Formation of twinned tetragonal ferromagnetic L1₀ - MnAl-C

The plate-like modification of the τ-MnAl-C (L1₀-structure) is a promising material for magnetoplastic applications. The formation of the metastable plate-like τ from the supercooled high- temperature ε-phase (A3-structure) is a discontinuous displacive process. It thus becomes possible to control the appearance of particular variants of the twin-related structural domains of τ at the intermediate stages of the ε → τ transformation. The displacive mechanism of the plate- like τ-formation was studied by transmission electron microscopy. The intermediate ε′-phase (B19-structure) forms from the ε-phase and transmits the crystallographic correspondence from the matrix ε to the plate-like τ. The structural domain boundaries of the intermediate ε′-phase are the nucleation sites of the plate-like τ. The crucial role of these structural domain boundaries for the formation of the plate-like τ-phase is demonstrated.