Effect of slightly faster strain rates and internal hydrogen on uranium-0.8 weight percent titanium alloy mechanical properties

摘要

Mechanical testing of uranium-0.8 wt % titanium (U-0.8 wt % Ti) alloys can affect the outcome of mechanical properties, primarily ductility, by varying the crosshead velocity, which changes the strain rate. However, most specifications that govern mechanical properties of this alloy reference ASTM E-8, which limits the speed to 0.5 in./in. of gage length per minute. Our current procedure for testing U-0.8 Ti is not at the maximum speed permitted in ASTM E-8, so an experiment was designed to evaluate the effect of maximizing the crosshead velocity per ASTM E-8. In order to create a fair assessment, tensile specimens were prepared that were low in internal hydrogen (0.02 ppM) and higher in internal hydrogen (0.36 ppM). External hydrogen effects were minimized by testing in a controlled environment that contained less than 10% relative humidity. Test results showed that for the low hydrogen test group, increasing the crosshead velocity caused a significant increase in reduction in area (RA), but not in elongation. For the higher hydrogen test group, increasing the speed resulted in a significant increase in RA and an increase, though not statistically significant, in elongation. Of equal importance was an observation that strongly suggests a correlation between material defects, like inclusion clusters, and higher hydrogen content, especially at the slower strain rate that would explain the erratic behavior in ductile properties associated with this alloy. As a result of this study, increasing the crosshead velocity to 0.32 in./min is recommended for mechanical testing of U-0.8 Ti alloys. 9 refs., 4 figs., 5 tabs.