Correlating Ultrasonic Attenuation and Microtexture in a Near-Alpha Titanium Alloy
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TRODUCTION
DWELL fatigue involves maintaining the peak stress constant for a certain period of time, usually 2 minutes in laboratory tests, rather than continuously cycling the sample. It has become widely known as a deleterious failure mechanism persistent in structural components made from near-a titanium alloys. Dwell fatigue was identified to cause early failure in titanium-based aeroengine components.[1,2] In the past few decades, significant efforts and progress were made to study both dwell fatigue and continuous cyclic fatigue behavior of titanium alloys.[2–26] Examination of titanium alloy
A. BHATTACHARJEE, formerly Postdoctoral Researcher, Department of Materials Science and Engineering, The Ohio State University, Columbus, OH 43221, is now Scientist and Head of Titanium Alloy Group, Defence Metallurgical Research Laboratory, Hyderabad 500058, India. A.L. PILCHAK, Materials Research Engineer, is with the Materials and Manufacturing Directorate, Metals Processing Group, Air Force Research Laboratory, AFRL/ RXLM, Wright-Patterson Air Force Base, OH 45433-7817. Contact e-mail: [email protected] O.I. LOBKIS, Research Scientist, and S.I ROKHLIN, Professor, are with the Department of Materials Science and Engineering, Edison Joining Technology Center, The Ohio State University. J.W. FOLTZ, formerly Graduate Research Associate, Department of Materials Science and Engineering, The Ohio State University, is now Research Metallurgist, ATI Wah Chang, Albany, OR 97321-0460. J.C. WILLIAMS, Professor and Honda Chair Emeritus, is with the Department of Materials Science and Engineering, The Ohio State University, Columbus, OH 43210. Manuscript submitted September 27, 2010. Article published online February 12, 2011 2358—VOLUME 42A, AUGUST 2011
samples that failed during dwell fatigue typically reveals a subsurface initiation site that contains flat, faceted features. Evans and co-workers[3,6–12] observed a substantial dwell life debit between components differentially subjected to pure fatigue and dwell hold periods, with dwell showing marked reduction in life. Prior research on titanium alloys attributes dwell sensitivity to a range of potential mechanisms.[3–22] These mechanisms include temperature effects,[5] time-dependent strain accumulation,[3,5] microstructural and microtexture influences,[5,8,12–18] stress ratio effects,[9] internal hydrogen embrittlement and environmental effects,[5,7,19] crystallographic orientation dependence,[11,12,19,20] synergistic interaction between fatigue and creep,[18,21,22] and subsurface crack nucleation from a in a crystallographically hard orientation (with its c-axis oriented approximately parallel to the macroscopic loading direction) or due to various dislocation reactions.[1,22–32] Extensive work by Sinha et al.[33–36] and the present authors, along with modeling efforts by Dunne et al.[37,38] and Ghosh and co-workers,[39,40] has shown that a major reason for dwell fatigue susceptibility is the presence and size of microtextured regions. This is largely controlled by processing
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