A Real Time Electrochemical Analysis of Co-Sputtered (Co-Cr) and (Co-Cr-Mo) Alloy Thin Film Libraries in Ringer’s Solution at 37 oc

Abstract

Cobalt-based alloys are used as total hip replacement prostheses due to their exceptional tribocorrosion properties in the human physiological environment[1]. Due to continuous mechanical and corrosive conditions, the dissolution of Cr and Co in the body fluid is unavoidable. These metallic particles and ions can cause cancer and gene mutation in the body, therefore their leaching should be diminished by proper passivation[2].In this work, two combinatorial thin film libraries namely a binary Co-Cr and a ternary Co-Cr-Mo were prepared by means of co-sputtering. Both libraries were characterized by state of the art high resolution scanning electron microscopy (SEM) and X-ray diffraction (XRD). The chromium content for binary Co-Cr library varied from 14-40 at.% (balanced Co) while for ternary Co-Cr-Mo library a compositional spread of Co (46-79 at.%), Cr (17-48 at.%) and Mo (3-11 at.%) was obtained. In both libraries roundish spike shaped grains were revealed at high cobalt content which gradually changed to refined and compact grains with the increment of Cr. Similarly, molybdenum (>-7 at.%) brought additional grain refinement. Furthermore, weak, and broad XRD peaks of rt HCP and ht FCC pure Co were disclosed at nearly all compositions. No intermetallic phase was determined in either library.The real time electrochemical screening and corrosion stability were accomplished by a in house-built flow type scanning droplet cell microscope (FT-SDCM) in conjunction with an inductively couple plasma optical emission spectroscope (ICP-OES). Various electrochemical techniques i.e. open circuit potential, linear sweep voltammetry and Tafel extrapolation were utilized. No significant passive behavior was obtained for the alloys containing the Co content higher than (68-70 at.%) irrespective of Cr and Mo concentration. However, further increment in the Cr content significantly improved the alloy nobility and restricted the active to passive dissolution. The addition of Mo improved the transpassive dissolution. A graphical model was developed on the basis of this study and a composition range of (7-10) at.% Mo and (36-48) at.% Cr (complementary Co) is recommended as likely candidate for biomedical use.