Crack growth in Alloy 800H in a temperature range of 650 to 900°C for various loading conditions was examined in this study. Creep and hold time crack growth rates were shown to be correlated satisfactorily by C* even for the hold period as short as 1 minute at 650°C. The fatigue loading portion of the cycle in hold time tests apparently has little effect on crack growth mechanisms at 650°C. This conclusion can be verified by 1.) load-line deflection versus crack length plots, 2.) microhardness profiles ahead of the crack tip, and 3.) examination of the fracture surfaces. At higher temperatures, C* still provides adequate correlation of creep crack growth rates in this alloy.
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