EFFECT OF SURFACE IMPERFECTIONS ON THE DUCTILITY OF PURE CHROMIUM

The fracture behaviour of high-purity polycrystalline chromium was inv estigated using bend tests at room temperature in air. It was found th at plasticity was dependent largely on surface imperfections. For exam ple, brittle fracture took place in a roughly polished specimen contai ning a large number of small cracks on the surface. However, once the specimen was polished finely or electropolished, it was able to be ben t by more than 90 degrees without showing any brittle fracture. Such a surface effect on the fracture mode is very similar to the observatio ns in glasses and in alkali halide crystals (for example, NaCl and LiF ).