Koji Tanoue1, Osamu Nakano2, Hisatoshi Mori3 and Hidehiko Matsuda1
1Department of Metal Processing Engineering, Kyushu Institute of Technology, Kitakyushu
Subsequent fabrication of powder metallurgy tungsten rods becomes often difficult because of their brittle fracture in the swaging process. Workable and unworkable lots are sampled to investigate the cause of brittleness in the paractical swaging process of 2.5 mm in diameter. While the fiber structure is well grown to be almost straight in the workable lots, it consists of many discotinuous arrays of wavy fibers in the unworkable ones. There is no direct relation between the workability and the segregation of impurities (O, C) to the boundary of fibers. The deflection to fracture in bending tests reflects the workability well, and the ductility is considerably improved by electropolishing the surface. Tensile tests shows that there is an intrinsic difference in the internal structure between the two lots, which may be caused by different degrees of the development of fiber textures. It is concluded from the results that the practical workability in the swaging process depends on the degree of texture development as well as the roughness of the surface.
powder metallurgy, workability, delamination tests, Auger electron spectroscopy, fiber structure, fractography, tungsten
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