Thesis
Understanding wear behavior of CoCrMo coatings on Ti6Al4V and tantalum coating on titanium for load-bearing implants
Washington State University
Master of Science (MS), Washington State University
05/2011
DOI:
https://doi.org/10.7273/000006227
Abstract
In this investigation negative biological effects of cobalt chrome alloy (CoCrMo) were reduced or eliminated while maintaining a low wear rate. This was accomplished in two ways first by creating a gradient CoCrMo-Ti6Al4V structure and secondly by replacing 100% cobalt chrome with a tantalum coated titanium. Both types of samples were made using a laser engineered net shaping (LENS) process. Novel, unitized structures, to minimize multiple parts for load-bearing implants, were fabricated with porous Ti6Al4V alloy on one side to encourage osseointegration and compositionally graded CoCrMo alloy on the surface, to reduce wear. Gradient structures with 50%, 70% and 86% CoCrMo alloy on the top surface showed high hardness between 615 and 957 HV. These gradient structures were evaluated for their in vitro wear rate and Co ion release in a simulated body fluid (SBF). It was determined the wear rate of ultrahigh molecular weight polyethylene and 100% CoCrMo alloy substrates depends on the hardness and microstructural features of the counter surface. In general, the wear rates of both substrates increased with a decrease in CoCrMo alloy concentration of gradient pins. However, high hardness gradient pins had a lower wear rate than 100% CoCrMo alloy pins. Gradient pins having 86% CoCrMo alloy had the lowest wear rates of 5.07 x 10-8 to 7.99 x 10-8 mm3/Nm. During in vitro wear testing the amount of Co released from gradient structures was, in the range of 0.38 and 0.91 ppm, whereas from 100% CoCrMo alloy it was 0.25 and 0.77 ppm. The second part of the study was focused on in vitro tribological performance of Ta coatings on Ti for load-bearing implant applications. Linear reciprocating wear tests in simulated body fluid showed a wear rate one order of magnitude lower, of the order of 10-4 mm3 (N.m)-1, for Ta coatings compared to control Ti plate. This result demonstrated that laser processed Ta coatings can minimize early-stage wear debris. In summary, results from both studies indicated that intelligent coatings can be designed and fabricated using agile manufacturing for loadbearing implants to enhance bioactivity and reduce wear using unitized structures.
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Details
- Title
- Understanding wear behavior of CoCrMo coatings on Ti6Al4V and tantalum coating on titanium for load-bearing implants
- Creators
- Stanley Alan Dittrick
- Contributors
- Amit Bandyopadhyay (Chair) - Washington State University, School of Mechanical and Materials EngineeringSusmita Bose (Committee Member) - Washington State University, School of Mechanical and Materials EngineeringNeal M Davies (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- School of Mechanical and Materials Engineering
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University
- Number of pages
- 63
- Identifiers
- 99901081340001842
- Language
- English
- Resource Type
- Thesis