Intergranular pitting corrosion of CoCrMo biomedical implant alloy

CoCrMo samples of varying microstructure and carbon content were electrochemically corroded in vitro and examined by scanning electron microscopy and electron backscatter diffraction techniques. The rate of corrosion was minimized (80% reduction from i(corr) = 1396 nA/cm(2) to i(corr) = 276 nA/cm(2)) in high-carbon CoCrMo alloys which displayed a coarser grain structure and partially dissolved second phases, achieved by solution annealing at higher temperatures for longer periods of time. The mechanism of degradation was intergranular pitting corrosion, localized at phase boundaries and grain boundaries of high energy (high-angle and low lattice coincidence, sigma 11 or higher); grain boundaries of lower energy did not appear to corrode. This suggests the possibility of grain boundary engineering to improve the performance of metal implant devices. (c) 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 102B: 850-859, 2014.