Conjoint corrosion and wear in titanium alloys

When considering titanium alloys for orthopaedic applications it is importa nt to examine the conjoint action of corrosion and wear. In this study we i nvestigate the corrosion and wear behaviour of Ti-6Al-4V, Ti-6Al-7Nb and Ti -13Nb-13Zr in phosphate buffered saline (PBS), bovine albumin solutions in PBS and 10% foetal calf serum solutions in PBS. The tests were performed un der four different conditions to evaluate the influence of wear on the corr osion and corrosion on the wear behaviour as follows: corrosion without wea r, wear-accelerated corrosion, wear in a non-corrosive environment and wear in a corrosive environment. The corrosion behaviour was investigated using cyclic polarisation studies to measure the ability of the surface to repas sivate following breakdown of the passive layer. The properties of the repa ssivated layer were evaluated by measuring changes in the surface hardness of the alloys. The amount of wear that had occurred was assessed from weigh t changes and measurement of the depth of the wear scar. It was found that in the presence of wear without corrosion the wear behaviour of Ti-13Nb-13Z r was greater than that of Ti-6Al-7Nb or Ti-6Al-4V and that in the presence of proteins the wear of ail three alloys is reduced. In the presence of co rrosion without wear Ti-13Nb-13Zr was more corrosion resistant than Ti-6Al- 7Nb which was more corrosion resistant than Ti-6Al-4V without proteins wher eas in the presence of protein the corrosion resistance of Ti-13Nb-13Zr and Ti-6Al-7Nb was reduced and that of Ti-6Al-4V increased. In the presence of corrosion and wear the corrosion resistance of Ti-13Nb-13Zr is higher than that of Ti-6Al-7Nb or Ti-6Al-4V in PBS but in the presence of proteins the corrosion resistance of Ti-13Nb-13Zr and Ti-6Al-7Nb an very similar but hi gher than that of Ti-6Al-4V. The wear of Ti-13Nb-13Zr is lower than that of Ti-6Al-7Nb and Ti-6Al-4V with or without the presence of proteins in a cor rosive environment. Therefore the overall degradation when both corrosion a nd wear processes are occurring is lowest for Ti-13Nb-13Zr and highest for Ti-6Al-4V and the presence of proteins reduces the degradation of all three alloys. (C) 1999 Elsevier Science Ltd. All rights reserved.