With a high degree of deformation, the grains become more fibrous due to the unidirectional nature of the processing (sheet rolling, rod extrusion, or swaging) and mechanical anisotropy develops. Strong crystallographic orientations and planar distributions of dispersed, insoluble phases (in the case of doped tungsten) are characteristic of the stage of heavily worked tungsten.
The grain size and grain structure of the final product have a great influence on the mechanical properties. They can be controlled by type of deformation, degree of deformation, and annealing processes both during and after machining.
Forming of tungsten is commonly carried out without protecting atmosphere. In air, tungsten is readily oxidized. Tungsten trioxide forms on the surfaces of the worked piece and, above 800℃, it volatilizes. The oxide layer acts as a protective layer against contamination from the working tools and is removed at certain stages of deformation by pickling and/or machining. Intermediate annealing and stress-relieving annealing is performed under hydrogen to avoid enhanced oxidation of the metal and sublimation of WO3.please visit our website www.tungsten-powder.com
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