Alumina and tricalcium phosphate added CoCr alloy for load-bearing implants

Cobalt-chromium (CoCr) alloys are used in load-bearing implants due to their excellent wear resistance. However, poor tissue-material interactions can originate due to the release of wear and corrosion-induced Co and Cr ions, motivating the use of surface modification to reduce such phenomena. Premixed feedstock powders of CoCrMo + 2 wt.% tricalcium phosphate (TCP, CoCr_TCP) and CoCrMo + 2 wt.% tricalcium phosphate + 4 wt.% Al₂O₃ (CoCr_TCP+Al) were used to surface coat CoCr alloy via Laser Engineered Net Shaping (LENS™) with the objective of increasing CoCr alloy's wear resistance. Electron micrographs of the microstructure revealed the dissociation of intergranular globular carbide phases and reprecipitation into a finer network-like microstructure with homogeneous distribution of Co and Cr. X-ray diffraction (XRD) spectra revealed texturing or preferential crystallographic orientation amongst the LENS™ processed materials, with the TCP added CoCr displaying some ε-phase stabilization. Tribological testing resulted in an 82.3% and 71.6% decrease in wear rate and wear coefficient, respectively, for CoCr_TCP when compared to commercially available CoCr alloy. Additionally, in situ tribofilm development was observed for the fabricated samples via an increase in contact resistance. The current study resulted in not only a decrease in wear volume but also a decrease in the overall degradation of the coated CoCr alloy.