Non-contact characterization of the modified surface layer was attempted by the quantitative analysis of the laser surface acoustic wave (SAW). Velocity and attenuation dispersion of the Rayleigh and Lamb waves were obtained by the novel laser SAW system, and used to estimate the thickness, elastic properties, density (purity) and further the bond quality and structure of the surface film. This paper introduces two laser SAW systems developed, sophisticated signal processing to obtain the velocity dispersion, and application to characterize the electro-plated silver layer, diffusion bonded metallic laminate, vapor deposited ceramic layer and porous silicon.
The formation mechanism of ferric oxide hydroxides, α-, β- and γ-FeOOH, is described in view of evolution of colloidal particles in aqueous solutions. The surface characterization of FeOOH particles by IR spectroscopy is cited. Finally, the adsorption interaction of H2O, SO2 and NO with the particles is explained based on their surface structures.
The effects of fluoride ion on the crevice corrosion for a FPM/metal of a type 304 stainless steel were studied in terms of repassivation potential (ER) measurements in neutral NaCl/NaF mixed solutions at 303K. It was found that the ER values shifted to the noble direction by presence of F-, sufficient concentrations of which promoted uniform dissolution of the nobly polarized stainless steel. There was a good correlation between ER and Vcrev.
The corrosion behavior of SS 400 (mild steel) was investigated in one component system of pure organic solvents (acetic acid, ethanol, diethylamine and acetone) and multi-component system of organic solutions containing additive agents (water, lithium perchlorate, sulfuric acid and nitric acid) by the corrosion weight loss tests, electrochemical measurements and surface analyses. From these results, the corrosion of mild steel was remarkably promoted by sulfuric acid and nitric acid in organic solutions. The corrosion rate increased in strong basic solvent (ethanol), and decreased in weak basic solvent (acetic acid) by addition of sulfuric acid. The passive state region was observed in wide potential range on anodic polarization curves, and the rest potential existed in passive state region in non-corrosion systems. In a.c. impedance measurements, the charge transfer process was observed in remarkable corrosion systems, and the film resistance of passive state was increased in non-corrosion systems. In surface analysis by XPS, the salt film of acetate on steel surface was observed in acetic acid of corrosion system, while the passive film made up by adsorption of solvent molecules and the oxides was observed in ethanol or acetone of non-corrosion systems.
A technical approach by an acoustic impact method was discussed for non-destructive evaluation of defects on materials. Non-contacted detector is attractive in many areas of non-destructive evaluation, and empirically used in industries. A fast Fourier transform frequency analysis enables to evaluate the vibrational damping of the specimen, and to detect the change in frequency due to a defect such as a crack. The detective frequency is generally audible and depends on ability of auditory sense in many cases. In this paper a frequency spectrum analysis at relatively high frequency has been fundamentally conducted with a square plate of brass and stainless steel specimens. Artificial cracks and holes were put on a given portion of the specimens in order to investigate acoustic response. The change in intensity and frequency of the spectrum caused by a small defect was remarkably appeared in a range of high frequency, and proved the validity of this type of acoustic impact method. A theoretical approach was discussed for the frequency spectrum obtained for the brass specimen.
Experimental testing of water-repellent materials under water-dipping conditions showed that a coating with less than 60% added polytetrafluoroethylene (PTFE) particles is deteriorated of its water repellency while one with more than 80% added PTFE particles is not. It is probably because of the differences in the surface structures of coatings. And, by controlling the dispersion of PTFE particles in the coating by the addition of perfluoroalkyl oxide, deterioration of coating water repellency is prevented.
Although TiAl has a great potential as future high temperature materials because of a good strength-to-weight ratio even at high temperature, it is not highly resistive against oxidation at high temperature. The oxidation behavior of Ti-Al intermetallic compounds (Ti-34%Al and Ti-37%Al) has been studied at 1173K and 1273K in Ar-20%O2 and in N2-20%O2 under atmospheric pressure. The microstructures of the specimens were controlled by heat treatment and/or isothermal forging. Mass gain of TiAl by oxidation in Ar-20% O2 was much smaller than that in N2-20%O2 in all cases. XPS analysis also showed the remarkable influence of nitrogen on the structure and composition of oxide layers. Titanium nitride was formed at the interface between oxidized surface and substrate at the initial stage of oxidation under N2-20%O2 atmosphere, resulted in the suppression of the formation of the continuous Al2O3 layer. Therefore, the oxidation of TiAl in N2-20%O2 was accelerated compared with that in Ar-20%O2. A model of the oxide layer growth is proposed to explain the role of nitrogen in the oxidation process.