Microstructural Influences on Very High Cycle Fatigue Crack Initiation in Ti-6246 (PREPRINT)
Abstract
The fatigue behavior of an alpha + beta titanium alloy, Ti-6Al-2Sn-4Zr-6Mo, has been characterized in the very high cycle fatigue (VHCF) regime using ultrasonic fatigue (20 kHz) techniques. Stress levels of 40 to 60% of the yield strength of this alloy have been examined. Fatigue lifetimes in the range of 10 (to the 6th) to 10 (to the 9th) cycles are observed and fatigue cracks initiate from both surface and subsurface sites. This study examines the mechanisms of fatigue crack formation by quantifying critical microstructural features observed in the fatigue crack initiation region. The fracture surface near the fatigue crack initiation site was crystallographic in nature. Facets, which result from the fracture of primary alpha grains, are associated with the crack initiation process. The primary alpha grains that form facets are typically larger in size than average. The spatial distribution of primary alpha grains relative to each other observed near the initiation site did not correlate with fatigue life. Furthermore, the spatial distribution of primary alpha grains did not provide a suitable means for discerning crack initiation sites from randomly selected nominal areas.
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 01, 2008
- Accession Number
- ADA490160
Entities
People
- C. J. Szczepanski
- J. W. Jones
- James M. Larsen
- Sushant K. Jha
Organizations
- Air Force Research Laboratory