2008 年 94 巻 12 号 p. 608-615
Mechanical milling is one of the severe plastic deformation processes and can give a heavy deformation to a metallic powder. Using such a mechanical milling process nano crystalline material can be produced with relatively simple equipment, low cost and short time. The mechanical milling process leads to finer grain than other severe plastic deformation for bulk materials and the grain size produced by mechanical milling is less than 10 nm. Nano grain structure by mechanical milling is finally formed with nano layered structure though the grain refinement rate depends on the milling method and the milling condition. The minimum grain size produced by mechanical milling is related to many factors such as melting point and stacking fault energy. The nano grain tungsten powder demonstrates a good workability and its sintered compact demonstrates the superplastic deformation at 1473K. When the milling intensity is suitable, mechanically milled powder consisting of shell and core can be produced. The compacts produced from such mechanically milled powder have the nano/meso hybrid microstructure and demonstrate advanced mechanical properties.