On the elastic moduli of nanocrystalline Fe, Cu, Ni, and Cu–Ni alloys prepared by mechanical milling/alloying

Abstract

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.

Deformation mechanisms in free-standing nanoscale thin films: A quantitative in situ transmission electron microscope study

“…We note that Shen et al (15) used nanoindentation technique to measure elastic modulus of polycrystalline Fe, Ni, Cu, and Cu-Ni alloys prepared by mechanical milling. The range of grain size was 17-27 nm for Cu, Ni, and Cu-Ni alloys, and 7-80 nm for Fe.…”

“…At smaller length-scales, straingradient-dependent strengthening disappears (7) and reverse Hall-Petch behavior is observed (8)(9)(10)(11)(12)(13). Another less understood size effect observed at nanoscale is the reduction of Young's modulus, which has been attributed to specimen density (13) and grain boundary compliance (14,15). Models that attempt to explain the nanoscale size effect are of two basic types: (i) models describing nanocrystalline materials as twophase composites with grain interiors and boundaries, where the mechanical properties are averaged by simple ''rule of mixtures'' (16,17); and (ii) models considering dislocation motion (10,18,19), grain boundary sliding (20,21), and diffusion (12,22) as competing deformation mechanisms.…”

Defect-dependent Elasticity: Nanoindentation as a Probe of Stress State

“…The sensitivity of the Au thin film's elastic response to applied stress, measured one week after deposition, is illustrated by the loading portions of three load-displacement curves (plotted on the same axes) in Fig (2,4,7). From this observation we conclude that using the wafer bending device does not significantly change the measurement compliance and bias the results.…”

“…In particular the correlation between mechanical response, stress state and deposition conditions have been documented for several materials but are not well understood [1,2]. Deformation properties unique to the nanoscale have been attributed to a material's high defect densities and to changes in the mechanisms accommodating deformation [2][3][4][5][6][7][8][9][10]. Such mechanical behavior has been observed in bulk samples with grain sizes below 10-20 nm for which a significant volume fraction of atoms reside in the intercrystalline grain boundary regions [3,4,[7][8][9][10].…”

“…Deformation properties unique to the nanoscale have been attributed to a material's high defect densities and to changes in the mechanisms accommodating deformation [2][3][4][5][6][7][8][9][10]. Such mechanical behavior has been observed in bulk samples with grain sizes below 10-20 nm for which a significant volume fraction of atoms reside in the intercrystalline grain boundary regions [3,4,[7][8][9][10]. For thin films the constraints of film thickness, adhesion to the substrate and non-random texture extend the range of grain sizes over which such 'nanocrystalline' mechanical properties are observed [1,2,5,8].…”