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College Park, Maryland      June 6 - 10 , 2004

M3-A5 (2:45 PM): Fatigue-Induced Martensitic Phase Formation and Its Deformation Behavior in a Cobalt-Based Superalloy

M. L. Benson, T. A. Saleh, P. K. Liaw, H. Choo (Department of Materials Science and Engineering, The University of Tennessee, Knoxville, TN 37996, USA.), M. R. Daymond (ISIS, Rutherford Appleton Laboratory), D. W. Brown (Spallation Neutron Source, Oak Ridge National Laboratory), X.-L. Wang, A. D. Stoica (Los Alamos Neutron Science Center, Los Alamos National Laboratory), R. A. Buchanan (Department of Materials Science and Engineering, The University of Tennessee, Knoxville, TN 37996, USA.), D. L. Klarstrom (Haynes International, Inc., Kokomo, IN 46904, USA.)

ULTIMET®, a cobalt-based superalloy, is known to go through a martensitic phase transformation from a metastable face centered cubic (fcc) phase to a stable hexagonal close packed (hcp) phase during deformation at ambient temperature. In-situ neutron diffraction measurements were performed to study the deformation behavior of ULTIMET® alloys during two types of cyclic loading tests, i.e. stress-controlled tension/tension and strain-controlled tension/compression fatigue tests. The relationship between the magnitude and sign of the applied stress (or strain), development of intergranular strains, and the evolution of deformation-induced hcp phase fractions during the fatigue testing will be discussed. Furthermore, differences in mechanical behavior between the two different types of fatigue experiments will be presented. The data obtained from these experiments will be used to explain the evolution of lattice strain in the two crystallographic orientations and in different phases during fatigue. A goal of this work is to use the information obtained to improve lifetime modeling techniques of this alloy.

Acknowledgements: The author acknowledges the financial support of the National Science Foundation, the Combined Research-Curriculum Development (CRCD) Programs, under EEC-9527527 and EEC-0203415, the Integrative Graduate Education and Research Training (IGERT) Program, under DGE-9987548, and the International Materials Institutes (IMI), under DMR-0231320, to the University of Tennessee, Knoxville, with Ms. M. Poats, Dr. W. Jennings, Dr. L. Goldberg, and Dr. C. Huber as contract monitors, respectively. In addition, the financial support of the Tennessee Advanced Materials Laboratory (TAML), with Prof. E. W. Plummer as director, is recognized.

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