IN SITU OBSERVATION OF DEFORMATION AND CRACK PROPAGATION IN DOPED TUNGSTEN WIRE

Abstract

It has been proved in our early work that the excellent sag resistance of doped tungsten wire mainly resulted from interaction between dislocations and dispersed potassium bubbles contained in doped tungsten wire. This work presents in situ observations under high voltage electron microscope (HVEM) that potassium bubbles obstruct moving dislocations and bend them and that dislocations are unpinned from potassium bubbles and move again. The role of potassium bubbles in crack nucleation and fracture has also been revealed in in situ tensile experiments. The whole process of crack nucleating at a grain boundary has been recorded. The experiments show that microeracks spread along potassium bubble rows in side grains as well as along grain boundaries. Thus, it is very important for the doped tungsten wire production to control the potassium bubble size and distribution and to make the bubble rows as fine and uniform as possible with the help of adequate deformation and heat treatment.