How Texture and Microtexture Influence Dwell Fatigue Lifetime in Forged IMI834 Titanium Alloys

IMI 834 specimens have been cut off from various regions of a forged disk and tested under cold dwell fatigue conditions. A large spread of dwell fatigue lifetime was observed. Bright regions on the fracture surfaces were related to numerous quasi cleavage facets and were identified as crack initiation and short distance propagation regions. EBSD measurements were performed to characterize the crystallography of these regions. It was found that sharp textured regions (called macrozones) prevailed with (c) over right arrow axes at less than 30 from the solicitation axis. A detailed analysis of the specimens with the shortest fatigue lifetimes shows that the crack nucleation and propagation regions were within such large macrozones well oriented for quasi-cleavage. This confirms that the presence of macrozones with a pronounced concentration of grains oriented at less than 30 from the solicitation axis strongly reduces the service life of specimens under cold dwell fatigue.