Positron annihilation study of vacancy-type defects in stoichiometric and non-stoichiometric Al-Cu-Fe quasicrystalline alloys

Vacancy-type defects in a non-stoichiometric quasicrystalline phase of Al-Cu-Fe coatings obtained by electron beam deposition have been studied using positron annihilation measurements. It is shown that quasicrystalline phase of non-stoichiometric composition in the coating contains more of vacancy-type defects than the stoichoimetric one in bulk specimen. Decomposition of the quasicrystalline phase during the annealing of the coatings is accompanied by the formation of microvoids, as a consequence of supply of vacancies from the icosahedral structure. The presence of vacancies which maintains the average electron concentration per unit cell at the appropriate value, may be reason of the extended compositional range of icosahedral phase in the coatings.