²⁷Al NMR measurement of fcc Al configurations in as-quenched Al₈₅Ni₁₁Y₄ metallic glass and crystallization kinetics of Al nanocrystals

The crystallization of melt spun Al₈₅Ni₁₁Y ₄ ribbon has been studied through systematic heat treatment in the 200-550 °C temperature range using the techniques of nuclear magnetic resonance (NMR) spectroscopy, electrical resistivity, differential scanning calorimetry (DSC) and X-ray diffraction (XRD). ²⁷Al NMR spectroscopy provides a direct and sensitive method for determining the atomic fraction of α-Al and analysis of the α-Al crystallization kinetics. NMR results revealed low concentrations (3.9 at.%) of α-Al configuration in the as-quenched material and confirm that they have α-Al short-range order. The ability of NMR to directly detect the α-Al configuration in the as-quenched state is compared and contrasted with XRD. Volume fractions of α-Al phase calculated from NMR are also compared and contrasted with that calculated from XRD for samples subjected to isothermal annealing. Qualitative and quantitative agreement between the two techniques is found after the XRD fractions are corrected according to literature methods. Heat treatment at moderate temperatures (200 °C) is shown to result in transformation kinetics dominated by the growth of α-Al consistent with heterogeneous nucleation, while higher temperatures (300 °C) lead to kinetics consistent with growth from homogeneous nucleation sites.