Structural phase transformations in quasicrystal-forming Al-Cu-Fe alloys and defects of the icosahedral phase

• Published in: Physics of metals and metallography 2010-04, Vol.109 (4), p.392-401
• Main Authors: Shalaeva, E. V., Prekul, A. F.
• Format: Article
• Language: English
• Subjects: Alloys; Aluminum base alloys; ANNEALING PROCESSES; Chemistry and Materials Science; COPPER ALUMINUM ALLOYS; COPPER IRON ALLOYS; Defect annealing; Defects; Diffusion; Icosahedral phase; Materials Science; Metallic Materials; Phase Transformations; PHASES; Quasicrystals; QUENCHING MECHANISMS; SOLID SOLUTIONS; Specialty metals industry; Structure; Transformations
• ISSN: 0031-918X; 1555-6190
• DOI: 10.1134/S0031918X10040137

Transmission electron microscopy was used to investigate structural and phase transformations and defects of the icosahedral (ι) phase that is formed upon isothermal annealings ( T ann = 550–700°C) of quenched quasicrystal-forming alloys Al 61 Cu 26 Fe 13 and Al 63 Cu 25 Fe 12 (β solid solution + ι phase). It has been established that in the Al 63 Cu 25 Fe 12 alloy there occurs a reversible ι- R -approximant transformation, whereas in the Al 61 Cu 26 Fe 13 alloy there is formed a single-phase ι structure with regions with a high density of randomly distributed planar defects ( T ann = 550°C), which are partially annealed at 650°C. The observed defects are, mainly, ultrathin interlayers (“intergrowths” to 3–5 nm in thickness) on quasicrystal planes with A 5 ι axes with an imperfect decagonal structure. As the basic mechanism, the growth mechanism of the formation of defects during the β → i transformation is proposed. The role of the alloy composition and low-temperature β → 3 C -phase transformation in the realization of this mechanism is discussed.