Fabrication of nanostructured W–Y2O3 materials by chemical methods

Abstract

A novel method for the fabrication of highly uniform oxide dispersion-strengthened (ODS) materials made by chemical processing is presented. The powders are fabricated by a two-step route starting with a chemical synthesis at room temperature, producing nanocrystalline yttrium doped tungsten trioxide hydrate precursor powders. Thermogravimetric analysis with evolved gas analysis revealed the presence of ammonium nitrate in the precursors. The second step is the reduction of the precursor in a hydrogen atmosphere at 600 and 800 C. The reduced powders, containing W-1.2%Y 2 O 3 , showed two types of tungsten particles, cube-shaped with a size less than 250 nm and finer particles (<50 nm) of both spherical and cubic shape. The powder was consolidated by spark plasma sintering at 1100 C, producing a bulk material with a relative density of 88%. Characterization of the sintered materials by high resolution scanning electron microscopy revealed a uniform microstructure with tungsten grains of less than 300 nm and nanosized oxide particles uniformly dispersed at the tungsten grain boundaries, as well as inside the tungsten grains. Experimental determination of the elastic properties was conducted by nanoindentation tests and fracture toughness was studied by radial indentation cracking.

Synthesis of TiC/W core–shell nanoparticles by precipitate-coating process

“…There are many reports on the preparation of W-TiC nanoparticles by mechanical alloying (MA) [13]. However, nanoparticles used to agglomerate to some extent because of the high surface energies introduced by MA [14]. Besides, the milling process itself also produce detrimental phase by the wear of the milling equipment and media [13].…”

“…And during the sintering process, TiC cores are expected to precipitate partially at the grain boundaries by precipitation from the supersaturated W matrix [10], resulting in homogeneous distribution of TiC nanoparticles in the matrix and grain boundaries. To prepare this core-shell structure, wet chemical method has shown high potential for industrialized manufacturing to produce molecular engineered nanomaterials with precise composition at very high purity, homogeneity, and controllable shape [14]. It is an efficient and low-cost method.…”

The relationship between the green density and as-sintered density of nano-tungsten compacts

“…For example, Wahlberg et al reported a synthesis method which could control particle growth to produce uniformly yttrium doped nano-sized tungsten powders [10]. Zhou et al have developed ultrafine grained tungsten using resistance sintering under ultra-high pressure (RSUHP) [12].…”

“…The first is top-down via severe plastic deformation (SPD) to reduce the grain size of a monolithic component, such as equal-channel angular processing (ECAP), high pressure Additions of grain growth inhibitors are advantageous, as well as high pressure-assisted sintering with short thermal exposure, both of which could assist in simultaneously obtaining high density and fine grain size [8][9][10][11][12]. For example, Wahlberg et al reported a synthesis method which could control particle growth to produce uniformly yttrium doped nano-sized tungsten powders [10].…”

Chemical Synthesis and Oxide Dispersion Properties of Strengthened Tungsten via Spark Plasma Sintering

“…However, the milling process results in a detrimental phase because of the wearing of the milling equipment and the media. A wet chemical process can effectively fabricate and prepare complex nanomaterials while maintaining a precise composition with high purity and homogeneity [10,11,12]. A major challenge in the sintering of nanopowders is the achievement of full densification while preserving the nanoscale.…”