Single Asperity Fretting Corrosion of Traditional and Additively Manufactured Metallic Biomaterials: Quantitative Analysis from Acetabular Tapers to Micron and Nanometer Scale Tribocorrosion

Mechanically assisted crevice corrosion (MACC) of metallic biomaterials continues to be a significant degradation mode. This is, in part, due to a lack of understanding of fundamental micron- and sub-micron scale mechanisms of metal degradation in biological environments. Metal-metal (or metal-hard) load bearing surfaces of hip arthroplasties are subjected to fretting crevice corrosion (FCC, one form of MACC). Current work in tribocorrosion involves large contact area tests with multiple asperities, with a distribution of load and wear that changes over time. A more systematic and controlled study of the FCC micro- and nanomechanics is needed.Therefore, the goal of this work was to develop and employ a tribocorrosion test using a single, inert, micron- to nano-scale hard asperity to address fundamental questions of metallic biomaterial FCC in biologically representative environments. Traditional biomedical alloys (CoCrMo, Ti-alloys and stainless steel) and novel additively manufactured alloys (CoCrMoW) were subjected to conditions simulating THA and dental implants in vivo, measuring effects of materials, load, potential and solution. Quantitative investigation of plastic deformation, debris generation, oxide repassivation, or ion dissolution which were measured as a percentage of the total fretting corrosion process of titanium alloys. Similar testing was done using atomic force microscopy methods, to expand the single-asperity fretting response as the wear depth decreased to the single atomic layer scale.This work focused on both the response to external variables and on internal alloy characteristics influenced by manufacturing method, chemistry, and microstructure, as it applies to the growing field of 3D printed biometals.