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The effects of electron beam 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 (KIc) and subcritical crack growth parameters were measured 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.
At intermediate stress intensity factors and within the data scatter for replicate tests, the growth rates of fatigue cracks sited in the fusion and heat-affected zones of electron beam weldments were temperature insensitive and nearly equivalent to rates for the base metal. However, electron beam welding introduced a zone of low fracture toughness at the heat-affected-zone/fusion-zone boundary. The KIc value for this boundary zone at liquid nitrogen temperature (76 K) was 51 MPa/m1/2, 16 percent lower than the base metal. The base metal fracture toughness increases between 4 and 295 K, with an abrupt transition to higher KIc 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.
titanium, electron beam welding, fatigue (materials), fracture properties, low temperature tests, mechanical properties, titanium alloys
Cryogenics Division, Institute for Basic Standards, National Bureau of Standards, Boulder, Colo.