Microstructure and Texture Evolution during Friction Stir Processing of Fully Lamellar Ti-6Al-4V

Abstract

Friction stir processing (FSP) was used to locally refine a thin surface layer of the coarse, fully lamellar microstructure of investment-cast Ti-6Al-4V. Depending on the peak temperature reached in the stir zone during processing relative to the b transus, three distinct classes of microstructures were observed. Using accepted wrought product terminology, they are equiaxed, bimodal, and lamellar, except for the case of FSP, the length scale of each was smaller by at least an order of magnitude compared to typical wrought material. The evolution of an initially strain-free fully lamellar microstructure to each of these three refined conditions was characterized with scanning electron microscopy, transmission electron microscopy and electron backscatter diffraction. The fundamental mechanisms underlying grain refinement during FSP, including both the morphological changes and the formation of high-angle grain boundaries, were discussed.

Early Stages of Microstructure and Texture Evolution during Beta Annealing of Ti-6Al-4V

“…Following beta annealing, an alternate method was applied to determine the orientations and hence texture of the underlying beta subgrains/grains for the beta-annealed samples from the measurements for the alpha phase. This method was similar to that developed by Humbert et al [22,23] and Glavicic et al [24,25] For the present technique, however, the quaternion parameterization of orientation space was used in conjunction with average alpha-colony orientations (as described by Pilchak and Williams [26] ) in contrast to the pixel-by-pixel methods employed by the previous researchers. This enabled complete reconstruction of the beta grains in an area measuring 6 mm 9 12 mm (at full resolution) in several minutes.…”

Variant Selection During Cooling after Beta Annealing of Ti-6Al-4V Ingot Material

“…The MRL-TiBor software uses a method similar to that developed by Humbert et al [30,31] and Glavicic et al [32,33] In this code, however, the quaternion parameterization of orientation space is used in conjunction with average alpha colony orientations (as described by Pilchak and Williams [34] ) in contrast to the pixel-by-pixel methods employed by the previous researchers. This enables complete reconstruction of the beta grains in an area measuring~25 mm 9 40 mm (at 10 to 15 lm resolution) in several minutes.…”

Thermal Stir Welds in Titanium

“…The high-temperature beta grain structure and crystallographic texture were revealed using the MRL-TiBor software package (Materials Resources LLC, Dayton, OH) using a quaternion parameterization of orientation space and average alpha colony orientations to facilitate the calculations as discussed by Pilchak and Williams. [28] This software uses a method similar to that developed by Humbert et al [29,30] and Glavicic et al [31,32] to determine the parent b grain orientations from a group of inherited a variants.…”