Fretting corrosion of CoCrMo alloy biomaterials: Instrumentation development, heredity integral modeling and the effect of frequency

Mechanically assisted crevice corrosion, a process of corrosion that generally occurs in joint replacements of the hip and knee, is a major problem for metallic biomaterials. Though extensive research has already been undertaken, the basic concepts of fretting corrosion including prediction of the instantaneous current response during fretting corrosion, still needs to be understood in a systematic form. The aim of this study is to present the mechanical and electrochemical elements of a model pertaining to the process of fretting crevice corrosion and the prediction of fretting corrosion current transients. The influence of sliding speed on fretting corrosion severity of CoCrMo alloys will also be measured. To be complete, a new fretting corrosion model that predicts instantaneous current versus time during fretting was developed to better explore the effect of instantaneous mechanical and electrochemical factors on fretting corrosion current. Based on the principle that there is a direct correlation between the oxide repassivation volume and the current, the method of the Duhamel Integral (Boltzman superposition) was used to link abrasion and repassivation of oxide film and the resultant current waveform. In addition, a new testing device was designed and built to observe fretting corrosion phenomena under microscopic conditions. The data collection and control systems that include displacement sensors and NI-DAQ board, as well as LabVIEW program, was also developed and is described. The effect of frequency/sliding speed on fretting corrosion current was explored in this thesis. All tests were performed by varying sliding frequency in PBS solution under fixed potential, load, displacement and surface roughness. The results demonstrated a strong correlation between model prediction and experimental data. This model gave a clear basis between fretting elements (abrasion per time) and current transients. For frequency tests, increased sliding speed resulted in proportional increases in fretting corrosion currents over the specific range from 0 to 400 μm/sec. The current stopped linearly increasing above 400 μm/sec, which is considered the maximum CoCrMo reformation rate under the conditions of this experiment. There were more sliding and sticking events, as well as fretting currents, in a unit time with increasing frequency. The rms fretting current was narrowed at higher fretting speed. Frequency does not have a significant effect on COF, frictional force or dissipated energy per cycle