Effects of precipitates and albumin in simulated body fluids on Pin-on-disk wear behavior of biomedical Co-Cr-Mo alloys

Pin-on-disk wear tests using Co-Cr-Mo (CCM) alloy pins and disks were conducted in 0.14 M NaCl solutions with and without albumin. To clarify the effect of precipitates in the CCM alloys on the alloy wear behavior, as-received (having precipitates) and solution-treated (having no precipitates) CCM alloys were used as specimens. Friction coefficients during wear testing were measured. After the wear testing, the mass loss of pins and disks, wear tracks on the disks, and the wear debris were examined using scanning electron microscopy (SEM) and laser microscopy (LM). The concentration of metallic ions in solution was analyzed by inductively coupled plasma-atomic emission spectroscopy (ICPAES). In the solution without albumin, the friction coefficient increased with increasing sliding time and discontinuous wear grooves with attached and detached sections were observed, indicating that adhesive wear was dominant. On the other hand, in the solution with albumin, the friction coefficient was constant independent of the sliding distance and continuous wear grooves were observed, indicating that abrasive wear was dominant. High amounts of mass loss were detected from the as-received alloys in the albumin solution, and it is theorized that the wear debris (including precipitates) enhanced the third-body wear. The concentration of Cr ions in solution was lower than the expected values based on the alloy composition. In the solution with albumin, it was thought that the Cr ions bonded with the albumin, increasing the amount of available Cr ions in solution.