Fretting corrosion of Si3N4 vs CoCrMo femoral heads on Ti-6Al-V trunnions

Fretting corrosion at the head-neck taper junction was compared between silicon nitride (Si3N4) and commercially available cobalt chrome (CoCrMo) femoral heads on titanium (Ti-6Al-4V) trunnions. An electrochemical setup was used to capture the fretting currents (characterized by oxide abrasion and repassivation) during cyclic loading. Onset load, pull-off force (disassembly load), short term and long term (1 million cycles) fretting currents were used to compare the fretting corrosion performance between the test group (Si3N4/Ti-6Al-4V) and the control group (CoCrMo/Ti-6Al-4V). Incremental cyclic fretting corrosion tests showed that the Si3N4/Ti-6Al-4V combination had statistically lower (P < .05) average fretting current of 0.189 mu A (SD = 0.114 mu A) compared to 0.685 mu A (SD = 0.630 mu A) for CoCrMo/Ti-6Al-4V for cyclic load of 3200 N. Similarly, for the one million cycle fretting corrosion tests, the Si3N4/Ti-6Al-4V couples had statistically lower (P < .05) average current (0.048 mu A, SD = 0.025 mu A) vs CoCrMo/Ti-6Al-4V couples (0.366 mu A, SD = 0.143 mu A). The Si3N4 heads also had higher onset loads (P < .05) for fretting (vs CoCrMo, 2200 N vs 1740 N) indicating a difference in surface contact mechanics between the two groups. Scanning electron microscopy with energy dispersive spectroscopy confirmed material transfer from the trunnions to the heads for both groups tested, and from head to trunnion for the CoCrMo heads. Minimal Si3N4 transfer was noted. The electrochemical, mechanical, and microscopic inspection data supported the hypothesis that Si3N4/Ti-6Al-4Vcombination had better fretting corrosion performance compared to CoCrMo/Ti-6Al-4V.