Extrusion Textures in NiAl and Reaction Milled NiAl/AlN Composites
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EXTRUSION TEXTURES IN NiA.
AND REACTION MILLED NiAl/AIN COMPOSITES
T.R. BIELER, R.D. NOEBE*, J.D. WHITTENBERGER*, and M.J. LUTON** Department of Materials Science and Mechanics, Michigan State University, East Lansing, MI 48824 *NASA-Lewis Research Center, Cleveland OH 44135 ** EXXON Research Center, Annandale, NJ 08801 ABSTRACT Extrusion textures in monolithic NiAl and an NiAl/AlN particle composite are compared. The NiAl has a generally increasing grain size with extrusion temperature, and a corresponding transition from to fiber texture. The results suggests that is more closely related to the deformation texture, while the is a recrystallization orientation formed by preferential growth. The composite exhibits fiber texture, and this is consistent with slip in directions. The effect of the AlN particles is to prevent the orientation changes observed in the monolithic NiAl during recrystallization. INTRODUCTION Extrusions are known to have fiber textures. The components and strength of the texture provide information about the changes in the microstructure that occur during deformation at elevated temperature. The effects of the dominant slip systems, and the mechanisms of recovery and/or recrystallization can also be studied'". Particle strengthened materials often exhibit different textures than monolithic materials,4 due to alterations in slip, recovery, and recrystallization behavior- . This information is useful in understanding subsequent microstructures and material properties. The variation in extrusion conditions can affect the microstructure in a controllable way, and provide a means for choosing an optimum processing strategy. Texture in extruded aluminides has not been extensively studied, however6 5 extrusion textures have been measured by Khadkikar, et. al. , and Stout and Crimp in nickel and iron aluminides. Khadkikar found (111) fiber texture in both castextruded and powder-extruded samples of NiAI, but their characterization was done using normal diffractometer scans of the sample in three orientations (normal, longitudinal, and 7 450 to the axis), and inverse pole figures were made using the method by Harris . Khadkikar mentioned a lack of agreement between measured and computed inverse pole figures, indicating that the fiber texture was not "pure". The current work started as an exercise to determine differences in creep behavior arising HIP'ing or extrusion of the NiAI/AIN composite. Since the extrusion texture discovered was unusual, the work expanded into a study of extrusion parameters on monolithic NiAl to provide a basis for comparison. In the process, the effect of extrusion temperature on texture became significant and in the end provides some insight on the texture evolution in the composite. Also, the current work allows a comparison between texture measurements using standard pole figure techniques, with the technique used by Khadkikar et.al. EXPERIMENTAL RESULTS The monolithic NiAl samples were produced by extruding pre-alloyed NiAl powder in 76 mm evacuated steel cans at a 16:1
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