A positron study of precipitation phenomena in AlGe and AlSi alloys

Abstract

The nucleation of precipitates and the precipitation process are studied in AlGe (0.2 and 1.2 at.%) and AlSi (0.5 at.%) by positron lifetime and angular correlation measurements during post-quench isochronal annealing. In the as-quenched samples small clusters of vacancies and solute atoms are observed. The vacancies disappear during first annealing steps, thereafter positrons are localized at incoherent Ge and Si particle-matrix interfaces. In AlGe (1.2 at.%) and in AlSi (0.5 at.%) above 150°C an increasing number of positrons are trapped by precipitates. Above 250°C the coarsening and dissolution of precipitates is detected. The density of Ge or Si particles estimated from the positron trapping rate agrees well with earlier SAXS and TEM results.