Structural features of Ag-1 wt% Mg alloys internally oxidized at high temperatures investigated by X-ray diffraction

摘要

A relatively concentrated Ag-Mg alloy (1 wt% Mg, corresponding to 4.3 at.% Mg) internally oxidized at high temperatures (750 and 850 degreesC) was investigated using X-ray diffraction. The formation of two correlated fcc phases (phase I and phase II) was observed. Phase I has a unit-cell parameter higher than the starting homogeneous Ag-Mg solid solution. This indirectly shows the formation of MgOnu, hyperstoichiometric clusters (nu > 1). Phase II has a unit-cell parameter close to that of pure Ag. The O excess in the MgOnu, clusters (phase I) has been calculated from the measured unit cell parameters, following an equation previously published by Rikel and Goldacker. The dependence of nu on the thermal treatment follows the trend already observed for dilute Ag-Mg alloys internally oxidized at lower temperatures (700 degreesC or below). Furthermore, a segregation of stoichiometric MgO crystallites of size about 200 Angstrom has been observed in all samples, even in those oxidized at 750 degreesC for a few minutes. [References: 17]