Convened under the auspicious of esteemed endorsers - ISTA

Friday, October 8, 2010, 10:20-11:00Session A12: MaterialsA NOVEL ROUTE for PROCESSING Co-Cr-Mo ORTHOPAEDICALLOYSBhairav Patel - UCL - London, UK*Mohan Edirisinghe - University College London - London, UKFawad Inam - Queen Mary, University of London - London, UKMike Reece - Queen Mary, University of London - London, UKWilliam Bonfield - University of Cambridge - Cambridge, UKJie Huang - University College London - London, UKArash Angadji - Furlong Research Charitable Foundation - London, UK*Email: m.edirisinghe@ucl.ac.ukMillions of people suffer from bone and joint inflammatory problems and usually result inextreme cases with total joint replacement. Most commonly affected joints are the hip and theknee. Over the past 20 years there has been a revival in interest of metal-on-metal hipreplacements. Various alloys have been used in joint replacement, the most successful in theCobalt-based alloys. As compared to others the cobalt based alloys have higher wear resistanceand therefore less risk of failure. The most common Co-based alloy used in clinical applicationis the ASTM F75 alloy, which is extensively used in femoral and acetabular components.Conventional methods to fabricate the alloy are via cast or wrought techniques. Wrought alloysare better than their cast materials due to their superior mechanical properties as the forgingprocess promotes plastic deformation. An alternative method of fabrication is via powderprocessing and has shown significant improvements to produce finer grained materials, whichrelate to enhancement in properties, such as strength, toughness, ductility.One of the key stages of powder processing is sintering of the powder to fuse the particlestogether. A superior but simple sintering processing is spark plasma sintering (SPS), whichproduces highly dense materials with minimum grain growth. This is achieved by a pulsedelectrical current heating the material while applying a pressure to compact the powderedmaterial. This process has the ability to densify nanopowders, in order to producemicrostructures with finer grains and superior mechanical properties.Using SPS and nanopowders for the first time, we have been able to prepare the ASTM F75cobalt–chromium–molybdenum (Co–Cr–Mo) orthopaedic alloy composition. In this work wehave investigated, the effect of processing variables on the structural features of the alloy(phases present, grain size and microstructure). We have been able to produce specimens of>99% of the theoretical density. The structures were free of carbides, which a vitalbreakthrough. Detrimental carbide phases in the microstructure as found in the moreconventional methods of fabrication have shown to cause problems in wear. The compacts areof higher hardness than cast or wrought products despite the absence of carbides in themicrostructure. The gain in hardness is because of the presence of oxides in the microstructureand we hope to quantify the oxide content in the future. The mechanisms of oxide formationare explained by considering chemical thermodynamics and kinetics. The next step is toevaluate the tribological performance (wear, friction, lubrication regimes) of this SPS-processedmaterial and compare its performance with conventional MoM products (cast and wrought).The SPS route offers significant advantages over the conventional cast and wrought routes usedto prepare this alloy for orthopaedic applications.file:///E|/ISTA2010-Abstracts.htm[12/7/2011 3:15:47 PM]