高温純水中腐食疲労破面

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Fractography is a very useful method to examine the fracture history of a failed element,. But in many cases the fracture surface has been scaled in the working environment or corroded before prepairing to observe. Therefore, the fracture surface must be often cleaned before the ovservation. In this report the fracture surface which had been scaled duringlow cycle fatigue testing at 288℃ in pure water was examined. In order to strip off the surface scales, the following five methods were employed; (1) ultrasonic vibration in 3% HCl solution, (2) ultrasonic vibration in 5% diammonium hydrogen citrate solution, (3) ultrasonic vibration in 5% NaOH solution, (4) ion sputtering method and (5) blank replica method. There was no trace of stripping off the scales by theNaOH solution, ion sputtering method and blank replica method, but the scales were stripped off by HCl solution and diammonium hydrogen citrate solution. The vibration in 3% HCl solution seemed to restore the original fracture surface. The corrosion fatigue fracture mostly started at the surface pitting corrosion. Therefore, it was very important to investigate the growth behavior of pitting corrosion for the study of corrosion fatigue machanism. So, the feature, size and number of pitting corrosion on the surface of fatigue specimens at high temperature in pure water were investigated. The total number of pitting corrosion examined were about 1 000. It was observed that the pitting figure was complicated at the initial stage, but it changed to circuler as it grew. The pitting size distribution at the occurance of fracture was expressible by an exponent by an exponent function. It was concluded that the probability density function of distribution was strongly affected by the testing strain rate.
社団法人日本材料学会の論文
1985-09-15

高温純水中腐食疲労破面

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