The mechanical properties of tungsten grown by chemical vapour deposition

The mechanical properties of polycrystalline tungsten grown by chemical vapour deposition (CVD) have been investigated. Fracture tests were performed on the material over the 24–967 °C temperature range at a low strain rate. The material was found to be brittle or semi-brittle across the entire temperature range investigated. This behaviour differs significantly from that previously found in conventionally-grown polycrystalline tungsten, which, under similar experimental conditions, is found to be ductile above approximately 120 °C. Energy dispersive X-ray analysis indicates that in the CVD tungsten, there is a significant concentration of fluorine at grain boundaries. It is therefore suggested that fluorine segregation to grain boundaries is responsible for the increased brittleness observed in the CVD tungsten.