Mechanical Properties of Bulk Nanocrystalline Silver-Using Compression Tests

Abstract

In this paper, the compression test on the bulk nanocrystalline sliver ( n Ag) with average grain size of 50 nm was made. The stress-strain curves under different strain rates were obtained by test. The test results show that the mechanical behavior of n Ag is rate-dependent, and the dynamic compress yield stress are about 1.5 times of that n Ag in static test condition; The effect of strain harding on n Ag is smaller than that of coarse-grained silver (c Ag) in plastic deformation; The relationship between the yield strength and the logarithm of strain rate is approximately linear.

Anomalous Hardening of Submicron Porous Silver at High Strain Rates

“…Also, consistent with the microscratch data in region II-III are the two data points plotted at 2.0•10 +3 and 6.3•10 +3 s -1 for dense silver. These high strain-rate H s -values for έ >10 +3 s -1 correspond with a scratch hardness computed by multiplying a factor of three (Tabor, 1970) times the shear-type flow-strength made using split Hopkinson pressure bar measurements (Hu & Hong, 2011) of dense silver with similar grain size. The m-values listed in Table 1 increase in the transition region II-III as a function of an increase in the pore size and porosity.…”

“…An evaluation of the grain size (h g ) effect through the Hall-Petch relationship on the extent of strengthening can be made using values reported for the strengthening coefficient (k σ ) (Aldrich & Armstrong, 1970) as 169 MPa•μm -½ and the friction stress (σ o ) (Gubicza et al, 2008) as 30 MPa for uniaxial loading at a strain rate of ~10 -4 s -1 . The grain size that corresponds with reported yield strengths (σ y ) as computed for dense silver samples are: 0.32 μm (versus 0.25 μm reported) for a 330 MPa equal-channel angular processed material (Gubicza et al, 2008); 14 μm for a 75 MPa coarse grain silver (Hu & Hong, 2011); 1 μm (versus 50 nm reported) for a 200 MPa fine grain silver (Hu & Hong, 2011) in compression; and 0.47 μm for the 275 MPa tensile strength of the dense foils used in this study. The compression test measurements should be comparable to the tensile test values.…”

“…In addition, the H s -values for dense silver show m-values that are similar from the 0.014 in tension (for region I) to 0.01 by microscratch (in region II). Similarly, an m-value of 0.025 is reported (Hu & Hong, 2011) for compression tests in Regions I-to-II over a strain rate range of 10 -6 to 10 -1 s -1 .…”