Abstract
The average longevity of hip replacement devices is approximately 10–15years, which generally depends on many factors. But for younger generation patients this would mean that revisions may be required at some stage in order to maintain functional activity. Therefore, research is required to increase the longevity to around 25–30years; a target that was initially set by John Charnley. The main issues related to metal-on-metal (MoM) hip replacement devices are the high wear rates when malpositioned and the release of metallic ions into the blood stream and surrounding tissues. Work is required to reduce the wear rates and limit the amount of metallic ions being leached out of the current MoM materials, to be able to produce an ideal hip replacement material. The most commonly used MoM material is the cobalt-based alloys, more specifically ASTM F75, due to their excellent wear and corrosion resistance. They are either fabricated using the cast or wrought method, however powder processing of these alloys has been shown to improve the properties. One powder processing technique used is spark plasma sintering, which utilises electric current Joule heating to produce high heating rates to sinter powders to form an alloy. Two conventionally manufactured alloys (ASTM F75 and ASTM F1537) and a spark plasma sintered (SPS) alloy were evaluated for their microstructure, hardness, tribological performance and the release of metallic content. The SPS alloy with oxides and not carbides in its microstructure had the higher hardness, which resulted in the lowest wear and friction coefficient, with lower amounts of chromium and molybdenum detected from the wear debris compared to the ASTM F75 and ASTM F1537. In addition the wear debris size and size distribution of the SPS alloy generated were considerably small, indicating a material that exhibits excellent performance and more favourable compared to the current conventional cobalt based alloys used in orthopaedics.
Highlights
The performance of metal-on-metal (MoM) hip replacement devices reported over the last decade has shown excellent results in terms of longevity of the implants, with most devices lasting around 15 years [1]
Three alloys were used in this work: ASTM F75 (Weartech, UK), ASTM F1537 (Lamineries Matthey SA, Switzerland) and an alloy produced via spark plasma sintering
The three alloys: F75, F1537 and spark plasma sintered (SPS) alloys were evaluated for their microstructure and phases
Summary
The performance of metal-on-metal (MoM) hip replacement devices reported over the last decade has shown excellent results in terms of longevity of the implants, with most devices lasting around 15 years [1]. Various materials have been processed for structural and functional uses and many innovative materials have been fabricated using this process [24] This process can sinter materials at fast heating and cooling rates and with high pressures, which can limit grain growth resulting in production of samples with improved performance [25]. It is a very cost effective method as processing time is reduced significantly compared to conventional sintering [26]. The tribological properties of the powder processed alloy are tested against the commercially used cobalt based alloy to determine its performance in terms of wear and the release of metallic content.
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