Grain Boundary Assisted Crevice Corrosion in CoCrMo Alloys

Cobalt chromium molybdenum alloys have been extensively used for biomedical implants, but are susceptible to grain boundary corrosion resulting from local chromium depletion, which is called sensitization. This work extended the understanding of chromium depleted zones in CoCrMo alloys and their role in corrosion to the nanoscale. Selected boundaries were analyzed from the millimeter to the nanometer scale in order to link the chemical composition and crystallographic structure to the observed local corrosion properties. The shape and severity of grain boundary corrosion crevices were measured, linked with the coincidence site lattice geometry. Additionally, direct high-resolution energy dispersive x-ray spectroscopy maps of chromium depleted zones at the grain boundaries were measured to completely characterize the grain boundary properties. Chromium depleted zones were found in 100% of corroded grain boundaries, yet were too small to follow classical models of sensitization. Nanoscale regions of chromiu...