Milling (MM) process, is applied to W powder and W-Re powder mixtures. Pure W powder and several W-Re powder mixtures are charged into vials with balls and rotated using a planetary ball milling. The MM powders are then sintered by spark plasma sintering (SPS) equipment. The compacts and powders are examined by means of XRD, SEM and TEM/EDS. As a result, in the MM powder a nano grain structure after MM for 360 ks forms. The nano grain structure has irregular boundaries; grain size is approximately 15 nm. The irregular grain boundary which can be called "non-equilibrium grain boundary" changes to a regular smooth grain boundary, i.e. "equilibrium grain boundary", by annealing at 1023 K for 3.6 ks and the nano grain structure is sustained less than 1273K. The W-10Re/MM compacts have excellent deformability at 1473 K. This compact is composed of equiaxed grains, whose grain size is approximately 420 nm, and has low dislocation density even after the large deformation. In addition, high temperature compression test revealed the strain-rate sensitivity, m-value, of 0.41 at 1473 K. These results indicate that nano structure W compacts show superplasticity around 1473 K.

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