Low-frequency internal friction studies of nanocrystalline copper

Abstract The low-frequency internal friction behavior of OFHC copper and mechanically milled copper was studied over a temperature range of 100–600 ° K at a frequency of approximately 3 Hz. The nanocrystalline copper was prepared by consolidating mechanically milled powders using hot isostatic pressing to form compacts from which bars were machined for testing. Samples studied included milled copper and commercial grade 101 copper bar which had been recrystallized. Powders were consolidated at 600 °C. The final particle size of the consolidated material was approximately 60 nm and the 101 material had a grain size of 32 μm. The internal friction studies indicated the presence of a large grain boundary peak in both materials at approximately 600 ° K which was superimposed on a high temperature background. The peak was significantly larger for the nanocrystalline material because of the increased grain boundary/interfacial area. The OFHC material exhibited at low temperature dislocation peak at approximately 125 °K which was absent in the nanocrystalline material, which is believed to be due to the lack of dislocation structures in heavily milled nanocrystalline materials.