Interface interactions between porous titanium/tantalum coatings, produced by Selective Laser Melting (SLM), on a cobalt-chromium alloy

Porous titanium and tantalum coatings were produced on cast cobalt-chromium alloy substrate plates (Co-28 Cr-6 Mo ASTM designation F75)) using the additive manufacturing process Selective Laser Melting (SLM). Both tantalum and titanium coatings where successfully produced, however, a poor interface bond was observed with the titanium coatings on the cobalt-chrome alloy. This was due to a eutectic reaction leading to the formation of a low melting point phase βTi(CoCr) which cracks during cooling, rather than the formation of titanium carbide, as previously reported. This cracking makes titanium an unsuitable material to coat cobalt-chromium alloys using SLM.Tantalum coatings, however, showed considerably improved performance in terms of interface compatibility when compared to titanium and therefore a Co-Cr/Ta system would seem feasible for the manufacture of porous structured devices when a bi-material approach is required. This would allow the advantages of a highly biocompatible structured coating to be combined with the mechanical performance of a less biocompatible substrate.