Irreversible Hydrogen Trapping in Welded Beta-21S Titanium Alloy

Abstract

β - 21S titanium alloy is ranked among the most important advanced materials for a variety of technological applications, due to its combination of a high strength/weight ratio, good corrosion behavior and oxidation resistance. However, in many of these technological applications, this alloy is exposed to environments which can act as sources of hydrogen, and consequently, hydrogen-induced cracking and property degradation, hydrogen-induced ductile-to-brittle transition associated with a change in the fracture mode from ductile, micro-void coalescence to brittle, cleavage have to be considered[1, 2, 3, 4]. In the aged β-21S alloy, the susceptibility to hydrogen induced cracking and the decrease in the alloy’s strength has been attributed to the -phase precipitated during the aging and the hydrogen-induced stabilization of the β-phase[1, 2, 5]. Hydrogen-induced intergranular cracking in the cathodically pre-charged β-21S alloy was significantly influenced by the preferential α precipitation at β grain boundaries[5]. Even without hydriding, the α-β interfaces could provide trapping sites and the accumulation of hydrogen at these interfaces could result in fracture. Pound[6] revealed that in aged β-Ti alloys the relationships among the trapping constants, resistance to hydrogen embrittlement and grain boundary are critical in determining the role of trapping in hydrogen embrittlement of these alloys.