A grain morphology index f1 characteristic of the configuration of secondary recrystallized grains grown in tungsten wires is derived after making their contours clear in three dimensions. Tensile and hardness tests are made using the wires with different grain morphologies at room temperature. It is then investigated through f1 how the grain morphology is connected to brittleness of doped wires. The fracture modes are classified to be ductile and brittle at each of the two regions, which are separated so that each of them is below and above a certain value of f1 respectively. The morphological features of grains to prevent fatal brittleness of wires are demonstrated.
