Nanostructured WC Research Articles

Comprehensive behavior of reduced graphene oxide (rGO) reinforced plasma sprayed nanostructured WC–Co coatings

The effects of reduced graphene oxide (rGO) as an additive on the microstructure, mechanical properties, and tribological behavior of air plasma sprayed (APS) nanostructured tungsten carbide–cobalt (WC-25 wt.%Co) coatings were studied. The rGO was added in three distinct weight percentage proportions of 0.5, 1, and 1.5 wt.%. The microhardness and surface roughness of the APS sprayed nanostructured WC-25 wt.%Co coatings reinforced with rGO were changed significantly. Microstructural alterations in the coatings were also noticed with the addition of additives. Gluing of rGO amid coating splats was also seen in the microstructure of the coatings. The coatings’ microstructure revealed the presence of tungsten (W), tungsten carbide (WC), and semi-tungsten carbide (W2C) as the primary phases. The existence of the W2C phase in the microstructure of the coatings was mostly due to the decarbonization of WC at higher temperatures during plasma spraying. It was also found that the amount of wear of the coatings was exceptionally low because the rGO could not be extracted from the 1.5 wt.% rGO-reinforced coatings particularly. The wear degradation in the 0.5 and 1.0 wt.% rGO added coatings was mostly due to delimitation and the subsequent pulverization, notably at loads and sliding speeds of 1.5 kgf and 0.17 m/s.

Effect of HVOF–sprayed nanostructured WC–10Co–4Cr coating on sliding wear and tensile–tensile fatigue properties of TC6 titanium alloy

Aerospace equipment has been placing greater demands on the wear resistance and fatigue strength of titanium alloys. In light of this, the research objective was to prepare a WC-10Co-4Cr coating with better performance through the utilization of the ultra-short distance high-speed oxygen fuel (HVOF) spraying process. Then the microstructure, microhardness, sliding wear, and fatigue performance of TC6 alloy reinforced with WC–10Co–4Cr coating were further explored and analyzed. The ultra–short distance HVOF spraying process was employed to suppress decarburization, resulting in a minimal amount of W2C phase in the coating. The WC–10Co–4Cr coating exhibited excellent surface characteristics, displaying minimal microcracks and a low porosity rate of 0.15 ± 0.08%. The interface between the coating and the substrate was sharp and clean, while the TC6 alloy retained its dual structural characteristics without any microstructural changes. The microhardness of the WC–10Co–4Cr coating exhibited a remarkable value of 1172.64 HV0.025, which is 3.2 times greater than that of the substrate. The coating exhibited a noteworthy decrease in wear rate, wear depth, and wear area, indicating superior wear resistance. Additionally, a thorough examination was conducted to uncover the underlying wear mechanism of the coating under different loads. The WC-10Co-4Cr coating, which was developed through this study, shows a minimal influence on the fatigue strength of the original base material. Furthermore, a comprehensive analysis was conducted to elucidate the factors contributing to the significant fatigue life of the WC–10Co–4Cr coating.

Corrosion and wear of coatings fabricated by HVOF-spraying of nanostructured and conventional WC–10Co-4Cr powders on Al7075-T6

The present work compares WC-10Co-4Cr coatings fabricated by HVOF spraying of a conventional powder (1.33 ± 0.67 μm) and a nanostructured powder (0.17 ± 0.06 μm) on Al7075-T6, in terms of microstructure and phase composition, microhardness and fracture toughness, corrosion performance in 3.5 wt% NaCl (potentiodynamic polarization, chronoamperometry, galvanic effect measurements and salt spraying) and sliding wear performance under lubrication. Τhe nanocoating, despite its greater microporosity and decarburization, displayed higher microhardness, fracture toughness and surface roughness compared to its conventional counterpart. A superiority of the corrosion behaviour and sliding wear behaviour of the nanocoating as compared to its conventional analogue was observed in terms of a higher resistance to general/localized corrosion, lower passive film conductivity, lower wear rate, subtler wear scars and greater occurrence of islands of tribofilms. The reasons for such superiority are being clarified. A good galvanic compatibility between the nanocoating and its substrate was manifested. Both coatings exhibited high corrosion resistance during salt spraying for 45 days. The mechanisms of corrosion and wear degradation are being proposed.

Investigating the Wear Resistance of 18Ni300 Steel Reinforced by Nanostructured WC Particles Using Molecular Dynamics Simulations and Experiments

Investigating the Wear Resistance of 18Ni300 Steel Reinforced by Nanostructured WC Particles Using Molecular Dynamics Simulations and Experiments

Rapid Sintering of Nanostructured WC-Graphene Composites and Their Mechanical Properties.

The current concern about WC focuses on its low fracture toughness below the ductile-brittle transition temperature despite its many attractive properties. To improve its mechanical properties, the approach generally utilized has been the addition of a second phase to form composites and to make nanostructured materials. In this paper, graphene was evaluated as the reinforcing agent in WC ceramics using a novel sintering method (high-frequency induction heated sintering method). Highly dense nanostructured WC and WC-graphene composites were obtained within two min at 1550 °C. The effect of graphene on the grain size and the mechanical properties (hardness and fracture toughness) of WC-graphene composites was evaluated.

Ternary Alloys AuPdPt Catalysts Supported on the Tungsten Carbide for Methanol Electrooxidation

Direct methanol fuel cell (DMFCs) is one of the best positioned toward widespread commercialization and the most viable alternative to lithium-ion batteries for portable applications. A major drawback of this technology is in large part related to the dependence on Pt-based electrocatalysts for methanol oxidation reaction (MOR) at the anode. To address this issue, low-Pt electrocatalysts are desired for keeping high performance of MOR. In this abstract, trimetallic AuPdPt nanocomposites supported on the tungsten carbide (WC) was prepared through two-step method, i) intermittent microwave heating method (IMH) and ii) direct chemical reduction method. Trimetallic AuPdPt nanoparticles are dispersed well on the nanostructured WC, confirmed by scanning electron microscopy (SEM), energy X-ray diffraction spectroscopy (EDX), and transmission electron microscopy (TEM). The electrocatalytical performance of the as-synthesized nanocomposite for MOR was tested using cyclic voltammetry and chronopotentiometry in alkaline media. The results revealed that the WC enhanced trimetallic AuPdPt nanocomposites has better performance of MOR and stability than that of commercial Pt/C catalyst. Alloying strategy and the introduction of WC support are good choices for preparation of MOR electrocatalysts with low loading of Pt.

Tungsten Carbide as Supports for Trimetallic AuPdPt Electrocatalysts for Methanol Oxidation

Direct methanol fuel cell (DMFCs) is one of the best positioned toward widespread commercialization and the most viable alternative to lithium-ion batteries for portable applications. A major drawback of this technology is in large part related to the dependence on Pt-based electrocatalysts for methanol oxidation reaction (MOR) at the anode. To address this issue, low-Pt electrocatalysts are desired for keeping high performance of MOR. In this article, tungsten carbide (WC) enhanced trimetallic AuPdPt nanocomposite was prepared through the two-step method, i) intermittent microwave heating method (IMH) and ii) direct chemical reduction method. Trimetallic AuPdPt nanoparticles are dispersed well on the nanostructured WC, confirmed by scanning electron microscopy (SEM), energy X-ray diffraction spectroscopy (EDX), and transmission electron microscopy (TEM). The electrocatalytic performance of the as-synthesized nanocomposite for MOR was tested using cyclic voltammetry and chronopotentiometry in alkaline media. The results revealed that the WC enhanced trimetallic AuPdPt nanocomposites has better performance of MOR and stability than that of commercial Pt/C catalyst.

WITHDRAWN: Wear resistance of nanostructured Cr-based WC hardmetals sintered by spark plasma sintering

WITHDRAWN: Wear resistance of nanostructured Cr-based WC hardmetals sintered by spark plasma sintering

Wear resistance of nanostructured Cr-based WC hardmetals sintered by spark plasma sintering

Nanostructured Cr-based WC hardmetals are successfully sintered by spark plasma sintering. The wear behaviour of these Cr-based WC hardmetals with different C contents ranging from 5.57 wt% to 6.91 wt%, is evaluated performing sliding wear tests under two different wear conditions. This work analyses the influence of the C content on the wear performance through the study of the phase formation and WC grain size. The Cr-based hardmetal with 5.57 wt% C content exhibits a lower wear rate than Co-based WC hardmetals tested under similar dry ball-on-plate wear conditions, even considering that these Co-based WC hardmetals have higher WC content (90 wt%) than Cr-based WC hardmetals (83.2 wt%). The combination of a nanosized WC grain and the avoidance of brittle (Cr,Fe)7C3 or soft graphite phases leads to a superior wear performance. Thus, the use of Cr-based binders in the hardmetal industry, alternatively to Co-based binders, is promising in applications in which high wear resistance is needed.

Laser synthesis and microstructure of micro- and nano-structured WC reinforced Co-based cladding layers on titanium alloy

Micro- and nano-structured WC reinforced Co-based cladding layers on Ti6Al4V substrates were synthesized by laser cladding. The structure, phase composition, and wear behavior were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and friction-wear tests. High-angle annular dark field-energy dispersive spectroscopy (HAADF-EDS), transmission electron microscopy (TEM) and lattice images confirmed the XRD and SEM results. The interfaces exhibited good metallurgical bonding between the cladding layer and substrate owing to their high chemical affinity for each other. The cladding layer was composed of α(α′)-titanium, eutectics of CoTi2, β-titanium, TiC, eutectics of TiCTiB2, VC (Cr3C2), (Ti, W)C1−x, W, TiB2, and Co3W3C phases formed by the dissolution of WC. VC inhibited grain growth more effectively than Cr3C2 or the combined effects of VC and Cr3C2. The wear resistance of the micro-/nano-WC cladding layers was markedly improved compared with those of Ti6Al4V. Nano-WC tended to convert into tungsten, however, the cladding layers easily became hard and brittle owing to aggregates of carbides or oxides. This effect resulted from interfacial boundaries formed by major differences at the α-Ti/α-Ti (Cr3C2, TiB2) interfaces in terms of the chemical and structural contributions to the surface energy.

Structure and cavitation erosion behavior of HVOF sprayed multi-dimensional WC–10Co4Cr coating

Abstract A new kind of multi-dimensional WC–10Co4Cr coating which is composed of nano, submicron, micron WC grains and CoCr alloy, was developed by high velocity oxy-fuel (HVOF) spraying. Porosity, microhardness, fracture toughness and cavitation erosion resistance of the multi-dimensional coating were investigated in comparison with the bimodal and nanostructured WC–10Co4Cr coatings. Moreover, the cavitation erosion behavior and mechanism of the multi-dimensional coating were explored. Results show that HVOF sprayed multi-dimensional WC–10Co4Cr coating possesses low porosity (≤0.32%) and high fracture toughness without obvious nano WC decarburization during spraying. Furthermore, it is discovered that the multi-dimensional WC–10Co4Cr coating exhibits the best cavitation erosion resistance which is enhanced by approximately 28% and 34%, respectively, compared with the nanostructured and bimodal coatings in fresh water. The superior cavitation resistance of multi-dimensional WC–10Co4Cr coating may originate from the unique micro–nano structure and excellent properties, which can effectively obstruct the formation and propagation of cavitation erosion cracks.

Oxidation behavior of HVOF-sprayed nanostructured and CeO2-modified WC–12Co coatings

Two types of WC–12Co coatings with different modifications were deposited on steel substrates using high velocity oxygen fuel (HVOF) spraying. The coated samples were oxidized at 550[Formula: see text]C and 650[Formula: see text]C in ambient atmosphere. Oxidation mass gain was measured by electronic balance. Phase composition and microstructure evolution of both coatings after oxidation were conducted by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Microhardness testing was performed before and after oxidation testing. The results showed that at 550[Formula: see text]C and 650[Formula: see text]C, the rare-earth modified WC–12Co coating has lower oxidation rates compared with the nanostructured WC–12Co coating. This might be due to the rare-earth modification coating reducing the porosity and oxygen diffusion in the coatings, therefore delaying the crack formation and propagation.

Synthesis of Nanostructured Tungsten Carbide (WC) from Ammonia Paratungstate-APT and its Characterization by XRD and Rietveld Refinement

The carbides of refractory metals like tungsten carbide (WC), tantalum carbide (TaC) and niobium carbide (NbC), has been extensively studied due to their applications in several areas of industry, because of their specific properties; such as high melting point, high hardness, wear resistance, oxidation resistance and good electrical conductivity. The tungsten carbide, particularly, is generally used at hardmetal industries due to its high hardness and wear resistance. New synthesis techniques have been developed to reduce the synthesis temperature of refractory metal carbides using more reactive precursors and gas-solid reactions for carbon reduction. The result is producing pure carbides suitable properties for production of high quality cemented carbides and more selective catalysts. In this work, pure and nanostructured WC was obtained from the ammonium paratungstate hydrate (APT), at low temperature and short reaction time. Hydrogen (H2) and methane (CH4) were used as a reducing gas and carbon source, respectively. The precursor and obtained product were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results obtained by diffraction of X-rays showed that complete reduction and carburization of APT have been took place resulted in pure WC formation. The average crystallite size was in nanometer order reaching values of approximately 20.8 nm and a surface area (BET) of 26.9 m2/g.

Pulsed Current Activated Rapid Sintering of Binderless Nanostructured TiC and WC and Their Properties

Pulsed Current Activated Rapid Sintering of Binderless Nanostructured TiC and WC and Their Properties

Improved Solar Absorptance of WC/Co Solar Selective Absorbing Coating with Multimodal WC Particles

One type of multimodal (comprised of nanometer and sub-micrometer WC particles) and two types of conventional (comprised of nanometer and sub-micrometer WC particles, respectively) WC/Co powders were deposited on AISI 304L stainless steel substrates by using high velocity oxygen fuel spraying. The use of multimodal WC particles was indicated to have a beneficial effect on the solar absorptance (α) of the WC/Co coatings. The α of the multimodal WC coating reached 0.87, which was much higher than what can be achieved by either fine (0.82) or coarse powders (0.80) alone. By microstructural analysis, the enhancement in solar absorptance of the multimodal WC/Co coating was ascribed to the layer of distributed WC particles. During the thermal spraying, the nanostructured WC particles underwent rapid melting for the large specific surface area while the aggregated powders were heated, but not necessarily melted. The molten nano-WC would fill the available pores between the softened and heated aggregates, providing a layered distribution of WC particles for the spray-deposited coating. In this condition, the light-trapping in the multimodal coating will be enhanced due to the efficient light reflection among the multimodal WC particles, which contributes to the enhancement of solar absorptance.

High-frequency induction-heated consolidation of nanostructured WC and WC-Al hard materials and their mechanical properties

The rapid sintering of nanostructured WC-Al composites in a short time was investigated with a focus on the mechanical properties (hardness and fracture toughness) and consolidation using high-frequency induction heated sintering. This process allowed very quick densification to near theoretical density and prohibited grain growth in the nano-materials. The addition of Al to WC facilitated consolidation and improved fracture toughness. The hardness and fracture toughness of WC with 5vol.% Al and WC with 10vol.% Al composites were higher than those of monolithic WC.

Carbothermic reduction of scheelite (CaWO4) doped with cobalt or nickel

Pure scheelite (CaWO4) and carbon black mixtures, containing 0 or 2wt% cobalt or nickel were prepared by 8 or 24h planetary ball milling (PBM). The mixtures were studied by thermal analysis (TGA-DTA), isothermal annealing at 950, 1000 and 1100°C, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Independently of the presence of transition metal (Co or Ni), the carbothermic reaction occurs through several steps, where the Ca:O atomic ratio goes from 1:4 to 1:1 according to the sequence: CaWO4→Ca3WO6→CaO, with concomitant development of gaseous CO and formation of metal tungsten. Finally, tungsten is carburized to give nanostructured WC.For the first time we here show that Co and Ni have a noteworthy catalytic effect on the carbothermic reduction of CaWO4. In particular, these transition metals catalyze both the two-step reduction of scheelite and the subsequent carburization of tungsten. In the latter case, formation of intermediate η phases (MexWyCz, with Me=Co or Ni) occurs.Doping with Co or Ni allows obtaining an almost quantitative (97%) conversion of scheelite into WC after 12h at a temperature as low as 950°C. The catalyst allows to reduce PBM duration as well, in that doped mixtures subjected to just 8h PBM give WC yields larger than 90% after 1h at 1100°C, being W2C the balance.The doping of CaWO4:C mixtures with few weight percent of Co or Ni allows to produce nanostructured WC by reducing both the milling time and the annealing temperature. These results are particularly appealing from both industrial and sustainability point of view since they allow performing less energy-intensive syntheses of nanostructured WC powders from scheelite.

Mechanical properties and rapid consolidation of nanostructured WC and WC–Al2O3 composites by high-frequency induction-heated sintering

The short-term rapid sintering of nanostructured WC and WC–Al2O3 hard materials was fabricated using the high-frequency induction-heating sintering (HFIHS) process. The sintering behaviors, microstructure, and mechanical properties of the WC and WC–Al2O3 composites were investigated. The addition of Al2O3 to WC can facilitate sintering, and the grain size of WC decreases as the addition of Al2O3 is increased; furthermore, the hardness and fracture toughness of WC-15vol% Al2O3 are greater than those of monolithic WC and Al2O3.

Structure-property correlations in nanostructured WC–12Co microwave clad

Nanostructured materials are known for enhanced properties as compared to their conventional counterparts. In the present work, microwave cladding technique was explored for depositing nanostructured WC–12Co clads on stainless steel substrates. Phase analysis of the WC–12Co microwave clads revealed the presence of Co6W6C, Co7W6, Co3W9C4, W2C and WC phases. The microstructure of the WC–12Co clads confirmed uniform distribution of nano-carbides in the form of clusters enclosed in the carbide network. Mechanical characterisation of the nanostructured clads was carried in terms of microhardness assessment and flexural strength measurement. The microwave induced clads exhibited excellent metallurgical bonding with the substrate and were free from interfacial cracks. The average microhardness of the developed clads was found in the order of 1760±128HV. The flexural strength of the developed clads was observed to be 671±28MPa. The nanostructured clads exhibited good adhesion with the substrate without getting peeled-off under a load of 3.75kN and a displacement of 3.72mm.

Enhancing stability of Co gradient in nano-structured WC–Co functionally graded composites using graphene additives

Enhancing stability of Co gradient in nano-structured WC–Co functionally graded composites using graphene additives