Sintered Tungsten Carbide Research Articles

Joint Low-Temperature Carbothermic Synthesis of WC-Co Alloy in Vacuum

A new method for obtaining submicron hard alloys based on sintered tungsten carbide with cobalt by joint low-temperature carbothermic synthesis in vacuum has been developed. The compositions of the initial components for the synthesis of powders of the composition WC-6%Co and WC-10%Co are calculated. The main component for the synthesis of submicron tungsten carbide powders is tungsten oxide WO2.9, obtained by reducing α-tungsten oxide WO3 in a hydrogen medium at a temperature of 500-550 °C. The powders obtained by synthesis are characterized by high hardness values (up to 94 HRA). Cutting tests of replaceable polyhedral plates made from the obtained powders for processing a heat-resistant alloy have shown satisfactory results. The microstructure of the alloys was analyzed using scanning electron microscopy.

Aspects Regarding the Operating Behavior of FSW Welding Tools

Welding tools are a determining factor in obtaining welded joints with desired characteristics. The international community pays great attention to research aimed at establishing the optimal characteristics of friction stir welding (FSW) tools. With the development of the FSW welding process with its own contributions, ISIM Timisoara has developed complex research resulting in the conception and design of (innovative) FSW welding tool solutions. A very important factor especially when welding high hardness materials is the durability / lifespan of FSW welding tools. The paper presents general considerations regarding the qualities that FSW welding tools must meet in general, but also ISIM achievements in the field of design and operation of welding tools. Studies regarding operating behavior of welding tools made of sintered tungsten carbide P20S, in terms of service life (wear), both in the case of applying the classical FSW welding process and the method of friction stir welding in inert gas environment (FSW-IG), when joining steels with wide industrial use (304L stainless steel, respectively DD13 steel), are also presented. Concrete data is presented with values of the degree of wear of the tools in the unit of time, in their critical areas: tools made of X38CrMoV5 steel alloy used for welding aluminum alloys with different characteristics, respectively tools made of sintered tungsten carbide P20S used for welding S 235 JR + N steel and 304L stainless steels.

Volume/shear work ratio influence on wear and stress of soil chisel tine modelled by DEM

Agricultural equipment is working in very high-stress conditions. However, it has a significant influence on the wear losses of soil processing parts. Chisel is operating at 30 cm working depth at a maximum of 12 km·h−1 working speed. Due to unpredictable soil conditions, chisel tines suffer high wear losses. It leads to time consumption and cost expenses during the soil preparation period. Wear resistance, and agronomical requirements (working depth, loosening of soil) are the main criteria of agricultural equipment producers. The discrete element method is a solution that simulates soil as sphere shape particles with soil properties. Wear results reveal the change of parts shape, acting forces, and stresses during the simulation in the virtual soil bin. The used Rocky DEM software uses a parameter C (volume/shear work ratio) to describe wear intensity, which varies for different geometry. Chisel tine geometry should be divided into sections with varied parameter C according to stress acting on the surface. The test conditions can be used for future wear analysis of varied tool geometry and protection (sintered tungsten carbide plates, hard-faced surface, etc.) agricultural tools to compare its durability in different soil conditions.

A review of fabrication and properties of spark plasma sintered tungsten carbide based advanced composites

The high-performance tool materials have been inevitably used for most of the cutting tool applications where high reliability and difficult to cut materials are of major demand. The cemented carbides and its composites offer an excellent combination of the properties where it can be used for tool materials due to its high wear resistance, high hardness at elevated temperatures, and considerable fracture toughness. However to obtain optimum values of mechanical properties and uniformly distributed ultrafine grains, a number of new fabrication techniques, alteration in the content of cemented carbide composition, and variation in the parameters of fabrication process have been employed. This review paper will come in handy for researchers and scientists working on advanced cemented carbides and spark plasma sintering as it overviews the recent work done on tungsten carbide composites using the novel spark plasma sintering technique considering different process parameters in order to achieve ultrafine microstructures of sintered specimens, enhanced mechanical properties of composites in addition to energy as well as time saving considerations. The thorough review of various research papers revealed that the parameters of the sintering (sintering temperature, applied pressure, surrounding environment), additives in sintering (both content and composition), reinforcement of cemented carbide with other materials, nano-filler/whisker addition, partial or complete removal of metallic phase from the cemented carbide affect the properties of sintered specimens and their calculated as well as optimum setting can provide an excellent combination of properties desired in cutting tool operations.

Tool wear in dry gear hobbing of 20MnCr5 case-hardening steel, 42CrMo4 tempered steel and EN-GJS-700-2 cast iron

The demand for higher power densities in gear applications leads to the use of high-strength materials. This poses a challenge for manufacturing technologies with regard to the machinability of these materials. Even though gear hobbing is one of the most common technologies for gear machining, only limited investigations on the machinability of high-strength materials have been carried out. In this paper, the machinability of different workpiece materials by gear hobbing under dry cutting conditions is investigated. The tool life and wear behavior of powder metallurgical high-speed steel PM-HSS S390 and sintered tungsten carbide – cobalt WC-Co K30 tools with an AlCrN coating were analyzed. 20MnCr5 case-hardening steel, 42CrMo4 tempered steel and EN-GJS-700-2 cast iron were machined using the fly-cutting trial as an analogy process for gear hobbing. To identify a respective target tool life of LT,10 = 10 m, the cutting speed was varied while the feed rate was defined based on the respective tool concept and cutting substrate. The experiments showed a good machinability of the soft state material 20MnCr5 with PM-HSS S390 tools up to a cutting speed of vc = 350 m/min. A machining of the high-strength materials 42CrMo4 and EN-GJS-700-2 resulted in high tool wear or catastrophic tool failure. Even at low cutting speeds of vc = 50 m/min, the target tool life LT,10 could not be reached. When using WC-Co K30 tools, tool lives of LT > 6 m and cutting speeds up to vc = 400 m/min were feasible when machining 42CrMo4 tempered steel. For the machining of EN-GJS-700-2 cast iron, high abrasive tool wear was observed, which led to short tool lives of LT < 4 m at cutting speeds above vc ≥ 200 m/min. By reducing the cutting speed to vc = 100 m/min, a tool life of LT > 15 m could be achieved.

Investigation and Modelling of Surface Roughness in Hard Turning of Sintered Tungsten Carbide (WC 25wt% Co) Using CBN Tool

Investigation and Modelling of Surface Roughness in Hard Turning of Sintered Tungsten Carbide (WC 25wt% Co) Using CBN Tool

Applicability of Diamond-Coated Tools for Ball End Milling of Sintered Tungsten Carbide

Sintered tungsten carbide which has high hardness and high heat resistance, has been widely used in molds and dies. Research on the development of a cutting technology for sintered tungsten carbide (sintered WC-Co alloy) has been pursued mainly with the use of a turning process. We focused on building an efficient milling method for sintered tungsten carbide by using diamond-coated ball end tools, and have investigated their basic properties under specific cutting conditions. This study extends our previous work by enhancing cutting distance in the milling of sintered tungsten carbide, especially that with a “fine” WC grain. The surface roughness of cut workpieces is evaluated from the point of view of the quality of surface roughness. A series of cutting experiments under different cutting conditions were carried out, and the possibility of deriving a suitable cutting condition for the ball end milling of sintered tungsten carbide is discussed.

Tribological properties of oxidized wood-derived nanocarbons with same surface chemical composition as graphene oxide for additives in water-based lubricants

The tribological properties of oxidized wood-derived nanocarbons (oWNCs), which have the same surface chemical composition as graphene oxide (GO), were investigated as additives in water-based lubricants using a sintered tungsten carbide ball and a stainless steel flat plate with a reciprocating sliding configuration. WNCs were synthesized from four kinds of Japanese wood powder by metal-catalyzed carbonization, and were strongly oxidized by a modified Hummer's method. The four oWNCs have aggregated chain-like nanostructures and maintain graphitic layers. In addition, the four oWNCs were well-dispersed in water due to their high level of oxidation. The four oWNC aqueous dispersions improved lubrication. In particular, the aqueous dispersion of the oWNC derived from Japanese cedar (J. Cedar) wood powder showed a very low friction coefficient and formed a thick tribofilm on the plate surface. The most distinctive properties of the J. Cedar oWNC, compared to the other oWNCs, were the small primary and secondary particle sizes, which were much smaller than those of the other oWNCs. The small-sized J. Cedar oWNC may possibly enter the frictional interface, preventing direct contact between the ball and plate surfaces and forming a tribofilm.

Polishing of Tungsten Carbide by Combination of Anodizing and Silica Slurry Polishing

Sintered tungsten carbide (WC) is widely used in precision molding of optical glass lenses, and is considered as a critical mold material for optical industry, due to its high hot hardness and low thermal expansion ratio. However, WC is also a well-known difficult-to-polish material owing to its high hardness and strong chemical inertness. In an effort to realize the high-quality and highly efficient polishing of WC, a two-step polishing process combining anodizing and soft abrasive polishing was developed. Experimental studies of the anodizing step and the slurry polishing step were conducted. Anodizing has been found to be able to quickly soften WC and realized a drastic decrease of its surface hardness from 22.1 GPa to below 2.0 GPa, which allows us to polish the substrate surface using soft silica abrasives. In the polishing step using silica slurry, the oxide layer was removed and it has been revealed that the surface quality of polished WC was greatly affected by the duration of anodizing and the type of polishing pad. A scratch-free, pit-free and smooth WC surface can be obtained by combination of 10 min of anodizing and 30 min of silica slurry polishing using a suede type polishing pad. This research offers a new method for achieving high-quality finishing of WC with high efficiency.

Elevated Temperature Fretting Wear Behavior of Cobalt-Based Alloys

Structural parts in gas turbines undergo fretting wear, and as clearances open up, it turns into impact wear. Uncoated cobalt-based substrates that are used in such applications show poor resistance to fretting/impact damage and undergo extensive/unacceptable level of degradation. Commonly used substrate materials such as uncoated cobalt-based materials show poor resistance to fretting/impact wear. This study is focused on assessing the performance of high velocity oxyfuel (HVOF) tungsten carbide (WC) coatings and sintered tungsten carbide inserts as potential solutions for mitigating this issue. Sintered WC12Co with grain size range from 0.2 μm to 4.5 μm and HVOF coating with composition of WC–17%Co was tested. It was found that the HVOF coatings performed better than sintered material and the behavior was attributed to the hard WC particles surrounded by the higher volume fraction of cobalt binder. In the HVOF coating, the normal load was better accommodated by the decarburized WC but a fairly tough binder-surrounding matrix. An additional factor is that the sintered WC had significant volume fraction of undesirable W2C phase, which apparently underwent fracture during the test, thus showing an inferior behavior compared to the HVOF WC coating.

Self-lubricating, low-friction, wear-resistant Al-based quasicrystalline coatings

After gas atomization, a quasicrystalline powder based on aluminium was used to prepare a thick coating by high-velocity oxygen-fuel flame torch spraying. This layer was deposited on top of a bond-coat layer on a steel plate. A post-spraying annealing treatment turned the two layers to their stable state, a γ-brass crystal and an icosahedral quasicrystal, respectively. The projection parameters were selected in such a way that the coating behaved like a self-lubricating material, which offered very good wear resistance (duration of pin-on-disk tests superior to 5 km with negligible material loss) and low friction (µ ≤ 6% against sintered tungsten carbide), in contrast to the state of the art. This property was achieved thanks to, on the one hand, excellent bonding to the substrate via the bound coat, and on the other hand, presence at the boundaries between quasicrystalline flakes of a mixture of both threefold and fourfold coordinated carbon originating from spray processing. Application to hard materials used in mechanical devices is appealing, especially because soft, lubricating additives may not be needed, thus considerably increasing the lifetime of the devices and reducing waste of materials.

Direct Carburization of Tungsten Trioxide by Mechanical Alloying

Tungsten carbide is the choice of predilection for producing parts requiring good wear resistance. In this context it is produced in large quantities by the carburization of tungsten trioxide under a stream of hydrogen at elevated temperature followed by grinding to achieve the required fineness. This work aims to study the conditions in which tungsten carbide can be produced by mechanical alloying method. Using this method would facilitate obtaining carbide through a simple and easy to use technology without prohibitive costs, directly by an end user. For this purpose the thermodynamic study is conducted to establish the conditions under which the carburizing reaction can take place. The condition for the reaction to occur spontaneously is reaching a temperature of 621°C. Carrying out this reaction in a system without external energy input seems impossible. Mechanical alloying experiments were carried out in a Fritch Pulverisette 7 premium line planetary mill, equipped with two bowls of 80ml capacity lined with sintered tungsten carbide. Each bowl contained 200 g of tungsten carbide balls with dimensions of 10 mm and 12 mm. The balls/load ratio was 10:1. Grinding was performed in steps of 3 hours, with breaks for sampling, with rotation speeds of 600 and 800 rpm. Tests conducted showed complete conversion of raw materials into tungsten carbide after different durations of time.

Machining of Sintered Tungsten Carbide for Die and Mold

In order to pursue possibility to machine sintered Tungsten Carbide by milling, series of ball end milling experiments are carried out with use of ball end mills made of sintered PCD and sintered CBN to machine flat inclined surface of sintered Tungsten Carbide. The experimental results show that the sintered Tungsten Carbide can well be machined by end milling. The ball end milling is also applied to finish rounding of the edges of the gear teeth. The maximum surface roughness of the finished gear teeth obtained is 1.1μm.

Fundamental investigation of ultra-precision ductile machining of tungsten carbide by applying elliptical vibration cutting with single crystal diamond

This paper presents essential investigations on the feasibility of ductile mode machining of sintered tungsten carbide assisted by ultrasonic elliptical vibration cutting technology. It lays out the foundations toward efficient application of elliptical vibration cutting technology on tungsten carbide. Tungsten carbide is a crucial material for glass molding in the optics manufacturing industry. Its grain size and binder material have significant influence not only on the mechanical and chemical properties but also on the machining performance of tungsten carbide. In order to investigate the influence of material composition on tungsten carbide machining, a series of grooving and planing experiments were conducted utilizing single crystal diamond tools. The experimental results indicated that as compared to ordinary cutting where finished surface deteriorates seriously, ductile mode machining can be attained successfully by applying the elliptical vibration cutting technique. It was also clarified that the binder material, the grain size, cutting/vibration conditions as well as crystal orientation of the diamond tool have significant influence on the tool life and the machined surface quality. Based on these fundamental results, feasibility of micro/nano-scale fabrication on tungsten carbide is investigated. By applying amplitude control sculpturing method, where depth of cut is arbitrary changed by controlling the vibration amplitude while machining, ultra-precision textured grooves and a dimple pattern were successfully sculptured on tungsten carbide in ductile mode.

Laser gas assisted treatment of tungsten carbide tile surface

In order to enhance structural integrity of sintered tungsten carbide tiles, a laser gas assisted melting of tungsten carbide surface is carried out. Metallurgical changes, in the surface region, are examined by using optical and electron scanning microscopes, energy dispersive spectroscopy, and X-ray diffraction. Microhardness and fracture toughness of the laser treated layer are obtained from the indentation data. Residual stress formed at the treated surface is determined through the X-ray diffraction technique. It is found that the treated surface is free from large scale asperities. Microhardness increases at the surface significantly because of formation of lamellar and acucilar morphology, which compose of WC–W2C composite in the dense layer. Fracture toughness of the treated surface reduces considerably due to microhardness enhancement at the surface. Residual stress in the surface vicinity is compressive, which is in the order of −2.1±0.06GPa.

Research on Cutting Force Characteristics of Laser and Ultrasonic Assisted Cutting of Sintered Tungsten Carbide with FEA Method

Based on the application of elliptical vibration cutting method to precision machining of hard and brittle materials and material softening technology through laser heating, a novel composite cutting technique, laser heating and ultrasonic elliptical vibration assisted cutting, is applied to process sintered tungsten carbide. The simulation of the orthogonal cutting process and the effect of frequency and amplitude of vibration and laser heating temperature on cutting force are discussed by using FEA method. Research results have revealed that the main peak of the transient force components increase with the increase of vibration frequency, decrease with the increase of vibration amplitude and laser heating temperature. Moreover, the friction reversal phenomenon is improved with the increase of vibration frequency and amplitude, resulting in the decrease of average cutting force. Compared to common cutting and traditional one-dimensional ultrasonic vibration cutting, the composite cutting technology put forward in this paper has unique cutting force characteristics for such super hard material because of combined action of friction reversal and intermittence cutting for ultrasonic elliptical vibration and material softening for laser heating. The research in the paper has provided a practical reference for the further experiments of laser and ultrasonic assisted cutting.

J111013 ナノダイヤモンド分散水の摩擦減少効果の摺動材料による影響(〔J111〕摩擦・磨耗制御のための材料及び表面改質)

Water lubrication, which uses water as lubricating fluid, has many advantages such as cost, environment, high thermal conductivity, and so on. However water has low lubricating property for steel materials. In this study, tribological property of nanodiamond, which is a few nanometer size diamond, as a water-based lubricant additive has been investigated between SUS304 ball -SUS304 plate and sintered tungsten carbide (WC) ball - SUS304 plate. It has found that adding nanodiamond in water can notably improve the water lubrication property such as the very low friction coefficient for the WC ball-SUS304 plate friction and low wear on the WC ball. However, friction forces and wears for the SUS304 ball-SUS304 plate was increased by adding nanodiamond.

Machinability of CBN Tool in Turning of Tungsten Carbide

Tungsten Carbide have extremely high hardness and wear-resistivity compared with conventional steel materials, and it is expected that the Tungsten carbide can be applied widely to dies and molds in the near future. In order to develop an efficient machining method of Tungsten Carbide for the dies and molds, series of cutting experiments were carried out to turn the sintered Tungsten Carbide materials with CBN tool. The selected sintered Tungsten Carbide workpieces are those containing Tungsten Carbide grains with mean grain size of 5μm, and 15wt%, 20wt% and 22wt% of Cobalt binder. The sintered CBN tool selected contains super-fine grains of CBN with mean grain size of 1μm. The cutting speed was varied from 10m/min to 60m/min, and the tool wear and the surface roughness were measured. It is concluded that the tool wear is less when cutting the sintered Tungsten Carbide containing larger amount of Cobalt binder. The surface roughness of about 2μm in Rz is obtained.

Influence of Material Composition on Ductile Machining of Tungsten Carbide in Elliptical Vibration Cutting

Tungsten carbide is a crucial material for glass molding in optical industry. The present study investigated a feasibility of ductile machining of sintered tungsten carbide for glass molding by applying ultrasonic elliptical vibration cutting technology with single crystal diamond tool. Grain size and binder material of sintered tungsten carbide have an influence on hardness and/or toughness of the material. Binder material also has a chemical affinity to diamond. In order to examine the influence of material composition on ductile machining of tungsten carbide, a series of grooving and planing experiments were conducted to several different tungsten carbide workpieces with the different binder phase and the different grain size. The experimental results indicated that micro grooving in a ductile mode can be attained successfully by applying ultrasonic elliptical vibration cutting, while finished surface deteriorates with brittle fractures in ordinary cutting. It was also clarified that grain size and binder material have significant influence on the deteriorations in the surface quality, the tool shape and the cutting forces.

Understanding the dry sliding wear behaviour of atmospheric plasma-sprayed rare earth oxide coatings

In this paper, the friction and wear behaviours of Yttria Stabilized Zirconia (YSZ) coatings; Lanthanum Zirconate (LZ) coatings and Inconel 738 base material (BM) sliding against a sintered tungsten carbide surface were studied and compared under unlubricated conditions. Sliding experiments were performed in a pin-on-disc configuration. Further, relationships among porosity, normal load and disc speeds with respect to wear loss were derived by using the response surface methodology, and the wear mechanisms were discussed adequately. It was found that the wear resistance of the ceramic coatings gets deteriorated with the increase in the percentage volume of porosity.