Abstract: The insitu-fabrication of TiCN ceramic coating by laser cladding-laser nitriding technique (LC-LN) was investigated. Pulsed YAG laser with the power of 500W was used as radiation source. Highly pure N2 was selected as the nitriding element; Titanium powder whose size is 20 m and the pure carbon powder were utilized as the coating materials. The influence of technology parameters such as pulse width, pulse frequency and scanning speed etc. on the insitu-formation of TiCN ceramic coating was studied. XRD results show that the main phases of the coating are TiC0.3N0.7 (or TiC0.2N0.8),TiN and TiN0.3. It was revealed that the appropriate process parameters for insitu-fabrication are the pulse frequency 15 Hz, pulse width 3.0ms, the scanning speed in the range of 9cm/min to 12cm/min, the pressure of N2 0.4MPa. The result of OM showed a metallurgical bonding without crack and bubble between the coating and the substrate was obtained. The microstructure of cladded coating is characterized by fine dentrites. The average microhardness in the coating is more than 1300HV which is about 4 times of that in the substrate.
Abstract: In order to improve the oxidation resistance of carbon/carbon (C/C) composites, a nano-SiC (SiCn) coating for SiC pre-coated C/C was prepared by a hydrothermal electrophoretic deposition process. The phase compositions, surface and cross-section microstructures of the SiCn coatings deposited at different voltages were investigated. XRD and SEM analyses show that SiCn outer layer without penetrative holes and cracks can be achieved at the deposition voltage range from 120 V to 210 V. The thickness and density of the SiCn coatings improve with the increase of deposition voltage. The multi-layer coatings deposited at 210 V can effectively protect C/C composites from oxidation in air at 1773 K for 202 h with a weight loss of 0.79%.
Abstract: Cristobalite aluminum phosphate (C-AlPO4) coatings were prepared by hydrothermal electrophoretic process on SiC coated C/C composites at different temperatures. The as-prepared C-AlPO4 coatings was characterized by SEM analyses. The influence of hydrothermal deposition temperature on the microstructures of the as-prepared coatings and the deposition kinetics mechanism were investigated. Results show that dense and homogeneous C-AlPO4 coatings on SiC coated C/C composites can be achieved at 373K and 220V deposition voltage; Kinetics investigations show that the deposition process of the C-AlPO4 coatings on SiC coated C/C composite is controlled by the diffusion rate of the charged C-AlPO4 particles to the cathode; the deposition rate increases with the increase of hydrothermal temperature. The diffusion equation and the kinetic expression of coating process follow the Fick’s second law and Ahrennius relationship. The deposition activation energy of the C-AlPO4 coatings fabricated by the hydrothermal electrophoretic process is calculated to be 21.88kJ/mol.
Abstract: Binary microstructures at both micro- and nano-scale are constructed by the electrochemical depositing Ni and TiO2 on the stainless steel surface. Superhydrophobicity is achieved with a water contact angle greater than 150° after modifying the textured surface with fluoroalkylsilane (FAS-17, CF3(CF2)7CH2CH2Si(OCH3)3). The morphology of the Ni-TiO2 compound coating is studied by scanning electron microscopy.
Abstract: Silicon carbide is one of the best materials for satellite mirror and chemical vapor deposition (CVD) is an effective method of preparing SiC whiskers and films. In this paper, SiC whiskers or films were deposited on substrates of RB-SiC in an upright chemical vapor deposition furnace of Φ150mm × 450 mm with methyltrichloride silicane (MTS) as precursor gas and H2 as carrier gas under dilute gases of different H2/Ar ratio and different deposition temperature between 1050°C and 1150°C. The morphology and composition of the CVD-SiC grown on RB-SiC substrate were determined by scanning electron microscope (SEM) and X-ray diffraction (XRD) respectively. As a result, whisker-like, worm-like or ball-like SiC can be respectively obtained dependent on different deposition conditions such as H2/Ar ratio and deposition temperature, and the composition of the productions are determined as β-SiC by XRD. Furthermore, the deposition mechanisms of different morphologies of SiC are introduced.
Abstract: Hydroxyapatite/Chitosan (HAp/CS) bio-coatings were prepared on the surface of carbon/ carbon (C/C) composites by hydrothermal electrophoretic deposition, using sonochemical process resulted HAp nanoparticles, isopropyl alcohol and chitosan as raw materials. The influences of hydro- thermal conditions and deposition voltage on the microstructures and morphologies of the as-prepared coatings were investigated. It was shown that homogenous and dense HAp/CS coatings on C/C composites are obtained by hydrothermal electrophoretic deposition. With the increase of deposition voltage, density and homogeneity of the as-prepared HAp/CS composite coatings are well improved. Due to the growth of HAp nanoparticles in the hydrothermal condition, the subsequent heat treatment of the HAp/CS coatings is not needed.
Abstract: W-TiO2 (W, tungsten) dual-layer thin films are deposited by RF magnetron sputtering onto glass substrates and annealed at 150oC~400oC for 4hrs. The crystal structure, morphology, and trans- mittance of annealed W-TiO2 dual-layer thin films are investigated by X-ray diffraction, FESEM, and UV-Vis spectrometer, respectively. The annealing temperatures have large effect on the properties of W-TiO2 dual-layer thin films. The band gap energy values of W-TiO2 dual-layer thin films are evaluated from (h)1/2 versus energy plots. The energy gap for un-annealed W-TiO2 dual-layer thin film is 3.16 eV. As the annealing temperature increases from 150oC to 400oC, the energy gap decreases from 3.16 eV to 3.10 eV.
Abstract: The palladium membrane has been developed for high temperature separation of hydrogen from other syngas molecules. In this study, tubular α-alumina substrate was used as a support for increase mechanical strength for thin palladium membrane. Prior depositing of palladium film, a dip-coating of palladium nuclei was performed to cover the substrate. Afterward, surface of activated support was modified with a thin intermediate layer for improving adhesion between support and Pd membrane. Electroless plating of dense palladium membrane was achieved from the plating bath containing EDTA stabilized palladium complex and hydrazine. The microstructural characteristics of palladium membranes were analyzed.
Abstract: This work aimed to investigate the effect of different sintering routes on properties of Ni-Al2O3 membrane. Alumina powder was mixed with 10 wt% nickel powder by dried ball-milling. Then, the mixture powder was uniaxially pressed to a bar shape and sintered via different sintering conditions. First route, the Ni-Al2O3 specimen was sintered at 1300°C for 2 h under air and then reduced at 900°C for 2 h under H2 atmosphere. Second route, the specimen was sintered at 1300°C for 2 h under argon. After sintering process, the physical and mechanical properties of membrane obtained from two routes were compared and discussed.
Abstract: Tape casting was used for the preparation of Mg-Cu systems density graded materials. A series of tapes with uniform compositions ranging from 100wt% Cu to 100wt% Mg were fabricated with sufficient strength to be handled during the post-processing stage. The effect of the tape casting process parameters on the properties of the tape were studied, such as the composition of the Mg-Cu and the solid loading. The rheology of the slurry of different Mg-Cu composition for tape casting was characterized by viscosity. The tapes characterized by microstructure, thickness and bulk density were outlined. The results demonstrated that the different Mg-Cu composition slurry with well-dispersed, high stability, certain solid loading from 45 ~70 wt% were obtained. The viscosity of the slurry and the density of the green tapes were increased with the increasing of the content of Mg. The thickness of tapes of compositions ranging from 100wt% Cu to 100wt% Mg with certain strength could be achieved 68-110μm and the density of the tapes was 0.74-2.42g/cm3. For 100wt% Cu tapes, when the solid loading was 68wt%, the high density tape was produced. The tapes with different thickness, density and different Mg-Cu compositions were obtained.