Thermodynamic Properties of Crystalline Al-Fe Alloys in the Region of Icosahedral Phase Precipitation

摘要

The currently available data on the thermodynamic properties and stability of quasicrystals are very scarce.The questions remain open as to what state (stable,metastable,or labile)corresponds to quasicrystals and whether a quasicrystal may be the stable ground state of an alloy.Icosahedral quasicrystals precipitate from both binary Al-Fe [1]compositions and ternary Al-Fe-Cu [2]alloys on their basis:Al_(0.86)Fe_(0.14)and Al_(0.63)Fe_(0.12)Cu_(0.25),respectively.To determine their thermodynamic nature,reliable data on the thermodynamic properties of the phases in the neighboring regions of the phase diagram are required.In spite of a considerable body of works devoted to determining the thermodynamic characteristics of solid aluminum-iron alloys,results of which have been summarized and systematized in the reference book [3],the published data are contradictory and are characterized by a wide scatter.In particular,the available data on the standard enthalpy of formation of the zeta phase (Al_2Fe)differ by more than 1.5 times (-26.5 kJ/mol [4],-18.83 +-6.3 kJ/mol [5]).This makes it impossible to extrapolate the functions to the conditions for precipitation of quasicrystals and analyze the thermodynamic driving force for their formation.