GEOMETRICAL PROPERTIES OF BUBBLES IN P M TUNGSTEN FINE WIRES AND COMPUTER-SIMULATION ON THEIR EFFECT ON ABNORMAL GRAIN-GROWTH/

Scanning electron microscopic (SEM) observation is made to examine the geometry of bubbles in P/M tungsten fine wires after their secondary recrystallization is completed. The effect of the geometrical properti es of bubbles on abnormal grain growth is then investigated using a Mo nte Carlo computer simulation technique. While bubbles, with the mean diameter of 25 nm, are present at grain boundaries with a high number density of rho = 10(13) m(-2), the number density of bubbles inside a grain is about 5% of rho. As the specimens are annealed, rho decreases rapidly and thereby the mean bubble diameter increases after many sma ll bubbles form at grain boundaries. The latter is thought to be the p rocess of bubble formation caused by the increase in the internal pres sure of potassium gas, while the former is considered to be the coarse ning process of large bubbles caused by the diffusion of potassium alo ng grain boundaries from smaller to larger bubbles. Moreover, it can b e concluded from the results of the computer simulation that the final abnormal grain structure is very much influenced by the mutual positi onal relation between the arrays of bubbles and the potential abnormal grains, being indirectly influenced by the bubble intervals in an arr ay, the growth of bubbles, the number of initial abnormal grains and s o on.