Characterization of the density fluctuations existing in amorphous alloys

点击翻译按钮获取中文摘要

For various amorphous alloys (a-alloys), we investigated the crystallization under electropulsing, the Young's modulus as a function of ε_t and f, E(ε_t, f), and an effect of electric current on E(ε_t, f), where ε_t is a strain amplitude and f is a frequency. The crystallization proceeds during electropulsing when I_<d0> is higher than the threshold I_<d0,c> and I_<d0,c> is a function of τ, where electropulsing was made by means of discharge of a condenser with the initial current density, I_<d0>, of the order of 10^9 A/m^2 and the decay time, τ, between 2 - 0.1 ms. The maximum increase in temperature during electropulsing is lower than the structural relaxation temperature, suggesting that thermal agitation is not responsible for the crystallization under electropulsing. Further, a new crystalline phase can be found after electropulsing. It is suggested that electropulsing excites a resonant collective motion of many atoms and modifies the thermodynamic free energy of phases too. E(10 … More ^<-6>,f) measured as a function of f commonly shows a decrease from E_0 in a frequency range of 10^1 Hz to 10^4 Hz, and local minimums near 10^2 Hz and between 10^3 and 10^4 Hz, where E_0 is the Young's modulus found in quasi-static tensile tests. E(ε_t, 10^2 Hz) increases with increasing ε_t and finally saturates at ε_t of 2 to 4 x lO^<-3>. We surmise that density fluctuations exist in amorphous alloys, where a high density region undergoes a resonant collective motion producing a resonant anelastic strain, and the high density regions show a distribution in dimension. An increase in E(10^<-6>,10^2 Hz ) due to an electric current is commonly observed for various a-alloys, suggesting that an electric current induces an internal stress due to an electromigration force concentration. We estimate the effective charge number, Z^* measuring the electromigration force concentration after a comparison between an increase in (10^<-6>,10^2 Hz ) due to an electric current and an increase in E(ε^t, 10^2 Hz) with increasing ε_t. A value of Z^* found is the order of 10^5 for various a-alloys, suggesting that the number of atoms associated with the collective motions excited at 10^2 Hz is between 10^3 and 10^4. The present work also suggests that a new materials can be found after electropulsing and the characteristic elastic properties may be applied to an electro mechanical device. Less