Strain rate sensitivity of nanocrystalline Au films at room temperature

Abstract

Dimitrios, "Strain rate sensitivity of nanocrystalline Au films at room temperature" (2010) AbstractThe effect of strain rate on the inelastic properties of nanocrystalline Au films was quantified with 0.85 and 1.76 lm free-standing microscale tension specimens tested over eight decades of strain rate, between 6 Â 10 À6 and 20 s À1 . The elastic modulus was independent of the strain rate, 66 ± 4.5 GPa, but the inelastic mechanical response was clearly rate sensitive. The yield strength and the ultimate tensile strength increased with the strain rate in the ranges 575-895 MPa and 675-940 MPa, respectively, with the yield strength reaching the tensile strength at strain rates faster than 10 À1 s À1 . The activation volumes for the two film thicknesses were 4.5 and 8.1 b 3 , at strain rates smaller than 10 À4 s À1 and 12.5 and 14.6 b 3 at strain rates higher than 10 À4 s À1 , while the strain rate sensitivity factor and the ultimate tensile strain increased below 10 À4 s À1 . The latter trends indicated that the strain rate regime 10 À5 -10 À4 s À1 is pivotal in the mechanical response of the particular nanocrystalline Au films. The increased rate sensitivity and the reduced activation volume at slow strain rates were attributed to grain boundary processes that also led to prolonged (5-6 h) and significant primary creep with initial strain rate of the order of 10 À7 s À1 .

Time-dependent deformation behavior of freestanding and SiNx-supported gold thin films investigated by bulge tests

“…The strain-rate sensitivity measured on freestanding gold films is, in comparison, much higher, which is consistent with the results reported in the literature 8,9 for submicrometer gold films tested in tension at similar strain-rates (m 5 0.05-0.17). This increase compared to both bulk-like and SiN x -supported samples strongly suggests that the freestanding condition prompts a major change in deformation behavior, not yet described in the literature.…”

“…8,9 The present experiments albeit reveal that the mechanism responsible for it causes a roughening of the surface of the samples. Therefore, while it is usually argued that a high strain-rate sensitivity is beneficial to ductility by preventing strain localization, 34 in the case of freestanding thin films, this positive effect is largely mitigated by the creation of surface defects prone to act as crack initiation sites.…”

“…[1][2][3][4] There is, on the other hand, only scarce data available on thin films-especially freestanding ones [5][6][7][8][9][10][11] -mostly due to the lack of suitable experimental techniques. The approach chosen for the present work was to build upon one of the most robust methods available for thin films, the bulge test.…”

High-temperature tensile behavior of freestanding Au thin films

“…Measurements performed at smaller strain rates also result in significantly lower flow stress, evidence of a strong strain-rate effect. Similar observations have been made at lower temperatures in prior studies on thin films of Au [21,[29][30][31] and other fcc materials, including Cu [32] and Ni [33]. Another interesting observation is that the flow stress of the 940 nm films is somewhat greater than that of the 450 nm films, and that this difference increases with increasing temperature, contravening the usual notion that smaller is stronger.…”

Indentation Fracture Response of Al–TiN Nanolaminates

“…The slower strain rates favour lateral shear bands and therefore radial fracture is decreased. For thin films, strain rate has been reported to influence the flow stress of nanocrystalline metals [29,30], and in future work we will be investigating the effect of strain rate on the fracture of metal-ceramic nanolaminates in stress states other than indentation.…”