Papers by Keyword: Tungsten Carbide

Abstract: In this study tungsten inert gas (TIG) surface melting of pre- plasma sprayed WC-14%Co low carbon steel has been studied. Surface melting was performed under different heat inputs by using various TIG parameters including intensity and kind of current. Microstructure and microhardness of surface alloyed specimens were then studied. Eutectic structures containing tungsten-rich carbides were shaped in a matrix including martensite lath, when high heat input was used. Decreasing at heat input affected the microstructure of the alloyed layers, and high amount of faceted tungsten-rich carbides (Fe₃W₃C) were formed in fairly low heat input. Microhardness of melted layers highly improved in comparison with that of the substrate.

Abstract: Thermally sprayed hardmetal coatings can be used to improve the wear or fatigue resistance of mechanical parts. Depending on the deposition conditions, their microstructure and phase composition are out of equilibrium at different levels due to the extreme heating/cooling rates. In the present study, the changes that occur with temperature variation are monitored by mechanical spectroscopy. Requirements to specimen of mechanical spectroscopy created the need to prepare WC-17%Co coatings of 1.2 mm thickness by high velocity oxy-fuel (HVOF) spraying. The coatings, separated from the substrate by spark erosion, were tested in a forced torsion pendulum between room temperature and 1570 K at a temperature scanning rate of 1K/min. The mechanical loss spectrum shows different features. At 800 K, a maximum M1 is observed in coincidence with a sudden increase of the elastic modulus. The change of the elastic modulus is due to a densification of the material possibly related to cobalt recrystallization. A relaxation peak located at about 1100 K is typically found in WC-Co hardmetals. It is attributed to the movement of dislocations in the cobalt phase. A sharp peak is observed at 1510 K on heating and at 1410 K on cooling. Such peak is due to the reversible transition from W₃Co₃C at high temperature to W₆Co₆C at low temperature as proven by X-ray diffraction. The reversibility of such transformation was observed for the first time.

Abstract: Powder injection moulding of 304L stainless steel - tungsten carbide (WC) composites were carried out in the present work. Two different WC particle i.e. WC having average size of 4.8 µm and 1.6 µm were used. Feedstock of powder loading up to 55 vol% were successfully prepared using binder composed mainly of polyethylene glycol (PEG) and a minor constituent of polymethylmethacrylate (PMMA). The mouldings were leached in water at temperatures of 40 °C and 60 °C from 30 minutes to 24 hours in order to study the effect of leaching conditions on the removal of the PEG. The remaining binder, PMMA, provided strength to the mouldings after leaching of the PEG and it could be removed by pyrolysis during ramping up to the sintering temperature. Specimens were sintered under hydrogen atmosphere at 1250 °C for 1 hour. Sintered components were subjected to testing and characterisation. Scanning electron microscope was used to observe microstructure of specimens after moulding, leaching and sintering. It was found that the hardness of the sintered specimens increased with either increasing the amount of the powder loading in the feedstock or reducing the average size of WC in the powder mixture. In addition, the water leaching of the PEG linearly correlates with the natural log of time and the equation predicts that PEG will be removed completely in 11.24 ± 1.31 hours which corresponds with the experiment result that PEG completely removed in 12 hours.

Abstract: — This paper presents an experimental investigation on the influence of cutting parameters of wire cut Electrical Discharge Machining (Wire-EDM) during the machining of tungsten carbide and optimization of machining parameters on kerf width. The investigation was conducted by considering the varying parameter of average machining voltage, spark on time, spark off time, and capacitance with Taguchi method as optimizing technique. L₉ orthogonal array has been used to determine the S/N ratio, analysis of variance and ‘F’ test values for indicating most significant parameter affecting the machining performance. The significant factors average machining voltage for kerf width. Spark on time, spark off time and capacitance are obtained as insignificant parameters. Further verification of improvements in the quality characteristics has been made through conformation test to the chosen initial parameter setting. The optimal combination of WEDM parameters satisfies the real requirement of quality machining of tungsten carbide.

Abstract: Force and specific energy are important factors in all abrasive machining operations especially in creep-feed grinding of hard materials. They have a high influence on the wheel wear, grinding accuracy, grinding temperature and surface integrity. This paper investigates the effect of grinding technological parameters on grinding force and specific energy in up-cut creep-feed grinding of cemented tungsten carbide with 20% cobalt using a resin-bonded nickel-coated diamond wheel. It was observed that increase of feed rate resulted in grinding force increase and specific energy decrease. Increased wheel-peripheral speed resulted in minor decrease of grinding force and specific energy increase.

Abstract: Rubbing tests between a diamond stick and a tungsten carbide plate and planing experiments of cobalt-free tungsten carbide using a mono-crystalline diamond tool are conducted, and the effect of lubricants on tool wear is investigated. Five kinds of lubricants such as: sulfur-base extreme-pressure additive; dimethyl-silicone; oleic acid; zinc dialkyldithiophosphate (ZnDDP); and chemical solution type coolant (FGC950) are chosen for the lubricants. Through the rubbing experiments, diamond stick wear is the greatest when using dimethyl-silicone, followed by FGC950 and it is the least using ZnDDP. On the other hand, tool edge chipping is the greatest when using FGC950, followed by sulfur-base extreme-pressure additive and it is the least using ZnDDP. Through the planing experiments, tool chipping is dominant in diamond-tool wastage in comparison with abrasive wear. Tool life is the longest when using ZnDDP and obtained surface roughness is 0.022 mm Ra after 177 m planing.

Abstract: Face cutting of tungsten carbide was conducted using two monocrystalline diamond tools and three polycrystalline diamond tools to investigate the wear characteristics in terms of the crystal structure and composition of the diamond. It was found that the wear of the monocrystalline diamond tool depends on the crystal planes that form the rake face and flank face of the cutting tool, and a cleavage fracture occurs when the cutting force acts as a shear force on the (111) crystal plane. The binderless nano-polycrystalline diamond tool exhibits excellent wear resistance beyond those of the sintered polycrystalline diamond tool and chemical vapour deposition polycrystalline diamond tool, as well as better wear resistance than the monocrystalline diamond tool.

Abstract: Hardfacing alloys reinforced with WC/W₂C on Q235 steel plates were prepared by the method of flux-cored wire TIG and MIG welding. The interface microstructure and carbide morphology were investigated using optical microscopy and scanning electron microscopy (SEM). The effect of dissolving of WC/W₂C on the interface microstructure was discussed. It indicated that the C-W-Fe ternary brittle compound has formed on the interface due to dissolving of WC/W₂C and the dissolving degree of the particles by TIG is less than by MIG. Abrasion resistance was evaluated by wet sand rubber wear tests and the wear mechanism was studied. The results show that WC/W₂C particles play a key role in improving abrasion resistance.

Abstract: Tungsten carbide (WC) is often induction welded to tougher and economical material, such as martensitic type 420 stainless steels (SS 420), to form a hybrid cutting tool stock. However, undesired softening in the SS 420 next to the fusion interface usually occurs. This softening is due to localized carbide precipitation in SS 420 matrix arising from heating during the induction brazing process. The aim of the present work is to investigate the soft zone of the SS 420 weldment by controlling the heat input during induction brazing. The result showed that cooling rate has a great effect on softening of the SS 420 weldment during induction brazing.

Abstract: Specific coatings are frequently used for increasing the life of mechanical parts undergoing severe corrosive and wearing environment. Plasma surfacing has been used to produce high quality coatings with the rapid development of coating technology. In this paper, the dissolution process of WC particles during the plasma surfacing with Fe-based and tungsten carbides composite coatings on AISI 316L stainless steel was studied .The dissolution process of WC particles is investigated by SEM, EDS and phenomenological analysis. Results show that the dissolution of WC particle during the plasma surfacing process is a successive process consisted of dissolution and reaction diffusion. Moreover, the effects of WC dissolved on micro-hardness of coating have been discussed.