Hard slip mechanisms in B2 CoTi

Deformation mechanisms in B2 CoTi have been examined using g · b analysis in a transmission electron microscope and in-grain misorientation axes (IGMA) obtained from electron-backscattered diffraction. The results from both techniques confirm that cube dislocations are activated at low stresses and that 〈1 0 0〉{0 1 1} and 〈1 0 0〉{0 0 1} are the dominant slip modes. However, in samples deformed beyond a transition in the strain hardening behavior, activation of a secondary deformation mechanism is confirmed. Transmission electron microscopy analysis unambiguously shows the presence of dislocations with 〈110〉 Burgers vectors, as well as the presence of dislocations which have the 〈110〉 or 〈111〉 Burgers vector. IGMA analysis indicates the activation of the 〈1 1 1〉{11¯0} slip mode. The slip of dislocations with 〈1 1 0〉 or 〈1 1 1〉 Burgers vectors can reduce stress concentrations that could otherwise lead to premature fracture, thus providing a satisfying explanation for the anomalous ductility of CoTi and related compounds, like CoZr.