Temperature Behavior of the Viscosity of Quasi Crystal-Forming Al–Cu–Fe Melts

Abstract

We have studied the temperature and the temporal dependences of the viscosity of quasi crystalforming Al–Cu–Fe melts within the range of i-phase (Al₆₂Cu_25.5Fe_12.5) stoichiometry with a change in the concentration of copper from 15.5 to 35.5 at % and in that of iron from 2.5 to 22 at % as well as within the concentration range in which the i-phase is the first to arise from the Al_{59.5 + x}Cu_35.5–xFe₅ melt (x = 0–15). We show for the studied alloys that prolonged (2 h or longer) relaxation processes take place directly after melting in the conditions of the viscosimetric experiment and that they should be taken into account when the temperature dependences of the viscosity are measured. In the equilibrium thermodynamic conditions, the viscosity polytherms coincide for the heating and the cooling regimes; they are monotonous and are well described by the exponential dependence. The activation energy of the viscous flow, depending on the composition, varies from 18 to 36 kJ/mol.