Hardness and microstructure of internally oxidized silver alloys

Alloys of Ag, Ag/1.12 at.% Mg, and Ag/0.25 at.% Mg-0.25 at.%Ni were internally oxidized at 450 to 825/spl deg/C and their hardnesses and microstructures were observed. Microhardness profiles showed that hardness was high near the surface and decreased with depth into the sample. Microstructures contained regions of small and large grains, where region sizes were dependent on treatment temperature. Transitions between small- and large-grained regions were abrupt. Treatments at higher temperatures failed to alter grain structure, indicating that Mg-O clusters had indeed pinned the grain boundaries. Clustering was shown to affect the hardness of oxidized alloys, not only by inhibiting grain growth, but also by inhibiting dislocation motion.