Junzo Fujioka

Preparation of PbTiO3 thin films at low temperature by an excimer laser ablation technique

We have formed PbTiO3 thin films on (100) SrTiO3 substrates at a temperature of 350 °C using an ArF excimer laser ablation technique. Until now, PbTiO3 films have not been formed at temperatures lower than 500 °C using other thin‐film techniques. The important points in the present study are the laser excitation of the substrate during the film growth and the lattice matching between the film and the substrate. The film deposited on the SrTiO3 substrate shows preferential orientation of the c‐axis perpendicular to the substrate surface.

Stress and structural properties of diamond-like carbon films deposited by electron beam excited plasma CVD

Abstract Diamond-like carbon (DLC) films prepared using CH 4 or C 6 H 6 with varying deposition parameters by an electron beam excited plasma CVD system were investigated for the internal stress, dynamic hardness and structural properties such as the film density, total, bonded and unbound hydrogen contents, sp 3 ratio and graphite crystallite. From the correlations between internal stress and structural properties, the following conclusions were derived. The fraction of unbound hydrogen to total hydrogen content was the most influential factor for the compressive stress of the DLC films deposited from CH 4 . It is suggested that unbound hydrogen may be trapped into the disordered microstructure of graphite crystallites embedded in the network of film. For the DLC films deposited from C 6 H 6 , it was shown that the compressive stress was correlated with not only the fraction of unbound hydrogen content but also the degree of cross-linking between graphite crystallites in the film.

Tribological characteristics of Si-containing diamond-like carbon films under oil-lubrication

Abstract Tribological behaviors of Si-containing diamond-like carbon (DLC) and DLC films deposited by an electron beam excited plasma (EBEP)–CVD system were investigated for applications to mechanical components. The ball-on-disc tests against bearing steel with oil-lubrication were performed for the Si-containing DLC and the DLC-coated carburized Cr–Mo steel discs. Two different oils with and without zinc dialkyldithiophosphate (Zn-DTP) additives were used as lubricants. The Si-containing DLC films deposited at SiH 4 flow ratios of 2.8 and 12.5% showed low coefficients of friction and wear resistance when lubricated in the oil with additives. The results from X-ray photoelectron spectroscopy (XPS) analysis indicated that it was due to the effect of formation of a boundary lubrication film including ZnO, ZnS, FePO 4 , FeS and FeS 2 compounds on the lubricated contact region.

Diamond-like carbon films deposited by electron beam excited plasma chemical vapor deposition

Abstract An electron beam excited plasma (EBEP) system can produce a high-density plasma by introducing a high-current and low-energy electron beam into a process chamber. Diamond-like carbon (DLC) films prepared by EBEP-CVD systems were investigated for deposition rate, dynamic hardness and microstructure. The substrate bias voltage, substrate position and source gas were varied as the deposition parameters. It was found that when a higher negative bias voltage was applied to the substrate during deposition, the concentration of the sp 3 sites, the size of the graphite crystallite and the total hydrogen content decreased, whereas the density increased. The differences in the substrate position and source gas strongly affected the microstructural properties of the deposited DLC films.

Mechanical properties of heat-resistant alloys exposed to air and HTGR helium at high temperatures

The effect of a corroded surface layer on the tensile properties and the high-temperature low-cycle fatigue life was studied on Hastelloy-X and on Incoloy alloys 800 and 800H by comparing the properties between specimens exposed to air and high-temperature gas-cooled reactor helium at 1000/sup 0/C prior to testing and specimens aged under the same temperature/time conditions as those of exposed specimens. The ratio of the corroded surface layer to the total cross-sectional area was controlled at 1000/sup 0/C by environment, exposure time, and shape/size combinations of specimens. Tensile strength could be quantitatively expressed in terms of the intergranular oxidation, irrespective of the variation of materials and corrosive conditions. By comparing the low-cycle fatigue lives at 1000/sup 0/C between exposed and aged materials, it was clarified that lifetime was remarkably reduced by the formation of a corroded surface layer. However, fatigue life of aged material was less than that of solution-treated materials. These two opposing effects of corrosion and aging brought about a small difference in fatigue life between solution-treated and exposed materials.

Gas-pressure Combustion Sintering of (MoSi2-SiC)/TiA1 Functionally Gradient Material (PGM) and its Residual Stress Analysis

Functionally Gradient Materials(FGMs) are expected to be applied, as advanced thermal barrier coating systems, to active cooling structures for air-frames and engines of hypersonic spaceplanes. In this paper, fabrication of (MoSi2-SiC)/TiA1 FGMs by the Gas-pressure Combustion Sintering is described and properties of the FGMs are discussed. Compositional distribution in the FGM was one of the most important determinants of residual thermal stress of an FGM, especially for radial stress on the MoSi2-SiC surface. Residual stress after fabrication was examined by thermal stress analysis, and experimental results were compared with analytical results. Static thermal stress in actual high-temperature environments was also examined analytically, and it was considered to be less critical than residual thermal stress after fabrication.

Epitaxial Growth of Thin Films of Ferroelectric Materials at Low Temperature by Excimer Laser Ablation Technique

We have formed PbTIO thin films on SrTiO 3 substrate (100) at low temperature of 350°C using an ArF excimer laser ablation technique. Until now, the PbTiO 3 films have not been formed at the temperature lower than 500°C using other thin film techniques. The Important points In the present study are the laser excitation of the substrate during the film growth and the lattice matching between the film and the substrate. The film deposited on the SrTiO 3 substrate, shows preferential orientation of the c-axis perpendicular to the substrate surface.

Thermal Expansion of C/C Composites with Modified Carbon Matrix

Carbon matrix of C/C composites were modified for the relaxation of thermal stresses between C/C composites and ceramic coatings. Porous C/C composites with various amounts of carbon matrix and porosity were prepared. Liquid silicon was impregnated into porous C/C composites and reacted chemically with carbon matrix to form silicon carbide. Thermal expansion of C/C composites could be controlled between 1.7 to 3.5×10-6/°C by altering the amount of silicon carbide in the matrix.