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Nickel based superalloys have been applied to gas turbine and aircraft jet engine parts due to superior high temperature strength and corrosion resistance. However, casting defect such as solidification cracking often occurs. In order to increase productivity of precision casting and various shape casting processes, predicting the occurrence of solidification cracking by using CAE(Computer Aided Engineering) should be essential. Therefore, it is necessary to obtain mechanical properties in the state of solid liquid coexistence. In this study, we try to get high temperature (around solidus temperature) mechanical properties of the nickel based superalloy such as Inconel 718 by using originally developed tensile test. In the previous reports, flat distribution of temperature in the gage length, and crack initiation strain were not ensured. On the other, the developed device ensured within 3°C of the temperature distribution in the gage length as to the Inconel 718. Tensile strain was measured by using in situ observation of marker on the surface of the specimen. As a result, Stress Strain curve, crack initiation stress, and crack initiation strain of Inconel 718 were obtained.

The effect of sulphate reducing bacteria on corrosion and cathodic protection of a steel has been studied in silt obtained from the bottom of Sumida River and in an inoculated midium consisted of peptone, yeast extract, MgSO4, Na2SO4, NaCI, lactic acid and water. Sulphate reducing bacteria accelerates corrosion by depolarizing cathodic reaction. The film formed on the steel surface through reaction with hydrogen sulphide, a metabolic product of the bacteria, is essentially protective but it tends to break down locally to form galvanic cells which accelerate corrosion. The critical potential for complete cathodic protection of the steel is -0.9 V (SCE) which is approximately 0.1 V more negative than the ordinary protection potential in the absence of the bacteria.

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