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Published on: March 13, 2018
Titanium-Silicon on CoCr Alloy for Load-Bearing Implants Using Directed Energy Deposition-Based Additive
Jose D Avila1, Murat Isik1, Amit Bandyopadhyay1
1W. M. Keck Biomedical Materials Research Lab, School of Mechanical and Materials Engineering, Washington State University, Pullman, Washington 99164, United States.
Abstract:
Cobalt-chromium (CoCr) alloys offer outstanding wear resistance when compared to other biocompatible metallic materials and are extensively used in articulating surfaces of total hip and knee arthroplasty. However, CoCr alloys' biocompatibility is known to be inferior to titanium (Ti). Wear- and corrosion-induced metal-ion release from CoCr alloys has been reported to cause cancer and negative physiological impacts. In this study, CoCr alloy was coated with commercially pure Ti (CpTi) and CpTi-Silicon (CoCrTi-Si) with the specific objective of reducing Co and Cr ion release during articulation, without degrading the excellent wear resistance of the CoCr alloy. Directed energy deposition (DED), a blown powder-based laser additive manufacturing technique, was utilized to process CpTi- and CpTi-Si-based coatings on Stellite 6B commercial CoCr alloy. Scanning electron microscopy (SEM), X-ray diffraction (XRD) analyses, and hardness testing found that refined carbides and titanium silicides increased the hardness from 321 ± 13 to 758 ± 48 HV0.5. Tribological studies determined a comparable wear rate between Stellite 6B alloy and CoCrTi-Si in DI water but a statistically significant reduction in Dulbecco's Modified Eagle Medium (DMEM). The wear rates for Stellite 6B were 8.5 ± 0.8 × 10-5 and 12.9 ± 0.4 × 10-5 mm3/Nm in DI water and DMEM, respectively. While the wear rates for CoCrTi-Si were 9.1 ± 0.5 × 10-5 and 8.9 ± 0.8 × 10-5 mm3/Nm in DI water and DMEM, respectively. Contact resistance acquisition displayed the presence of a passive film formation during tribological testing. ICP-MS results for Stellite 6B and CoCrTi-Si concluded a reduction of Co ions release in DI water from 149.8 ± 66.7 to 17.5 ± 0.7 ppb and a reduction in Cr ions release from 66.7 ± 32.4 to 18.0 ± 0.5 ppb, respectively. In DMEM media, Co ion release for Stellite 6B and CoCrTi-Si reduced from 10.1 ± 1.4 to 4.1 ± 0.2 ppb and Cr ion release for Stellite 6B and CoCrTi-Si reduced from 8.7 ± 0.2 to 5.0 ± 0.7 ppb, respectively. The current study revealed a new mode of manufacturing for CoCr alloy-based load-bearing implants that can reduce toxic metal ions release due to wear- and corrosion-induced damages.
