Room-temperature deformation and stress- induced phase
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I.
INTRODUCTION
LAVES phases are the largest class of intermetallic compounds. All of them have one of the three following structure types: cubic C15 (MgCu2), hexagonal C14 (MgZn2), or dihexagonal C36 (MgNi2). Laves phases are among those intermetallic compounds being considered as strengthening components for future high-temperature structural alloys. Ill High-temperature deformability of Laves phases has been studied mostly in C14 and C15 structures by many investigators. It was found that the Laves phases showed considerable ductility at high temperatures. A major concern now, however, is their brittleness at ambient temperatures, at least in single-phase alloys. It was recently demonstrated that in a two-phase alloy deformed at room temperature, a cubic Laves phase based on HfV2 deformed plastically, predominantly by mechanical twinning, t2] It is important to determine whether such room-temperature deformability was limited to HfV2 (which has unusual elastic properties) or whether other Laves phases in two-phase alloys also exhibit deformability at room temperature. The present study concerns the deformation at room temperature of Fe-Zr alloys containing substantial amounts of Fe2Zr Laves phase. II.
EXPERIMENTAL
The Fe-10 at. pct Zr alloy used in the study was prepared by arc melting. Samples for compression testing were then cut from the arc-cast ingots using an electric discharge machine. The size of the samples was 5 × 5 × 5 mm. Samples were encapsulated in a vacuum of 10-6 torr and annealed at 1190 °C for 48 hours. Compression experiments were performed at room temperature with a crosshead speed of 2.5 x 10 -3 cm/min. Transmission electron microscopy (TEM) specimens approximately 0.4-mm thick were cut from the undeformed and compressed samples using a diamond saw, ground to a thickness of 0.1 mm, and electropolished in a solution of 10 pct perchloric acid-90 pct methanol. Ion milling was also used in some samples to get better thin areas for high-resolution microscopy. A JEOL 200CX YAPING LIU, Graduate Student, JAMES D. LIVINGSTON, Senior Lecturer, and SAMUEL M. ALLEN, Professor of Physical Metallurgy, are with the Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139. Manuscript submitted June 2, 1992. METALLURGICAL TRANSACTIONS A
and an Akashi EM-002B high-resolution transmission electron microscope operating at an accelerating voltage of 200 kV were used in the microstructure analysis. The TEM samples were also used in scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM). A Cambridge 250 Mk3 scanning electron microscope was employed for the sample surface observation, and a Vg HB5 scanning transmission electron microscope with a minimum probe size of 0.5 nm was used in the compositional microanalysis. The thin sections cut from undeformed and compressed samples were also used in X-ray diffraction experiments, which were performed on a Rigaku RU300 diffractometer with Cu-K,, radiation and a rotating anode. In or
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