INTERPRETATION OF THE MEASUREMENT OF ACTIVATION PARAMETERS IN L1(2) ALLOYS

Trying to connect microscopic interactions with macroscopic mechanical measurements is one of the goals of plasticity studies. The measureme nt 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) strai n rate epsilon<over dot>(p0) at the beginning of the relaxation test. A careful theoretical analysis is therefore given. One interesting res ult is that both the strain rate sensitivity, or equivalently the acti vation area, and the initial (plastic) strain rate epsilon<over dot>(p 0) can be unambiguously determined in current relaxation tests. The me thod is applied to the case Ni3Al,X single crystals of various composi tions. The initial (plastic) strain rate epsilon<over dot>(p0) is foun d to depend markedly on the plastic deformation preceding the relaxati on test and to be strongly influenced by temperature. A discussion on the transition between the elastic and plastic deformation of these al loys is given. (C) 1997 Elsevier Science S.A.