Creep Fatigue Environment Interactions PDF Download

The fatigue-creep-environment interactions in nickel base superalloys were investigated from 650 C to 760 C in the low cycle fatigue range and in the crack growth mode as a function alloy chemistry and microstructure. Three alloys, conventionally cast and forged Waspaloy, powder metallurgy as-hot isostatically pressed low carbon Astroloy, and powder metallurgy superplastically forged IN-100 were compared by room and elevated temperature low cycle fatigue testing under control of total strain range. It was found that at 427 C and 649 C Waspaloy had the longest fatigue lifetimes followed by low carbon Astroloy, then IN-100, but IN-100 had the highest cyclic flow stress and Waspaloy the lowest. On the basis of its relatively good combination of fatigue properties, homogenity and isotropy resulting from powder processing, and because it can be heat treated to a wide variety of different microstructures, one alloy, low carbon Astroloy was selected for a program to systematically determine the effects of changes in microstructure on elevated temperature fatigue behavior. Low carbon Astroloy was heat treated to four very different microstructures with various combinations of fine (500A) and coarse (2000-8000A) matrix gamma and grain boundaries with and without carbides and primary gamma'.