Microstructure and Texture Evolution During Hot-Pack Rolling of Nickel-Base Superalloys to Thin Sheet and Foil
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INTRODUCTION
DEFORMATION and recrystallization textures of face-centered-cubic (fcc) metals subjected to plane-strain compression (PSC) have been the topic of much research.[1–9] This research has focused on a wide range of alloy compositions (aluminum, copper, and nickel), deformation temperatures (cold, warm, and hot rolling), and total reductions. The resultant textures all share a common feature. In particular, analysis of the orientation distribution has revealed the presence of a cube texture after deformation, which tends to increase in intensity with additional straining and during subsequent recrystallization heat treatment. Often, the cube component, which aligns a {100} plane with the rolling plane and adirection with the rolling direction, is referred to as a recrystallization-texture component, although it is usually present at low intensities in the deformation texture as well.[10] The intensity of the cube component in the deformation texture or recrystallization texture depends strongly on alloy composition and rolling temperature.[9] The mechanism controlling the formation of the cube texture has been the subject of a long debate.[7,11] One hypothesis, which is referred to as oriented nucleation (ON), postulates a frequency advantage of A.L. PILCHAK, Visiting Scientist, is with the Materials and Manufacturing Directorate, Metals Processing Group, Air Force Research Laboratory, AFRL/RXLM, Wright Patterson Air Force Base, OH 45433, and Research Scientist, with Universal Technology Corporation, Dayton, OH 45432. Contact e-mail: adam.pilchak@ wpafb.af.mil D.L. BALLARD, Senior Materials Research Engineer, D.S. WEAVER, Materials Research Engineer, and S.L. SEMIATIN, Senior Scientist, are with the Materials and Manufacturing Directorate, Air Force Research Laboratory. Manuscript submitted June 11, 2010. Article published online November 2, 2010 METALLURGICAL AND MATERIALS TRANSACTIONS A
cube-oriented nuclei over those in other orientations; i.e., cube-oriented nuclei predominate in the deformed structure prior to recrystallization heat treatment. The frequency advantage is quantified by the factor a = ao/ ar, in which ao denotes the fraction of cube-oriented grains in the recrystallized microstructure, and ar is the cube fraction in a randomly textured material. In an alternate interpretation, which is known as preferential or oriented growth, cube-oriented grains grow more quickly than those in other orientations and, thus, constitute a greater total volume fraction of the recrystallized microstructure. The size advantage is described by the factor b3; b is defined as the ratio of the cube to noncube grain sizes (diameters). As discussed by Samajdar and Doherty,[7] these factors can be used to quantify the relative importance of each mechanism regardless of their physical origin, which makes them unbiased parameters. Although PSC deformation and recrystallization textures of fcc metals have been investigated frequently, the spatial distribution of the grains constituting the various texture components ha
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