Synthesis of Tungsten Carbide by Electric Explosive Wire Method

WC has always attracted much attention due to its unusual and unique physical and mechanical properties. WC is characterized by high melting point, high hardness, high fracture toughness, low friction coefficient, high chemical inertness, strong oxidation and corrosion resistance, and good electrical conductivity. WC is used in industry to produce cutting and stamping tools, mining tools, drilling tools and wear-resistant applications, as well as heterogeneous oxidation green catalysts, hydrogen evolution and oxygen reduction reactions, electrocatalysis, fuel cells, petroleum processing, and more.

Wear parts, knives, and non-ferrous alloys are now typically produced using powder injection molding (PIM) technology, which requires highly dispersed WC powders.

There are many processes for synthesizing WC powder, but all have one thing in common: the formation of metallic tungsten from a precursor, followed by carburizing. In many cases, WC powder is produced by direct carburization of tungsten powder mixed with carbon. This process is time-consuming and often requires maintaining high carburizing temperatures for long periods of time.

The interaction of tungsten and carbon usually proceeds in a solid-solid reaction, in which carbon diffuses into the metal particles, followed by a chemical reaction of the reagents, which can form the tungsten hemicarbide W2C. Further carburization will convert W2C to WC.

The chemical reactions of nanoparticles proceed at higher rates and start at lower temperatures than reactions of micron-sized particles. The properties of nano-tungsten enable the preparation of WC by direct carburization. Nanomaterials have many surface atoms, making them highly surface active and exhibiting high reactivity.

In PIM technology, particle size affects the production process and the performance of the final part. The finer the powder used, the better the properties of the part. This is because the lower the surface roughness of the part, the smaller the pore size, the denser the material.

However, the reduction in particle size can also lead to significant changes in the physical and mechanical properties of the powder. Nanopowders have low flowability and high oxidative activity; they exist as porous agglomerates with poor mixing with each other and among microparticles. A relatively homogeneous mixture can be formed only with threshing particles of approximately the same size.

A combination of microparticles and nanoparticles in a certain proportion (bimodal material) is a more suitable material. In bimodal materials, nanoparticles fill the voids between submicron-scale particles, resulting in low porosity of the material. The use of bimodal compositions can also improve the mechanical properties of the part, such as microhardness and tensile strength. Likewise, compositions using WC bimodal powders will produce similar effects.

At present, bimodal powders are mainly obtained by powder mixing, and large-scale production is currently not possible. One of the effective methods for producing metal, alloy and ceramic powders is EEW. This method is versatile, has less waste and is environmentally friendly. The main advantage of EEW is that low aggregation bimodal powders can be produced. Unlike micro/nano powder mixtures, the resulting powder is homogeneous and does not separate.