Effect of sodium-ion implantation on the properties of the surface layers formed on CoCrMo alloy (Endocast SL)

This paper is concerned with the surface modification of a cobalt alloy (Endocast) by sodium-ion implantation and with the effect of this modification on its corrosion resistance. The Na ions were implanted at doses of 1×1017 and 2×1017 ions/cm2 at energy of 25 keV. The chemical composition of the surface layers formed during the implantation was examined by secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS), and their microstructure by transmission electron microscopy (TEM). The corrosion resistance was determined by electrochemical methods in a simulated body fluid (SBF) at a temperature of 37 °C. Prior to the measurements, the samples were exposed to the test conditions for 13 h to allow the corrosion potential Ecorr to stabilize, and for 181, 733 and 2200 h to investigate how the long-time exposures affect the corrosion resistance. The surfaces of the samples were examined by optical microscopy and by SEM-EDS. The TEM results indicate that the surface layers formed during the Na-implantation are amorphous. The results of the electrochemical examinations obtained for the Na-implanted Endocast samples indicate that the corrosion resistance of the alloy is reduced.