Microscopic fracture mechanism of sintered high purity chromium

The microscopic fracture mechanism was examined experimentally for high purity chromium. With the specimens prepared by sintering and swaging, a series of tensile tests was carried out in various test conditions. The high purity chromium became more ductile as the test temperature increased, but the ductile-to-brittle transition temperature (DBTT) was not found clearly in the temperature range of 300–623 K. In addition, it was very brittle when tested in water, probably due to hydrogen embrittlement. From a fractographical analysis, it was shown that there were many micro-voids on the fracture surface, when the test temperature was less than 423 K. These micro-voids on a local region in the grain boundary seemed to grow up during deformation and to act as the initiation sites of intergranular fracture, and subsequently followed by transgranular cleavage fracture. The fracture strain increased with decreasing size of micro-voids, irrespective of the test conditions. The growth of the micro-voids was supposed to be one of the predominant factors for controlling the fracture of high purity sintered chromium.