profilemetry analysis showed that Al pin material transferred to the D2, hardened D2 and TiN coating surface and caused adhesive wear, which may negatively influence product quality in machining/forming applications. The TD-VC coating on D2 steel has a good adhesive wear resistance and anti-sticking of aluminum performance, which is a promising material used for dry machining/forming of aluminum.

Abstract: The aluminizing process by solid powder on the surface of GH4169 superalloy with different Y₂O₃ content and different aluminizing temperature was investigated in this paper. The results show that the crystalline phase of aluminized coating is composed of AlNi, FeNi and AlNi3, and the phase of AlNi reaches 78.1%, which indicates that aluminium atom has infiltrated into the alloy surface. Y₂O₃ can greatly improve compactness of the aluminized coating, increase thickness, surface micro-hardness and high temperature oxidation resistance of the aluminized coating. The thickness of the coating increases with the increase of temperature, but the microstructure of the aluminized samples cannot obviously divided into aluminized layer, transition layer and matrix when the aluminizing temperature is too high (980°C) or too low (920°C), and even the aluminized coating is porous and coarse at 980°C. The high temperature oxidation resistance of all the aluminized samples is improved compared to without aluminized samples. According to the microstructure, thickness, surface micro-hardness and high temperature oxidation resistance of aluminized coating, the optimal aluminizing process is 950°C×7h with 4%Y₂O₃.

Abstract: Linear low density polyethylene (LLDPE) was chemically modified with grafting maleic anhydride (MAH) monomer on its backbone by melting blending. Nano-particles SiO2 was modified by cationic surfactant hexadecyl trimethyl ammonium bromide (CTAB) and anionic surfactant sulfosalicylic acid (SSA) and added to PE coating respectively. Measurement of membrane potential showed that the coating containing modified SiO2 nano-particles had characteristic of ion selectivity. The properties of the different coatings were investigated according to relative industrial standards. Experimental results indicated that PE coating with ion selectivity had better performances, such as adhesion strength, cathodic disbonding and anti-corrosion, than those of coating without ion selectivity. Crystal structure of the coatings before and after alkali corrosion was characterized by Fourier transform infrared spectra (FTIR) and X-ray diffraction (XRD). Structure of the coating without ion selectivity was damaged by NaOH alkali solution, causing mechanical properties being decreased. And the structure of the ion selective coatings was not affected.

Abstract: Nanostructured WC-17Co coating was prepared by means of High Velocity Oxygen Flame (HVOF) technique. Characteristic of nano-structure of the coating was analyzed. The coating seems to be of lamination structure formed by fully or partially melted powder. It shows that the coating consists of melted and recrystallized zone, semi-molten zone and un-melted zone. Amorphous phase and nanocrystalline phase co-existed in the coating is due to the rapid heating and cooling during spraying. The nanostructured coating possesses excellent mechanical properties, which are closely related to the unique nanostructures existed in the coating.

Abstract: This study reports the statistical optimization of experiments, designed by Taguchi, to improve the wear-resistance of the tungsten carbide/cobalt-based coatings applied using high-velocity oxygen-fuel (HVOF) spraying processes. In this study, a group of needlelike textures appeared in the HVOF WC-Co coatings. The structures were evenly distributed and compacted closely, showing a more dense and homogenous configuration. The coating that formed with a large amount of pores, microcracks and unmolten particles was much looser, and the interface was locally prone to defects. The coatings were obviously not homogenous. Experimental results show that the wear-resistant coatings are highly dense, with an elastic lamellar structure. The tribological properties were significantly improved and the surface textures showed uniformity, in a molten droplet flattened formation. A homogenous, morphological structure, with local small aggregation, was more obvious after HVOF WC-Co coating. Accordingly, it is clear that the surface properties determined proved favorable to the mechanical properties of the WC/Co coatings. In addition, we compared the linear models with the quadric models, using RSM methods, in all the experiments. Statistically, the linear models produced an average error of 8.285％, while the quadric models generated an average error of 1.399％. It is clear that the RSM models successfully fitted the HVOF WC-Co coating process and the quadric models yielded more accurate predictions than the linear models, in most cases. The proposed procedure was applied to HVOF spraying of WC-CO coatings. The results demonstrated its feasibility and its effectiveness in improving the HVOF WC-Co coating.

Abstract: Silicone-modified butyl acrylate-methyl methacrylate copolymer latex was prepared via semi-continuous emulsion polymerization. Octamethyl cyclotetrasiloxane (D4) was used to link acrylate and potassium persulfate was used as initiator (KPS). Effect of D4 content on polymerization of acrylate and properties of latex film were discussed in details. The results showed that the properties of acrylate could be improved by the introduction of D4. Dynamic mechanical analysis showed that the freeze resistance of copolymer was effectively improved. In addition, effect of D4 content on adhesive strength of copolymer was also investigated.

Abstract: Ceramic particulate-reinforced Ni-based composite coatings are commonly used in the industry for protection against wear. With an aim to investigate the properties of this coating, ceramic coating reinforced by in-situ synthesized (Ti,Cr,Nb,Mo)xCy particles was prepared on AISI 1045 steel substrate by tungsten insert gas cladding. The microstructure and microhardness of the coatings were analyzed by scanning electron microscopy (SEM) and microhardness tester. The results showed that excellent bonding between the coating and the AISI 1045 steel substrate was uniform, continuous and almost defect-free. The maximum hardness value achieved 1013HV, which is about 5 times compared to that of the AISI 1045 steel substrate.

Abstract: In order to solve the practical problem of deburring and surface finishing of internal hole surface, mold cavity, complex surface, etc., a new viscoelastic magnetic abrasives is proposed based on analysis of field characteristic and existing finishing process. Viscoelastic magnetic abrasives are prepared, and motion locus of abrasives are discussed. An experimental investigation is engaged on direct hole, keyway surface through a simple test device designed by ourselves. Theoretical analysis and experiments show that all burrs is removed, the edges are rounded off and the surface is smooth, the value of surface roughness Ra drops from 0.53μm to 0.05μm. It’s successful application will effectively solve the practical difficulty of deburring and surface finishing for special shapes such as groove, keyway, etc. and fulfil the quantitative finishing of complex surfaces. It will produce a positive impact on precision surface finishing technology.