Materials Engineering Department
BS in Materials Engineering
A test was developed to determine relative adhesion of Teflon-coated 304 stainless steel guide wires. Two sets of wires were provided by Abbott Vascular for testing: one set was known to have poor Teflon adhesion, the other had acceptable adhesion. A prototype device was designed and manufactured that produced a shear force on the coating by dragging the wire under a ½ inch-diameter 440C hardened stainless steel cylinder. Testing consisted of increasing the force on the wire during each consecutive pass with the cylinder until the Teflon coating failed. The force on the wire during the failure producing pass was recorded as the failure weight. Failure was determined using a low magnification microscope. When the Teflon had been removed and the bare wire was visible, the coating had failed. The prototype was successful in showing a difference in adhesion between the two sets of wires; the test produced a higher average failure weight for the well adhered wires than the poorly adhered wires. An independent sample t-test was conducted to compare the results of the prototype after testing poorly adhered and well adhered wires. There was a statistically significant difference between the two distributions with a p-value less than 0.001. The test was altered to include electrical continuity as a more objective method of detecting failure. The test was successful in using electrical continuity to determine a statistical difference between the two adhesion levels. The latest test method and prototype were then used to test samples of one batch of wire at three different processing steps: as-coated, as-straightened, and post burn-in. All three processing steps were statistically different; straightening caused a decrease in adhesion levels, while burn-in caused a slight increase in adhesion.