Growth of α-Fe-Co particles on [001] symmetric tilt boundaries in Cu bicrystals

Abstract

Recently, using orientation-controlled bicrystals, Fujii et al. investigated the growth of {alpha}-Fe-Co precipitate particles on [011] symmetric tilt boundaries with misorientation angles of {theta} = 5--50.5{degree} in a Cu-Fe-Co alloy aged at 873K. The development of precipitate-free zones (PFZs) during aging also was examined. They showed that the power n for r{sup n} = Kt varied systematically from 3 to 5 as the misorientation increases from 10 to 50.5{degree}, while the relationship d{sup 2}{proportional_to}t held between the width d of PFZs and aging time t for all the bicrystals investigated. The change in the n values was explained reasonably by considering the relative contribution of bulk diffusion and dislocation pipe diffusion towards the particle growth. It is well known that bulk diffusivity decreases remarkably with decreasing temperature in comparison with grain-boundary diffusivity. This means that the relative contribution of the bulk diffusion towards the growth of {alpha}-Fe-Co particles on a boundary should become smaller as aging temperature becomes lower. Therefore, it is very probable that, if aging temperatures lower than the temperature of 873K, adopted by Fujii et al., are chosen, n would become closer to 4, independent of the boundary character. With this in mind, the coarsening of boundarymore » {alpha}-Fe-Co particles is investigated for various [001] symmetric tilt boundaries in cu-Fe-Co alloy bicrystals aged between 673 and 723K. Furthermore, the activation energy for the particle growth is estimated as a function of the misorientation angle.« less