WC Grain Size Research Articles

Spark plasma sintering on nanometer scale WC–Co powder

Nanometer scale WC–11Co powder was sintered by spark plasma sintering (SPS) process in order to improve the properties of the cemented carbides. Properties such as density and hardness were measured. The microstructures of sintered WC–11Co cemented carbides were observed. The grain size of WC in alloys was also obtained. The results showed that spark plasma sintering could lower the sintering temperature, increased the density and circumscribed the growth of grain size of WC. Besides, the hardness of the sintered cemented alloys that was dependent on the grain size and densification could also be improved by SPS. SPS was an effective method to get WC–11Co cemented carbides with fine grain size and good properties.

Abrasive wear of WC–FeAl composites

The abrasive wear behavior of tungsten-carbide iron-aluminide composite materials was investigated using a pin-on-drum wear-testing machine. Samples were prepared by uniaxially hot pressing blended powders. The wear rates of specimens containing 40 vol.% matrix of atomic composition, Fe 60Al 40, were measured and results compared with those of conventional WC–10 vol.% Co hardmetal. They were found to be comparable to those of WC–10% Co hardmetal, when abraded by 120 μm SiC papers under identical conditions. The wear resistance of WC–Fe 60Al 40 composites increased with reduction in WC-grain size and associated with increase in composite hardness. Scanning electron microscopy revealed that the wear surfaces of WC–40% Fe 60Al 40 composites and WC–Co hardmetal were similar in appearance. The higher hardness and work hardening ability of Fe 60Al 40 binder, as compared to Co metal, are believed to be responsible for the excellent abrasive wear resistance of WC composites containing iron aluminide binder.

Microstructure and properties of ultrafine WC–0.6VC–10Co hardmetals densified by pressure-assisted critical liquid phase sintering

Ultrafine grained WC–0.6VC–10Co hardmetals are produced by monoaxial vacuum hot pressing (MVHP) between 1280 and 1320°C around the eutectic temperature of the alloy. The microstructure and properties of the resulting hardmetals show that fully densified alloys can be obtained when MVHP is carried out at temperatures ≥1300°C starting from commercially available ultrafine WC and cobalt powders. In the fully densified hardmetals, the grain size of WC is not increased. The average grain interception is between 169 and 179nm and hardness values are over HV30 2000. The Palmqvist toughness (Kc) of the hardmetals increases with sintering temperature; the highest value obtained is 517N/mm at 1320°C. The distribution of the Co binder is almost completely homogeneous at micro level but still inhomogeneous at submicron level. In order to further improve the toughness of the ultrafine WC–VC–10Co hardmetals, the optimization of the composition, the use of pressure-assisted liquid phase sintering, and the optimization of the milling regime are discussed.

Preparation of W-C-B Composites by Reactive Resistance-Heated Hot Pressing

Dense WC-base W-C-B composites were prepared by the reaction sintering of B4C-WWC (mole ratio 1 : x : 80 or 130, x = 1-9) powder mixtures using resistance-heated hot pressing. Sintered bodies were composed of different products depending on x both in B4C-xW-80WC and - 130WC: WC + WB when x ≤ 3, WC + W2B + WB when x = 5, and WC + W2B + W2C when x ≥7. They had the highest Young's modulus values 706 and 705 GPa for -80WC and -130WC at x = 3, respectively. The hardness was increased with x, depending on a decrease in the grain size of WC. Its highest value was 24.5 GPa both for -80WC and -130WC at x = 9. For the fracture toughness, the highest value 6.1 MPa m1/2 was obtained for -130WC at x = 5.

ＷＣ‐（０‐１６）ｍａｓｓ％Ｃｒ３Ｃ２‐１５ｍａｓｓ％Ｎｉ 超硬合金の組織と機械的特性及び腐食特性

Microstructures, some mechanical properties and electrochemical corrosive behavior of WC-(0-16)mass% Cr3C2-15 mass% Ni alloys were studied as a function of carbon and Cr3C2 contents of these alloys.It was found that solid solubility of Cr into γphase (Ni phase) of WC-Cr3C2-15 mass%Ni alloy was about 2% and 4mass% Cr3C2 in high and low carbon alloys, respectively. In the range of the excess Cr3C2 content more than the solubility limit of Cr, some phases of WC+γ+M2C+M6C (θ) (M =(Cr, W, Ni), M6C=θphase), WC+γ+M2C, WC+γ+M2C+M3C2, WC+γ+M3C2 to WC+γ+M3C2+FC appeared with increasing carbon content in the alloys.Hardness of the alloys increased with increasing the amount of Cr3C2. On the other hand, the transverse rupture strength reached the peak value at the solubility limit of Cr because of the finer grain size of WC by the effect of grain growth inhibition. More than the solubility limit of Cr, the transverse-rupture strength decreased with increasing the amount of Cr3C2, which was considered to be caused by crystallized MxCy acting as fracture source.On the anodic polarization curve in 3%NaCl solution, corrosive current density of these alloys decreased with increasing the amount of Cr3C2 within the solubility limit of Cr in yphase, but it was saturated more than the solubility limit of Cr.

Spark plasma sintering behavior of nanocrystalline WC–10Co cemented carbide powders

Microstructure and mechanical properties of WC–10Co cemented carbides fabricated by spark plasma sintering (SPS) process were investigated. Nanocrystalline precursor powders were prepared by spray drying process from solution containing ammonia meta-tungstate and cobalt nitrate, and followed by reduction and carbonization into nanocrystalline WC/Co composite powders by a mechano-chemical process. The WC particles of about 100 nm in diameter were mixed homogeneously with Co binder. The nanocrystalline WC–10Co powders were consolidated by SPS process at temperature ranged 900–1100 °C and under a pressure of 50 or 100 MPa, respectively. Optimum consolidation conditions, such as temperature and pressure, were determined by analysing the dimensional changes of powder compact during SPS process. Hardness and fracture toughness of consolidated WC–10Co cemented carbide were measured by using a Vicker's indentation test. The solute content within the Co binder phase of WC–10Co cemented carbide was evaluated by measuring the saturated magnetic moment. It is found that the hardness of cemented carbide was dependent on the density and grain size of WC. The fracture toughness of cemented carbides increased with increasing the saturated magnetic moment, while decreased rapidly when the liquid Co phase was formed during sintering.

The structure and properties of a hard alloy coating deposited by high-velocity pulsed plasma jet onto a copper substrate

Using a plasmatron operating in specially calculated regimes, tungsten carbide (WC) based coatings were deposited onto a copper crystallizer plate. It was found that a local hardness of the WC-Co coating may reach up to 1.3×104 N/mm2 and the coating adhesion to substrate may be as high as 270 MPa. The elemental and phase compositions of coatings were studied by Rutherford backscattering spectroscopy, X-ray diffraction, and transmission electron microscopy with electron diffraction. The surface morphology and depth-composition profiles of the coatings were studied by optical and scanning electron microscopy. The coating is composed of WC crystal grains with hexagonal close packed (hcp) lattice, α-and β-Co grains, and cubic WC grains. The average size of the hcp WC grains is 0.15 μm and that of the cobalt particles is about 25 nm. In addition, the grain boundaries contain W3Co3C particles with an average size of 15 nm.

Semi-empirical relationship between the hardness, grain size and mean free path of WC–Co

The Vickers hardness of several well-characterized grades of WC–Co (23 in total) was measured. The mean grain size of these samples ranged from 0.6 to 5.0 μm and the cobalt content from 6 to 50 wt%. An empirical formula between hardness of WC–Co, grain size of WC and mean free path in Co was obtained. It was found that the empirical formula fitted our measured hardness well. However, when used against results of other researchers, it did not reproduce them satisfactorily at values higher than 1500 HV. A theoretical model, based on the assumption that plastic deformation of WC–Co begins at the WC–WC necks and that the mean length of the cross-section of the WC–Co necks is proportional to the square root of the mean WC grain size, was subsequently derived. The results obtained from this model were in good agreement with those of the empirical formula and like the empirical formula, did not reproduce high hardness values of other researchers. Thus, the model was modified by introducing semi-empirical terms which led to a satisfactory fitting of the data.

Processing of functionally graded WC/Co/diamond nanocomposites

A new method of processing functionally graded WC/Co/diamond nanocomposites has been developed. The starting particle size of WC grains is ∼100nm. The critical step in processing is the generation of pore size gradient using electrochemical etching of cobalt. This leads to the generation of larger pores on the surface. After etching; Pores are filled with carbon by chemical vapor infiltration; Using catalytic decomposition of methane. This carbon rich sample is then subjected to a high pressure/high temperature treatment to convert carbon into diamond. The resulting functionally graded nanocomposite contains higher amount of diamond on surface leading to higher wear resistance; And higher amount of WC/Co in the core leading to higher toughness.

The effect of ruthenium additions on the hardness, toughness and grain size of WC–Co

This paper reports the results of a systematic investigation into some of the effects of ruthenium additions to WC–Co. The results show that the hardness of WC–Co increases and the toughness decreases with increasing the ruthenium content and that ruthenium is a weak inhibitor of WC grain growth. Ruthenium has been found to improve the abrasion resistance of WC–Co on account of the hardening of the binder phase.

Deposition and characterization of nanostructured WC–Co coating

Nanostructured WC–Co coatings were prepared with the vacuum plasma spraying process. The microstructure of the as-prepared coatings was determined with SEM, TEM and XRD. The results show that the main structure of the coatings is composed of WC grains with a mean particle size of 35 nm, which have a similar grain size to the primary powders. However, in some regions, the grain size of WC is reduced to about 10 nm due to the melting of the WC–Co powders. In some regions, WC grains are completely melted forming an amorphous phase. In some regions, WC grains have grown to 100 nm; in other regions, the second recrystallization occurred, strip-shaped and square-shaped structures are formed, which are as large as 500 nm. The main phase of the as-prepared WC–Co coating is WC with minor phases of α-W 2C, β-WC1-x, and W 3Co 3C. The hardness of the coating is about 18 Gpa with a wide distribution.

Hardmetals star at South Africa's PM symposium

Functionally graded cemented carbides (FGCCs) usually have a coarse-grained surface layer. In order to refine the grain size of WC and to improve the mechanical properties, VC and NbC as grain growth inhibitors, were added to WC–6Co FGCCs. The grain growth kinetics of WC was investigated, and both the room temperature and high temperature mechanical properties were tested. The results show that the additions of NbC and VC reduce the thickness of the gradient layer in FGCCs. The addition of VC reduces the thickness of the gradient layer by half, while that of NbC is less effective. The additions of NbC and VC refine the grain size by suppressing the adsorption/desorption processes of WC grains in Co phase during the pre-sintering and the carburizing processes, and VC is more effective than NbC. The addition of NbC increases the transverse rupture strength of FGCCs, because of the fine microstructure, and the solution strengthening in Co phase. Both the additions of NbC and VC increase the high temperature hardness of FGCCs due to improved oxidation resistance, more homogeneous and finer microstructures.

Thermo-chemical treatment of PM materials with carbon and nitrogen: V.Iancau et al. (Technical University of Cluj-Napoca, Cluj-Napoca, Romania.)

Coarse grained WC–9Co cemented carbides with 0–1.0% TaC (mass fraction) were fabricated by HIP-sintering and gas quenching. The effects of TaC on the microstructures and mechanical properties were investigated using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS), X-ray diffractometry (XRD) and mechanical properties tests. The results show that the maximum values of hardness and strength are HV 1124 and 2466 MPa respectively when 0.4% TaC is added. When the content of TaC is more than 0.6%, the grain size of WC is no longer affected by the amount of TaC, and (W,Ta)C occurs as well. Moreover, the strength and fracture toughness increase and the (Ta+W) content decreases with the increase of TaC content. The dependence of (Ta+W) content on the mechanical properties indicates that (Ta+W) content in Co should be decreased as low as possible to improve the mechanical properties of coarse grained WC–TaC–9Co cemented carbides with the microstructure of WC+γ two phase regions.

A comparison between magnetic properties and grain size for WC/Co hard materials containing additives of Cr and V

The magnetic properties of cemented carbides are often used as an indirect measure of the microstructure. For this purpose, models relating coercive force with WC-grain size have been developed. In this study, it is investigated how well magnetic models describe the microstructure of cemented carbides (WC/Co) for samples containing different kinds of commonly used grain growth inhibitors, varying carbon content, and cooling conditions. We found that small amount of V (0.2 wt%) and Cr (0.4 wt%) influence the magnetic properties differently. Even so, commonly applied models relating magnetic properties with WC-grain size may be applied, but the importance to account for variation in saturation magnetisation in the analysis is stressed.

Novel Tungsten Carbide Nanocrystalline Composites by Pulsed Laser Deposition

ABSTRACTWe have developed a novel processing technique to fabricate “artifact free” tungsten carbide (WC) nanocomposites. In this method, pulsed laser deposition of WC in conjunction with a few monolayers of nickel aluminide (NiAl) is used to control the grain size of nanocrystalline composites. The grain size of WC was controlled by the thickness of tungsten carbide and the substrate temperature. The role of NiAl is to ensure the nucleation of tungsten carbide islands, and it is also insoluble in WC. Using this approach, we have fabricated nanocomposites of grain sizes ranging from 6 nm to 35 nm. The hardness of the composite increases with the decrease in grain size, following approximately Hall-Petch relationship. The role of NiAl in grain boundary deformation is of particular interest in strengthening the nanocrystalline composites. The potential of this technique to go to even lower grain sizes is discussed.

606 超硬合金の摩耗に及ぼすCo量とWC粒径の影響(機械要素・潤滑)

WC cemented carbide are used as many dies to improve abration resistance. Mechanical properties of the cemented carbide were influenced by Co content and WC grain size. In this study, effects of Co content and WC grain size of WC cemented carbide on wear were examied. We prepared 13 cemented carbides with different Co content and WC grain size. Wear test was carried out against S45C under dry condition at 98N and 232mm/s. From the results. We found that wear increased with both Co content and WC grain size. However, specific wear rate was range 10^<-7>mm^3/Nm.

Kinetics of WC-Co oxidation accompanied by swelling

The oxidation behaviour of WC-Co sintered carbides with 3–5 μm grain size of WC and 6–15 vol.% of cobalt have been studied in air in the temperature range 650–800 °C. The intensive swelling of up to 350% of initial specimen size and linear kinetics of the growth of the porous WO3 layer were observed during the oxidation. The final shape of the specimen after oxidation was dependent on its initial shape. The apparent activation energy of the dimension and weight gain kinetics were within the range 32–67 kJ mol−1 and the process was proposed to be controlled by the reaction at the interface. The oxidation rates and swelling coefficients increased when the mean size of WC grains was decreased and cobalt content increased. The possible model of WC-Co alloys' oxidation and swelling was proposed for the observed shape development and kinetics of oxidation.

微粒ＷＣ‐Ｎｉ合金中に生じるポア

It has been known by the present authors that mechanical properties of WC-Ni alloy were improved towards the values of WC-Co alloy with decreasing grain size of WC, and also the micro-grained WC-Ni alloy could be obtained by the addition of VC, etc., with the result that small pores were apt to appear in the micro-grained WC-Ni alloy in the sintered state, differing from the case of micro-grained WC-Co alloy. Then, the study on this subject, that is, on the reason why small pores often appear in the micro-grained WC-Ni alloy was carried out. The WC-10mass%Ni alloy containing VC up to 5 mass% in binder was used as specimens.It was suggested that the fact that the Ni rich agglomerates peculiar to WC-Ni alloy (consisting of Ni and fine WC particles) formed during ball-milling of mixture could not perfectly be removed from the ball-milled mixture, and the fact that the temperature at which liquid phase appeared was higher in WC-Ni alloy by about 701C, comparing with in WC-Co alloy, were the most responsible for the above subject.

各種炭化物を添加した微粒超硬合金の高温硬度

Effects of 1 mass% of each of ZrC, VC, MO2C, Cr3C2, and TaC addition on micro structure, high and room temperature Vickers hardness, and transverse rupture strength of submicron WC-8mass%Co hardmetal were investigated.Results obtained were summarized as follows: Grain growth of mean grain size of WC was inhibited, and the mechanical properties of submicron hardmetals were improved by the addition of each carbide.This raising of hardness was seemed to be governed by refinement of WC grains by the carbide addition. Vickers hardness of submicron hardmetals with carbide additions, at elevated temperature, are higher than that of these hardmetals without carbide addition. There are two different ranges of temperature dependence on hardness of submicron hardmetals. In this paper, the point of refraction is defined as temperature. The softening temperature was higher in the order of no addition, VC, TaC, ZrC, MO2C, and Cr3C2 addition.This reason has been estimated to be solid solution strengthening of cobalt binder phase.

工業用純チタンの被切削性に及ぼすＫ種超硬工具の影響

Sintered WC tools are known to be effective and economical cutting tool for titanium alloy. Carbide tools with various grain size, content of WC and side rake angle were tested to evaluate the cutting performance-tool wear, cutting force and finished surface-in machining of commercial pure titanium. The wear resistance of the tools changes with the grain size of WC, in such a way that the tool with 1μm WC grain is the best. The wear of the tool with 94wt% WC is the smallest among the composition range of WC between 93 and 97wt% under the grain diameter of WC fixed to about 1μm. The tool wear progresses slowly and the level of cutting force is low for the tools with pressed chip breaker, regardless of WC content. An excellent cutting performance is found to be obtainable with the tool which has a side rake angle between -π/39 and π/36 rad.