Working group
It is known that special care must be taken when welding titanium to protect against interstitial pick-up (e.g. contamination from O2, N2, and H2) and a corresponding ductility loss resulting from a reduction in active slip systems. Hydrogen is of particular concern, because it can further embrittle titanium through hydride formation. Never the less, there exists no clear defined, alloy specific hydrogen toleration limit established for titanium welds. Working towards this end, a preliminary study was undertaken at BAM to examine hydrogen effects in three different alloys: Grade 2, Ti-64, and β-21S, representing α, α+β, and β alloys, respectively. Hydrogen, introduced to the weld through the arc shielding gas, was found to reside in weld metal at high levels (around 400 ppm). Thermal desorption analysis (TDA), performed in cooperation with Ben Gurion University in Israel, indicated that hydrogen is being held at strong trapping sites [9, 10].
Results from TDA showing desorption peaks for Ti beta alloy weld metal indicating hydrogen trap sites with high activation energy (enlarged picture)
Welds subjected to bend tests showed the β alloy to exhibit the greatest ductility loss from hydrogen, with the α alloy showing no hydrogen effect [11]. This behavior is contrary to what was expected, since β alloys have greater solubility for hydrogen. It is of interest to look at this behavior in greater detail, looking at both lower and higher strain rates.
Brittle fracture in Titanium β-21S weld metal containing hydrogen. Failure occurred in tension during bend test
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