Papers by Keyword: WC-Co

Abstract: Cemented tungsten carbides have been paid much attention due its better mechanical properties with excellent combination of hardness and toughness characteristics. The hard WC particles in the coating provide hardness and wear resistance, while the ductile binder such as Co and Ni contribute to toughness and strength. WC-17wt.% Co and WC-9wt.% Ni powders have been sprayed by the HVOF method to form coatings approximately 300μm and 150μm thick onto AISI 1018 steel substrate. Both coatings have been prepared and supplied by an external vendor. The coatings were examined using optical microscope (OM), scanning electron microscope (SEM), and X-Ray diffraction (XRD). The hardness of both coatings were also measured using Vickers micro-hardness tester. The microstructure of the coatings has been analyzed and found to consist of WC, brittle W₂C phase, metallic W phase, and amorphous binder phase of Co and Ni. It is found that WC-Ni has a higher hardness value compared to WC-Co due to high porosity distribution.

Abstract: Metal-ceramic composite or cermet coatings have become popular due to their enhanced wear and corrosion resistance properties. Cermet consists of ceramic particulate embedded in a metallic binder. WC-Co coatings are often used in applications that require wear resistance, but there are many applications in which thermally sprayed coatings have been deposited on components that operate under both abrasive and corrosive condition. Thus, in this study, the corrosion behavior of WC-12wt%Co in different electrolyte has been evaluated. Electrochemical test has been done in three electrolytes namely 0.5 M hydrochloric acid, HCl, 0.5 M sulfuric acid, H₂SO₄ and 0.5 M sodium hydroxide, NaOH. It is found that corrosion potential of this coating in acidic environment is more positive compares to in alkaline environment. Both in acid and alkaline electrolyte, binder dissolution were preferential. It may be concluded that this coating have higher corrosion resistance in alkaline electrolyte than in acid electrolyte.

Abstract: It is well known that grain-refinement has a positive impact on the mechanical properties of WC-Co cemented carbide. The effect of VC inhibitor and microwave on density, microstructure and mechanical properties of the sintered WC–12wt%Co alloy was investigated in the present study. The ball milled WC-12wt%Co-xVC composites were compressed and fabricated by using microwave sintering method. The experimental results indicate that the microwave sintering cycle was significantly shorter to that of vacuum processing, and the density of bulk alloys increased with VC inhibitor contents and microwave sintering temperatures. Moreover, the microstructure observation of the sintered samples suggests that VC inhibitor had prominent inhibitory action on WC grains in microwave exposure, and the WC average grain size of alloy with 0.7wt%VC inhibitor was 0.43μm when the sintering temperature reached 1420°C. It is also evident that WC-12wt% alloys with an appropriate proportion of VC inhibitor exhibited higher hardness (92.1HRA) and better transverse rupture strength (2380MPa). And finally the mechanism of inhibitory effects on WC grains under microwave irradiation was discussed.

Abstract: In cermet coating such as WC-based coating, the coexisting of ceramic and metal results in micro-galvanic corrosion due to different corrosion potential of each element. In this study, WC-17wt%Co was used. The corrosion behaviour of the coating was evaluated by potentiodynamic test in two different electrolyte which are 0.5 M sulphuric acid and 3% by weight alkaline drilling fluid. This coating shows higher corrosion potential in acid electrolyte compares to in alkaline electrolyte. Clear passivation is seen for both cases. Raman shift is able to detect WO₃ and WO₃H₂O as a corrosion product after corrosion test. Keywords: corrosion, WC, Raman shift

Abstract: Wire Electrical discharge Machining plays an important role in the field of electrically conductive material machining. The process has grown exponentially in the past decade due to advantages like high accuracy, precision, ability to achieve complex, intricate shapes on components, unruffled by material hardness, less noise, leaves little residual stress on work piece and the advantage of unmanned machining. A stochastic process in nature, it is difficult to determine parameters that improve cutting rate and surface roughness, the main stay of the metal machining industries. Tungsten carbide is widely used in tool and die making industry mainly due to its extreme hardness; wear resistance, toughness and high temperature stability. Finding optimized parameters for machining performance improvement and optimization would help the manufacturing community. Design of experiments with an orthogonal array of L 27, on four critical parameters On-Time, Off-Time, Wire Speed and Peak current with three levels had been carried out. The experimental results were optimized using Taguchi analysis. Analysis of variance was done. Confirmation tests validated that the results for material removal rate and surface roughness, 5.021mm3/min and3.26μm with improvement. The most influential parameters were off-time, wire-speed and on-time for material removal rate and wire-speed current and on-time for surface roughness. The optimum levels were reported.

Abstract: WC-8wt%Co nanopowder was consolidated by spark plasma sintering at process temperatures (T_SPS) from 1100 to 1400 °C. The nanoindentation hardness and Young’s modulus of the consolidated specimens were measured under different peak load levels (P_max). The hardnesses and modulus of WC-8wt% Co shows a clear dependence on the microstructures and peak load levels. At 1200 and 1300 °C, the hardness and modulus were higher than those at 1100 and 1400 °C due to the higher relative density and fine grain size. The relationship of stiffness (S) and contact depth (h_c) of nanoindentation was discussed.

Abstract: WC-Co hardmetals are widely known wear resistant materials, their properties depend strongly on the WC grain size; commonly fine grained materials exhibited higher properties. One opportunity to produce fine grained materials is reactive sintering. Reactive sintering is a novel processing method, where the synthesis of the carbide phase is combined with solid and liquid state sintering of the composite during a single heating cycle. WC-co hardmetals where synthesized in situ from the elemental powders of W, Co and C. To investigate the influence of grain growth inhibitors the Cr₃C₂ and VC were also included to powder mixtures. To investigate the influence of carbon content composites with different amounts of C were produced. The microstructures, hardness and three-body abrasive wear resistance of reactive sintered WC-Co hardmetals with grain growth inhibitors depending on carbon content in initial powder mixture is exhibited.

Abstract: The mechanical properties and microstructures of WC-Co are highly dependent on its cobalt content, grain size of the WC particles and sintering temperature. In this work, the effect of addition of VC powder on the mechanical properties and microstructures during the consolidation of process will be investigated. The WC-Co and WC-Co-VC cutting tool inserts were fabricated using powder metallurgy route. The powders were wet mixed with heptane in turbula mixer for three hours, dried and then granulated. The mixed powders were uniaxially pressed at a pressure of 625 MPa and cold-isostatic pressed at a pressure of 200 MPa. The compacted samples were sintered in the temperature range of 1350 1450°C under nitrogen-based atmosphere. The mechanical properties of the samples are analyzed using Vickers microhardness tester, universal tensile machine and the microstructures of the sintered sample were observed using field emission scanning electron microscope. Microstructural examinations showed that VC particle is good as grain growth inhibitor as a result of good precipitation of VC in WC grain boundaries. However the addition of VC in WC-Co hardmetal resulted in the reduction of hardness and transverse rupture stress due to increase of pores in the microstructures of sintered samples.

Abstract: The properties of WC-Co are greatly improved with the use of submicron powders. However, grain growth tends to occur during the sintering process which causes the properties to deteriorate to some extent. Free carbon and vanadium carbide are added in this study to serve as grain growth inhibitor. The effect of these two materials is evaluated based on WC-Co properties. In this work, the powders are mixed together via wet mixing process, compacted and undergo cold-isostatic pressing (CIP) before the samples are sintered in the temperature range of 1350-1450°C under nitrogen-based atmosphere. The physical and mechanical properties of the WC-Co sintered powders were analysed. Based on the work done, the WC-Co-C has a better properties compared to WC-Co-VC.

Abstract: Nickel enables nucleation and growth of well oriented diamond crystals from the small lattice mismatch between nickel and diamond. However, its solubility for carbon causes carbon loss during diamond deposition and, consequently, results in poor nucleation density. In this study, carburizing of Ni/WC-Co specimens in high temperature furnace with inert gas atmosphere was adopted to provide nickel with sufficient carbon prior to diamond deposition. This process was carried out using charcoal powder as source of carbon at different treatment temperatures (750°C and 850°C) and durations (20min and 60min). Effect of the process in altering the nickel layer composition was characterized by microscopy, element analysis, and phase identification techniques. Results show that carburization leads to formation of metallic phases, such as nickel carbide and nickel cobalt, which are considered beneficial for diamond nucleation and growth.