Single nanocrystalline tungsten carbide (WC) was first synthesized on the tips of vertically aligned carbon nanotubes (VA-CNTs) with a hot filament chemical vapor deposition (HF-CVD) method through the directly reaction of tungsten metal with carbon source. The VA-CNTs with preservation of vertical structure integrity and alignment play an important role to support the nanocrystalline WC growth. With the high crystallinity, small size, and uniform distribution of WC particles on the carbon support, the formed WC–CNTs material exhibited an excellent catalytic activity for hydrogen evolution reaction (HER), giving a η10 (the overpotential for driving a current of 10 mA cm–2) of 145 mV, onset potential of 15 mV, exchange current density@ 300 mV of 117.6 mV and Tafel slope values of 72 mV dec–1 in acid solution, and η10 of 137 mV, onset potential of 16 mV, exchange current density@ 300 mV of 33.1 mV and Tafel slope values of 106 mV dec–1 in alkaline media, respectively. Electrochemical stability test further ...

WC Nanocrystals Grown on Vertically Aligned Carbon Nanotubes: An Efficient and Stable Electrocatalyst for Hydrogen Evolution Reaction

Twelve commercially available WC–Co powders with different average WC grain sizes (0.2, 2, and 6 μm) and cobalt contents (8, 12, 17 and 25 wt.%) were sprayed on carbon steel substrates using High Velocity Oxy-Fuel (HVOF) spraying process. Hardness, Young's modulus, and fracture toughness of the coatings were measured. While the hardness and Young's modulus decreased with increasing cobalt content from 1600 to 1100 Hv and from 400 to 300 GPa respectively, the fracture toughness remained in the range from 4 to 6 MPam 1/2 . The coatings with 2 μm carbide showed lower hardness than those deposited from 0.2 and 6 μm carbide. These measured mechanical properties were discussed with the help of microstructures of the coatings investigated by scanning electron microscopy, X-ray diffraction and chemical analysis. Finally, the hardness of the binder phase in these coatings was estimated to range from 1000 to 1300 Hv by applying the mixture rule for composites to the experimental data, demonstrating that such hardening of the binder phase is a key factor affecting the mechanical properties of the coatings.

Effects of carbide size and Co content on the microstructure and mechanical properties of HVOF-sprayed WC–Co coatings

The capability of machining intricate features with high dimensional accuracy in hard and difficult-to-cut material has made electrodischarge machining (EDM) process as an inevitable and one of the most popular non-conventional machining processes. In recent years, both EDM and micro-EDM processes are being used extensively in the field of mould making, production of dies, cavities and complex 3D structures using difficult-to-cut tungsten carbide and its composites. The objective of this paper is to provide a state of the art in the field of EDM and micro-EDM of tungsten carbide and its composites. The review begins with a brief introduction on the EDM and micro-EDM processes. The research and developments in electrodischarge machining of tungsten carbide are grouped broadly into conventional EDM of tungsten carbide, micro-EDM of tungsten carbide and current research trends in EDM and micro-EDM of tungsten carbide. The problems and challenges in the area of conventional and micro-EDM of tungsten carbide and the importance of compound and hybrid machining processes are discussed. A summary of the future research directions based on the review is presented at the final section.

A review on the conventional and micro-electrodischarge machining of tungsten carbide

Friction and wear behaviour of cemented carbides

Grinding of WC-Co hardmetals

Tribofilm formation on cemented carbides in dry sliding conformal contact

In order to study wear mechanisms on WC-based face seals, lubricated seal tests have been performed. The tested materials were WC–Co, WC–Ni and a WC–TiC binderless carbide. The tests lasted for 700 h and all seals were still fully functional at the end of the tests. The worn surfaces have been studied with a range of different techniques including focused ion beam and transmission electron microscopy (TEM). All tested seals showed a periodic wear pattern extending perpendicular to the sliding direction. On the metal bonded cemented carbides the pattern included cracks penetrating about 40 μm into the material. In connection to each crack on the WC–Co seals, a damaged subsurface zone with altered structure was found. X-ray analysis of the altered zone revealed the presence of oxides in the vicinity of the cracks as well as an enrichment of Cl in the crack tips. The mechanisms that may have caused the surface damages are discussed.

Wear phenomena on WC-based face seal rings

Grooving wear of single-crystal tungsten carbide

A cutting tool for woodworking applications has a tungsten carbide substrate and a hard layer bonded to the substrate at high temperature and high pressure, i.e. where diamond or cubic boron nitride is thermodynamically stable. The hard layer comprises polycrystalline diamond or polycrystalline cubic boron nitride, and a supporting cobalt phase including adjuvant alloying materials for providing oxidation and corrosion resistance. Typical alloying elements include nickel, aluminum, silicon, titanium, molybdenum and chromium. Such materials also retard transformation of cobalt from the HCP to the FCC crystal structure at high temperature. The hard layer has an as-pressed surface parallel to the substrate and is only about 0.3 millimeters thick. An additional secondary phase including a carbide, nitride and carbonitride of metals such as titanium may also be present in the PCD or PCBN layer.

PCD or PCBN cutting tools for woodworking applications

According to the present invention there is provided a wear resistant material consisting of 3-60 % by volume of diamond in a matrix containing at least one hard constituent consisting of carbide, nitride and/or carbonitride of one metal of group IV, V and VI in the periodic table and a binder-phase based upon Co, Ni and/or Fe at which the diamonds are surrounded by a layer > 1 µm of refractory metals, carbides, nitrides, oxides, borides or silicides. In this way a dissolution of diamonds during the sintering is prevented by a special combination of layer material and sintering/compaction process.

Stefan Ederyd

Papers

Tribofilm formation on cemented carbides in dry sliding conformal contact

Wear phenomena on WC-based face seal rings

Grooving wear of single-crystal tungsten carbide

PCD or PCBN cutting tools for woodworking applications

Diamond-containing hard material