Effect of thermal treatment on failure modes in tungsten wire

The modes of failure, from microvoid coalescence to transgranular cleavage, are documented in tungsten wire as a function of thermal history. The failure is primarily ductile at room temperature due to an initial highly elongated fine grain structure. When heat treated at temperatures of approximately 1350 K, strong evidence of transverse grain boundary formation is evident on the primarily intergranular failure surfaces. However, when subjected to heat treatments at 1630 K for 5 min, transgranular cleavage dominates both at temperature and after cooling to room temperature. It is suggested that this change is indicative of strengthening grain boundaries at the higher temperature heat treatments. In all of the cases examined, the fractography of tungsten wire allows the thermal history of the specimen to be determined.