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

铬及其合金具有低密度、高蠕变强度和良好的高温抗氧化性能，是一种很有前途的高温材料。但是，由于其室温延展性差，在实际应用中仍存在很大的障碍。本研究的目的有两个。一个是阐明铬脆化的机制，实验上使用弯曲试验和小冲杆试验。二是通过在铬中添加合金元素来改善多晶铬的塑性，结果表明，高纯多晶铬的塑性主要取决于表面缺陷。表面上小裂纹的存在导致它非常脆。此外，观察到大的环境影响的延展性铬。例如，测试环境中存在的水分增加了纯铬的延展性，这与其他金属材料如金属间化合物（例如金属间化合物）的观察结果相反。例如，在一个实施例中，FeAl TiAl）。此外，还首次发现纯铬对氢脆有抑制作用。在纯铬中观察到的所有这些现象在铬合金中也被发现。此外，在包括3d、4d和5d过渡金属的各种合金元素中，钒的添加显示出在改善铬的延展性方面最有效。因此，目前的结果为我们提供了重要的信息，提高铬的延展性的方法。

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.