Synthesis, structure and mechanical properties of ice-templated tungsten foams

Abstract

Tungsten foams with directional, controlled porosity were created by directional freeze-casting of aqueous WO 3 powder slurries, subsequent freeze-drying by ice sublimation, followed by reduction and sintering under flowing hydrogen gas to form metallic tungsten. Addition of 0.51 wt% NiO to the WO 3 slurry improved the densification of tungsten cell walls significantly at sintering temperatures above 1250°C, yielding densely sintered W-0.5 wt% Ni walls with a small fraction of closed porosity (,5%). Slurries with powder volume fractions of 15-35 vol% were solidified and upon reduction and sintering the open porosity ranges from 27-66% following a linear relation with slurry solid volume fraction. By varying casting temperature and powder volume fraction, the wall thickness of the tungsten foams was controlled in the range of 10-50 lm. Uniaxial compressive testing at 25 and 400°C, below and above the brittle-to-ductile-transition temperature of W, yields compressive strength values of 70-96 MPa (25°C) and 92-130 MPa (400°C).

Additive Manufacturing of Metal Structures at the Micrometer Scale

“…A route to significantly increase the range of metallic elements would be the use of metal oxide nanoparticles combined with subsequent annealing in a reducing atmosphere. Dunand and co‐workers developed a method of macroscopic 3D printing with oxide particles and showed that most oxides can be reduced to their metallic state after printing . Yet, the significant volume loss upon reduction of the oxide is a considerable drawback of this approach.…”

Synthesis of bioinspired ice-templated bulk metallic glass-alumina composites with intertwined dendritic structure

“…The intertwined dendritic structure of the ice-templated BM -alumina composite offers no direct path for cracks to propagate perpendicular to the loading axis, which serves to suppress brittle fracture in the BM. Although the present ice -templated BMalumina composites showed lack of plasticity in compression, the ductility of icetemplated BM composites may be enhanced by the infiltration of freeze -cast metals such as Mo [32] or W [18], which have been considered as a ductile reinforcement for BMs [2,13]. However, the best means to optimize the microstructure to improve both strength and ductility in these composites is still unclear, and consequently merits further investigation.…”

“…From the perspective of processing BM -ceramic composites, freeze-casting (icetemplating) represents an effective technique to synthesize anisotropic foam materials using ice to generate bioinspired "nacre-like" hierarchical architectures [16][17][18]. Porosity can be modified between 0-100 % and lamellae thickness and spacing is tailorable at the micron-scale in the freeze-cast foams by controlling processing parameters [16][17][18][19].…”

Ice-Templated W-Cu Composites with High Anisotropy

“…The process is schematically summarized in Figure 1. The effects of processing parameterspowder fraction in the slurry, freeze-casting and sintering temperatures as well as the influence of nickel -on the final scaffold microstructure, in particular open porosity and structural wavelength, have been reported in detail in a previous publication 25 gravitational forces. After solidification and cooling of the composites to room temperature, cylindrical compressive specimens (5-6 mm diameter and height/diameter aspect ratio of 2:1) were machined on a lathe.…”