Effects of Grain Boundary Misorientation and Chromium Segregation on Corrosion of CoCrMo Alloys

Abstract

The influence of grain boundary interfacial energy on the structure of carbides and the local segregation of chromium were investigated at the nanoscale for coincident site lattice boundaries in a CoCrMo alloy. Grain boundaries of varying degrees of misorientation were examined by optical profilometry and transmission electron microscopy, and samples of the grain boundary precipitates were analyzed with energy dispersive x-ray spectroscopy. Low-Σ coincident site lattice boundaries were found to have both fewer carbide precipitates and smaller degrees of sensitization, and are more resistant to intergranular attack. Similar to general high-angle boundaries in this material, the combination of chromium depletion and the grain boundary energy acts as the initiator of corrosion. After initiation, crevice corrosion enlarges the initial site of the attack.