Abstract
For titanium alloys, crack initiation as a result of plastic strain accumulation has been shown to govern fatigue life under the high cycle fatigue regime. In this study, the early plastic slip activity and fatigue crack initiation was studied using a cyclic four point bending test at 10 Hz with a load ratio of 0.1, up to 90% of the proof stress. The plastic slip in the high stress area was monitored by interrupting the test and performing optical microscopy. Following fatigue crack initiation, scanning electron microscopy (SEM) combined with electron backscatter diffraction (EBSD) was used to identify the slip and crack initiation mode in a 600 x 600 μm2 area. Using slip trace analysis, it was shown that primary alpha grains offered dominant plastic deformation with basal slip activation. Cracking along basal planes was determined to be the dominant damage mode.
Highlights
TIMETAL®834 is a near-α titanium alloy developed for high temperature service parts in gas turbine engines [1]
We focus on the micromechanical plastic deformation and mechanisms of fatigue crack initiation in bimodal TIMETAL®834 alloy
scanning electron microscopy (SEM) observation reveals that 95% slip activity is restricted to primary alpha grains which accommodate the dominant plastic deformation
Summary
TIMETAL®834 is a near-α titanium alloy developed for high temperature (up to 600 oC) service parts in gas turbine engines [1]. Its bimodal microstructure consisting of equiaxed primary alpha (αp) grains located at the triple-point of the β grain boundaries and secondary alpha (αs) colonies is produced by deformation in the α+β phase region with subsequent recrystallization and ageing. TIMETAL®834, with a bimodal microstructure and around 15% primary alpha grains exhibits well-balanced creep-fatigue properties [2]. Numerous experimental studies have reported that the mechanism of fatigue crack initiation is correlated with the slip bands across primary alpha grains or secondary alpha colonies in bimodal microstructures [7, 8, 10, 11]. We focus on the micromechanical plastic deformation and mechanisms of fatigue crack initiation in bimodal TIMETAL®834 alloy. The studied areas covered hundreds of grains and slip trace analysis was used to identify active slip systems in the same area by SEM combined with grain orientation data by Electron Backscatter Diffraction (EBSD)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
