Deformation, recovery, and recrystallization behavior of nanocrystalline copper produced from solution-phase synthesized
- PDF / 499,140 Bytes
- 9 Pages / 612 x 792 pts (letter) Page_size
- 38 Downloads / 190 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Deformation, recovery, and recrystallization behavior of nanocrystalline copper produced from solution-phase synthesized nanoparticles R. Suryanarayanan, Claire A. Frey, and Shankar M. L. Sastry Materials Science and Engineering Program, Department of Mechanical Engineering, Washington University, St. Louis, Missouri 63130-4899
Benjamin E. Waller and William E. Buhro Department of Chemistry, Washington University, St. Louis, Missouri 63130-4899 (Received 18 May; accepted 13 October 1995)
Nanocrystalline copper produced by a solution-phase chemistry approach and compacted by hot pressing was subjected to room temperature deformation. Uniaxial compression and rolling were used to deform the samples to .90% reduction in thickness. Samples were subjected to several heat treatments to study microstructure and property evolution as a function of heat treatment. Thermal response of the as-pressed and deformed nanocrystalline Cu was also studied by differential scanning calorimetry. Optical metallography, scanning and transmission electron microscopy, and selected area diffraction were used to characterize microstructures after heat treatments. Samples exhibited an endotherm upon heating at 322 ±C which was reversible upon cooling. This was attributed to either dissolution and formation of Cu–B precipitates or the diffusion of B from the grain boundaries to the bulk and back to the grain boundaries. Exaggerated recrystallization occurs in the temperature range of 399 –422 ±C. Samples maintained high dislocation density, deformation bands, and fine grain size up to 322 ±C. Beyond the recrystallization temperature, grains grew at a faster rate to submicron or micron levels. The strain hardening observed in the samples 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 the grain boundaries leading to strengthening of grain boundaries, and (ii) formation of Cu–B nanoprecipitates leading to precipitation strengthening.
I. INTRODUCTION
Drastic grain refinement to the nanometer regime (,100 nm) leads to interesting mechanical behavior of materials. Microhardnesses that are two to ten times that of coarse-grained material have been reported for nanocrystalline metals, ceramics, and intermetallics. In the as-produced state, these materials have shown an increase in hardness with a decrease in grain size, according to the Hall–Petch (H-P) relationship.1–5 The inverse Hall–Petch relationship has been reported for materials with grain sizes of only a few nanometers. In some studies,6–8 inverse Hall–Petch behavior has been observed in as-prepared samples. In these cases, the inverse Hall–Petch behavior is attributed to increasing volume fraction of the intercrystalline (triple junction and grain boundary) region, as the grain size is reduced to the ,20 nm regime. This phenomenon has been also reported in the cases9–13 where hardness measurements are made on a single sample that is successively annealed to o
Data Loading...
