College - Author 1
College of Engineering
Department - Author 1
Materials Engineering Department
Degree Name - Author 1
BS in Materials Engineering
College - Author 2
College of Engineering
Department - Author 2
Materials Engineering Department
Degree - Author 2
BS in Materials Engineering
Date
6-2023
Primary Advisor
Blair London, College of Engineering, Materials Engineering Department
Abstract/Summary
Superelastic nitinol is competitive in the medical device industry due to its unique properties. Typical processing methods, such as electropolishing and etching, can introduce hydrogen into nitinol’s microstructure, which is known to affect its tensile properties. Due to the lack of information about hydrogen content in processed nitinol, an experiment was designed to find a relationship between hydrogen content and SE508 nitinol wire’s tensile strength, permanent set, ductility, and mode-of-failure of the fracture surface. Using a 50% sulfuric acid to mimic industry practices, five wire samples were exposed to the acid solution at seven different time intervals (ranging from 0 to 60 minutes) with additional groups of three samples at 24 hours and four days. Segments from two samples at each time interval were evaluated for hydrogen content, which revealed a consistent increase in hydrogen with time in the etchant. Each sample was tensile tested at a rate of 5 mm/min. The data showed little change in tensile strength and permanent set due to hydrogen, keeping at a consistent permanent set of around 0.20% and ultimate tensile strength of around 1080MPa. Ductility by measuring maximum elongation did not show a clear negative trend due to hydrogen under 150 wt.ppm. The fracture surfaces were imaged under the SEM, where a mixed mode of failure was characterized above 140 wt.ppm hydrogen. Adding between 0 and 150 wt.ppm hydrogen did not have major effects on the tensile properties of superelastic nitinol but had a noticeable impact on the fracture morphology at high concentrations.
URL: https://digitalcommons.calpoly.edu/matesp/270