Ag effects on the elastic modulus values of nanoporous Au foams
- PDF / 845,267 Bytes
- 7 Pages / 584.957 x 782.986 pts Page_size
- 38 Downloads / 191 Views
M.M. Biener, J. Biener, O. Cervantes, and A.V. Hamza Nanoscale Synthesis and Characterization Laboratory, Lawrence Livermore National Laboratory, Livermore, California 94550 (Received 30 July 2008; accepted 15 January 2009)
To study both the effect of Ag and the relative density on the elastic properties of nanoporous Au (np-Au) foams, partially as well as fully dealloyed np-Au samples with various ligament sizes were prepared. Additionally, Ag-coated np-Au samples were synthesized by immersing np-Au in a 1 M Ag nitrate solution, followed by drying and thermal decomposition of the deposited Ag nitrate salt to Ag, NO2, and O2. Crosssectional analysis revealed that this method yields a homogeneous Ag distribution and that the Ag concentration can be adjusted within the range of 0 to 20 at.%. Mechanical testing was performed by depth-sensing nanoindentation. It was observed that the effect of the relative density on the elastic properties of np-Au seems to be much stronger than predicted by the Gibson and Ashby relationship: Even Ag contents as low as 1 at.% can significantly change the modulus values. On the other hand, the elastic modulus of np-Au seems to be independent of the ligament size.
I. INTRODUCTION
Nanoporous metals, in particular nanoporous Au (npAu) foams have gained much interest due to the wide range of rapidly emerging applications.1–3 One of the unexpected properties of np-Au is its high yield strength,4 which can be higher than the strength of the fully dense bulk material and that despite their high porosity of 60 to 80%.5,6 Current testing on nanoporous foam has been focused on strength measurements by techniques ranging from nanoindentation to beam bending tests.5–11 The elastic properties of nanoporous Au, on the other hand, have attracted less interest, and consequently there are fewer data available. Most studies report Young’s modulus values in the 5 to 13 GPa range with relative densities ranging from 25 to 40%.4,6,8,10 The data seem to be consistent with the scaling predictions made by Gibson and Ashby12 if one uses the bulk modulus of Au (80 GPa), but the scatter of the data points is too large to make definitive conclusions. The narrow range of most of the available data seems to indicate that there are little or no size effects in the elastic properties. An exception to this is the recent study by Mathur and Erlebacher9 who reported a fourfold increase in the Young’s modulus, from 10 to 40 GPa, as the ligament a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0184
1600
http://journals.cambridge.org
J. Mater. Res., Vol. 24, No. 4, Apr 2009 Downloaded: 19 Mar 2015
diameter decreases from >12 to 3 nm. This result was attributed to a combination of surface stress, density increase caused by shrinkage, and a higher bending stiffness of smaller ligaments. However, in general elastic length scale effects are not observed in nanoscale materials.13–15 For example, the modulus of Au nanowires (70 GPa) is independent of their diameter (at least in
Data Loading...
