Evolution of Pore Ensembles Located at the Grain Boundaries in Cu and Cu-5 at.% Sn

The kinetics of pore coalescence in ensembles located at the grain boundaries in Cu and Cu-5 at. % Sn has been studied by optical and scanning electron microscopy at 500 and 800°C. In the case of pure Cu the evolution of the pore ensemble followed the kinetical law ¯4 t, where ¯ is the average pore radius and t is the ageing time. This law is typical for a grain boundary diffusion controlled process. However, in the case of the Cu-5 at. % Sn alloy the kinetical law obeyed the ¯3 t relationship, which is characteristic for a reaction controlled process. The reaction in question is the generation of vacancies on the surfaces of the pores. The importance of the surface reaction controlled mass transfer process in alloys is discussed. The grain boundary self-diffusivity and the kinetical coefficients of the reaction are determined and analyzed.