Characterization of oxide dispersion strengthened copper based materials developed by friction stir processing

• Elaboration of an yttria Cu based composite by friction stir processing.
• Intercrystalline fracture of the powder particles reaching 10 nm sized particles.
• Yttria particles distribution finer and more homogeneous with the number of passes.
• Large strain hardening capacity associated to yttria particles.

The current study aims to show for the first time the ability of friction stir processing (FSP) in incorporating yttria particles into copper to produce an oxide dispersion strengthened material. The microstructure of the as-developed composites was characterized at various scales by light microscopy, electron probe microanalysis (EPMA) and scanning and transmission electron microscopy. The powder was found to be distributed in the Cu matrix as confirmed at various length scales from the micrometric to the nanometric level. The increase of the number of FSP passes leads to a more homogeneous and finer distribution of the particles as it favored the dissociation of the clusters of initial powder particles and the intergranular fracture of individual elemental particles. Transmission electron microscopy observations reveal that the constitutive crystallites of the initial powder, typically 10 nm in size, are frequently dissociated and dispersed into the copper matrix. In spite of their very low volume fraction, these 10 nm sized fragments which present the highest density among the various size classes of particles, exert a strengthening and work hardening effect.