BS in Materials Engineering
Materials Engineering Department
The platinum alloy used by Abbott Vascular in guidewire tips exhibits a yielding behavior characterized by an abrupt transition from elastic to plastic zones and high ductility. This yielding behavior was hypothesized to be a result of one of three structural phenomena: ordering, solute strain aging, or interstitial strain aging. To test for these strengthening mechanisms in the wire, X-ray diffraction analysis, heat treatments, and tensile testing were completed. The wire has a diameter of 0.0025 inches and was supplied in two forms, the final stress relieved state, and as-drawn from the production line. Heat treatments were performed at 130oC, 250oC, 400oC, and 600oC for a period of one hour. Heat treatments were also performed at 250oC for four hours and eight hours. Heat treating in the theoretical ordering range, between 130-400oC, revealed an increased tensile strength of the wire from 1600 MPa to 1800 MPa. Once heat treated outside of the possible ordering region, at 600oC, the wire showed the same characteristics in tension as the stress relieved wire, which could to be due to an annealing and strain aging mechanism. X-ray diffraction was performed using the Siemens D5000 diffractometer to characterize the crystal structure of the wire. XRD revealed an FCC structure corresponding to the platinum 27 at. % nickel lattice constant, with little evidence of ordering. Superlattice reflections, which appear in XRD and indicate ordering, were not detected. This may have been due to sample preparation, or because the wire is highly textured from the manufacturing process of wire-drawing. Although the XRD failed to find evidence of ordering, this does not mean it is not present within the wire. Strain aging may also be present within the wire, but could not be found due to the nature of Cottrell atmospheres and the difficulty of finding interstitial atoms without proper equipment.
Available for download on Monday, June 08, 2020