Coated Tungsten Carbide Research Articles

Preparation of nickel-coated tungsten carbide powders by room temperature ultrasonic-assisted electroless plating

In this paper nickel (Ni)-coated tungsten carbide (WC) composite powders have been synthesized by ultrasonic-assisted electroless plating with a simplified pretreatment at room temperature as the conventional sensitization and activation steps have not been employed. The growth mechanism of Ni layers and surface morphologies and composition of initial WC powders, pretreated WC powders and Ni-coated WC powders were analyzed by field emission scanning electron microscopy, and energy dispersion spectrometry. The results shows that uniform Ni-coated WC composite powders were successfully synthesized without conventional sensitization and activation steps by ultrasonic-assisted electroless plating at room temperature. The growth mechanism of Ni layers appears as follows: the surfaces of pretreated WC powders appear step-like defects which act as activated sites. Nucleation and the growth of nickel grains take place on the activated sites of pretreated WC powder, and the process repeats continuously on the lath particles with reticulate structure on the as-coated surfaces of previously deposited Ni-cells, finally Ni cells grow up and merge into a layer.

Deposition of alpha-WC/a-C nanocomposite thin films by hot-filament CVD

Nanostructured tungsten carbide coatings containing amorphous carbon (a-C) phases are interesting composite materials. The incorporation of the a-C phase simultaneously improves the thermal stabilization of the carbide phase and the coatings' friction coefficient. Such nanocomposite coatings are also electrically conducting with resistivity values comparable to the transition metals, which make them useful for a number of electrochemical and electronic applications. Many deposition techniques have been used for the synthesis of these coatings. However, most of them lead to the formation of complex crystalline structures consisting of more than one carbide phase and varying amorphous contents.The novelty of this work is the formation of WC coatings with controllable film thickness and a-C content, almost fully composed by α-WC phase. Tungsten carbide coatings were deposited on silicon substrates using a hot filament chemical vapor deposition (HFCVD) equipment with hydrogen and methane as the deposition gasses. Two types of nanocomposite coatings were obtained with significant variations of the carbide phase and a-C contents.The results point to the W vaporization time as the main parameter influencing the film thickness. We also conclude that the formation of α-WC phase is the combining result of W filaments vaporization in vacuum and the carbon incorporation at low substrate temperature. The small crystallite size of the carbide grains (5–6nm) could also explain the rapid diffusion of C through the tungsten-containing layer. Preliminary results show that the amount of a-C incorporated in the film is not only dependent on the CH4/H2 ratio but also on the substrate temperature.

Friction measurement in precision glass molding: An experimental study

Understanding the frictional behavior between glass and metals at elevated temperatures is necessary for accurate modeling and simulation of the state of the art applications such as the PGM process, pressing of micro lens arrays, hot embossing, and extrusion or drawing of glass fiber. In this research, the frictional behavior of N-BK7, an oxide glass, at elevated temperatures in contact with polished and coated tungsten carbide (WC) material and under conditions similar to the PGM process has been studied. The experimental results show that the friction coefficient between a polished and coated WC mold and N-BK7, which is a typical material for glass molding, and in conditions similar to those used in the PGM process ramps up to 0.7 and then levels off around 0.6 with a smooth transition, meaning that there is not a specific point to differentiate between static and dynamic friction. The friction coefficient of 0.6 is reported in literature for best fitting in micro lens molding simulation. Moreover, increasing the temperature in the transition regime in the mold/glass interface causes the friction force to increase which is in good agreement with the data published for the friction between soft polymeric material and metal in the transition regime.

Wear behavior of some cutting tool materials in hard turning of HSS

This study presents an assessment of the performance of four cutting tool in the machining of medium hardened HSS: polycrystalline c-BN (c-BN+TiN), TiN coated polycrystalline c-BN (c-BN+TiN), ceramic mixed alumina (Al 2O 3+TiC), and coated tungsten carbide (TiN coated over a multilayer coating (TiC/TiCN/Al 2O 3)). The Al 2O 3+TiC and the coated carbide tools can outperform both types of c-BN at high cutting speeds. Raman and SEM mapping revealed an alumina tribo-layer that protects the surface of the Al 2O 3+TiC cutting tool. The high chemical and thermal stability of Al 2O 3 tribo-films protects the tool substrate because it prevents the heat generated at the tool/chip interface from entering the tool core.

Sharpening of CVD diamond coated tools by 0.5−10 keV Ar + ion beam

CVD diamond coated tungsten carbide tools have been used for cutting and drilling of soft materials such as aluminum and copper alloys. However, it is very difficult to obtain a tool having a sharp tip of the order of sub-μm by mechanical abrasive polishing methods. Therefore, we applied ion beam processing for sharpening the cutting edge of diamond coated tungsten carbide tools. Result shows that it is possible to obtain a 20–80 nm order tip width of a CVD diamond coated knife processed by a 0.5–10 keV Ar + ion beam, and the sharpening speed of a tip of the knife depends on the ion beam energy. Namely, a tip width of a knife processes by a 1.0 keV Ar + ion beam at an ion dose of 2.7 × 10 20 ions/cm 2 becomes 20 nm, and a tip width of a knife processed by a 10 keV Ar + ion beam at an ion dose of 5.4 × 10 19 ions/cm 2 becomes 40 nm. However, a facet with an apex angle in the range of 60–100° was formed on the cutting edge of a knife with an initial apex angle of 55°, and we found that the facet angle can be controlled by choosing ion beam energy of 0.5–10 keV. Moreover, results show that the processed knife machined by a 0.5 keV Ar + ion beam has very smooth rake and flank faces, and also has a small line edge roughness of the cutting edge compared to those of the sharpened knife by a 1.0–10 keV Ar + ion beam.

Cryogenic Turning of AISI 304 Stainless Steel with Modified Tungsten Carbide Tool Inserts

The machining of stainless steel inherently generates high cutting temperature, which not only reduces tool life but also impairs the workpiece surface quality. Conventional cooling methods are ineffective in controlling the high cutting temperature and rapid tool wear. In the present research work, the effect of liquid nitrogen as a coolant applied through holes made on the rake and flank surfaces of the PVD TiAlN coated tungsten carbide turning tool inserts of ISO CNMG 120412 MP–KC5010 on the turning of AISI 304 stainless steel is studied. The influence of cryogenic cooling on the cutting temperature, cutting force, surface roughness, and tool wear, has been compared with those of wet machining. It has been observed that in the cryogenic cooling method, the cutting temperature was reduced by 44–51%, the cutting force was decreased to a maximum of 16%, and the surface roughness was reduced by 22–34% over that of wet machining. Cryogenic cooling using liquid nitrogen reduced tool wear through the control of temperature-dependant wear mechanisms.

Effects of Anode Arc Root Fluctuation on Coating Quality During Plasma Spraying

To obtain a coating of high quality, a new type of plasma torch was designed and constructed to increase the stability of the plasma arc and reduce the air entrainment into the plasma jet. The torch, called bi-anode torch, generates an elongated arc with comparatively high arc voltage and low arc fluctuation. Spraying experiments were carried out to compare the quality of coatings deposited by a conventional torch and a bi-anode torch. Alumina coatings and tungsten carbide coatings were prepared to appraise the heating of the sprayed particles in the plasma jets and the entrainment of the surrounding air into the plasma jets, respectively. The results show that anode arc root fluctuation has only a small effect on the melting rate of alumina particles. On the other hand, reduced air entrainment into the plasma jet of the bi-anode torch will drastically reduce the decarbonization of tungsten carbide coatings.

Experiments and finite element simulations on micro-milling of Ti–6Al–4V alloy with uncoated and cBN coated micro-tools

This paper presents experimental investigations and finite element simulations on micro-milling of Ti–6Al–4V alloy with fine grain uncoated and cBN coated micro-end mills. Micro-milling of Ti–6Al–4V using uncoated and cBN coated tungsten carbide micro-end mills are conducted; surface roughness, burr formation and tool wear are measured. Effects of machining parameters on surface roughness, burr formation, and tool wear for uncoated and cBN coated micro-tools are investigated. Finite element modelling is utilized to predict forces, temperatures, and wear rate for uncoated and cBN coated micro-tools. Predicted temperature and tool wear contours for uncoated and cBN coated micro-tool edges reveal advantages of cBN coatings. Optimization studies on the experimental results are also conducted to identify the optimum process parameters which minimize both surface roughness and burr formation concurrently.

Taguchi-fuzzy multi output optimization (MOO) in high speed CNC turning of AISI P-20 tool steel

This paper presents the application of Taguchi method with logical fuzzy reasoning for multiple output optimization of high speed CNC turning of AISI P-20 tool steel using TiN coated tungsten carbide coatings. The machining parameters (cutting speed, feed rate, depth of cut, nose radius and cutting environment) are optimized with considerations of the multiple performance measures (surface roughness, tool life, cutting force and power consumption). Taguchi’s concepts of orthogonal arrays, signal to noise (S/N) ratio, ANOVA have been fuzzified to optimize the high speed CNC turning process parameters through a single comprehensive output measure (COM). The result analysis shows that cutting speed of 160m/min, nose radius of 0.8mm, feed of 0.1mm/rev, depth of cut of 0.2mm and the cryogenic environment are the most favorable cutting parameters for high speed CNC turning of AISI P-20 tool steel.

A Multifeature Approach to Tool Wear Estimation Using 3D Workpiece Surface Texture Parameters

This work presents a new way to determine the condition of a cutting tool based on 3D texture parameters of workpiece surface. Recently, a laser holographic interferometer has been developed to rapidly measure a large workpiece surface and generate a 3D surface height map with micron level accuracy. This technique enables online surface measurement for machined workpieces. By measuring and analyzing workpiece surface texture, the interaction between the tool’s cutting edges and the workpiece surface can be extracted as a spatial signature. It can then be used as a warning sign for tool change because the workpiece produced by a heavily worn tool exhibits more irregularities in its surface texture than that produced by a normal tool. Multiple texture parameters such as image intensity histogram distribution parameter, 3D peak-to-valley height, and 3D surface waviness parameter are employed to indicate the onset of severe tool wear. In this work, aluminum (Al308) and compacted graphite iron parts were machined by a polycrystalline diamond insert and a multiphase coated tungsten carbide insert, respectively. After that, multiple 3D surface texture features of workpieces samples under different phases of tool wear were analyzed in order to assess tool wear conditions. The experimental results verify that these surface texture features can be used as good indicators for online tool wear monitoring.

Investigation on wear behaviour of cryogenically treated TiAlN coated tungsten carbide inserts in turning

Cryogenic treatment has been ascribed as a way of improving the cutting life of tungsten carbide turning inserts. Most of the research conducted till date has not reported any effort to excavate the effect of cryogenic treatment on the performance of coated tungsten carbide inserts in terms of adhesion strength of coatings deposited on tungsten carbide substrate. In order to understand the effect of cryogenic treatment on the adhesion strength of coatings, a comparative investigation of the wear behaviour and machining performance of cryogenically treated coated tungsten carbide inserts in orthogonal turning has been carried out in this study. The commercially available TiAlN coated square shaped tungsten carbide inserts (P25) were procured and subjected to cryogenic treatment at two levels −110 °C (shallow treatment) and −196 °C (deep treatment) of temperature independently. The criterion selected for determining the turning performance was based on the maximum flank wear (0.6 mm) as recommended in ISO 3685-1993. The results showed that shallow cryogenically treated coated tungsten carbide inserts performed significantly better as compared with deep cryogenically treated and untreated inserts. Major outcome of the present study includes a substantial decrease in tool life of deep cryogenically treated inserts as compared to untreated inserts indicating the destructive effect of deep cryogenic temperature (−196 °C) on TiAlN coated inserts which is further supported by VDI-3198 indentation test.

Effect of binders and surface finish on wear resistance of HVOF coatings

The high velocity oxygen fuel (HVOF) thermal spray process produces highly wear and/or corrosion resistant coatings. Tungsten carbide with a metallic binder is often used for this purpose. In this work, tungsten carbide coatings containing cobalt or nickel binder were produced by HVOF and characterised by optical and electron microscopy, hardness and a dry sand/rubber wheel abrasion test. The HVOF process produced dense coatings with low porosity levels and high hardness. The wear resistance of the specimens, which were surface treated, increased as the roughness percentage decreased. Tungsten carbide nickel based coating yielded the best wear resistance in the as sprayed condition. However, the wear rate and wear of the two coatings converged to the same values as the number of revolutions increased. Wear behaviour in the ground condition was similar, although the tungsten carbide cobalt based coating yielded better performance with increasing distance travelled during the wear test.

Wear Resistance and Microstructural Study of Diamond Coated WC Tools

Diamond composite materials are classified as superhard and exhibit exceptional abrasive resistance. Cemented tungsten carbide tools with a thick coating of diamond composite material (PCD) are finding increased usage in materials cutting operations in manufacturing, mining, minerals, gas and petroleum exploration and civil construction industries. Two major advantages derived from these coated tools are: (a) increased wear resistance and hence increased life-span of these tools and (b) their proven ability to handle “difficult-to-machine” materials as well as high-strength, extremely abrasive materials such as quartz-rich rocks, granites and basalts. In this research, the variability of the wear resistance of PCD coated tungsten carbide is correlated with microstructural variations. A detailed study of the microstructure and distribution of phases was performed using SEM, cathodoluminescence (CL) imaging, direct x-ray imaging, Raman spectroscopy as well as residual stress measurements using neutron diffraction.

Grinding of Arc-Sprayed Tungsten Carbide Coatings on Machining Centers - Process Configuration and Simulation

This paper describes the special demands placed on the grinding of arc-sprayed WC-Fe coatings on a conventional machining center. Basic process configuration, experimental results, measurement methods and an approach for a hybrid simulation system are presented.

Laser removal of TiN coatings from WC micro-tools and in-process monitoring

Current environmental challenges require sustainable and extended use and re-use of materials. For example, the service life of engineering tooling can be extended by using thin film coatings such as titanium nitride (TiN). However, when errors arise in the coating process or when the tooling needs to be re-used it is necessary to remove the coating. Decoating is also useful when a large batch of cutting tools needs to be re-directed for a different application, which requires a new generation of coating. Existing technology uses chemical methods which are not environmentally friendly or ideal for selective removal. In this work, excimer laser striping of TiN from coated tungsten carbide (WC) micro-tools has been demonstrated as a viable alternative to chemical methods. Also, in order to raise the integrity of the decoating process and to make the process more accurate and reliable, two online monitoring systems were developed exploiting probe beam reflection (PBR) and laser plume emission spectroscopy (PES). The online monitoring system facilitated a simultaneous prediction of surface elements as coating layers are progressively removed and ensures better control over the laser irradiation process so as to avoid under or over stripping of the coating.

Effect of machining parameters on surface roughness and material removal rate in finish turning of ±30° glass fibre reinforced polymer pipes

This paper studies the effect of varying machining parameters in turning on surface roughness and material removal rate (m.r.r.) for ±30° filament wound glass fibre reinforced polymers (GFRP) in turning operations using coated tungsten carbide inserts under dry cutting conditions. The paper describes the development of an empirical model for turning GFRP utilising factorial experiments. Second order predictive model covering speed, feed, depth of cut and tool nose radius has been developed at 95% confidence interval for surface roughness and material removal rate. Contour plots of the surface roughness and m.r.r. for different machining conditions have been generated from the empirical equations. Overlaid contour graph help in obtaining iso-value of roughness for different values of m.r.r.

Investigations on the effects of multi-layered coated inserts in machining Ti–6Al–4V alloy with experiments and finite element simulations

This paper presents investigations on turning Ti–6Al–4V alloy with multi-layer coated inserts. Turning of Ti–6Al–4V using uncoated, TiAlN coated, and TiAlN + cBN coated single and multi-layer coated tungsten carbide inserts is conducted, forces and tool wear are measured. 3D finite element modelling is utilized to predict chip formation, forces, temperatures and tool wear on these inserts. Modified material models with strain softening effect are developed to simulate chip formation with finite element analysis and investigate temperature fields for coated inserts. Predicted forces and tool wear contours are compared with experiments. The temperature distributions and tool wear contours demonstrate some advantages of coated insert designs.

Hard corrosion-resistant coatings for constructional applications

This is an overview of modern methods used to harden metal products. Capabilities and drawbacks of each method are analyzed with respect to requirements imposed on coatings intended for use in precision engineering. A fundamentally new approach to the creation of nanostructured hardening layers at low temperatures has been proposed. Three classes of tungsten carbide coatings that mutually differ by the combination of their microhardness, viscosity, and thickness have been described. Some physicochemical features of the synthesis of tungsten carbide compounds, their structure, and their mechanical properties have been established. According to tribological tests, the abrasive resistance of tungsten semicarbide is almost twice as high as the abrasive resistance of the VK-6 hard alloy. The absolute abrasive wear resistance of the carbide coating in the presence of a lubricant is ten times higher than that of the hard alloy. Particular applications of the tungsten carbide coatings and their advantages over commercially available materials and coatings have been described.

Parametric study on near-dry wire electrodischarge machining of polycrystalline diamond-coated tungsten carbide material

Polycrystalline diamond (PCD)-coated tungsten carbide (WC) is a high-performance cutting tool material widely used in industry for cutting or ultra-precision cutting of advanced engineering materials, but it is difficult to machine using conventional machining techniques owing to its high hardness. However, wire electrical discharge machining (wire EDM) offers advantages in machining PCD-coated WC in terms of process reliability and flexibility to machine different shapes. To relieve pollution issues associated with traditional wet wire EDM, the present study investigated the feasibility of near-dry wire EDM of PCD-coated WC cutting tool material using deionized water and air mist. A parametric study on spark cycle and spark duration was carried out, and the effect of these two important wire EDM process parameters on machining performance in terms of material removal rate (MRR) and surface roughness ( Ra) was analysed. Compared with conventional wet wire EDM, near-dry wire EDM consistently produces better Ra values on the PCD-coated WC workpiece, but near-dry wire EDM produces lower MRR than wet wire EDM under some conditions.

Synthesis of nanostructured aluminium matrix composite (AMC) through machining

In recent years, the nanostructured materials played a vital role in materials science engineering. Because of a reduction in the characteristic length such as the grain size or the cluster of molecular size, the normal properties of materials are drastically changed. By large strain plastic deformation of materials the grain sizes are refined in the range of submicrometer level. In this research Aluminium Metal Matrix composites (AMC) casting consisting of 85%Vol. Aluminium alloy (LM25) and 15%Vol. Silicon carbide (SiC) particle has been prepared through stir casting. A preliminary study has been carried out in oblique cutting conditions so as to obtain a high strain rate. The casted AMC was machined using coated tungsten carbide cutting tools and the collected chips were characterized using SEM and XRD. The result shows that machined chip microstructures are refined in the submicrometer level due to large strain deformation imposed by the cutting tool. Crystalline sizes and microhardness values have also been studied.