Microstructure and room temperature hardening of ultra-fine-grained oxide-dispersion strengthened copper prepared by cryomilling

The microstructure of ultra-fine-grained (UFG) oxide-dispersion strengthened (ODS) copper, produced by mechanical alloying at low temperatures (cryomilling) and subsequent hot pressing under protective argon atmosphere of copper powder and 3 vol.% of yttrium and calcium oxides, respectively, was examined by means of high-resolution scanning electron microscopy. Compressive deformation experiments at room temperature yield a substantial increase of the 0.2% yield strength of the UFG ODS copper when compared with pure copper. The very high yield strength (σ0.2 = 600 MPa) is the result of a simultaneous occurrence of grain boundary strengthening and particle hardening. The overall yield strength could be best modelled by a linear superposition of the Orowan stress for particle hardening and of the contribution from fine grain strengthening after Hall–Petch.