The microstructure of rolled and annealed tungsten rod |
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Authors: | C L Briant E L Hall |
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Affiliation: | (1) Research and Development Center, General Electric Company, P.O. Box 8, 12301 Schenectady, NY |
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Abstract: | This paper reports a study of the microstructural changes that occur when potassium-doped tungsten ingots are rolled at elevated
temperatures. The effect of annealing on the microstructure of the rolled material is also considered. All samples were rolled
on a Kocks mill. At low levels of deformation, the grain boundaries are primarily high-angle boundaries, and many grains are
dislocation free. Both of these features probably result from dynamic recrystallization during rolling. As deformation increases,
the grains become more elongated, and more low-angle boundaries are found within the material. Also, the potassium gets drawn
into narrower and longer tubes. When these rolled rods are annealed at temperatures between 1275 ‡C and 1950 ‡C, several changes
occur in the microstructure. The material undergoes abnormal grain growth. The temperature at which this occurs depends on
the length of the anneal, the amount of de-formation the rod has received, and the spatial location in the rod. This spatial
distribution most likely results from strain gradients that exist in the rolled rod. The abnormal grain growth is accompanied
by a decrease in hardness. The potassium-containing tubes in the rod also break up into bubbles during annealing. The temperature
at which this breakup occurs again depends on the length of the anneal and the amount of deformation. |
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