Plastic Deformation of Al–Li Single Crystals Containing Al3Li Particles

Abstract

The effect of the presence of the ordered particles, Al₃Li, on plastic deformation was studied at room temperature and at −196°C by using Al–3%Li single crystals. The volume fraction and the size of Al₃Li ranged between 0.6 and 22% and 35 and 850Å respectively. Stress-strain curves and slip morphology were investigated. Microstructures of the deformed specimens were also observed by means of transmission electron microscopy. Sharp serrated flow which accompanied the formation of distinct and inhomogeneous slip bands was observed. For all the volume fractions and the sizes of the precipitate particles investigated, the particles were found to be sheared with only a few percent of elongation. The inverse temperature dependence of flow stress which is observed for a single phase alloy with the Ll₂ structure was also detected in the crystals with high volume fractions of Al₃Li. From its orientation dependence this phenomenon was explained on the basis of the frequency of pinning of dislocations caused by cross slip of a pair of superlattice dislocations into a cube plane. It has been established that the precipitation hardening at sufficiently low temperatures at which the cross slip does not occur can be determined by the resistance induced when a pair of superlattice dislocations cuts through the ordered particles.