Papers by Keyword: rogen Microprint Technique (HMT)

Abstract: In order to investigate the influence of hydrogen on the fatigue strength of Type 304 meta-stable austenitic stainless steel, specimens were cathodically charged with hydrogen. Hydrogen-charging led to a marked decrease in fatigue crack growth life. Crack growth paths and slip bands morphology were changed by the hydrogen-charging. To elucidate the mechanism of the degradation by hydrogen, the surfaces of both the uncharged and charged specimens were examined by the hydrogen microprint technique (HMT). In the uncharged specimen, no hydrogen emission from specimen surface was observed. On the other hand, in the hydrogen-charged specimen, a hydrogen emission was observed, especially in the vicinity of fatigue cracks. Hydrogen was mainly emitted from slip bands. These results suggest that the degradation of fatigue crack growth resistance in hydrogen-charged specimens was caused by the diffusion of hydrogen to slip bands, which accelerated the dislocation mobility and thereby facilitated the fatigue crack growth.

Abstract: High-magnesium Al-Mg alloys are known to be sensitive to stress corrosion cracking involving environmental hydrogen, hydrogen invading from the corrosive environment. In this study, the behavior of the environmental hydrogen in Al-6%Mg and Al-8%Mg binary alloy sheets stretched by 10% during exposure to 3.5%NaCl solution has been investigated by means of hydrogen microprint technique. Microprint image is observed on one surface while the other surface is exposed to the solution. In both alloys, the silver particles corresponding to the sites where hydrogen atoms are emitted from the inside of the sheets are shown on the slip lines. It is shown that the hydrogen atoms are transported with moving dislocations in the alloys.

Abstract: Aluminum alloy is one of the candidates for the liners of compressed hydrogen tank mounted to fuel cell vehicles. It is crucial to elucidate the behavior of hydrogen in the alloy sheet with one side being exposed to hydrogen gas. In the present work, using the hydrogen microprint technique, in 6061 and 7075 aluminum alloy sheets, relationship between hydrogen pressure and the molar quantity of hydrogen emitted from the inside has been investigated. Under any pressure, the quantity of emitted hydrogen is about 10 times smaller in the 7075 alloy than in the 6061 alloy. This indicates that the amount of hydrogen atoms accumulating in the 7075 alloy may be much larger than that in the 6061 alloy.