PLASTIC-DEFORMATION OF AL-LI SINGLE-CRYSTALS CONTAINING AL3LI PARTICLES

The purpose of the investigation was to clarify the effect of previously reported ordered Al//3Li precipitates, with an Ll//2 structure, in aged Al-3Li alloys on plastic deformation of single crystals whose melting point is relatively low. Stress-strain curves at room temperature and at minus 196 degree C were measured, slip morphology and dislocation configurations were observed by means of optical and transmission electron microscopy. Sharp serrated flow which accompanied the formation of distinct and inhomogeneous slip bands was observed. For all the volume fractions, 0. 6 to 22%, and sizes, 35 to 850 A, 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 Ll//2 structure was also detected in the crystals with high volume fractions of Al//3Li. The mechanism is explained in terms of dislocation theory.