Deformation of two C36 laves phases by microhardness indentation at room temperature
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I.
INTRODUCTION
LAVES phases are the largest class of interrnetallic compounds and are attracting increasing interest due to their potential as high-temperature structural materials. Most prior studies have addressed their high-temperature deformation behavior. A major concern now is their roomtemperature properties, especially what seems to be inherent brittleness at ambient temperatures. An improved understanding of room-temperature deformation mechanisms, such as dislocation structures, slip systems, and factors controlling the deformability, is needed for the improvement of the mechanical properties of the phases. Among the three Laves-phase crystal structures (C15, C14, and C36), the dihexagonal C36 is the most complex structure and has received the least study. Our previous work has shown that the room-temperature compression of a two-phase alloy containing ZrFe2 Laves phase can cause a stress-induced phase transformation between C15 and C36. HI Room-temperature compression of a two-phase alloy containing C36 MgNi2 results in nonbasal slip on various planes in the Laves phase. 121 Additional information on the deformability of the brittle C36 structure is of great value. For this purpose, the microhardness test has proven to be a valuable technique in the general study of plastic deformation of some hard, brittle materials, pl Because high hydrostatic pressures are developed beneath the indenter, full relaxation of the load by brittle fracture cannot occur, and the large shear stress necessary to initiate generalized plastic deformation apparently can be developed even at low temperature. In the present study, 2 two-phase alloys, Fe-10 at. pct Zr and Ni-15 at. pct Mg, containing C36 Laves-phase ZrFe2 or MgNi2, and a more ductile Fe-rich or Ni-rich solidsolution phase were used. YAPING LIU, Postdoctoral Associate, SAMUEL M. ALLEN, Professor, and JAMES D. LIVINGSTON, Senior Lecturer, are with the Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139. Manuscript submitted August 16, 1994.
METALLURGICAL AND MATERIALS TRANSACTIONS A
II.
EXPERIMENTAL
The Fe-10 at. pct Zr and Ni-15 at. pet Mg alloys were prepared by arc melting. Samples of the alloys were cut from the arc-cast ingots using a diamond saw and encapsulated in a vacuum of 10 -6 tort. Fe-10 at. pct Zr samples were annealed at 1190 ~ for 48 hours; Ni-15 at. pct Mg samples were annealed at 900 ~ for 75 hours. Vickers microhardness indentations were made at room temperature using a 50-g load, and 10 x 10 arrays of indentations were made on the central part of alloy disks 3 mm in diameter and 300/,tm in thickness. The indentation samples for transmission electron microscopy (TEM) observation were polished and dimpled to 3 0 / z m followed by atom-mill thinning to electron transparency. Only the face of the samples opposite from the microhardness indentation was thinned. JEOL* *JEOL is a trademark of Japan Electron Optics Ltd., Tokyo, Japan.
200CX and Akashi EM-002B high-resolution transmission elec
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