• Korean Journal of Materials Research
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• v.11 no.10
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• pp.907-911
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• 2001

In order to improve the grindability of magnetic abrasive, Fe-WC magnetic abrasives were made by a plasma melting method after ball milling at various times. This study aims to investigate homogeneously distributed hard phases in Fe matrix and strong bonding between the Fe-matrix and the hard phase. According to XRD, SEM and OM observation, Fe-WC magnetic abrasive powders exhibit the best grindability by plasma melting for 30h ball milling. As a result of magnetic abrasive polishing, the surface roughness, R_{max}$ 5.0$\mu\textrm{m}$, before magnetic abrasive polishing, was reduced to R_{max}$ 2.4$\mu\textrm{m}$. The new magnetic abrasive polishing process is thought to be the useful methods for the automation of three dimensional surface polishing.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.6
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• pp.1-8
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• 2007

The ultra-fine tungsten carbide(WC) powders have been actively used in the cemented carbides industry, because they have excellent mechanical properties such as high hardness, strength, and toughness. In this study, ultra-fine WC-Co alloys powders have been fabricated by thermochemical and thermomechanical process such as spray conversion process or high energy ball milling. The non-coated end-mill which is made of ultra-fine tungsten carbide is investigated by measuring cutting force, tool wear, tool life, and surface roughness profile according to cutting length. The machining test was conducted with high hardened workpiece and their performances are investigated in high speed cutting conditions. Also, the relationship between the machining characteristics and the Co contents are investigated under various high speed cutting conditions.

• Journal of the Korean Ceramic Society
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• v.44 no.3 s.298
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• pp.152-156
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• 2007

Tungsten carbide powder was synthesized by SHS (self-propagating high-temperature synthesis). Except $WO_{3}$, each concentration of raw material ($WO_{3},\;Mg,\;NaCl,\;Na_{2}CO_{3},\;C$) was investigated. Final product was characterized by XRD and SEM. X-ray data demonstrated that the $NaCl+Na_{2}CO_{3}$ combined mixture has superiority in the WC formation process. Single phase and submicrometer WC powder was synthesized at the temperature below $1600^{\circ}C$. The role of sodium salts in combustion process was discussed, and chemical mechanism of WC formation was proposed. WC powder prepared by salt-assisted combustion synthesis has a size $0.2{\sim}3\;{\mu}m$ and low agglomeration degree.

• Korean Journal of Materials Research
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• v.18 no.7
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• pp.357-361
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• 2008

Microstructure and mechanical properties of WC-3 wt% Co cemented carbides, fabricated by a spark plasma sintering (SPS) process, were investigated in this study. The WC-3 wt%Co powders were sintered at $900{\sim}1100^{\circ}C$ for 5min under 40MPa in high vacuum. The density and hardness were increased as the sintering temperature increased. WC-3 wt%Co compacts with a relative density of 97.1% were successfully fabricated at $1100^{\circ}C$. The fracture toughness and hardness of a compact sintered at $1100^{\circ}C$ were $21.6 MPa{\cdot}m^{1/2}$ and 4279 Hv, respectively.

• Journal of Welding and Joining
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• v.18 no.5
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• pp.112-116
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• 2000

The development of new spraying processes has increased the demand for high quality protective coatings. Many thermal spraying processes have been developed to obtain coatings for a wide spectrum of materials and substrates. The plasma spray process was used to deposit coatings of WC-12%Co powders on mild steel substrate, and the characteristics of as-sprayed and vacuum heat treated coatings have been investigated. The variations of microhardness and bond strength in WC-12%Co coatings after heat treatment under vacuum circumstance have been investigated. The effects of phases and morphologies of WC-12%Co coatings have been investigated by utilizing X-ray diffraction and scanning electron microscopy, respectively. The microhardness and bond strength of the coatings were increased with increasing the temperature in the temperature range of $700^{circ}C~1000^{\circ}C$. The bond strength was obtained 49 MPa after vacuum heat treatment at $1000^{\circ}C$.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.889-890
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• 2006

In recent years, PCB drills with smaller diameters less than 0.1 mm are used and thus there are growing needs for ultra-fine grained cemented carbides. However, ultra-fine WC powder usually causes extraordinary grain growth during sintering which weakens mechanical strength of ultra-fine grained cemented carbides. So we examined several kinds of WC powders to make new ultra-fine grained cemented carbides having superior performance. We found that direct carburized WC powder is very good as a WC raw material. The PCB drills made of the developed ultra-fine grained cemented carbides have higher hardness, toughness and stiffness than conventional ones.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.346-347
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• 2006

New manufacturing processes, such as thermochemical, mechanochemical and chemical vapor condensation processes have been developed to obtain nanostructured WC/Co materials. Nanoscale size WC/Co composite powders of near 100-150nm can be synthesizes by thermochemical and mechanochemical processes using water soluble precursors. Non-agglomerated and nano sized WC powder can be synthesized by the chemical vapor condensation process using metallorganic precursors as starting materials. In this paper, the scientific and technical issues on synthesis and consolidation of nanostructured WC/Co alloys produced by new chemical processes are introduced.

• Journal of Powder Materials
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• v.10 no.2
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• pp.108-117
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• 2003

WC and dense WC-10 vol%Co materials with grain size of~1${\mu}m$ were synthesized by high-frequency induction heated combustion synthesis (HFIHCS) method in one step from elemental powders of W, C and Co within several minutes. Simultaneous combustion synthesis and densification were accomplished under the combined effects of an induced current and mechanical pressure. In the absence of cobalt additive, WC can be formed, but its relative density was low (about 73%) under simultaneous application of a 60 MPa pressure and the induced current. However, in the presence of 10 vol.%Co, the relative density increased to 99% under the same experimental condition. The percentages of the total shrinkage occurring before and during the synthesis reaction of WC-10 vol.%Co were 5% and 51%, respectively. The fracture toughness and hardness values of WC-10 vol.%Co were 10 MPa . m$^{1/2}$ and 1840 kg/$mm^2$, respectively.

• Korean Journal of Materials Research
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• v.31 no.7
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• pp.392-396
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• 2021

Expensive PCBN or ceramic cutting tools are used for processing of difficult-to-cut materials such as Ti and Ni alloy materials. These tools have the problem of breaking easily due to their high hardness but low fracture toughness. To solve these problems, cutting tools that form various coating layers are used in low-cost WC-Co hard material tools, and research on various tool materials is being conducted. In this study, binderless-WC, WC-6 wt%Co, WC-6 wt%Co-1 wt% Mo₂C, and WC-6 wt%Co-2.5 wt% Mo₂C hard materials are densified using horizontal ball milled WC-Co, WC-Co-Mo₂C powders, and spark plasma sintering process (SPS process). Each SPSed Binderless-WC, WC-6 wt%Co-1 wt% Mo₂C, and WC-6 wt%Co-2.5 wt% Mo₂C hard materials are almost completely dense, with relative density of up to 99.5 % after the simultaneous application of pressure of 60 MPa and almost no significant change in grain size. The average grain sizes of WC for Binderless-WC, WC-6 wt%Co-1 wt% Mo₂C, and WC-6 wt%Co-2.5 wt% Mo₂C hard materials are about 0.37, 0.6, 0.54, and 0.43 ㎛, respectively. Mechanical properties, microstructure, and phase analysis of SPSed Binderless-WC, WC-6 wt%Co-1 wt% Mo₂C, and WC-6 wt%Co-2.5 wt% Mo₂C hard materials are investigated.

• Journal of the Korean Ceramic Society
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• v.42 no.3 s.274
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• pp.171-177
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• 2005

The effect of variation in particle size of WC and Co powder on the properties of WC-Co alloys was investigated. WC and Co powders having different particle sizes were used in the fabrication of $WC-10\;wt\%$Co composites. High hardness and low fracture toughness alloy was obtained with the decrease in WC particle size regardless of Co particle size. It was newly found in this investigation that the initial particle size of Co as well as WC had a great role in the microstructure and properties of WC-Co hard materials. The average grain size and fracture toughness of WC-Co alloys using same WC powder size increased and their hardness decreased with the use of relatively finer Co binder.