DEFORMATION, RECOVERY, AND RECRYSTALLIZATION BEHAVIOR OF NANOCRYSTALLINE COPPER PRODUCED FROM SOLUTION-PHASE SYNTHESIZED NANOPARTICLES

Nanocrystalline copper produced by a solution-phase chemistry approach and compacted by hot pressing was subjected to room temperature defor mation. Uniaxial compression and rolling were used to deform the sampl es to >90% reduction in thickness. Samples were subjected to several h eat treatments to study microstructure and property evolution as a fun ction of heat treatment. Thermal response of the as-pressed and deform ed nanocrystalline Cu was also studied by differential scanning calori metry, Optical metallography, scanning and transmission electron micro scopy, and selected area diffraction were used to characterize microst ructures after heat treatments. Samples exhibited an endotherm upon he ating at 322 degrees C which was reversible upon cooling. This was att ributed to either dissolution and formation of Cu-B precipitates or th e diffusion of B from the grain boundaries to the bulk and back to the grain boundaries. Exaggerated recrystallization occurs in the tempera ture range of 399-422 degrees C. Samples maintained high dislocation d ensity, deformation bands, and fine grain size up to 322 degrees C. Be yond the recrystallization temperature, grains grew at a faster rate t o submicron or micron levels. The strain hardening observed in the sam ples of the present study is attributed to the presence of boron. Two mechanisms are suggested for the role of B: (i) segregation of B to th e grain boundaries leading to strengthening of grain boundaries, and ( ii) formation of Cu-B nanoprecipitates leading to precipitation streng thening.