Mechanisms of Ductility in CoTi and CoZr B2 Intermetallics

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.