Mechanisms of Ductility in CoTi and CoZr B2 Intermetallics |
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Authors: | J.A. Wollmershauser C.J. Neil S.R. Agnew |
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Affiliation: | (1) Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA 22904, USA; |
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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 á 100 ñ { 0 1 1 } leftlangle { 100} rightrangle 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 á 1 10 ñ { [`1] 10 } leftlangle { 1 10} rightrangle left{ {overline{1} 10} right} or á 1 1 1 ñ { 1[`1] 0 } leftlangle { 1 1 1} rightrangle left{ {1overline{1} 0} right} slip mechanisms coupled with á 1 0 0 ñ leftlangle { 1 0 0} rightrangle 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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