The Relation between the Portevin-LeChatelier Effect and the Solid Solubility in Some Binary Alloys

Effects of composition and temperature on the occurrence of the Portevin-LeChatelier effect were investigated in the literature and the experiments in some alloys. These investigations show that the alloy systems are divided into two groups according to the minimum solute concentration below which the P-L effect does not occur. The first group, including Al-Mg, Al-Cu, Al-Ag, Cu-Sn and so on, consists of the alloy systems in which the P-L effects occurs at the solute content less than 1 atomic percent. A common feature of these systems is that they have small solubility of solute (the latter elements such as Mg in the Al-Mg system). On the other hand, in the systems such as Cu-Al, Cu-Zn and Ni-Cr classified in the second, the P-L effect does not occur at the solute content less than 5 atomic percent and the solute solubility is large. These results suggest that the P-L effect is related to the solubility limit or precipitation. In the current theory relating the P-L effect to the interaction of dislocations with solute atoms, the cause of interaction energy was mainly attributed to the size effect. But it is difficult for the theory to explain that although the P-L effect occurs at 0.5 at%Ag in the Al-Ag system (the atomic radii of the components are nearly equal), the P-L effect does not occur at 9 at%Al in the Cu-Al system (the atomic radius of Al (solute) atom is about 7% larger than that of Cu). We propose a new theory for the P-L effect that the precipitates or the short range ordered regions are formed in materials by the action of vacancies created by plastic deformation and interact with the dislocations.