Key Engineering Materials Vols. 317-318

Abstract: The adhesive and wear properties of ITO thin film have been investigated using the scratch and wear tests. ITO thin film was fabricated on glass substrate using RF magnetron sputter and strip lines were formed by selective etching. In the scratch test, the normal load on WC micro-blade was increased and kept constant as it was drawn over the films. In the wear test, sapphire, SUS and WC balls slided repeatedly on the films with the constant normal load. During the scratch and wear, the ESR and the acoustic signal were monitored and recorded. In order to study the adhesive and wear properties of ITO thin films, it was desirable to use the ESR rather than the acoustic signal. From the change in the ESR, it was possible to measure the critical load to cut through ITO film completely and the critical number of sliding to wear ITO film completely.

Abstract: The TiN/DLC nanocomposite coatings were grown on Si wafers using Ar/CH4/TDMAT (Ti[(CH3)2N]4N2) gas mixtures by r.f. plasma enhanced chemical vapor deposition. The sliding friction tests were carried out using a ball-on-flat type tribometer. The different test parameters such as applied loads, counterpart materials and environment were applied to understand the tribological behavior in terms of friction and wear. The coatings provided a low friction coefficient and high wear resistance depending on the friction test conditions.

Abstract: The corrosion rate (Cr) of commercially available ball bearings made of silicon nitride (Si3N4) of high degree (HD) and standard quality (S) was measured at hydrothermal conditions in different aqueous concentrations of sulphuric acid (H2SO4) and sodium hydroxide (NaOH). The Cr magnitude for the materials diminished when increasing the acid concentration. At higher concentrations of H2SO4 (98%) the formation of SiO2 on the surface of the balls inhibited the progress of corrosion. The corrosion rate of the materials was increased when the sodium hydroxide solution concentration was increased. The surface of the materials was analyzed by means of scanning electron microscopy (SEM), while the corrosion rate was determined based on weight losses.

Abstract: In order to improve the durability of Pt coated Ti electrodes as an anode of the sulfuric acid system electrolysis, tantalum oxide (Ta2O5) additions have been used widely. However that is not enough for uses under severe conditions. In this study,
boric acid (H3BO3) was added into the Pt coating during manufacturing process of Ti/Pt-coated electrodes, and the (Pt + B2O3)/Ti electrodes were obtained. The effect of H3BO3 addition on the microstructure, surface area, and lifetime of (Pt + B2O3)/Ti electrodes was also investigated in detail. Commercially available titanium plates (10
10
0.5mm) were employed for prepare Ti/ (Pt + B2O3) electrodes, where it was confirmed by XRD that B2O3 formed by heating the boric acid was amorphous in the temperature range of 250 to 550. The coating solution of 2 μl of H2PtCl66H2O (Pt:50 g/l) dissolved in butanol and 5~20 mass% H3BO3 mixture was spread over the etched Ti plates. After drying at 70 for 30 min, the substances were heated at 250 to 550 for 10 min. The lifetime of the electrodes was examined by a direct current of 1 A using Pt plate as the counter electrode in 1 M H2SO4 solution at 40. The end of life was determined as the time when the cell voltage changed 2 times of the beginning.

Abstract: In this study, the effect of composition of intergranular glass on superplastic compressive deformation of
-Si3N4 has been studied by compression tests. Oxide additives were used to form Y2O3-Al2O3-SiO2 melt and, with increasing temperatures, an oxynitride melt (Y-Al-Si-O-N) by dissolving Si3N4. The relation between flow stress and glass composition qualitatively corresponded to the effect of chemical composition on viscosity of Y2O3-Al2O3-SiO2 glass. However, the rate of increase of the flow stress was not proportional to the viscosity of Y2O3-Al2O3-SiO2 glass, probably because the composition of intergranular glass phase had changed by dissolving Si3N4 and by crystallization of Si2N2O.

Abstract: High-strain-rate superplasticity and low-temperature superplasticity are favorable for making the use of superplastic forming for engineering ceramics even more wide spread. In this study, a silicon nitride based nanocomposite was developed for the purpose of improving the superplasticity. An amorphous powder was prepared by mechanical alloying of silicon nitride and metal titanium. A Si3N4-Si2N2O-TiN nanocomposite was fabricated by hot isostatically pressing the amorphous powder compact. A compression test was performed in the temperature range of 1573 K to 1873 K. The nanocomposite could be deformed at a strain rate of 10-2s-1, which was more than 100 times faster than that available for conventional superplastic Si3N4 at 1873 K. Furthermore, the nanocomposite was superplastically deformed in compression at low temperatures from 1573 K to 1673 K. The stress exponent and the activation energy of the nanocomposite were close to those of submicron-silicon nitride.

Abstract: Superplastic behaviors were investigated for fine-grained yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) from a viewpoint of GeO2 or TiO2 doping. It was found that both dopants enhance the ductility in TZP. In particular, elongation to failure of 988% could be obtained in 3Y-TZP co-doped with 2mol%GeO2 and 2mol%TiO2. In addition, it was revealed that lower flow stress did not always give a larger elongation in this system. On the other hand, the strong segregation of dopants along grain boundaries was confirmed by high-resolution electron transmission microscopy study (HRTEM) with X-ray energy dispersive spectrometer (EDS). The unique phenomena observed in the relation between flow stress and ductility is closely related to the strong segregation of dopants along grain boundaries in this system. The grain size at fracture is determined by covalency because of the dopant segregation. It could be concluded that elongation to failure is closely related to a balance between grain size at fracture and grain growth rate during deformation.

Abstract: Using the ab initio pseudopotential calculations, the surface diffusion and incorporation process at the interface of Fe-Al multilayer system were quantitatively investigated. The hollow site was most stable adsorption site on both Al (001) and Fe (001) surface. The adsorption energies were 8.62 eV for Fe/Al (001) and 5.30 eV for Al/Fe (001) system. The calculated energy barriers for the surface diffusion of adatom were 0.89 eV and 0.61 eV for each system. The energy barrier for the incorporation of Fe adatom into the Al substrate was calculated to be 0.38 eV and the energy gain of the system was 0.49 eV. However, the Al adatom required relatively large energy barrier, 0.99 eV for the incorporation into the Fe substrate resulting in 0.13 eV increase in total energy of the system.

Abstract: Grain boundary diffusion coefficients of oxygen (δDgb) at 1793K in high purity α-alumina bicrystals with Σ7{2 _ ,310}/[0001] and Σ31{7 _ ,1140}/[0001] symmetric tilt grain boundaries were measured by means of the isotopic exchange and diffusion depth profiling using SIMS. δDgb of both grain boundaries were determined to be 7.1x10-24 [m3/sec] for Σ7 grain boundary and 5.3 x10-24 [m3/sec] for Σ31 grain boundary, respectively. These results indicate that Σ values do not directly relate to grain boundary diffusion properties.

Abstract: Oxynitirde glasses are found at triple point junctions and as intergranular films in silicon nitride based ceramics. The glass chemistry, particularly the content of modifyer,usually Y or a rare earth (RE) ion, and the volume fractions of these oxynitride glass phases within the ceramic control the properties of silicon nitride, in particular, creep at high temperature. It is known that, as nitrogen substitutes for oxygen in silicate and aluminosilicate glass networks, increases are observed in glass transition and softening temperatures, viscosities (by two to three orders of magnitude), elastic moduli and microhardness. If changes are made to the RE:Si:Al ratios or different rare earth cation are substituted, properties such as viscosity can be increased by a further two to three orders of magnitude. These effects have implications for the high temperature properties of silicon nitride based ceramics, especially creep resistance. This paper provides an overview of oxynitride glasses and outlines the effect of composition on properties such as glass transition temperature and viscosity and discusses the effects on high temperature behaviour of silicon nitride ceramics.