Influence of simultaneous addition of carbon nanotubes and calcium phosphate on wear resistance of 3D-printed Ti6Al4V
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Influence of simultaneous addition of carbon nanotubes and calcium phosphate on wear resistance of 3D-printed Ti6Al4V Kevin Stenberg, Stanley Dittrick, Susmita Bose,b) and Amit Bandyopadhyaya),b) W. M. Keck Biomedical Materials Research Lab, School of Mechanical and Materials Engineering, Washington State University, Pullman, Washington 99164-2920, USA (Received 9 March 2018; accepted 29 May 2018)
Seeking to improve the wear resistance of the Ti6Al4V (Ti64) alloy for biomedical applications, carbon nanotubes (CNTs) and calcium phosphate (CaP) ceramics were added to Ti64 powder and successfully 3D-printed using a commercial laser engineered net shaping (LENS™) system. It was hypothesized that CNTs would allow for in situ carbide formation during laser processing, resulting in increased surface hardness. It was also hypothesized that CaPs would allow for protective tribofilm formation during wear, reducing material loss from wear-induced damage. Scanning electron microscopy images reveal defect-free microstructures with fine carbides evenly distributed, while X-ray diffraction confirms the presence of carbides without additional unwanted intermetallic phases. Vickers microhardness shows an increase in surface hardness in coatings containing both CNTs and CaPs. In vitro tribological studies found reduced coefficient of friction, reduced wear rates, and reduced metal ion-release concentrations in coatings containing both CNTs and CaPs. This study demonstrates the efficacy of CNTs and CaPs to improve wear resistance of Ti64 for potential applications in articulating surfaces of load-bearing implants.
I. INTRODUCTION
Orthopedic implants are life changing alterations that can give people abilities and freedoms back that once thought lost.1 Moreover, over 1 million implants are used in the United States alone for total hip and total knee replacements every year.2,3 A large number of those patients are below 60 years of age and those implants are expected to perform over 20 years in vivo. Hence, there is a continuous need to improve the quality of these implants to offer better solutions than before.4 In a similar manner that no material has been made synthetically to mimic and withstand the fatigue the human heart undergoes, no material has been found to ideally withstand the repeated wear ensued by load-bearing articulating surfaces such as the hip and knee joints. For load-bearing articulating surfaces, CoCr-based alloys are still the best choice and used extensively. CoCr-alloys offer exceptional resistance to abrasive wear but suffer from the potential for Co and Cr ion leaching, which can lead to metallosis, the death of cells from metal ion attachment and can be highly carcinogenic and cause different forms a)
Address all correspondence to this author. e-mail: [email protected] b) This author was an edi
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