Nano-sized WC Powder Research Articles

Obtaining fine-grained hard alloys homogeneous in carbide grain

The actual task of this work is to obtain homogeneous hard alloys with fine carbide grains, combining high hardness and strength. Studies were carried out to establish the most favorable phase compositions of hard alloys and the most rational technical methodology for their production. In this research work, a nanostructured WC-TiC-Co powder charge was obtained by mechanochemical synthesis. Nanosized WC powder and nanopowder with precipitated Co were added to the hard alloy charge by mixing in a ball planetary mill. The process of pressing the powder charge at a pressure of 100-1000 MPa, as well as the sintering process at a temperature within the range of 1450-1600℃ was applied. The chemical-metallurgical method of deposition of metal layers from salt solutions was applied to obtain the WC-Co hard alloy. X-ray structural analysis and scanning electron microscopy were applied. The effect of the preparation method on the phase composition of WC-TiC-Co consolidated samples was studied. In the microstructure of these hard alloys, intercrystalline particles of (Ti,W)C are observed, and the presence of the liquid phase can lead to a rounded shape. It was found that the addition of nano-sized WC powder leads to an increase in pressed density. It was revealed that the addition of WC nanosize additives or WC nanopowder with deposited cobalt makes it possible to obtain a fine-grained structure with a grain size of not more than 4-6 microns. It was found that the addition of WC nanopowder with precipitated cobalt to the alloy has the highest Brinell hardness values; in addition, it leads to an increase in the bending strength.

Preparation of nano-sized tungsten carbide via fluidized bed

Abstract Ultrafine or nano-sized of tungsten carbide (WC) is the key material to prepare ultrafine grained cemented carbides. In this paper, nano-sized WC powders were directly prepared by using industrial nano-needle violet tungsten oxide (WO2.72) as the raw material, a fluidized bed as the reactor, and CO as the carbonization gas. The relationship between particle sizes and reaction temperatures, residence times, atmospheres has been investigated systematically. In addition, the physical–chemical indexes (such as residual oxygen, total carbon and free carbon) of the products were measured. The results indicated that the particle size of WC increased with the increase of temperature from 800 to 950 °C. As the residence time increased, the particle size decreased gradually, and then increased due to slight sintering. The introduction of hydrogen reduced the carbonization rate, and is not beneficial to obtaining nano-sized WC. Products that satisfy the standard were obtained when WO2.72 reacted with CO at 850 °C, 900 °C and 950 °C for 3.0 h, 2.5 h and 2.0 h, respectively. The particle sizes of the three samples calculated from the specific surface area were 46.4 nm, 53.2 nm and 52.1 nm, respectively.

The effect of input parameters of electro discharge process on physical properties of synthesized nano-tungsten carbide

Nanostructure tungsten carbide powder has been successfully synthesized using electro discharge process, i.e., submerged tungsten and graphite electrodes in deionized water. The effects of discharge parameters, e.g., current and pulse duration of discharge process, on structure and morphology of synthesized powder were studied using XRD patterns and TEM images, respectively. Furthermore, the effect of discharge parameters on size distribution and shape of particles were investigated using PSA and SEM tests, respectively. Last but not least, the effect of input parameters on the rate of production was studied. On the other hand, mono-tungsten carbide (W2C) was carburized under argon atmosphere for production of WC phase. FE–SEM test concludes the evaluation process of nano-sized WC powder.

WC platelet formation via high-energy ball mill

This work investigates the factors affecting the morphology of WC powder. WO3–C mixtures were prepared by high-energy ball milling and nano-sized WC powder was obtained in the form of platelets with a high aspect ratio (5–20) carbothermally. We observed that the WC powder contains excess (101) plane along with high level of strain during initial heating stage. Further, the temperature for the platelet formation coincides with that for the reduction of (101) peak intensity in the XRD pattern. From this study we found that the presence of excess (101) plane and high strain promoted the formation of platelet WC effectively.

VC and Cr3C2 doped WC-based nano-cermets prepared by MA and SPS

WC powders with average crystallite size of 10nm were obtained through planetary ball milling of micron sized WC powder. Nanosized-WC powders were then mechanically milled with both 9 and 12wt% Co, and the grain growth inhibitors VC and Cr3C2 in the range 0.2–0.8wt%. Powder mixtures were then consolidated using spark plasma sintering (SPS) at two different temperatures, i.e. 1200 and 1300°C. The microstructure, densification and mechanical properties of the resulting sintered nano-cermets were analyzed as a function of the type and amount of grain growth inhibitors, Co content, and sintering temperature. In general, the addition of VC and Cr3C2 was found to reduce densification. Nevertheless, the effect was found to be lower in Cr3C2 containing compositions with higher Co contents. The grain size variation was found by both a conventional line intersection method on FESEM micrographs, and by using grain analyzer software. VC was found to be comparatively more effective in restricting undesirable grain growth during the sintering processes. Moreover, the micro-hardness (HV30) and fracture toughness were measured using micro-indentation and the results were compared for each composition to comparatively assess the individual effect of the inhibitors. Increasing the concentration of inhibitors was found to restrict grain growth even more and higher hardness values were obtained but only up to a critical inhibitor concentration, beyond which the hardness degrades.

Synthesis mechanism and sintering behavior of tungsten carbide powder produced by a novel solid state reaction of W2N

Nanosized WC powder was synthesized by solid state reaction between tungsten nitride (W2N) and carbon black. The reaction path and the phase evolution during the synthesis were studied. It was found that W2N firstly decomposed to tungsten metal in the middle stage of synthesis, and then it reacted with carbon black to form W2C and WC in sequence. Using this WC powder as the starting material, binderless WC hardmetals were prepared by hot pressing, and the microstructure and mechanical properties of the material were investigated.

Use of Ti in hard metal alloys – Part II: mechanical properties

AbstractWC‐Co hard metal is a material of high hardness, high compressive strength and wear resistance while maintaining good toughness and thermal stability. Samples of nanosized WC powders with 10 wt% Co, WC‐10 wt% Ti, WC‐9 wt% Ti‐1 wt% Co were cold pressed at 200 MPa and sintered at 1500°C during 1 hour under vacuum of 10–2 mbar. The characterization of the sintered materials was performed by the measurements of densification, HV30 hardness, fracture toughness and compression strength. The results showed that it is possible to process a hard metal through a Powder Metallurgical conventional route from nanoscaled WC grains, using Ti (or a Ti‐Co mixture) as a binder phase, with good mechanical properties.

Fabrication of Nano-Sized WC/Co Composite Powder by Direct Reduction and Carburization with Carbon

Direct reduction and carburization process was thought one of the best methods to make nano-sized WC powder. The oxide powders were mixed with graphite powder by ball milling in the compositions of WC-5,-10wt%Co. The mean size of mixed powders was about 250 nm after milling. The mixture was heated at the temperatures of 600~800°C for 5 hours in Ar. The reaction time of the reduction and carburization was decreased as heating temperatures and cobalt content increased. The mean size of WC/Co composite powders was about 260 nm after the reactions. And the mean size of WC grains in WC/Co composite powder was about 38 nm after the reaction at 800°C for 5 hours.

ＷＯ３の直接炭化反応によるナノＷＣ粉末の製造

Nano-sized WC powder that is expected as the raw material for nano-sized WC-Co hardmetals with high hardness and strength was developed. The reaction path and morphological change in the reaction process of WO3 with carbon powder (direct carburization) were firstly investigated by thermogravimetric analysis. The proper reaction condition examined by the thermogravimetric analysis was developed to trial production by direct carburization facilities.The direct carburization reaction from WO3 to WC occurred through the generation of several intermediate products in the order of WO3 → WO2.72 → WO2 → W → W2C → WC. The nano-sized particles were generated at the stage from WO2.72 to WO2. We succeeded in the development of nano-sized WC powder less than 100 nm by controlling the reaction conditions for each intermediate products.

SANS investigation of sintering process based on nano-crystalline powder

At the Budapest Research Reactor, we plan to initiate the systematic SANS investigation of nano-crystalline-based sintered composite materials. The results of preliminary SANS experiments carried out on pure nanosized WC powder samples reveals different particle sizes in the initial materials due to the different milling technologies.