Mechanical Spectroscopy of Nanocrystalline Metals and Nanometer-Thick Films: Characteristic Properties Originated in Nanostructures

Abstract

Nanocrystalline (n-) Au shows a large internal friction accompanied with the modulus defects above ~200 K. After the creep test, the strong <111> preferred texture changed to rather random one but the mean grain size was unchanged.In situSTM observation indicated that the crystallites can independently move during the creep deformation. Quasi-two phase state composed of solid crystallites and anelastic/viscoelastic grain boundaries (GBs) is proposed to explain these characteristic mechanical properties ofn-Au. Further, GBs show the glass-transition-like change at around 200 K, anelastic/viscoelastic transition at ~30 MPa and dynamical state change above ~200 MPa. The high vacancy-type-defect concentration plays an important role on stabilization of the quasi-two phase state inn-Au.

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

“…2). We tentatively surmise that the peak at around 80 K of n-Ag is also owing to the grain boundaries 3 . The internal friction spectra of n-Ag, n-Cu (the mean grain size ~10 nm) 7 and n-Au (~30 nm) 14 are compared in Fig.…”

“…The density of n-Ag was measured by Archimedes method with high purity ethanol. The mean grain size of n-Ag used in the present study was about 30 nm and the density relative to the p-Ag value (10.50 g/cm 3 ) was 97%. Figure 1 shows the temperature changes in the resonant frequency and internal friction of n-Ag.…”

“…Since no grain growth was observed after the creep deformation, it was surmised that a quasitwo-phase state composed of the crystallites and the grain boundaries was attained in n-Au 4 . In contrast, the creep deformation behavior at liquid nitrogen temperature was much different from that at room temperature and the no viscoelastic nature of the grain boundaries was suggested 3 . The internal friction measurement is a powerful and sensitive tool to study behavior of the grain boundaries.…”

“…At the same time, the (111) preferred orientation where the most of the crystallites aligned as the <111> directions were normal to the specimen surface was changed to the random texture by the creep deformation, but the mean size was almost unchanged. Further, the independent movement of the crystallites through the grain boundary sliding with keeping the crystallite shape was observed from the scanning tunneling microscopy under the creep deformation 3 . These observations suggested that the crystallites are connected with the viscoelastic grain boundaries in n-Au.…”

“…When the grain boundary state of n-metals is different from that of conventional p-metals, the mechanical property n-metals becomes considerably modified from the p-metal counterparts combined with the much increased factional volume. For the plasticity measurement, it was reported that the creep rate of n-Au showed a sudden increase with several orders in magnitude at the applied stress above 350 MPa at room temperature 3 . At the same time, the (111) preferred orientation where the most of the crystallites aligned as the <111> directions were normal to the specimen surface was changed to the random texture by the creep deformation, but the mean size was almost unchanged.…”