Glassy embrittlement of chromium metal and its improved ductility by alloying elements

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Chromium and its alloys are ones of the promising high temperature materials since they exhibit the excellent combination of low density, high creep strength and good oxidation resistence at high temperatures. However, there is still a large barrier to the practical use because of the poor ductility at room temperature. The purposes of this study are two-fold. One is to elucidate the mechanism for the embrittlement of chromium experimentally using a bend test and a small punch test. The other is to investigate a method for improving the ductility by the addition of alloying elements into chromium.As the result, it was found that plasticity of high-purity polycrystalline chromium was dependent largely on surface imperfections. The existence of small cracks on the surface induced it to be very brittle. Also, large environmental effects were observed on the ductility chromium. For example, the moisture existing in the test environment increased the ductility of pure chromium, which is in contrast to the observations in other metallic materials such as intermetallic compounds (e. g., FeAl TiAl) . In addition, it was shown for the first time that pure chromium exhinbited hydrogen embrittlement. All these phenomena observed in pure chromium were also found in Chromium alloys. Furthermore, the vanadium addition was shown to be most effective in improving the ductility of chromium among a variety of alloying elements including 3d, 4d and 5d transition metals. Thus, the present results provided us important information on the method for improving the ductility of chromium.