The effects of electron beam (EB) welding on the fracture behavior of a recrystallization annealed, extra-low-interstitial Ti-6A1-4V alloy have been investigated at temperatures in the ambient-to-cryogenic range. Plane strain fracture toughness (K T) and subcritical crack growth parameters were measured Ic using compact specimens 10 to 25.4 mm thick. These parameters can be used to predict the safe operating lifetimes of cryogenic pressure vessels and other welded Ti-6A1-4V structures. Although EB welding transforms the base metal microstructure extensively, its effects on the material's fatigue crack propagation resistance at intermediate stress intensity factors are negligible. The growth rates, da/dN, of fatigue cracks sited in the fusion and heat-affected zones of weldments were temperature insensitive and nearly equivalent to rates for the base metal. However, welding introduces a zone of low fracture toughness at the heat-affected-zone/fusionzone boundary. The K value for this boundary zone at liquid 3/2 nitrogen temperature (76 K) was 45 MN/m , 16% lower than the base metal. The base metal fracture toughness increases between 4 and 295 K, with an abrupt transition to higher K values occurring at temperatures between 76 and 125 K. Static load cracking, temperature effects, and specimen orientation effects on the fracture behavior of this titanium alloy are central topics of discussion.
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