Devitrification phase transformations in amorphous Al85Ni7Gd8 alloy

Non-isothermal devitrification phase transformations in amorphous Al85Ni7Gd8 over the temperature range from 100 to 1300 °C were systematically investigated using differential scanning calorimetry (DSC), differential thermal analysis (DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) techniques. Continuous heating DSC scans revealed that the crystallization proceeds through multiple stages. The only crystalline phase formed in the first two stages is fcc-Al, appearing exclusively as dendritic single crystals. A metastable phase (τn) is formed in the 3rd stage, and another metastable phase (τu) is formed in the 4th stage, together with the equilibrium ternary compound τ1. The equilibrium “binary” compound M3Gd (M=Al, Ni) with 0.4 at.% Ni solubility is formed only in the 5th stage. Further heating initiates eutectic melting at 635 °C, followed by other melting events at higher temperatures, until fully liquid when T>919 °C. Isothermal annealing at 260 °C readily induces formation of another metastable phase (τm) and fcc-Al. Fcc-Al nanocrystal development and interpretation of isothermal DSC technique is discussed.