Effect of reversible structural relaxation on diffusion in bulk metallic glasses

Abstract

Long time relaxation at temperatures below the calorimetric glass transition causes reversible structural changes in metallic glasses. The resulting enthalpy recovery was measured by means of DSC in Zr 46.8Ti 8.2Cu 7.5Ni 10Be 27.5- and Pd 40Cu 30Ni 10P 20-bulk glass annealed for different times at 553 K and 542 K, respectively. Relaxation times of about 10 6 s and 10 4 s, respectively, were determined. The diffusion coefficients of B, Fe and Co were measured above and below the calorimetric glass transition temperature. Whereas the temperature dependence of these diffusion coefficients in the non-relaxed glasses shows “non-linear” Arrhenius behaviour with a break near the glass transition, the diffusion in the long time relaxed glasses follows a uniform temperature dependence over the entire temperature range with considerably reduced diffusion coefficients below the glass transition. This behaviour can be reversed by annealing the relaxed glasses again at higher temperatures indicating the strong effect of the reversible structural relaxation on the diffusion coefficients.