Ph.D. Thesis Defense by Dana Ray Swalla
Friday, August 1, 2003

(Dr. Richard Neu, advisor)

"Microstructural Characterization of Titanium Alloys with Fretting Damage"

Abstract

The primary focus of this work is to understand the role of microstructure in the fretting damage process and develop quantifying measures in fretting damage accumulation in a dual phase Ti-6Al-4V as well as two single phase materials: commercially pure titanium (CP-Ti), which consists of pure a-phase titanium, and a near-a Ti-5Al-2.5Sn. The size and distribution of crystallographic orientation of the a-phase, which has an HCP crystalline structure, is significant in fretting crack formation. In particular, the effect of slip displacement amplitude and number of fretting cycles on the evolution of grain morphology, grain orientation, misorientation distribution, composition, and microhardness is investigated. The fretting behavior is also related to the macroscopic monotonic and cyclic deformation response. The research goals are accomplished using state-of-the-art surface characterization tools such as orientation imaging microscopy (OIM) using electron backscatter diffraction (EBSD), energy dispersive X-ray analysis (EDX) and nanoindentation. This study is the first of its kind to use OIM to characterize fretting damage and also makes contributions to the body of knowledge about deformation mechanisms in titanium alloys. The results provide a foundation for developing and validating computational crystal plasticity models and their application to fretting and sliding contact problems. New fretting assessment measures have also been identified and have application for components that suffer from fretting wear and/or fatigue related failures