Abstract

The purpose of this research is to identify the effects of the carbon-infiltrated carbon nanotube (CICNT) growth process on the material properties of 316L stainless steel, particularly those properties which are essential for biocompatibility. Physically altering the micro-topography of a surface can dramatically affect its capacity to support or prevent biofilm growth. Growing CICNTs on biomedical materials is one approach which has demonstrated success at preventing biofilm growth. Unfortunately, the high temperature and carbon-rich gas exposure required for this procedure has proven to have deleterious effects. Rusting has been observed on samples that have been coated with CICNTs and then placed in culture media. A proper understanding of this rusting phenomenon, along with an exploration of other material properties which could be affected by the procedure, is a necessary prelude to further development of this novel antibacterial method. This thesis proposes a kinetic model derived from Fick's Second Law to predict the growth of chromium carbide as a function of temperature and time. Chromium carbide formation is shown to be the mechanism of corrosion, as chromium atoms are leeched from the the material, preventing the formation of a passivating chromium oxide layer that protects iron oxide from forming. The model is validated using experimental methods, which involve immersion in culture media, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and double loop electrochemical potentiokinetic reactivation (EPR) testing. This thesis further explores how the CICNT growth procedure affects the mechanical properties of 316L stainless steel as a function of temperature, time exposure to ethylene gas flow, and sample geometry. It is shown that the CICNT growth procedure effectively carburizes the stainless steel surface. Tensile tests demonstrate that the carburized surface leads to brittle failure for thin samples that have a relatively small ductile interior. This thesis also examines the adhesion and wear of the CICNTs on the surface of the 316L stainless steel. Tape tests and torsional shearing show strong adhesion between the CICNTs and the metal substrate. External fixator pin drilling also shows remarkably good wear properties for the CICNT surface. The changes in mechanical properties and the overall adhesive performance must be considered and properly managed by biomedical engineers hoping to use CICNT coatings.

Degree

MS

College and Department

Ira A. Fulton College of Engineering and Technology; Mechanical Engineering

Rights

https://lib.byu.edu/about/copyright/

Date Submitted

2021-04-02

Document Type

Thesis

Handle

http://hdl.lib.byu.edu/1877/etd11553

Keywords

CICNT, corrosion, stainless steel, carburization, adhesion, sensitization

Language

english

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