The unusual temperature dependence of /sup 57/Co grain boundary diffusion in tungsten

Because of the high atomic mobility in grain boundaries relative to that in the bulk grain boundary diffusion plays an important role in the kinetics of microstructural changes during metallurgical processes and applications. One of the technologically important examples is the well known activated sintering of tungsten powder due to small additions of transition metals. This process allows an enormous reduction of the sintering temperature to the range of about 1500 K. It is generally accepted that the enhanced sinterability of W is initiated mainly by promoting diffusion processes along W-grain boundaries in the presence of such additive metals. This argument is supported by the observation that grain boundary self-diffusion in W is considerably increased if Ni is allowed to penetrate into the grain boundaries. For a quantitative analysis of the sintering kinetics in tungsten, therefore, a detailed knowledge of grain boundary diffusion, especially of the additives and their influence on self-diffusion, is required. In spite of their technical importance, however, very few investigations on these problems have been published