Cavitation erosion under static applied stress and/or alternating stress was studied using steel specimens which were set in close proximity to an oscillating horn in ion-exchanged water. Effect of applied stress on erosion is remarkably large at a suitable cavitation intensity and quite small at either higher or lower cavitation intensity. However, this effect is difficult to determine because the ratio of cavitation intensity to applied stress becomes larger at higher intensity and the cavitation damage is very much smaller at lower intensity. The erosion damage (weight loss and weight loss rate) under static applied stress or alternating stress does not vary in a monotonic fashion, but first decreases to a minimum, then increases to a peak and decreases again with increasing applied stress. Generally, applied stress decreases erosion damage over all stress levels except for given limited levels of applied tensile stress and alternating stress. Erosion damage under applied tensile stress decreases due to the fact that erosion cracks propagate perpendicular to the surface and erosion particles are not easily formed. Under applied compressive stress, erosion cracks are seldom initiated and then propagate diagonally to the surface, resulting in decreased erosion damage. It is found that applied stress increases the erosion damage up to only about 10 percent in the worst case in our experiments.

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A newly designed Ag-AgCl internal reference electrode for high temperature and high pressure use has been constructed. This reference electrode equips the small compartment of porous Al₂O₃ tube in which an Ag-AgCl chip is contained, the filling of porous Al₂O₃ fragments which surrounds the compartment and the flexible electrode body of thin PTEF tube which keeps a 0.1kmol·m^-3 KCl solution. Both the compartment and filling are soaked in the solution. A Nernstian response up to 523K, a good stability at high temperatures and a high durability for repetitive use have been confirmed on the reference electrode.
Using the reference electrode, measurements of anodic polarization curves of Type 304L stainless steel in Na₂SO₄ solutions up to 563K have been performed. Effects of temperature, pH, Na₂SO₄ concentration and scan rate on the polarization curves have been examined.
It was found that the appearance of active, passive and transpassive regions in the polarization curve depended on the condition of measurement: With increasing temperature from 473 to 563K, Na₂SO₄ concentration from 0.001 to 0.5kmol·m^-3 and scan rate from 6.94×10^-6 to 4.17×10^-4V·s^-1, and also with decreasing pH from 8 to 2, the transition from one region to another became distinguishable and the current density for each region became large.

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Short range order (SRO) structure of amorphous “ferric oxyhydroxide gel” was derived from radial distribution function (RDF) applied to its X-ray scattering intensities, I(s). The SRO structure was different from that of any well defined iron-compounds, such as iron oxides or oxyhydroxides. To determine the observed SRO structure, reduced RDF's, G(r)'s, simulated from these compounds, were compared with observed ones. The simulation was executed by use of a structure derived from hydrolytic polymeric condensation of hexaaquoiron (III) complex in which lattice sites were occupied by Fe³⁺ ions with a successive occupation probability for octahedral and tetrahedral sites. Namely, the structure was changed from a NaCl type of deficient structure, Fe³⁺_1-xO, to a modified type of spinel one, γ-Fe₂O₃. Here O^2- sites in the structure are assumed to be equally occupied by O^2- and OH^- ions to reflect chemical constituent of the gel, FeO·OH. From these G(r)'s simulated above it was found that the rapidly dried gel specimen has site's occupation probabilities(%) of AS(tet)=30.0 and BS(oct)=85.0, and those of slowly desiccated one are AS(tet)=80.0 and BS(oct)=60.0, respectively. The structure successfully explains Mössbauer spectrum, magnetic nature and density of the gel. This structure is believed to be also useful to introduce information on “passive films”.

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The automatic crack-tracing apparatus has been developed in cooperation with Shimadzu Corporation and Digital and Control Engineering Co., Ltd.. Such apparatus can trace the propagating crack tip automatically and type out the time, crack length, crack propagation rate and load in the selected time interval.
The crack propagation rate was measured by this apparatus in SCC and fatigue test of SCM 3 steel, 7075 T-6 aluminum alloy and SUS 304 steel.
Such data were found in good agreement with ones measured by the cathetometer and compliance method.

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There are many high temperature corrosion environments in which several different kinds of corrosion proceses occur simultaneously. Therefore, it is key point for selection of resistant material to understand the environmental chemistry, interaction mechanism, and role of alloying elements for each corrosion phenomena. On high temperature corrosion phenomena such as oxidation, sulfidation, carburization, nitriding, halogenation, V₂O₅ and Na₂SO₄ attack, their corrosion mechanisms and effects of alloying elements for each process are briefly described and discussed.

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