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DEFORMATION MECHANISMS IN A LAVES PHASE Yaping Liu, Samuel M. Allen and James D. Livingston Department of Materials Science and Engineering Massachusetts Institute of Technology Cambridge, MA 02139, USA ABSTRACT The stress-inducedphase transformation between C36 and C15 structures in Fe2Zr is studied by electron microscopy. The nucleus of the transformation is believed to be some pre-existing C15 layers in C36 particles. Microstructural evidence for three mechanisms of growth Of a new phase were found: Fault accumulation and rearrangement,moving of individualpartialdislocationsbetween two phases, and the migration of microscopic ledges composed of a series of Shockley partials between C3_6 and Ci5. Plastic deformation by slip on non-basal planes of C36 caused by indentationis studied. I. INTRODUCTION Stress-induced phase transformation has been found to be one of the martensitic transformation mechanisms in steels, many alloys and even semiconductors. However, there has been comparatively little work on this mechanism in Laves phases, probably due to the difficulty involved in the shear deformation in the phases of complex structure. Y. Ohba and N. Sakuma[l] observed a gum elastic deformation in MgCu 2 Laves phase when it was rapidly cooled from the melt, which was considered to be due to the stress-induced transformation, at a condition of very low stress and room temperature. Our previous work[2) used X-ray diffraction and electron microscopy to show that such a transformation could occur in a two-phase Fe-Zr alloy during uniaxial compression in room temperature. The present paper provides further results and discusses observations related to the nucleation and growth mechanism of the transformation in the Fe-10 at% Zr alloy. Laves phases have three structure types: Cubic C15 (MgCu 2), hexagonal C14 (MgZn 2) or dihexagonal C36 (MgNi2). The structure type appearing in a Laves phase is mainly determined by the electronic factor. Many studies suggested favorable ranges in terms of valence electron-to-atom ratios for the formation of Laves phases[3]. In FeZr system, Kai et al.[4] found from their results of X-ray and magnetic measurements that two single-phase regions of dihexagonal (MgNi 2-type) and of cubic (MgCu 2 ) Laves phase are located in two separate composition ranges from 27.3 to 31.4 at% Zr and from 32.8 to 34.0 at% Zr, respectively. Because of the eutectic point at 8.8 at% Zr, The 10 at% Zr alloy used in the present study contains substantial amounts of both eutectic and pro-eutectic Fe 2Zr Laves phases. 1I. EXPERIMENTAL The Fe-10 at% 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 5x5x5 mm. Samples were encapsulated in a vacuum of 10-6 Torr and annealed at 1190 0 C for 48 hours. Compression experiments were performed at room temperature with a crosshead speed of 2.5x×10 cm/min. Indentations were performed at room temperature in a DM 400 Microhardness Tester, and