ON THE ELASTIC-MODULI OF NANOCRYSTALLINE FE, CU, NI, AND CU-NI ALLOYS PREPARED BY MECHANICAL MILLING/ALLOYING

Young's moduli of nanocrystalline Fe, Cu, Ni, and Cu-Ni alloys prepared by mechanical milling/alloying have been measured by the nanoindentation technique. The results indicate that Young's moduli of nanocrystalline Cu, Ni, and Cu-Ni alloys with a grain size ranging from 17 to 26 nm are similar to those of the corresponding polycrystals. The dependence of Young's modulus of nanocrystalline Fe on grain size corresponds well to a theoretical prediction, which suggests that the change in the Young and shear moduli of nanocrystalline materials, free of porosity, with a grain size larger than about 4 nm, should be very limited (< 10%). It is likely that reported large decreases in the Young and shear moduli of nanocrystalline materials prepared by gas-condensation/vacuum consolidation result from a relatively large volume fraction of pores.