Characterization of a duplex coating (boriding + sputter-deposited AlCrON) synthesized on an ASTM F-75 cobalt alloy

Metallic biomaterials have been widely used due to their excellent mechanical properties. Cobalt-chromium-molybdenum alloys, in particular are among the safest for the fabrication of orthopedic prostheses. Nevertheless, the liberation of metallic ions as a result of wear has become a problem due to adverse biological reactions. Thus, surface modification through thermochemical treatments and ceramic coatings may be used to improve the tribological properties of the alloy. In this work, a duplex coating obtained from a boriding thermochemical treatment plus an aluminum-chromium oxynitride coating created by physical vapor deposition was synthesized on an ASTM F-75 cobalt alloy. This surface condition was compared with a borided and an untreated ASTM F-75 cobalt alloy. Surfaces were characterized using scanning electron microscopy (SEM) with energy dispersive spectroscopy, X-ray diffraction, and nanoindentation test. The tribological response was studied by means of a ball-on-disc tribometer under dry-sliding conditions tracking the coefficient of friction, volume loss, wear rate, and surface damage by stereoscopy, profilometry, optical 3D measurements, and SEM. Duplex coating increased the wear resistance 7 times relative to the wear resistance of the untreated sample, and 1.5 times relative to the borided sample.