VACANCIES AND PRECIPITATES IN AL-1.9 AT-PERCENT CU STUDIED BY POSITRONS

Experimental and theoretical investigations of positron trapping by disk shaped Guinier-Preston zones as appearing in AlCu alloys are performed. Using positron lifetime and angular correlation S-parameter measurements the decomposition phenomena are studied in an Al-1.9 at% Cu alloy. The energy and the wave function of a positron within a cylindrical shaped trap is calculated using Ritz's variational principle. Although a weak localization of the positrons by multilayer Guinier-Preston zones (GP zones) is to be expected from theory, the experimental spectra are dominated by positron annihilation in vacancies surrounded by Cu atoms. Above 200-degrees-C positron trapping by semicoherent and incoherent precipitates is found.