Structural Phase Transformations in Quasicrystal-Forming Al—Cu—Fe Alloys and Defects of the Icosahedral Phase

摘要

Transmission electron microscopy was used to investigate structural and phase transformationsand defects of the icosahedral (t) phase that is formed upon isothermal annealings (T_(ann) = 550-700℃) ofquenched quasicrystal-forming alloys Al_(61)Cu_(26)Fe_(13) and Al_(63)Cu_(25)Fe_(12) (β solid solution + ι phase). It has beenestablished that in the Al_(63)Cu_(25)Fe_(12) alloy there occurs a reversible ι—R-approximant transformation, whereasin the Al_(61)Cu_(26)Fe_(13) alloy there is formed a single-phase t structure with regions with a high density of ran-domly distributed planar defects ( T_(ann) = 550℃), which are partially annealed at 650℃. The observed defectsare, mainly, ultrathin interlayers ("intergrowths" to 3-5 nm in thickness) on quasicrystal planes with A5, axeswith an imperfect decagonal structure. As the basic mechanism, the growth mechanism of the formation ofdefects during the β->i transformation is proposed. The role of the alloy composition and low-temperature β->3C-phase transformation in the realization of this mechanism is discussed.