Electromagnetic NDE of Interstitial Contamination in Titanium Alloy Weldments,
MASSACHUSETTS INST OF TECH CAMBRIDGE DEPT OF MATERIALS SCIENCE AND ENGINEERING
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The direct effect of dissolved oxygen and other interstitials on the electrical resistivity of titanium alloys is generally small relative to the resistivity of the alloy itself. However, there are special cases where the microstructural effects e.g., alpha precipitation of the oxygen may be large enough to cause detectable changes in the resistivity. We have measured this effect by four-point probe and ac susceptibility, in five Ti-6211 specimens and seven Ti-6Al-4V weldments provided by an ONR-sponsored project at M.I.T. In the forged and annealed Ti-6211 specimens, there was no detectable relationship between the resistivitysusceptibility and the oxygen content. On the other hand, the weld metal specimens did exhibit measurable oxygen sensitivity, approximately 7 percent of the base resistivity per pct. oxygen. Control experiments on the base metal from the weldments showed a resistivity variation of 1 percent or less. We conclude that microstructural effects of oxygen contamination on electrical resistivity of weldments are large enough to measure these effects are wiped out by annealing. Thus, the resistivitysusceptibility method cannot be used generally on ti alloys regardless of history but is a valid and convenient specific approach to NDE of ti welds.