Preferred orientations in extruded nickel and iron aluminides
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I.
INTRODUCTION
P R E F E R R E D orientations and textures have been extensively studied over the years, primarily in technologically important fcc and bcc metals and alloys. I',21 However, with few exceptions, t3,41preferred orientations in intermetallic alloys have not been investigated. With the recent interest in the development of intermetallics for structural applications, there appears to be a need to characterize preferred orientations in intermetallic alloys. The difficulties for detailed studies of preferred orientations and textures in intermetallic alloys have been outlined in a recent paper, tSj where the authors investigated the compound A l a C u 9. In the present investigation, nickel (NiA1 and Ni3AI) and iron aluminides (FeA1) were studied, as these represent some of the most widely investigated intermetallic alloys in recent years, t61 Although no studies on preferred orientations in these materials are available, some interesting comments and data, which may be related to preferred orientations, are found in the literature. For instance, Thornton et al. ETI noted that an equiaxed grain structure in the cast and homogenized Ni3A1 had no roomtemperature tensile ductility, but bars with a columnar grain structure produced by electron beam zone melting possessed a fair degree of ductility. In the case of NiAI, Rozner and Wasilewski I81 as well as Hahn and Vedula t91 report a finite and reproducible tensile ductility at room temperature in the cast and extruded alloys. These resuits are in contrast with the work of Ball and Smallman ~~ and many other unpublished results which show no ductility at room temperature in cast NiA1, even in compression. These examples suggest that preferred orientations in these alloys play an important role in determining the mechanical behavior of these alloys. The purpose of this paper is limited to characterization of the preferred orientations in powder-extruded and cast
P.S. KHADKIKAR, formerly Research Associate, Case Western Reserve University, is Research Specialist with Therm-O-Disc, Inc., Mansfield, OH 44907. G.M. MICHAL and K. VEDULA, Associate Professors, are with the Department of Materials Science and Engineering, Case Western Reserve University, Cleveland, OH 44106. Manuscript submitted April 11, 1988. METALLURGICAL TRANSACTIONS A
and extruded nickel (NiA1 and Ni3A1) and iron (FeA1) aluminides.
II.
EXPERIMENTAL PROCEDURES
A. Materials
Binary B2 NiA1 (=45 at. pet AI), B2 FeA1 (=40 at. pet AI), and L12 Ni3AI (-~24 at. pct A1) alloys were investigated. These alloys were obtained by hot extrusion of prealloyed powders. The powders were canned in mild steel cans which were then evacuated, sealed, and extruded at an area reduction ratio of 16." 1. Cast billets of FeA1 and NiA1 approximately 50 mm in diameter were also extruded at an area reduction ratio of 16:1 and 14:1, respectively. The extrusion temperatures and analyzed chemical compositions of all these materials are listed in Table I. Mild steel cans were removed from the extruded rods either by cen
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