A. Itakura

D. Kato

H. Sakaue

M. Tosa

S. Suzuki

S. Takagi

Y. Murase

Y. Sakai

National Institute for Fusion Science (NIFS-Repository)

Hydrogen diﬀusion in metals has attracted atten-tion in hydrogen embrittlement, hydrogen storage andmaterials for fusion reactor or ultrahigh vacuum cham-ber. However, it is diﬃcult to observe directly hydrogendiﬀusion in metals. The following methods have beenreported. One is observations of hydrogen mapping us-ing microprint technique or fracture cross section aftertensile test with a scanning electron microscope (SEM)after cathodic charging of hydrogen to specimens. An-other is nuclear reaction method for analyzing depth pro-ﬁling. However, these methods are not available to anobservation in real time. In our experiment the spatialdistributions of hydrogen on the specimen are visualizedsequentially by protons emitted by electron stimulateddesorption process with the SEM. This method can notonly make clear the diﬀusion pass of hydrogen by com-paring to surface grain structure, but also obtain physicalinformation on diﬀusion by acquiring the images sequen-tially in diﬀerent specimen temperature.Fig. 1: Experimental setup.The specimens used in this experiment are twokinds of SUS304, whose thicknesses are 100 (S1) and200 µm (S2) and each cold working rate is 20 (S1) and10% (S2), respectively. Therefore, these specimens arecharacterized by dual phase structure, where a part ofaustenite phase transfers to martensite. The austenitegrain sizes are about 100 µm , which is comparable tothe thickness of S1. The schematic diagram of experi-mental setup is shown in Fig.1. The hydrogen reservoirattached specimen is installed in the sample chamber ofthe SEM. Hydrogen is supplied to the reservoir up to5×10−4 Pa after evacuation. The specimen is exposedfrom the back side and the permeated hydrogen to theopposite observation side is observed by desorbed ion im-ages in real time. The specimen is heated in incrementalsteps from R.T. to 573 K by the halogen lamp. Thespecimen temperature is measured by T thermocouple.The residual gas in the sample chamber is analyzed bythe quadrupole mass analyzer during the experiment.600550500450400350300Number of ESD ions [counts]Sample temperature [K](x103) 1816141210864100 μm H2100 μm 200 μm H2200 μm  Fig. 2: Dependence of ESD ions on temperature.Fig.2 shows the number of detected ESD ions ateach temperature for specimens of S1 and S2, which aremarked by circles and triangles, respectively. Solid marksrepresent the result with hydrogen gas, and open markswithout gas. In S1 the number of ions increases stepwiseat 323 and 423 K. Each increase corresponds to contri-bution of the diﬀusion through martensite and austenitephases, respectively. The increase at 573 K may be dueto unknown diﬀusion path. S2 is diﬀerent from S1 inion yield behavior for heating. In no hydrogen supplythe ion yield is more than S1 and in hydrogen the yieldis almost constant for heating and less than S1. Thesefeatures are due to the followings, that is, in S2 residualhydrogen contributes signiﬁcantly to yield of ESD ionsand permeation of hydrogen is suppressed. The diﬀer-ence between two specimens is whether there exists grainboundary between both sides throughout the specimen.The grain boundary suppresses hydrogen diﬀusion.600550500450400350300Ion current [A]Sample temperature [K](x10-11) 43210D2H2Fig. 3: Dependence of partial pressure on temperature.Fig.3 is response of hydrogen partial pressure inthe sample chamber of the SEM for temperature eleva-tion, solid circles and triangles being the results for H2and D2, respectively. The release to the vacuum occursfrom about same temperature for both hydrogens butthe amount of D2 is about half of H2.358§39. Measurement of Hydrogen Permeation of Stainless Steel by Electron Stimulated Desorption (ESD) MethodTakagi, S., Sakai, Y., Suzuki, S. (Dept. Phys. Toho Univ.), Murase, Y., Tosa, M., Itakura, A. (NIMS), Sakaue, H., Kato, D.

Measurement of Hydrogen Permeation of Stainless Steel by Electron Stimulated Desorption (ESD) Method

Measurement of Hydrogen Permeation of Stainless Steel by Electron Stimulated Desorption (ESD) Method

Abstract

Similar works

Full text

Available Versions

National Institute for Fusion Science (NIFS-Repository)