Microstructural changes of oxide dispersion strengthened copper powders fabricated by mechanical alloying

Oxide dispersion strengthened Cu alloys (ODS-Cu) having dispersed yttria (Y2O3) fabricated using hot isostatic pressing (HIP) of mechanically alloyed (MA) Cu-Y powders. They exhibited a heterogeneous mixed grain structure, which were composed of a large and small Cu grain area. In the small Cu grain regions, Y2O3 particles were segregated along the grain boundaries, and acted as a crack propagation path, leading to brittle fracture. Therefore, we investigated the microstructural changes by the MA and heat treatment processes for the microstructure optimization. The powders of 4 to 32 MA hours formed a nested crust-like layered structure with large and small Cu grains. The layers were destroyed by heat treatment at 500 degrees C, because recrystallization and grain growth of Cu occurred in the temperature range of 310 - 330 degrees C. It was considered that Y2O3 was moved out to the circumferential area of the powders. Based on these results, it was suggested that the structural changes inside MA powders during HIP are the essential factor of the Y2O3 distribution within the Y2O3-added ODS-Cu alloys.