Figure 1: (a.) The elongation ratio plotted as a function of electrochemical potential for grade 2 and grade 3 titanium. The crosshead speeds are given in the figure. (b.) The elongation ratio plotted as a function of crosshead speed for grade 2 and grade 3 titanium. for both grade 2 and grade 3 titanium plotted as a function of crosshead speed. The results show that as the crosshead speed decreased the elongation ratio stayed approximately constant for grade 2 titanium, whereas the elongation ratio dropped for samples of the grade 3 titanium. Examination of the fracture surfaces showed that under all conditions the grade 2 titanium underwent ductile failure. An example is shown in Figure 2a. The grade 3 titanium had a similar fracture surface when tested in oil or under anodic conditions. However, as the elongation ratio decreased for the grade 3 titanium, the fracture surface showed new features. These included brittle secondary cracks on the surface, some evidence of large voids on the surface, and evidence of a new population of fine scale voids. A micrograph is shown in Figure 2b. Additional information was obtained by examining the hydride that formed on the surface of a sample after cathodic charging. In the case of the grade 2 titanium, we found that there was a thick layer of hydrides, as shown in Figure 3a, but that beneath this layer few hydrides were observed. In the grade 3 material, this thick layer was also observed, but in addition there were hydrides beneath this thick layer extending into the matrix, as shown in Figure 3b. In flat samples charged for 24 hours at an electrochemical potential of –1000 mVSCE, hydrides extended Figure 2: Scanning electron micrographs of (a.) grade 2 titanium tested at –400 mVSCE and (b.) grade 3 titanium tested at –1400 mVSCE. The arrow points out fine microvoids.
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