• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.211-212
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• 2002

Friction and wear of pressureless sintered Ti(C,N)-WC ceramics were studied using a ball-on-reciprocating flat apparatus in open air. The silicon nitride ball and the cemented carbide (WC-Co) ball were used against the Ti(C,N)-WC plate samples. The friction coefficients of the Ti(C,N)-WC samples against the silicon nitride ball and the cemented carbide ball were about 0.57 and 0.3, respectively. The wear coefficient of the sample without WC addition was 5 times as large as that of the sample with 10 mole % WC addition when tested against the silicon nitride ball under 98 N. The higher wear coefficient of Ti(C,N)-0WC was explained in part by larger grain size. Wear occurred mainly by grain dislodgment after intergranular cracking mainly caused by the accumulated stress within the grains.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2008.11a
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• pp.153-154
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• 2008

High velocity oxy-fuel (HVOF) thermal spraying coating has been used widely throughout the last 60 years mainly in defense, aerospace, and power plants. Recently this coating technique is considered as a promising candidate for the replacement of the traditional electrolytic hard chrome plating (EHC) which pollutes the environment and causes lung cancer by toxic hexa-valent $Cr^{6+}$. In this study, two kinds of cermet coatings, WC-CoCr and WC-CrC-Ni, are formed by HVOF spraying. The wear properties of coatings are evaluated comparatively by reciprocating sliding wear tests at $25^{\circ}C$, $250^{\circ}C$ and $450^{\circ}C$ respectively. Wear rates show that WC-CoCr coatings have better sliding wear resistance than WC-CrC-Ni coatings regardless of temperature due to more, compact and homogeneously distributed WC particles, less metal content, Co, Cr rich metallic bindermatrix with higher fracture strength and better adhesive strength with WC particles.

• Journal of the Korean institute of surface engineering
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• v.40 no.4
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• pp.170-174
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• 2007

High Velocity Oxygen Fuel (HVOF) thermal spray coating of nano size WC-Co powder (nWC-Co) has been studied as one of the most promising candidate for the possible replacement of the traditional hard plating in some area which causes environmental and health problems. nWC-Co powder was coated on Inconel 718 substrates by HVOF technique. The optimal coating process obtained from the best surface properties such as hardness and porosity is the process of oxygen flow rate (FR) 38 FMR, hydrogen FR 57 FMR and feed rate 35 g/min at spray distance 6 inch for both surface temperature $25^{\circ}C\;and\;500^{\circ}C$. In coating process a small portion of hard WC decomposes to less hard $W_2C$, W and C at the temperature higher than its decomposition temperature $1,250^{\circ}C$ resulting in hardness decrease and porosity increase. Friction coefficient increases with increasing coating surface temperature from 0.55-0.64 at $25^{\circ}C$ to 0.65-0.76 at $500^{\circ}C$ due to the increase of adhesion between coating and counter sliding surface. Hardness of nWC-Co is higher or comparable to those of other hard coatings, such as $Al_2O_3,\;Cr,\;Cr_2O_3$ and HVOF Tribaloy 400 (T400). This shows that nWC-Co is recommendable for durability improvement coating on machine components such as high speed spindle.

• Transactions of Materials Processing
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• v.31 no.6
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• pp.376-383
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• 2022

The potential damage region of a WC-Co cemented carbide die is investigated for cold forging process of a wheel-nut by numerical simulation with its chemical composition considered. Numerical simulation is utilized to calculate internal stress, especially for the WC-Co die, during the forging process. Finite element model is established, in which the elasto-plastic properties are applied to the work-piece of bulk steel, and elastic properties are considered for the lower die insert of the WC-Co alloy. This stress analysis enables to distinguish the potential damage regions of the WC-Co die. The regions from calculation are comparatively analyzed along with the crack area observed in the die after repetitive manufacturing. Effect of chemical composition of the WC-Co is also evaluated on characteristics of potential damage region of the die with variance of mechanical properties considered. Derived from Mohr-Coulomb fracture model, furthermore, a new stress index is presented and used for die stress analysis. This index inherently considers hydrostatic pressure and is then capable of deducing wide range of its distribution for representing stress state by modification of its parameter implying pressure sensitivity.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.04a
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• pp.38-38
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• 2006

• Journal of the Korean Ceramic Society
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• v.26 no.5
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• pp.645-654
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• 1989

Specimens of WC-Co were indented to measure the resulting crack size and unindented samples were fractured in 3-point flexure to obtain the strength and to measure characteristic features on the fracture surface. Fracture toughness was determined using fractography and compared to those determined using identation techniques. We show that principles of fracture mechanics can be applied WC-Co composites and can be used to analyze the fracture process. The fracture surfaces were examined by scanning electron microscopy and optical microscopy. Characteristic feature observed in glasses, single crystals and polycrystalline materials known as mirror, mist, hackle, and crack branching were identified for these composites. We discuss the importance of fracture surface analysis in determining the failure-initiating sources and the failure behaviorof WC-Co composites.

• Journal of Powder Materials
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• v.18 no.4
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• pp.332-339
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• 2011

Cemented tungsten carbide has been used in cutting tools and die materials, and is an important industrial material. When the particle size is reduced to ultrafine, the hardness and other mechanical properties are improved remarkably. Ultrafine cemented carbide with high toughness and hardness is now widely used. The objective of this study is synthesis of nanostructured WC-Co powders by liquid phase method of tungstate. The precursor powders were obtained by freezen-drying of aqueous solution of soluble salts, such as ammonium metatungstate, cobalt nitrate. the final compositions were WC-10Co. In the case of liquid phase method, it can be observed synthesis of WC-10Co. The properties of powder produced at various temperature, were estimated from the SEM, BET and C/S analyser.

• Journal of Powder Materials
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• v.5 no.3
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• pp.178-183
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• 1998

Ultrafine WC-10wt.%Co cemented carbides powders were synthesized by direct carburization. W-Co composite powders and carbon black powders were mixed by wet ball milling and dried. The mixed powders were heated to 800 $^{\circ}C$ with heating rate of 8.2$^{\circ}C$/min and held for various times in flowing $H_2$. For carbon addition of 140%, the carburization was completed by heating at 80$0^{\circ}C$ for 4 hours. The carburization time decreased with increasing amount of carbon and carburization was completed by heating at 800 $^{\circ}C$ for 2 hours with carbon addition of 150%. WC-10 wt%Co cemented carbides powders fabricated by direct carburization have nanoscale WC($\/leqq$100 nm) size.

• Journal of Powder Materials
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• v.10 no.4
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• pp.249-254
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• 2003

WC-6wt%Co hard metal powders were sintered by a 2.45 GHz multimode microwave applicator in Ar atmosphere. Microwave sintering of WC-6wt%Co powder lowered the sintering temperature and shortened the processing time in less than two hours than by a conventional method. Microstructures of the sintered specimen were studied with scanning electron microscope (SEM) and no abnormal grain growth was observed. Mechanical properties were similar to the values of the specimens sintered by a conventional method. Specimen sintered at 135$0^{\circ}C$ for 30 minutes ,hewed 99%, 20.5 GPa and 8.1 MPa$\sqrt{m}$ of theoretical density, hardness and fracture strength, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.452-455
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• 2000

Diamond thin films were synthesized on WC-Co substrate at various experimental parameters using 13.56MHz RF PACVD(radio frequency plasma-assisted chemical vapor deposition). In order to increase the nucleation density, the WC-Co substrate was polished with 3$\mu\textrm{m}$ diamond paste. And the WC-Co substrate was pretreated in HNO$_3$: H$_2$O = 1:1 and O$_2$ plasma. In H$_2$-CH$_4$gas mixture, the crystallinity of thin film increased with decreasing CH$_4$concentration at 800W discharge power and 20torr reaction pressure. In H$_2$-CH$_4$-O$_2$gas mixture, the crystallinity of thin film increased with increasing O$_2$concentration at 800W discharge power, 20torr reaction pressure and 4% CH$_4$concentration.