Plastic flow instabilities of L1 2 Co 3Ti alloys at intermediate temperatures

Abstract

The serrated flow of L1 2 Co 3Ti alloys was investigated by tensile tests in terms of the effects of temperature, strain rate, alloy stoichiometry and cooling rate after annealing. The serrated flow was most strongly observed at 673 K and at a strain rate of 3.2×10 −4 s −1. Correspondingly, the maximum stress amplitude and the lowest (negative) strain-rate sensitivity were observed at 673 K. The serrated flow was more significant as the alloy departs from a stoichiometric composition, and also less significant in a water-quenched sample than in a furnace-cooled sample. The static aging at 673 K resulted in a reduced flow stress. The activation energy of the serrated flow was estimated to be about 84 kJ/mol and almost one-half of that of lattice diffusion of the excess Co atoms. The serrated-flow behavior is explained qualitatively on the basis of consideration of the dynamics of the dislocation core structure, and is also discussed in association with the strength anomaly.