Materials Science Forum Vols. 654-656

Abstract: In this study, an SMR-based filter was fabricated by dc/rf magnetron sputtering and photolithography, and a thermal annealing treatment was adopted to improve the frequency response. The SMR-based filter is composed of a ZnO piezoelectric thin film onto SiO2/W Bragg reflector. ZnO thin films were prepared by two-step sputtering with various deposition temperatures to obtain good piezoelectric properties. ZnO layers deposited at the temperature of 200 °C exhibit a highly c-axis preferred orientation, good crystalline characteristics and low surface roughness. The filter is thermal treated by a rapid thermal annealing (RTA) technique. The thermal annealing treatment has improved the film properties of ZnO layers, resulting in a higher c-axis preferred orientation and a lower surface roughness of ZnO films than those of as-deposited ZnO films. The atomic ratio of Zn to O in ZnO film approaches one at the annealing temperature of 400 °C, which results in a comparatively oxidized stoichiometric ZnO film. Finally, the frequency response of the annealed filter is improved, and a lower insertion loss is obtained.

Abstract: Ba0.6Sr0.4TiO3 (BST)/MgTiO3 (MT)/ Ba0.6Sr0.4TiO3 multilayer thin films were deposited on LaNiO3 (100)/Pt/Ti/SiO2/Si (100) substrates by pulsed laser deposition. It was found that the film orientation and dielectric properties of BST/MT/BST multilayer thin films are strongly dependent on MT interlayer thickness. Pure BST thin film exhibits a (100) preferred orientation, while BST thin films with a MT interlayer exhibit a random orientation. Residual stress is relaxed dramatically due to a closer match of thermal expansion coefficients between the BST and MT interlayers. The largest figure of merit of 18.7 is achieved in the multilayer thin film with a 50-nm-thick MT interlayer, which exhibits a tunability of 30% and a lost tangent of 0.016. Dielectric constant and loss tangent decrease with increasing MT interlayer thickness due to a series dielectric dilution effect.

Abstract: Nanocontacts Magneto-Resistive (NCMR) Spin-Valve devices using NOL (Nano-Oxide Layer) have been reported to show some kind of a new MR effect. If the NC resistivity nears to the bulk's value without limit, the NC resistance will be almost dominated by the sharvin resistance at the NC with 1 to 2nm size, which conductance regime dominates the NC resistance of our NCMR attract much interest for understanding MR mechanism of our NCMR, where the NC size is certainly just 1 to 2nm but the NC resistivity is still unknown. So, in this study we constructed the home-made circuit for directly measuring each conductive channel-current through each nano-contact with in-situ conducting AFM and tried to evaluate quantitatively the resistivity of each single NC in the NOL.

Abstract: High current pulsed electron beam has been developing as a useful tool for surface modification of materials. This paper presents our research on the surface treatment of 316L stainless steel with an equipment of working parameters as electron energy 20-30keV, pulse duration 1.5µs and energy density ~6J/cm2. The surface microstructure was characterized with metallography, X-ray diffractometry and electron backscatter diffraction (EBSD) techniques. It was found that the modified samples showed significant improvement on corrosion resistance when using increased pulse number and higher energy density. This result is discussed in relation to the coupled temperature-stress fields formed after the absorption of electron beam energy.

Abstract: High current pulsed electron beam is an effective technique for surface sealing of ceramic thermal barrier coatings prepared by electron beam physical vapor deposition. Due to the rapid remelting and solidification, the outer layers of ceramic coatings become smooth and dense, and the protective performance for turbine blades is effectively improved. Because of the complex multi-layered structures in the coatings, a high-current pulsed electron beam treatment requires specific parameter inputs which are related to the temperature field induced by electron energy deposition in the coatings. In this paper, a two-dimensional temperature simulation was performed to demonstrate the melting depth and temperature evolution in ceramic coatings treated by high-current pulsed electron beam. Different energy densities and pulses were studied and discussed for obtaining optimized parameters.

Abstract: The effect of a modified layer caused by pre-deforming on the low temperature plasma nitriding of AISI 304 austenitic stainless steel was investigated. The aim of using the deformed layer is to produce a thicker nitrided layer and to decrease the nitriding temperature due to the much faster diffusion of nitrogen. The pre-deformed sample was prepared by the rolling in 0, 1, 2, 3, and 4% ratios. Plasma nitriding was carried out at 673 and 723 K for 18 ks under 600 Pa pressures in presence of N2/H2 in 50:50 ratio. The microhardness, thickness and phase composition of nitrided layers formed on the surface of pre-deformed and non-deformed samples were investigated using Vickers microhardness tester, optical microscope and X-ray diffraction techniques, respectively. After nitriding, maximum hardness ~1150 HV was achieved on the pre-deformed sample. XRD pattern showed that most dominant phase of the nitrided layer consisted of the expanded austenite (S phase). In addition, the pre-deforming by rolling had a significant influence on the hardness and thickness of the S phase. That is, the hardness and thickness of the S phase were increased by applying the pre-deformation.

Abstract: Inorganic protective silica film was tried on the surface of stainless steel using a sol-gel chemical route where tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES) were used. In the coating solution silica nanoparticles with different sizes were mixed. Then the film was deposited on the stainless steel substrate. It was intended that by mixing the small and the large particles at the same time a sufficient consolidation of the film was possible because of the high surface activity of the small nanoparticles and a modest silica film would be obtained with a low temperature heat treatment at as low as 200 °C. The prepared film showed enhanced adhesion when compared with a silica film without nanoparticle additions. The films also showed improved protect-ability against corrosion. Scanning electron microscopy (SEM), scratch test, potentiodynamic polarization scan and electrochemical impedance analysis were also used to characterize the films.

Abstract: The No. 1 continuous coil coating line of Dongbu Steel produces 70,000 tons of commercial quality products annually, and the pre-coated metal (PCM) products are widely used for a home appliances or building materials. The lines are consisted of pre-treatment, painting, curing and tension levelling processes. The typical curing methods are injection of hot air, infrared rays, electron beam, or induction heated oven. Peak metal temperature (PMT) is the vital factor that determines the product quality. The curing oven of No. 1 continuous coil coating line revamped from injection of hot air to infrared rays type and operated from 2007. A PMT setup model was developed for control the strip temperature, and applied in site, and systemized. The operation results showed that the accuracy of the setup model achieved above 96% consistently.

Abstract: The separator is one of the most important parts in PEM fuel cells. Stainless steels are widely used as separator for its good mechanical properties and mass production. However, for a good chemical compatibility, stainless steels need to have high chromium content or surface treatment, which makes separator high cost. Low cost of separator is important for commercial use. In this study, conventional low carbon steel is used as base metal of separator. Low carbon steel is low at cost, but has poor chemical properties for separator. For a good corrosion resistance, low carbon steel needs to be surface treated. To make a uniform surface treated layer on low carbon steel, chromium is conventionally electroplated on the steel and thermally nitrided. Surface treated low carbon steel is investigated using microstructure and element analysis tools. Interfacial contact resistance and polarization test is applied for the properties of fuel cell separator. The results show that chromium nitrided layer uniformly formed on low carbon steel. And the surface treated steel showed a good corrosion resistance as a separator.

Abstract: Aeronautic gas turbine blades, vanes and combustion chambers are protected against high temperature oxidation and corrosion by single or multilayered coatings. These include environmental coatings, generally based on Pt-modified Ni aluminides or MCrAlY overlays (where M = Ni and/or Co), thermal barrier coating (TBC) systems including a ceramic thermally insulating layer, and abradable seals. The present work shows the ability of the Spark Plasma Sintering technique to rapidly develop new coatings compositions and microstructures. This technique allows combining powders and metallic foils on a superalloy substrate in order to obtain multilayered coatings in a single short production step. Fabrication of MCrAlY overlays with local Pt and/or Al enrichments is shown, as well as fabrication of coatings made of -PtAl2, -PtAl, α-AlNiPt2, martensitic and (Ni,Pt)Al or Pt-rich ’ phases, including their doping with reactive elements. The fabrication of a complete TBC system with a porous and adherent Yttria Stabilized Zirconia (YSZ) layer on a bond-coating is also demonstrated, as well as the fabrication of a CoNiCrAlY-based cermet coating for abradable seal application. Difficulties of fabrication are reviewed, such as Y segregation, risks of carburization, local over-heating, or difficulty to coat complex shaped parts. Solutions are given to overcome these difficulties.