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The creep crack growth behavior of Alloy 800H has been characterized at temperatures of 677C (1250F) and 732C (1350F) in controlled-impurity helium. Cold-worked material in various recrystallized conditions, expected to be encountered in elevated-temperature service, was tested in center-cracked tension specimen form under constant load. The tests were conducted under dominantly steady-state conditions where the estimated transition time to steady-state creep for each test is a small fraction of the total test time. The results indicate that the crack-tip field parameter, C*, as was experimentally measured, is a good descriptive parameter for the steady-state creep crack growth rate of this material. In fact, the crack growth rate, da/dt, versus C* data from all five tests spanning three different material conditions, two temperatures, and three orders of magnitude of crack growth rates appeared to consolidate into a single straight line on a logarithmic plot. The metallographic results show that crack extension occurs dominantly by the intergranular creep camage mechanisms anticipated in service.
Alloy 800, Alloy 800H, cold working, creep, crack growth, crack propagation, fracture mechanics, high-temperature fracture, Incoloy 800, Incoloy 800H, recrystallization, nonlinear fracture mechanics
Staff engineer, Failure Analysis Associates, Palo,