Effect of activity differences on hydrogen migration in dissimilar titanium alloy welds |
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Authors: | J R Kennedy P N Adler and H Margolin |
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Affiliation: | (1) Corporate Research Center, Grumman Corporation, 11714 Bethpage, NY;(2) Department of Materials Science and Engineering, Polytechnic University, 11201 Brooklyn, NY |
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Abstract: | The effect of alloy composition on hydrogen activity was measured for seven titanium alloys as a means to determine the tendency
for hydrogen migration within dissimilar metal welds. The alloys were: Ti-CP, Ti-3A1-2.5V, Ti-3Al-2.5V-3Zr, Ti-3Al-2Nb-lTa,
Ti-6A1, Ti-6A1-4V, and Ti-6Al-2Nb-lTa-0.8Mo. Hydrogen pressure—hydrogen concentration relationships were determined for temperatures
from 600 °C to 800 °C and hydrogen concentrations up to approximately 3.5 at. pct (750 wppm). Fusion welds were made between
Ti-CP and Ti-CP and between Ti-CP and Ti-6A1-4V to observe directly the hydrogen redistribution in similar and dissimilar
metal couples. Hydrogen activity was found to be significantly affected by alloying elements, particularly Al in solid solution.
At a constant Al content and temperature, an increase in the volume fraction of β reduced the activity of hydrogen in α-β
alloys. Activity was also found to be strongly affected by temperature. The effect of temperature differences on hydrogen
activity was much greater than the effects resulting from alloy composition differences at a given temperature. Thus, hydrogen
redistribution should be expected within similar metal couples subjected to extreme temperature gradients, such as those peculiar
to fusion welding. Significant hydrogen redistribution in dissimilar alloy weldments also can be expected for many of the
compositions in this study. Hydride formation stemming from these driving forces was observed in the dissimilar couple fusion
welds. In addition, a basis for estimating hydrogen migration in titanium welds, based on hydrogen activity data, is described. |
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