Room temperature deformation and stress-induced phase transformation in Laves phase Fe2Zr

Abstract

Laves phases have three structures: Cubic C15 (MgCu2), hexagonal C14 (MgZn2) and dihexagonal C36 (MgNi2). Their high-temperature deformability has been studied by many investigators. But the study of their room-temperature deformation is very limited. By such studies, it may be possible to enhance the room-temperature deformability of Laves phases.In the present study, arc-melted samples of Fe-10 at% Zr, containing α-Fe and Fe2Zr Laves phase, were annealed at 1190°C for 48 hr and then compressed at 0.001 inch/min to strains of 46∼48% at room temperature. The 0.2% offset yield stress is about 75 kg/mm2. Micrographs revealed dislocation structures in α-Fe and cracks in proeutectic Fe2Zr after deformation. X-ray diffraction patterns show that the crystal structure of Fe2Zr is mainly C36 before deformation. After compression, the C15 peaks, which overlap other peaks in the pattern, increase in intensity, as seen in Fig. 1. This demonstrates that a phase transformation occurred as a result of deformation. The detail and mechanism of the transformation were studied by TEM. A characteristic banded structure which was rarely found in undeformed sample was frequently observed in the compressed Fe2Zr particles, as shown in Fig. 2. Electron diffraction patterns and high-resolution TEM showed that these bands have a C15 structure with a {111} plane parallel to the basal plane of C36 structure in the adjacent parts of a particle. Fig. 3 is a high-resolution TEM picture showing the stacking sequence of the close-packed planes of the particle containing the C15 band in Fig. 2. It has a ABCABC stacking sequence in the central part (C15) and ABAC on the two sides (C36). Inside the C15 band there are many stacking faults on {111} planes. A twinned region (C15T) is also seen to the right of the C15 region.