Fabrication of Nano Grain Tungsten Compact by Mechanical Milling Process and Its High Temperature Properties
Mechanical milling (MM), which is one of SPD process, is applied to W powder and W-Remixed powder. MM processed W and W-Re powders easily form nano grain structure even though they have high melting temperature. The nano grain formation mechanism in these powders is as follows: multi axial deformation of the powders by milling, at the temperature of 333K at most, produces pan-cake grain structure at first. Extremely dense dislocations result in grain sub-division, and finally nano grain structure with high angle boundary forms. Nano grains with approximately 10 nm in diameter are obtained. The MM powders are sintered using Spark Plasma Sintering process. Sintering and high temperature deformation behaviors of the MM powders are also investigated. The MM treatment enables W powder to be able to sinter at 1273 K while the powder without MM could never sintered at the same temperature. Re addition prevents grain growth during sintering and thus increases hardness of the compacts. A large deformation of W-10mass%Re sintered compact, whose grain size is approximately 450nm, is observed at elevated temperatures.
E. Oda et al., "Fabrication of Nano Grain Tungsten Compact by Mechanical Milling Process and Its High Temperature Properties", Materials Science Forum, Vols. 503-504, pp. 573-578, 2006