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

• The powders after MA consisted of large- and small-Cu grain layers due to inhomogeneous distribution of yttrium atoms. • Areal fraction of small Cu grain layer increases with increasing MA duration. • The powders after ball-milled have exothermic reaction at around 310°C, which may be recrystallization and grain growth of Cu grains. • During heat treatment above 300°C after MA, yttrium atoms are diffused into the outer peripheral region and forms a new small-Cu grain area. Oxide dispersion strengthened Cu alloys (ODS-Cu) having dispersed yttria (Y 2 O 3) 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°C, because recrystallization and grain growth of Cu occurred in the temperature range of 310 - 330°C. It was considered that Y 2 O 3 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 Y 2 O 3 distribution within the Y 2 O 3 -added ODS-Cu alloys. [ABSTRACT FROM AUTHOR]