The influence of annealing atmosphere on the formation of nanocrystals from devitrification of a Ti38.5Cu32Co14Al10Zr5.5 amorphous alloy

The kinetics of the polymorphic transformation of a Ti38.5Cu32Co14Al10Zr5.5 glassy alloy to an ordered bcc phase was determined by means of combined DSC, XRD and TEM experiments. Samples annealed isothermally under Ar at 723 K for 5, 10, 15, 20 min contain crystals up to 20 nm in size. After the quick formation of nanocrystals, growth is almost blocked. Samples contained in Al pans sealed in a glove box, gave DSC signals significantly displaced at longer times showing an effect of the annealing atmosphere on the crystallization kinetics. This was confirmed by annealing other samples in vacuum. The size of the crystals after these longer annealings is still in the nanometer range. The size distribution, determined on TEM micrographs is compatible with nucleation on homogeneously distributed impurities.