Development of structure and porosity in cast Al 5 CuZr 2 and Al 66 Mn 9 Zr 25 intermetallic compounds
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I.
INTRODUCTION
R E C E N T L Y , there has been considerable interest in A13Ti intermetallic, which has several attractive properties, such as low density (3.3 g/cm3[~]), relatively high elastic modulus (166 GPa t21) for such a low-density material, and much better oxidation resistance than that of TiA1. t31 These properties make A13Ti an attractive material for high-temperature applications. Unfortunately, it has the low-symmetry, ordered tetragonal D022 structure which limits the number of independent slip systems to less than five, and A13Ti exhibits poor low-temperature ductility and toughness, t41 Raman and Schubert tSl and Virdis and Zwicker ~6~ showed that the DOzz structure of At3Ti can be transformed into an ordered cubic L12 structure by alloying with Cu, Ni, and Zn. Markiv et al. rT] and Seibold I81have shown that substitution of Fe for A1 in AI3Ti produces the same change into an Llz structure. A verification of the D0z2-to-L12 transformation by alloying with Ni, Cu, and Fe has recently been made by Mazdiyasni et al. i9j The L12 structure has the requisite number of five independent slip systems required for homogeneous deformation, tl~ Recent rediscovery of these early works on the transformation of 13012 al3Ti to the L I / s y s t e m brought about high expectations that the ductility of these modified A13Ti-base alloys might be considerably improved. The structure and mechanical properties of A13Ti modified with such elements as Ni, tlI 16] Cu,[12,17-19] Fe and V, 117,20,21,22] Pd, [231 Mn, [24,251 and C r [25'26] have been extensively investigated. Similar transformation of the low-symmetry tetragonal structure to the high-symmetry cubic L12 structure occurs in A13Zr. It was first shown by Schubert et al. t271 that the tetragonal D0z3 crystal structure of A13Zr intermetallic can be changed to the related cubic LI2 crystal structure by alloying with Ni (AIsNiZr2) and Cu (A15CuZr2). Recently, Schneibel and Porter I281 reported I.S. VIRK, Graduate Student, and R.A. VARIN, Associate Professor of Materials Science and Engineering, are with the Department of Mechanical Engineering, University of Waterloo, Waterloo, ON N2L 3GI, Canada. Manuscript submitted November 26, 1990. METALLURGICAL TRANSACTIONS A
that they modified A13Zr with Fe, Cr, Cu, and Ni and obtained nearly single-phase materials with the L12 structure. However, in contrast to a quite substantial number of publications on the modified A13Ti-base alloys, so far only two articles have been published on the structure and mechanical properties of A13Zr modified with Fe (AI-6 at. pct Fe-25 at. pct Zr). f22,281 In our laboratory, we initiated a research program devoted to structural and mechanical characterization of modified A13Zr-base alloys. The present article describes results of an investigation of the structure in specimens cast by various methods, as well as details of the structure and porosity development after homogenization. Two alloy systems based on AI3Zr were investigated: modified with Cu (A15CuZr~) and modified with Mn (A166Mn9
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