Advanced Materials Research Vols. 314-316

Abstract: In order to improve the bonding properties between poly (m-phenylene isophthalamide) (PMIA) fibers and PMIA-pulp and to improve the mechanical strength of aramid sheets, PMIA fibers have been treated with various chemical modifying agents. The surface morphology of the treated fibers has been analyzed and the mechanical properties of aramid sheets made from the treated PMIA fibers and PMIA-pulp have been investigated. The results show that silane coupling agent modification, phosphoric acid modification and nitrification/reduction modification of PMIA fibers are all helpful for improving the tensile strength and tear strength of aramid sheets, however, they have different effect on the mechanical strength of aramid sheets, and the concentration of chemical modifying agents also has considerable influence on the surface properties of aramid fibers and the mechanical properites of aramid sheets. Aramid handsheets made from PMIA fibers treated with 20% phosphoric acid have the highest mechanical strength, and the tensile strength and tear strength of them are 23.4% and 31.6% higher than that of aramid handsheets made from untreated fibers, respectively, because the treated fiber surface has more oxygenous functional groups and is more rough than the untreated fiber surface.

Abstract: In this paper,TiAlN films were deposited on the surface of tool steel substrates using multi-arc ion plating technology at the assistance of hollow cathode（HC）electron beam. The influence of hollow cathode electron beam on the phase composition、microstructure and the performance of TiAlN films were studied.The phase composition，microstructure，surface profile and adhesive strength of the films to the substrate were investigated by X-ray diffraction（XRD）,scanning electron microscopy(SEM),Profilemeter and UNMT-1 Multi-specimen Test System respectively.The results show that with the increase of the current of the hollow cathode, the preferred orientation of（200）was weakened，and the surface of TiAlN films become smooth and the macroparticals decreased obviously.The hollow cathode electron bean can remarkably improve the adhesive property of TiAlN films，and the scratching test show that the critical load from 38N increase to 61N.

Abstract: In this paper, iridium coating was produced by double glow plasma on various substrates. Microstructure, mechanical property, thermal stability and ablation resistance of the iridium coating were investigated. The coating was the columnar grains with a preferred (220) orientation. The adhesive force of the coating on carbon substrate was smaller than that of the coating on the refractory metals and carbide. After heat treatment above 1400oC, many micropores appeared on the surface of the coating. The surface of the coating also presented micropores after ultrahigh temperature ablation. The iridium coating could endure the high temperature up to 2000oC and could protect the substrate from oxidation.

Abstract: HIPIB irradiation experiment is carried out at lower energy density of 0.55 J/cm2 with shot number from 1 to 10, and dry sliding wear behavior is investigated in order to explore the low energy-modification of magnesium alloy by HIPIB. It is found that HIPIB irradiation leads to the increase in surface hardness and therefore the improvement in wear resistance compared with the original sample. The improved wear resistance is mainly ascribed to the enhanced surface hardness induced by HIPIB irradiation.

Abstract: In this paper, the thermal shock induced cracking behavior of a segmented coating on the outer surface of a hollow cylinder has been investigated. The driving force for the propagation of multiple segmentation crack, represented by the Thermal Stress Intensity Factor (TSIF), was determined by combination of the principle of superposition and the finite element method. The maximum TSIF has been shown to occur neither at the beginning nor at the steady state of thermal transients, but at an intermediate instant. As the spacing between multiple segmentation cracks decreases, the magnitude of TSIF first plateaus, and then decreases sharply. This quantitative mechanistic result rationalizes the experimental observations that a segmented coating can exhibit much higher thermal shock resistance than an intact counterpart, if only the segmentation crack spacing is narrow enough. Some other parameters affecting TSIF, such as segmentation crack depth and convection severity, were also discussed.

Abstract: Using SiO₂ – Al₂O₃ – B₂O₃ – K₂O – Na₂O system glaze as base material, adding silicon powder or alumina powder with grain size 15μm by the mass percent of 10%, 20%, 30%, respectively, melting properties of glaze were investigated. Slilica solution as binder, the anti-oxidation coating were prepared. Oxidation resistance was determined by coating to the surface of the Al2O3-C specimens. The results show that additives can raise flow temperature prominently, but has little influence on softening point and semi-sphere point; Glazing temperature ranges are obtained with different additive contents; Glazing temperature rises with addition of silicon; Glazing temperature range widens with silicon adding; Glazing temperature ranges were not strictly corresponding with softening temperature point and flow temperature point; But differences were not tremendous; glazing temperature ranges can be estimated from softening temperature point and flow temperature point. Alumina has not prominent influence on glazing temperature, but glaze forms smoothly with alumina, and oxidation resistance was good.

Abstract: The Ni/ZrO2 composite powder was used as raw materials to fabricate the surface infiltrated composite layer on cast steel substrate through vacuum infiltrated casting technology. The microstructure indicated that the infiltrated composite layer included surface composite layer, Ni-based alloying layer and diffusion transition layer. The thickness of diffusion transition layer deceased with the increasing thickness of preform. The surface infiltrated composite layer was composed of ZrO2 ceramic particles, Cr2B and NiB intermetalic compounds as well as Ni-based solid solution. The Ni-based solid solution and Fe-based solid solution was the main composition for diffusion transition layer. The change of micro-hardness of surface infiltrated composite layer presents gradient from surface of infiltrated layer to substrate.

Abstract: Microarc oxidation coatings on biomedical NiTi alloy were prepared in aluminate electrolytes with and without hypophosphate addition. The effect of hypophosphate concentrations on the characteristics of micro-arc oxidation coatings has been studied. The compositions and surface morphologies of the coatings prepared in different hypophosphate concentrations were determined by energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Surface roughness (Ra) and bonding strength of the coatings were measured by surface roughmeter and a direct pull-off test, respectively. The corrosion resistance of the coatings was evaluated in Hank’s solution using potentiodynamic polarization tests. The results show that all of the coatings exhibit a typical porous surface structure and mainly consist of γ-Al2O3 crystal phase. With increasing the hypophosphate concentrations, the elemental contents of Ni, Ti and P increase while Al decreases; the pore sizes and surface roughness of the coatings decrease firstly, reaching a minimum value at 0.01mol/L, and then increase; at the same time, the bonding strength increases up to 60MPa, and then decreases. The corrosion resistance of the coatings decreases with the increase of the hypophosphate concentrations, but all of the coated samples is better than that of the uncoated NiTi alloy.

Abstract: The Ni-based WC alloy coatings were successfully fabricated on NAK80 mold steel by Nd:YAG and CO2 lasers. The microstructure and properties of the laser cladded coatings were analyzed by SEM, EDS, XRD and microhardness tester. The results show that phase constituents of both coatings are mainly composed of tungsten carbide (WC+W2C), Cr23C6, NiCr, CrB2 and γ-Ni. The excellent metallurgical bondings have formed at the interface between the substrate and the laser cladded coatings. Dendrite and white and block WC phase were observed in two kinds of laser cladded coatings, but the dendrite in Nd:YAG laser cladded coating is more fine. The microhardness of NAK80 mold steel is greatly improved by laser cladding, however the microhardness of the CO2 laser cladded coating is even higher than the Nd:YAG laser cladded coating.

Abstract: To improve the AO erosion resistance of siloxane coating, the Si ion implantation with nominal dosage of 7×1016 ions/cm2 in siloxane coatings on the polyimide substrate was carried out by using the plasma immersion ion implanter. The Si implanted siloxane coatings before and after AO exposure in the ground-based AO simulation facility were investigated by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS). The results of mass measurement shown that, in initial stage of AO exposure the implanted sample had a small mass change, and then was stabilized. The erosion yield of the implanted siloxane coating decreased by a factor of more than two orders of magnitude compared with that of the polyimide film, and decreased by a factor of more than an order of magnitude than that of unimplanted siloxane coatings. The results through SEM and XPS indicated that a continuous high-quality protective SiO2 surface layer was formed on the implanted siloxane coatings after the AO exposure. It can prevent further degradation of the underlying polymer with increased exposure to the AO flux and provide high-quality erosion protection for these materials. The Si implanted materials have a markedly increased erosion resistance than unimplanted siloxane coatings in AO environment.