Void Growth Mechanism in Bubble Strengthened Tungsten

Bubble-strengthened tungsten lamp filaments must exhibit not only excellent high temperature creep strength but also poor susceptibility to cavitation. The paper presents a study on the mechanism of void formation in KSiAl-doped tungsten. It was concluded that even if no preexisting bubbles of critical size are present in the initial bubble network, during lamp operation, as a result of bubble coarsening, bubbles can become large enough to act as nuclei for stress assisted void growth. In this case the void formation process can be separated into three regimes by two critical sizes. It was also suggested that the presence of very high potassium pressures in the smallest bubbles reduces the surface diffusion coefficient and, hence, the rate at which the bubbles can move and coalesce.