Thermal Stability of Nano Grain Structure Tungsten Prepared by SPD-PM Process

Abstract

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.

Fabrication of Tungsten-Rhenium Cladding materials via Spark Plasma Sintering for Ultra High Temperature Reactor Applications

“…W-Cu [14] and W-Mo [15] alloys have been successfully produced using SPS. There were a few published papers by a single research group in Japan [16,17].…”

Development of Nanostructured W and Mo Materials

“…The starting powder of pure materials and solid solution alloys is subjected to mechanical milling (MM) or mechanical alloying (MA) [25], followed by sintering processes for densification at relatively low temperatures where nano-grained structures produced by MM or MA can be essentially maintained. A beneficial effect of MMed or MAed powder is its good sinterability [26], leading to highly densified compacts. Since the high internal energies stored in the MMed or MAed powder may also cause significant grain growth of the compacts even at relatively low sintering temperatures, hot isostatic pressing (HIP), spark plasma sintering (SPS) or pulse plasma sintering (PPS) processes are effective in suppressing grain growth.…”