Influence of Hold Time on Dwell Fatigue Behavior in IMI834 Disc Forging

Abstract

The potential cold dwell fatigue failure in the titanium components of gas turbine engines is still a troublesome industrial issue. Based on small-scale laboratory specimens tangentially extracted from a disc forging of IMI834, the influences of dwell period and microstructural conditions on dwell sensitivity have been investigated. The fatigue fracture features and deformation mechanisms were characterized using SEM, XCT and TEM. EBSD was utilized to examine the microtexture of representative locations in the disc. The results demonstrated that large differences in dwell sensitivity of the IMI834 disc depended on dwell time and crystal orientation distribution. A significant dwell effect generated in the bimodal microstructure was attributed to the intense planar slip and relatively high intensity of major texture component (5.95 times the random level), where a dwell time of 120 s was basically enough for the effect to reach a saturation. For the location with low dwell sensitivity, extending the hold time would further increase the dwell debit and strain accumulation, which was manifested in enhancing planar slip density. The quantitative influence of crystal orientation, texture intensity and dwell time have been experimentally revealed, and the results could be useful when assessing and optimizing the dwell performance of large size parts.