THE INFLUENCE OF LI ON THE NUCLEATION OF DEFECTS IN QUENCHED AL-LI ALLOYS

The nucleation and kinetics of defects formed by quenching in two Al-L i alloys having Li content of 1.7 and 3.74 at.%Li have been studied by positron annihilation spectroscopy. It has been found that the defect formation is sensitive to the aging time at the temperature from whic h the samples are quenched. This fact has been related to the Li loss experienced by the alloys aged at high temperature. The quenched-in de fects have been identified as vacancy-Li clusters and dislocation loop s. The latter are formed by the collapse of the Li-rich vacancy comple xes and are very sensitive to the Li content; as a consequence, the lo ops are decorated by Li-rich zones and are revealed as very effective positron traps in comparison to the vacancy-Li complexes, giving rise to an enhanced trapping.