Plastic flow instabilities of L12Ni3Al alloys at intermediate temperatures

Abstract

The serrated plastic flow of L12 Ni3Al alloys at intermediate temperatures was investigated using tensile tests. The effects of temperature, strain rate and composition were examined. The serrated plastic flow accompanied by the lowest (negative) strain-rate sensitivity was observed most strongly at 673 K and at a strain rate of 3.2 × 10−4 s−1. The serrated plastic flow became more significant as the alloy departed from a stoichiometric composition. The static strain aging at 673 K resulted in a reduced flow strength. The activation energy of the serrated plastic flow was estimated to be about 66 kJ/mol, which suggests that it is smaller than that for lattice diffusion of solutes in L12 lattices. The serrated plastic flow behavior of the Ni3Al alloys was compared with that of the L12 Co3Ti and Ni3(Si,Ti) alloys, and is qualitatively explained on the basis of the dynamics of solutes in the core of dissociated screw dislocations.