Tungsten Carbide Materials Research Articles

Sintering of tungsten carbide cermets with an iron-based ternary alloy binder: Processing and thermodynamic considerations

Cemented tungsten carbide materials are traditionally bonded using a cobalt matrix, resulting in a material that possesses a unique combination of exceptional properties. However, cobalt has been recently classified as “reasonably anticipated to be a human carcinogen,” and thus, removal of this hazardous phase is desired for many applications. This research focuses on the production of tungsten carbide bodies cemented with a non-hazardous iron-based alloy binder phase. This binder has roots in the previous transition metal binders and additives for tungsten carbide and is based on the principles of high-entropy alloys; however, it relies on a novel means of carbide formation and dispersion from prior investigations. Sintering studies were conducted through uniaxial hot pressing, field-assisted sintering techniques, and pressureless sintering techniques. While some of the results of hot pressing and field-assisted sintering technique were positive, the resultant mesostructure exhibited an undesired, graded, heterogeneous form. Pressureless sintering, on the other hand, was capable of producing a homogeneous microstructure with high theoretical density along with promising hardness and indentation toughness values.

Design of cemented tungsten carbide and boride-containing shields for a fusion power plant

Results are reported on cemented tungsten carbide (cWC) and boride-containing composite materials for the task of shielding the centre column of a superconducting tokamak power plant. The shield is based on five concentric annular shells consisting of cWC and water layers of which the innermost cWC shield can be replaced with boride composites. Sample materials have been fabricated changing the parameters of porosity P, binder alloy fraction fbinder and boron weight fraction fboron. For the fabricated materials, and other hypothetical samples with chosen parameters, Monte Carlo studies are made of: (i) the power deposition into the superconducting core, (ii) the fast neutron and gamma fluxes and (iii) the attenuation coefficients through the shield for the deposited power and neutron and gamma fluxes. It is shown that conventional Co-based cWC binder alloy can be replaced with a Fe–Cr alloy (92 wt.% Fe, 8 wt.% Cr), which has lower activation than cobalt with minor changes in shield performance. Boride-based composite materials have been prepared and shown to give a significant reduction in power deposition and flux, when placed close to the superconducting core. A typical shield of cemented tungsten carbide with 10 wt.% of Fe–8Cr binder and 0.1% porosity has a power reduction half-length of 0.06 m. It is shown that the power deposition increases by 4.3% for every 1% additional porosity, and 1.7% for every 1 wt.% additional binder. Power deposition decreased by 26% for an initial 1 wt.% boron addition, but further increases in fboron showed only a marginal decrease. The dependences of power deposited in the core, the maximum neutron and gamma fluxes on the core surface, and the half attenuation distances through the shield have been fitted to within a fractional percentage error by analytic functions of the porosity, metallic binder alloy and boron weight fractions.

Dynamic hardness of cemented tungsten carbides

Cemented tungsten carbides are composed of a hard tungsten carbide (WC) phase held together by a soft, ductile binder phase, typically cobalt (Co). This study examines the role of the binder composition and content on the Knoop hardness at quasi-static and dynamic strain rates. Seven different tungsten carbide materials were tested: four WC-Co systems containing 10%, 15%, 20% and 25% cobalt, two with a chromium‑nickel alloy binder phase, and one “binderless” tungsten carbide. Quasi-static Knoop hardness testing was performed at strain rates of 10−3 s−1 and at indentation loads between 300 and 30,000 g using a Wilson Tukon 2100 unit. Dynamic Knoop hardness testing was conducted at strain rates of 103 s−1 using a Dynamic Indentation Hardness Tester over a range of indentation loads. All of the materials exhibited a rate-dependent Knoop hardness, with the hardness increasing by up to 60% with increasing strain rate.

Fabrication of dense nano-laminated tungsten carbide materials doped with Cr3C2/VC through two-step sintering

This work investigates the critical roles of two-step sintering (TSS) and laminated structure on the sintering behavior and mechanical properties of functionally graded WC-TiC-Al2O3 nanostructured composite materials doped with Cr3C2/VC. Results show that excellent mechanical properties are achieved for tailored TSS conditions with a hardness of 27.91 ± 2.3 GPa and a flexural strength of 1423.3 ± 23.5 MPa. The desirable mechanical properties are attributed to the suppressed grain growth without densification deterioration. TSS is more effective in facilitating the favorable dispersion of secondary phase toughening nano-particulates in a WC matrix than conventional sintering (CS). Cr3C2/VC dopant plays an important role in maximizing and shifting the temperature range of the kinetic window for WC-Al2O3 composites. Al2O3 crack deflection, transgranular Al2O3, microcracking, WC crack bridging and plate-like WC crack deflection are the major toughening mechanisms. Residual surface compressive stress induced by the graded structure is also an appreciated contribution to the improvement of mechanical properties.

Oxygen reduction electrocatalysis on transition metal-nitrogen modified tungsten carbide nanomaterials

Considering the technological importance of the oxygen reduction reaction (ORR) and the cost constraints of highly catalytically active precious metals, recent research efforts have been focused on designing and synthesizing earth abundant non-precious metal catalysts for this reaction. Among recent advances in this area, transition metal-nitrogen modified tungsten carbides can be pointed as prominent candidates as ORR electrocatalysts. Nevertheless, mechanistically understandings of which active sites are responsible for the ORR electrocatalysis on these materials are required for the rational design of suitable materials. In the present work, various tungsten carbides and iron-nitrogen modified tungsten carbides catalysts are synthesized and in-depth characterized through various physical and electrochemical techniques towards gaining insights on the ORR process on these materials in both acidic and alkaline media. High performance materials are developed, with the most active presenting only a ca. 0.060 V increase in the ORR overpotential, compared to a standard platinum catalyst in an alkaline medium. The in-depth analyses allowed for suggestions on reaction pathways for the oxygen reduction on the hybrid Fe/N/WC/C nanomaterials in terms of active sites. These finds might direct further developments in the research on transition metal-nitrogen modified tungsten carbide materials.

Increased tool performance with niobium carbide based cutting materials in dry cylindrical turning

Niobium carbide (NbC) shows promising results as an alternative cutting tool material to tungsten carbide (WC) for turning of iron-based materials. Due to its hot hardness and low solubility of binderless NbC in solid chrome, nickel, cobalt, or iron, it presents excellent properties for cutting tool applications. These advantages result in a reduced tendency to adhesive and diffusion wear, which affects cutting tool lifetime and process stability. In order to investigate a possible substitution of the conventional substrate material tungsten carbide, the BAM Federal Institute for Materials Research and Testing and the Institute for Machine Tools and Factory Management (IWF) of the Technische Universität Berlin analyze the suitability of NbC for the use as a cutting tool in turning processes. Two different straight NbC materials are included in the machining trials prepared by Katholieke Universiteit Leuven, Belgium each differing in chemical composition and mechanical properties. A cobalt (Co) bonded niobium carbide defined as NbC0.88-12Co, a nickel (Ni) bonded NbC with the specification (NbC1.0-10TiC)-6Ni7.5VC and a commercially available cermet with a niobium content of wt.-%NbC = 25 % are selected and compared to submicron grain WC-6Co tool material. Carbon steel C45E and gear steel 42CrMo4+QT are chosen as workpiece materials of different representative technological applications for dry external cylindrical turning tests. A variation of cutting speed is carried out to show the impact of higher thermomechanical load during machining. The results evaluate the cutting performance of NbC compared to WC regarding material removal VW and crater wear KT. In contrast to WC tools NbC cutting tools show constant material removal VW at increased cutting speed vc combined with a higher process reliability.

X-ray focusing with efficient high-NA multilayer Laue lenses

Multilayer Laue lenses are volume diffraction elements for the efficient focusing of X-rays. With a new manufacturing technique that we introduced, it is possible to fabricate lenses of sufficiently high numerical aperture (NA) to achieve focal spot sizes below 10 nm. The alternating layers of the materials that form the lens must span a broad range of thicknesses on the nanometer scale to achieve the necessary range of X-ray deflection angles required to achieve a high NA. This poses a challenge to both the accuracy of the deposition process and the control of the materials properties, which often vary with layer thickness. We introduced a new pair of materials—tungsten carbide and silicon carbide—to prepare layered structures with smooth and sharp interfaces and with no material phase transitions that hampered the manufacture of previous lenses. Using a pair of multilayer Laue lenses (MLLs) fabricated from this system, we achieved a two-dimensional focus of 8.4 × 6.8 nm2 at a photon energy of 16.3 keV with high diffraction efficiency and demonstrated scanning-based imaging of samples with a resolution well below 10 nm. The high NA also allowed projection holographic imaging with strong phase contrast over a large range of magnifications. An error analysis indicates the possibility of achieving 1 nm focusing.

Effect of direct current patterns on densification and mechanical properties of binderless tungsten carbides fabricated by the spark plasma sintering system

Binderless tungsten carbide materials (bWCs) were fabricated by the spark plasma sintering (SPS) system. Ultrafine WC powders with adjusted oxygen contents and C/W atomic ratios were used as raw materials. Constant and pulsed direct current patterns (constant DC and pulsed DC) were chosen as the power supplies. The results indicate that for WC starting powders with either low (0.31%) or high (0.95%) oxygen contents, a relative density larger than 99.0% can be reached by pulsed DC at 1820°C. Nevertheless, the severely oxidized WC powders cannot be well-densified by constant DC. A high degree of densification of bWCs facilitates the collaborative improvement of the toughness and hardness. The existence of W2C facilitates the improvement of the hardness at the high expense of the toughness. The existence of graphite phase is substantially detriment to the toughness. The grain coarsening facilitates the improvement of the toughness with sacrificed hardness. The related mechanism is discussed.

Material-Technology Index to evaluate micro-EDM drilling process

This research aims to study the influence of the process parameters and the thermal and electrical properties of workpiece and electrode materials on the performance of micro-EDM drilling. An experimental campaign was carried out using different workpiece materials such as stainless steel, tungsten carbide and aluminum and as electrode materials tungsten carbide and brass. Material Removal Rate (MRR) and Tool Wear Ratio (TWR) were assumed as performance indicators. The geometrical characteristics of micro-holes were evaluated by taking into account Diametral Overcut (DOC) and Taper Rate (TR). A “Material-Technology Index” (MTI), taking into account EDM process parameters, electrical and thermal properties of workpiece and electrode materials, was defined for each indicator. The effect of the MT indexes on the process performance and geometrical indicators was studied and proper fitting equations, having satisfactory coefficients of determination, were used to summarize the analyzed behaviors. Finally, a surface integrity analysis was carried out on the micro holes obtained in different conditions.

Effects of Mechanical Alloying on Sintering Behavior of Tungsten Carbide-Cobalt Hard Metal System

During the last few years, efforts have been made to improve the properties of tungsten carbides (WCs) by preparing composite materials. In this study, we prepared WC particles by mechanical alloying and investigated the effects of mechanical alloying conditions, such as mechanical alloying time and mechanically alloyed powder ratio, on the properties of 94WC-6Co. According to experimental studies, increasing the mechanical alloying time causes an increase in the density of tungsten carbide samples and a decrease of crystal sizes and inner strength of the prepared materials. With the increase of mechanical alloying time, fine particle concentrations of tungsten carbide samples have increased. It is observed that increasing the mechanical alloying time caused a decrease of the particle surface area of tungsten carbide samples. Besides, the amount of specific phases such as Co3W3C and Co6W6C increases with increasing mechanical alloying time. As another subject of this study, increasing the concentration of mechanically alloyed tungsten carbides caused an increase in the densities of final tungsten carbide materials. With the concentrations of mechanically alloyed materials, the occurrence of Co6W6C and Co3W3C phases and the increase of crystallization are observed.

Near Ductile Regime Machining of Tungsten Carbide insert through Control of Cutting Speed Parameter While Using a Poly-Crystalline Diamond Tool

Grinding is an acceptable manufacturing process for processing tungsten carbide components but grinding a pocket for manufacture of a die & mold still remains as a daunting task despite of the developments on the cutting tools and machining systems. A study was attempted to understand the high speed machining behavior for tungsten carbide materials while using the Poly-crystalline diamond tools. An experimental set up with a comprehensive data acquisition system was developed to conduct the machining experiments. The literature review enabled to select the cutting conditions: depth of cut, feed rate and cutting speed. Bifano's equation was used to find the critical depth of cut for configuring the near-ductile regime machining conditions. The machining performance characteristics in terms of: cutting force, tangential force, friction ratio, shear angle, cutting ratio and shear strain are unveiled.

Application of Deep Cryogenic Treatment to Uncoated Tungsten Carbide Inserts in the Turning of AISI 304 Stainless Steel

This study investigated the effects of deep cryogenic treatment (DCT) on the wear performance of uncoated tungsten carbide inserts. AISI 304 austenitic stainless steel, widely used in industry, was selected as the workpiece material. Cutting experiments showed that the amount of wear significantly increased with increasing cutting speed. In addition, it was found that DCT contributed to the wear resistance of the turning inserts. The treated turning inserts were less worn by 48 and 38 pct in terms of crater wear and notch wear, respectively, whereas they exhibited up to 18 pct superior wear performance in terms of flank wear. This was attributed to the precipitation of new and finer η-carbides and their homogeneous distribution in the microstructure of the tungsten carbide material after deep cryogenic treatment. Analyses via image processing, hardness measurements, and SEM observations confirmed these findings.

Potential failure cause analysis of tungsten carbide end mills for titanium alloy machining

Abstract Tungsten carbide end mills have been widely used for titanium alloys machining, but they have severe problems of high damage rate, which lead to abnormal increase of the machining cost. Although there are many relevant research such as the material preparation and the structural design of cutting tools, the parameter optimization of titanium alloys machining process and so on, but this problems still have not been solved very well. Therefore, other possible influencing factors must also be considered. The present study focuses on the preparation of tungsten carbide end mills, an experimental study was conducted which includes the microstructure comparative analysis of the material surface layer in the different positions of tungsten carbide end mills, and the grinding effect comparison of tungsten carbide materials between different grinding parameters. The main findings include: (1) The internal micro cracks already exist in surface layer of cutting edge even these tungsten carbide end mills have not been involved in machining process; (2) In the surface layer of tungsten carbide tools, different types and levels of residual stress will be generated by different grinding process parameters, once they are engaged in the intermittent cutting process, the internal micro cracks and residual stress in the surface layer will have complex interaction with the cutting force and temperature, which can prompt the propagation of the cracks and eventually lead to catastrophic destruction of the cutting edges. It can provide an important basis for the preventive measures to eliminate the potential factors that affect the service life of the cutting tool in the fabrication stages.

Application of ASTM C1421 to WC-Co fracture toughness measurement

The accurate measurement of fracture toughness of cemented carbides is essential for material development, characterization, and application; however, varying methodologies are used to characterize this critical material property. In this study, the surface crack in flexure and single-edge precracked beam methods in ASTM C1421, along with the Palmqvist indentation/crack length method outlined in ISO 28079, were used to determine the fracture toughness of tungsten carbide (WC) materials containing between 10 and 25wt.% cobalt (Co). The surface crack in flexure method was not successful because an appropriate precrack did not form underneath the Knoop indentation in any of these compositions. Cracks also did not form at the tips of the Vickers indentations in WC with 15% and higher Co content, rendering the Palmqvist method useless for these materials. The single-edge precracked beam method was the only method that yielded consistent and repeatable toughness values for all compositions.

The Coating Technology with the Wire Electrode

The purpose of this study is to address requests for higher quality and productivity improvement through wire electrode coating technology. A prime example of high quality is the improved life of tungsten carbide. When a tungsten carbide material is cut in water, the cobalt binder starts to dissolve. As a result, the material becomes weak. In this study, we experimentally examine the effect of coating the cutting surface with wire brass. We found that the life of molds could be thereby extended. As an example of productivity improvement, we show a method for core processing automation. When the operator completes a rough cut for all shapes leaving uncut parts, the operator must move the axis manually for each shape in order to finish the uncut part and remove the core. We studied the effect of coating the cutting surface with brass wire in this context, as well. Accordingly, we found that brass could be coated on a part 1mm from its upper face and could hold the cores. The operator can then cut away the coated part by simply tapping on the cores.

Investigation on Machining of Holes and Channels on Borosilicate and Sodalime Glass Using μ-ECDM Setup

Electro Chemical Discharge Machining (ECDM) is a non-conventional machining process used to machine various conducting and non-conducting engineering materials. The non-conventional machining processes, uses some form of energy to machine materials. These some form of energies includes mechanical, thermal, chemical etc. Some of the mechanical machining processes are Water Jet Machining (WJM), Abrasive Jet Machining (AJM), Ultra Sound Machining (USM) etc., thermal machining processes are Electro Discharge Machining (EDM), Ion Beam Machining (IBM), Plasma Arc Machining (PAM), Laser Beam Machining (LBM) etc., and chemical machining processes are Electro Chemical Machining (ECM), Electro Chemical Grinding (ECG), etc. EDM and ECM machining processes are well developed and established commercially. Currently the main focus is on hybrid machining processes to utilize the advantages of one and overcome the disadvantages of others. ECDM is one such process which combines the features of EDM and ECM to machine non-conducting materials. ECDM process is mainly used for machining, scribing hard and brittle non-conducting materials like soda lime glass, borosilicate glass, PMMA material, silicon wafers etc. In the present work, experiments are conducted to machine holes and channels with a developed μ-ECDM setup. Design of Experiments (DOE) is used to plan and conduct the experiments. Optimized combinations of process parameters- voltage, duty factor and electrolyte concentration are obtained for responses- maximum Material Removal Rate (MRR), minimum Tool Wear Rate (TWR) and Radial Over Cut (ROC) are obtained using main effect plots. Repeatable holes and channels are machined using the obtained optimized parameter for maximum MRR. The response- diameter of micro holes of 0.92mm, micro channels of length 14mm, 0.34mm and 0.63mm width are obtained on borosilicate and sodalime glass with tool diameter 0.3mm of tungsten carbide and tungsten copper alloy material.

Morphology and Wear Behaviour of Single and Multi-layer Electrical Discharge Coatings

Electrical discharge coating (EDC) is a version of electrical discharge machining (EDM) which can produce a coating of material from a tool or from a powder suspended in the oil, onto a workpiece. Since spark temperatures are high, a large range of materials, such as hard ceramics, can be melted and deposited in the coating. These material properties, combined with the rapid quenching of the EDC layer, result in coatings which are typically very hard. Since EDC is an adaptation of EDM, coatings can be produced on components with conformal surfaces. In this study, hard ceramic materials tungsten carbide and powder-sintered titanium carbide are used as negative polarity tool electrodes, from which material is donated to produce hard coatings. The workpiece material is 304 stainless steel. Mechanical properties of the single and multi-layer coatings are assessed by dry sliding wear testing using the ball-on-flat method. Morphology and composition both on the surface and in cross-section are also analysed using SEM and EDX. The TiC single layer coating produced the best wear results for the conditions of the experiment, with the lowest and most constant coefficient of friction of approximately 0.2-0.3 despite cracking remaining in this layer. The TiC + Si double coating, despite better morphology including eliminated surface cracks, produced worse friction characteristics compared to TiC.

Numerical simulation and experiment on split tungsten carbide cylinder of high pressure apparatus.

A new high pressure device with a split cylinder was investigated on the basis of the belt-type apparatus. The belt-type die is subjected to excessive tangential tensile stress and the tungsten carbide cylinder is easily damaged in the running process. Taking into account the operating conditions and material properties of the tungsten carbide cylinder, it is divided into 6 blocks to eliminate the tangential tensile stress. We studied two forms of the split type: radial split and tangential split. Simulation results indicate that the split cylinder has more uniform stress distribution and smaller equivalent stress compared with the belt-type cylinder. The inner wall of the tangential split cylinder is in the situation that compressive stress is distributed in the axial, radial, and tangential directions. It is similar to the condition of hydrostatic pressure, and it is the best condition for tungsten carbide materials. The experimental results also verify that the tangential split die can bear the highest chamber pressure. Therefore, the tangential split structure can increase the pressure bearing capacity significantly.

Study on stress distribution of tangent split high pressure apparatus and its pressure bearing capacity

The ultra-high pressure device with tangent split tungsten carbide cylinder is investigated on the basis of the belt-type apparatus. The cylinder is divided into six blocks and the dividing line is tangent to the inscribed circle of the regular hexagon inner hole. Then the divided bodies assemble the high pressure cylinder. This structure of cylinder eliminates the tangential tensile stress and produces a great tangential compress stress through the friction and squeeze each other on the contact surface between the divided bodies. Simulation results show that the maximum shear stress and equivalent stress on the tangent split cylinder are much smaller than those on the belt-type cylinder. The principal stresses on the inner wall of the tangent split cylinder are all compressive stresses. And the situation that compressive stress is in three directions is akin to the condition of hydrostatic pressure, the best condition for tungsten carbide materials. The experiment results also prove that the tangent split die can bear higher oil pressure than the belt-type die.

Investigations of tungsten carbide nanostructures treated with different temperatures as counter electrodes for dye sensitized solar cells (DSSC) applications

Tungsten carbide (WC) materials are synthesized and sintered at 800, 900 and 1000 °C. The differently treated tungsten carbide nanostructures (WC-NSs) have been investigated as counter electrode (CE) catalysts to replace the expensive platinum (Pt) for dye sensitized solar cells (DSSC) towards better power conversion efficiency. The synthesized samples were structurally characterized by powder X-ray diffraction (PXRD) which reveals that the sintering temperatures strongly affect the structure of WC-NSs. The surface morphology and chemical compositions were examined by scanning electron microscope (SEM) fitted with energy dispersive X-ray analysis (EDAX). The electrochemical studies of WC-NSs suggest that increasing the sintering temperature leads to increase in the charge transfer resistance and results in decrease of the catalytic activity of the WC-NSs CE. The power conversion efficiency of the WC-NSs materials sintered at 800 °C is higher than that of 900 °C and 1000 °C sintered materials. It is found that the photovoltaic performance was strongly affected by the sintering temperature of the WC-NSs materials. The tungsten carbide nanorods sintered at 800 °C showed better photovoltaic parameters such as Jsc, Voc, FF and η of 2.71 mA cm−2, 0.53 V, 0.28 and 0.41 %, respectively when compared to the WC-NSs sintered at 900 and 1000 °C. The optimally modified WC-NSs could be a useful substitute.