3.2 Shaping. Compared to ductile metals and alloys, the fabricability of tungsten is rather poor: Tungsten should always be heated before shaping. The temperature range for forming has a lower limit, set by the brittle-to-ductile transformation temperature, and an upper limit, set by the recrystallization temperature. This temperature is mainly dependent on the purity, the history of deformation, and heat treatment of the material. Highly deformed products, such as thin tungsten wires, ribbons, or foils, are ductile at room temperature.
Thin, strongly deformed sheet and foil have a pronounced structure in the longitudinal direction due to elongation of the grains during rolling. The bending properties long the direction of rolling are therefore different from those across it. Therefore, tungsten sheet should always be bent in a way such that the bending edge is perpendicular to the rolling direction. If bending in the longitudinal direction cannot be avoided, owing to the design, much higher bending temperatures are required. At high temperatures, tungsten sheet can be stamped, punched, and sheared. Sharp tools are essential to clean cutting action without sheet cracking or delamination. Tungsten cylinders and cones can be formed by spinning, flow turning, or forging. The use of stress-relieved tungsten is suggested for optimum fabrication results.
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