| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2016) | |
| Thin Films | Wednesday Sessions |
| Session TF-WeP |
| Session: | Thin Films Posters Session II |
| Presenter: | Naoya Miyauchi, Toho University, Japan |
| Authors: | N. Miyauchi, Toho University, Japan Y. Murase, National Institute for Materials Science, Japan H.A. Sakaue, National institute for fusion Science, Japan A.N. Itakura, National Institute for Materials Science, Japan S. Takagi, Toho University, Japan |
| Correspondent: | Click to Email |
Hydrogen outgassing from an inside wall is the most important issue for vacuum chambers in ultrahigh vacuum (UHV) and extremely high vacuum (XHV). In addition, the behavior of hydrogen in metals should be made clear to understand the mechanisms of hydrogen embrittlement and storage. We have observed the behavior of hydrogen in metals by visualizing sequentially spatial distributions of permeated hydrogen on the surface of stainless steel membrane. The distributions of surface hydrogen were obtained using ions emitted by the method of desorption induced by electronic transition (DIET) process with the scanning electron microscope (SEM).The diffusion pass of hydrogen can be revealed from comparison of hydrogen maps obtained by this technique with the surface grain structure. In addition, physical information on permeation, which contains the processes of solution, diffusion, adsorption, is obtained by conjunction with a measurement on time dependence of permeated hydrogen pressure in the vacuum.The experimental setup is shown in Figure 1. We equipped the SEM (JEOL JAMP10) to the sample holder with hydrogen supply system and collecting electrode of DIET ions, the detection system of DIET ions and the quadrupole mass analyzer (Pfeiffer Vacuum QMG220). The collecting electrode is attached due to focusing DIET ions on the detector system. The DIET signals are measured in two-dimensional pulse counting system constructed by LabVIEW. This two-dimensional pulse counting system is synchronized with the scanning electron beam. The sample is SUS304 stainless steel, which has austenite structure with martensite dislocations caused by cold working of 20 %. The sizes of austenite grains are about 100 μm. The thickness of membrane is 200 μm. After outgassing of hydrogen in the sample (573K: 48 hours) the following experiments were performed under the outgassing temperature. The back side of SUS membrane was exposed to hydrogen (2.7×105 Pa) and the permeated hydrogen on the opposite observation side was observed by DIET method. The vacuum chamber was evacuated by the sputter ion pump (100 l/s) under the experiments. The pressure was 1x10-7 Pa under the experiment. Both H2 and D2 gases were used to investigate an isotope effect for permeation.
Figures 2 and 3 are the secondary electron image and the permeated hydrogen map, which is obtained by accumulating DIET ions for 50 hours at 473 K, respectively. A comparison of two kinds of image suggested that the hydrogen permeation from the inside of grain and more permeation in austenite grains than martensite grains.