Abstract
The present research is conducted in order to elucidate the operative deformation mechanisms allowing ductility in the B2 (CsCl) intermetallics CoTi and CoZr. A twofold approach combines in-situ neutron diffraction during uniaxial compression with elastoplastic self-consistent (EPSC) polycrystal modeling. Tensile and compression tests of CoZr and CoTi confirm that both intermetallics are ductile at room temperature. Low compressive yield points of −62 and −50 MPa are identified for CoTi and CoZr, respectively. Analysis of stress-strain curves, in-situ neutron diffraction internal strain measurements, and EPSC modeling confirm that the initial plasticity is accommodated via the established \( \left\langle { 100} \right\rangle \left\{ {0 1 1} \right\} \) slip mode. However, a sudden decrease in the hardening rate observed in the macroscopic stress-strain curve and apparent in the internal stress developments signals the activation of a secondary mechanism, which helps to explain the anomalous ductility. The EPSC simulations involving either \( \left\langle { 1 10} \right\rangle \left\{ {\overline{1} 10} \right\} \) or \( \left\langle { 1 1 1} \right\rangle \left\{ {1\overline{1} 0} \right\} \) slip mechanisms coupled with \( \left\langle { 1 0 0} \right\rangle \) slip can reproduce the observed transitions at −350 and −250 MPa for CoTi and CoZr, respectively. Implications related to previous observations of a yield strength anomaly and the possible influence of kink banding are discussed.
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Acknowledgments
This work was supported by the National Science Foundation (Arlington, VA) through a CAREER Grant No. DMR-0547981. The authors thank Drs. Saurabh Kabra and Bjørn Clausen, Los Alamos National Laboratory, for helping with neutron diffraction experimental design and data analysis. The authors are also grateful to Mr. Cecil A. Carmichael, Jr. and Dr. Evan Ohriner of the ORNL for performing the arc casting and hot extrusion used in this work.
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This article is based on a presentation given in the symposium “Neutron and X-Ray Studies of Advanced Materials,” which occurred February 15–19, 2009, during the TMS Annual Meeting in San Francisco, CA, under the auspices of TMS, TMS Structural Materials Division, TMS/ASM Mechanical Behavior of Materials Committee, TMS: Advanced Characterization, Testing, and Simulation Committee, and TMS: Titanium Committee.
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Wollmershauser, J., Neil, C. & Agnew, S. Mechanisms of Ductility in CoTi and CoZr B2 Intermetallics. Metall Mater Trans A 41, 1217–1229 (2010). https://doi.org/10.1007/s11661-009-9990-2
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DOI: https://doi.org/10.1007/s11661-009-9990-2