Anelasticity Study on Motions of Atoms in the Grain Boundary Regions in Nanocrystalline Gold

Abstract

High-density nanocrystalline (n-) Au was prepared by the gas deposition method. Various anelastic and plastic creep processes associated with the grain boundary (GB) regions were observed. The vibrating reed measurements at 10 2 Hz with strain amplitude of 10 À6 show a very broad internal friction peak near 95 K, Q À1 p,95 K , and a steep increase in the anelastic strain above 200 K, " a-I,>200 K . The tensile tests show a steep increase in the anelastic strain above 200 K, " a-II,>200 K , for the stress beyond a few MPa and a linear plastic creep strain above 200 K, " pc-1 , for stress range between 30 MPa and 150 MPa. The activation parameters, 1= 0 of 3 Â 10 11 s À1 and E of 0.16 eV, are found for Q À1 p,95 K , where 0 and E are a pre-exponential factor and an activation energy of the relaxation time . We surmise that simple relaxation processes are responsible for Q À1 p,95 K . The values of 1= 0 and E found for " a-I,>200 K and " a-II,>200 K decrease with increasing the applied stress or the temperature, indicating that their atomic processes are the same feather. Further, E found for " pc-1 is similar to or slightly smaller than that of " a-II,>200 K . These observations indicate that the atomic motions in the GB regions of n-Au develop in scale in the order of the underlying processes for " a-I,>200 K , " a-II,>200 K and " pc-1 , and are so different from those in the conventional polycrystalline Au.

Thermo-mechanical properties of nano-scale freestanding aluminum films

“…Therefore we suggest that the contrast changes could be due to grain rotation or sliding due to dislocation activities at the grain boundaries. For grain sizes smaller than that reported in this study, the inverse dependence of this ratio with grain size predicts pronounced effects of the grain boundary diffusion that can possibly introduce anelasticity at the room temperature, as observed in other studies [17,22].…”

“…However, the number of thermomechanical studies involving freestanding thin films is rather limited [14,15], which provides the motivation for studying mechanical properties of freestanding thin films at elevated temperatures. It is important to note that similar studies on bulk nano-crystalline materials have provided significant insight on the length-scale and temperature dependence of the mechanical properties at the nano-scale [16,17].…”

Characterization and Determination of Elastic Property of High-Density Nanocrystalline Gold Prepared by Gas-Deposition Method

“…Further, " an,>200 K -II is also associated with a certain anelastic process in the GB regions because it can be observed in n-Au specimens but not in poly-Au specimens. A certain characteristic process associated with several atoms in the GB of the n-metals appears to be responsible for " an,>200 K -I and " an,>200 K -II, 6,33) however, the detailed mechanisms are not known at the present.…”

Low-Temperature Anelastic Property of Nanocrystalline Ag Fabricated by Gas Deposition Method

“…In the gas deposition method, ultrafine metallic particles formed by the inert-gas condensation process were directly deposited on a glass substrate by using a He gas jet-flow 5 . The purity of He used for the gas condensation and jet-flow was kept better than 99.9999% by a purification system.…”

“…The internal friction measurement is a powerful and sensitive tool to study behavior of the grain boundaries. For the elasticity measurement, we reported that the internal friction of n-Au showed a rapid increase linearly with temperature above 200 K accompanied with a decrease in dynamic Young's modulus 5,6 . Since the amount became small with a progress of the grain growth by annealing, the rapid increase of internal friction above 200 K was attributed to a certain anelastic relaxation process in the grain boundaries.…”