The Activated Sintering of Tungsten with Group VIII Elements

Abstract

Small additions of Group VIII transition elements permit the densification of tungsten powder compacts at temperatures well below those employed for sintering commercial purity tungsten powder. The mechanism of this process has been examined using the model concepts of current general sintering theories. The added solid element accelerates mass transport along its interface with a tungsten particle. This process, together with sintering in the presence of a liquid phase or a volatile component, comprises the three types of carrier phase sintering in which one of several possible pure component solid‐state sintering mechanisms is selectively accelerated.

Nanoscale segregation behavior and high-temperature stability of nanocrystalline W–20at.% Ti

“…In our preliminary letter [13], nanocrystalline W-Ti alloy powder with enhanced thermal stability was introduced; with a 20 at.% addition of Ti, we reported that a nanoscale grain structure (grain size of ~20 nm) could be retained at the target consolidation temperature of 1100°C [14,15] for one week. Even though the conventional equilibrium phase diagram for this system expects a single-phase solid solution of W and Ti for these conditions, we observed a well-defined nanostructure with patterns of solute enrichment and depletion throughout the structure.…”

Influence of size of nanoparticles and plasma pressure compaction on microstructural development and hardness of bulk tungsten samples

“…Herein, activated sintering refers to a combination of processing approaches that reduces the amount of activation energy that is required for sintering. One such technique that has been used to activate sintering is by the addition of small amounts (usually less than 1.0 pct) of the transition metals in Group VIII of the periodic table of elements [5][6][7][8]. The sintering temperature of tungsten can be lowered from 2800°C to 1400°C by the addition of less than 1 weight percent of transition metals, such as palladium and nickel [8].…”

Fabrication of homogeneous tungsten porous matrix using spherical tungsten powders prepared by thermal plasma spheroidization process

“…In addition, to manufacture dispenser cathode, homogeneous pore distribution and open pore channel of the tungsten matrix are essential for uniformly distributed and supplied in time of the emissive material [2,3,11], which favors the realization of continuous and steady electrons emission. Moreover, The addition of small amounts of some transition metals such as nickel could lower the activation energy of sintering, which make it possible to reduce the sintering temperature of tungsten significantly [12,13]. Therefore, fabrication of porous tungsten matrix with homogeneous and interpenetrated open porosity is crucially important to further obtain outstanding properties materials.…”