Titanium nitride coatings on surgical titanium alloys produced by a powderimmersion reaction assisted coating method: residual stresses and frettingbehavior

Titanium and Ti-6Al-4V alloy samples were coated using a powder Immersion R eaction Assisted Coating (PIRAC) nitriding method in order to modify their surface properties. Depending on the processing temperature, strongly adher ent single(TiN)- or double(Ti2N/TiN)-layer coatings were obtained on both s ubstrates. Several characteristics of PIRAC-coated Ti alloys relevant to th eir applications in total joint replacements were studied. Residual stresse s in PIRAC coatings measured by sin(2)psi X-ray diffraction method were fou nd to be compressive in nature and were significantly lower than those repo rted for PVD TiN layers on similar substrates. In vitro fretting tests of P IRAC nitrided Ti-6Al-JV-to-Ti-6Al-4V couples simulating in vivo conditions at the interface of modular orthopedic implants demonstrated a major reduct ion in fretted areas, as well as a remarkable reduction of the corrosion po tential drop at the initial stages of fretting as compared to the uncoated alloy. In addition, a 25% reduction of fretting-induced dissolved Ti ions c oncentration in testing solution was measured by EAAS. The results of the r esearch suggest that titanium nitride PIRAC coatings can provide surgical t itanium alloys with the longed-for fretting wear and corrosion resistant su rface thereby minimizing the ion- and particulate-generating potential of m odular orthopedic implants. (C) 2000 Elsevier Science S.A. All rights reser ved.