The corrosion behavior of amorphous Ni-15Cr-Ta-17P and Ni-38Cr-20Mo-10P alloys in a 63% P₂O₅ (87% H₃PO₄) solution at 433K was investigated. The corrosion rate of the Ni-15Cr-3Ta-17P alloy was about 0.109gh^-1m^-2 which was one order of magnitude as high as that of the crystalline tantalum metal. The surface film was composed of a high concentration of phosphate and the significant deficiency of nickel took place in both the surface film and the underlying alloy surface. The amorphous Ni-38Cr-24Mo-10P alloy passivated spontaneously and its corrosion rate was about 0.040gh^-1m^-2. The passive film on the spontaneously passive alloy consisted mainly of hydrated oxyhydroxide of chromium and molybdenum, and the composition of the underlying alloy surface was not greatly different from the bulk alloy composition.

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Plasma CVD of molybdenum from Mo(CO)₆ is tried on several substrates for protective coating. The film deposited is metallic Mo containing carbon and has an amorphous or a semiamorphous structure. The effect of carrier gas, substrate temperature, pressure of plasma reactor, supply rate of Mo(CO)₆, glow discharge current and AC frequency on growth of Mo(C) films is studied. It is concluded that (1) H₂ gas is more favorable for a carrier gas of Mo(CO)₆ than inert He gas because the former suppresses the formation of powdery molybdenum oxide, (2) increase in substrate temperature brings about high deposition rate but this effect is not so large below 200°C, (3) lower pressure of plasma reactor is favorable for higher deposition rate so long as stable glow discharge is possible, (4) deposition rate is dependent on AC frequency as well as discharge current, and (5) larger discharge current brings about higher deposition rate but excessive increase in current, compared to the supply rate of Mo(CO)₆, is ineffective. The protectiveness of the plasma CVDed substrate in iodine atmosphere is good when copper is selected as the substrate.

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The stress corrosion cracking of SUS 310 austenitic stainless steel in hydrochloric acid as functions of stress and temperature, and SUS 430 ferritic stainless steel in acidic chloride/sulfate solutions as a function of stress has been investigated using constant load method. Three parameters (t_f, ε_ss, and t_ss) obtained from corrosion creep curve as a function of stress are divided into three regions for both steels, stress, SCC and corrosion regions, respectively. In SCC region, the ratio of t_ss (transition time) to t_f (time to failure) holds constant with the value of 0.57±0.02 irrespective of material, stress, anion species and temperature. The logarithmic relationship between ε_ss (steady state creep rate) and t_f shows the linear function for both steels regardless of stress, anion species and temperature, which implies that ε_ss becomes the parameter for prediction of t_f as well as in the case of SUS 304 and SUS 316 already reported. However, the slope of logε_ss-logt_f equation obtained as a function of stress is smaller for SUS 430 than for SUS 310. In addition, the critical temperature (T_cri) for SUS 310 is estimated as T_cri≈289K, on the basis of the fact that ε_ss becomes also a parameter for assessment of SCC susceptibility. A mechanism of SCC for SUS 430 and SUS 310 is qualitatively discussed and is found to be basically in agreement with that for SUS 304 and SUS 316.

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Corrosion fatigue crack growth behavior of HT 80 steel was studied in synthetic sea water under various frequencies and potentials for the purpose of corrosion fatigue life prediction. In general, the slower the load frequency was, the faster the crack growth rate was. When ΔK<5MPam^1/2 or ΔK>20MPam^1/2, crack growth curves under various frequencies were parallel to each other, but when 5MPam^1/2<ΔK<20MPam^1/2, the acceleration of the crack growth rate cased by intergranular cracking was observed on the parent metal but not on the weld metal. The crack growth rate at 0.3Hz was minimum at potential of -0.7V (Ag/AgCl) in all tested ΔK regions. There was a good correlation between the acceleration rate of the crack growth and the transition rate from the bare metal to the steady-state metal. The corrosion fatigue life was estimated by using the crack growth curves and the theoretical curve well fitted to the experimental data. From this, it is proved that the corrosion fatigue life can be predicted if the crack growth properties at low ΔK regions is understood properly.

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Analytical results of the questionnaire on External Stress Corrosion Cracking (ESCC) of austenitic stainless steel equipments and pipe lines in Japan is introduced. Analyses of 110 cases shows that ESCC in the absence of thermal insulation is becoming a new characteristic feature. This technical reports reveals the following key parameters associated with wide spread ESCC in Japan: 1) Types of materials and their structure susceptible to ESCC, 2) temperature range of ESCC susceptibility, 3) chloride ion concentration and it sources. Countermeasure to ESCC in the absence of insulation or underneath thermal insulation, and future problems are also discussed.

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Fundamental problems of fretting wear was reviewed in the recent studies. Topics listed below were taken mainly from the research being conducted in the author's laboratory. (1) Direct observation and fundamental behaviour of fretting phenomena. (2) Theoretical analysis of fretting wear. (3) Direct observation of wear debris and the mechanism to initiate wear. (4) Effect of stiffness of the apparatus on fretting wear. (5) Relation between dissipation energy and fretting wear. (6) Fretting wear of ceramics and wear-resistant materials.

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