Volume 8, Issue 5 (May 2011)
Effects of the Environment on the Crack Propagation Behavior of IN718 in the Temperature Range of the Dynamic Embrittlement
IN718 is a standard nickel-base alloy for high temperature usage, e.g., as forged gas turbine disks. At elevated temperatures IN718 is prone to cracking by dynamic embrittlement. Dynamic embrittlement is caused by oxygen diffusion along the grain boundaries, resulting in a time-dependent intergranular decohesion. The result is a fast brittle intercrystalline crack propagation. In contrast, vacuum testing shows a drastic reduction of the crack propagation rate and a ductile, transcrystalline fracture morphology. Objective of this investigation is to gain a better understanding of the dynamic embrittlement process. In the present study the crack growth rate has been measured with an alternate current potential drop system (ACPD) and a far-field microscope during dwell-time testing at 650°C, a positive stress ratio and two different load schemes.