Interpretation of the measurement of activation parameters in L12 alloys

Trying to connect microscopic interactions with macroscopic mechanical measurements is one of the goals of plasticity studies. The measurement of relaxation kinetics has been shown to provide the determination of the so called activation area, i.e. the area swept by a dislocation during the elementary glide process. It is shown that all the methods used so far neglect a relevant physical quantity: the (plastic) strain rate gep0 at the beginning of the relaxation test. A careful theoretical analysis is therefore given. One interesting result is that both the strain rate sensitivity, or equivalently the activation area, and the initial (plastic) strain rate gep0 can be unambiguously determined in current relaxation tests. The method is applied to the case Ni3Al,X single crystals of various compositions. The initial (plastic) strain rate geinp 0 is found to depend markedly on the plastic deformation preceding the relaxation test and to be strongly influenced by temperature. A discussion on the transition between the elastic and plastic deformation of these alloys is given.