Development of fcc-Al nanoparticles during crystallization of amorphous Al–Ni alloys containing mischmetal: Microstructure and hardness evaluation

In the present work, fcc-Al nanoparticle development in Al90−xNi10MMx (MM: Ce mischmetal; x=2, 4) amorphous alloys was studied via non-isothermal differential scanning calorimetry, X-ray diffraction, transmission electron microscopy, and nanoindentation test. Results showed that the crystallization of Al88Ni10MM2 alloy occurred by the precipitation of fcc-Al nanoparticles followed by the crystallization of Al11MM3 and Al3Ni phases. Transmission electron microscopy revealed that the aluminum precipitates had an average size of ~12 nm with a round morphology. Increasing the mischmetal content to 4 at% (Al86Ni10MM4 alloy) caused a three-stage crystallization process with a change in the size and morphology of fcc-Al precipitates. Here, fcc-Al nanoparticles got an irregular and cluster-like morphology with an average size of about 50 nm. The crystallization mechanism of fcc-Al nanoparticles formation was evaluated. The results indicated the complex nature of the primary crystallization behavior of these amorphous alloys. Results of nanoindentation test revealed that controlled crystallization of the amorphous alloys significantly increased the strength, owing to the solute enrichment of the amorphous matrix.