• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09a
• /
• pp.646-647
• /
• 2006

Nano-sized WC particles in WC/Co composite powders were synthesized by mechanochemical method. The raw powders$(WO_3,\;Co_3O_4,\;VC,\;Cr_3C_2$ and graphite) were mixed by planetary milling for 30 hours. The compositions were WC-10 and -20 wt% Co added VC and $Cr_3C_2$. The direct reduction and carburization of the mixed powders were carried at $900\;^{\circ}C$ for 1 to 3 hours under flowing Ar gas. The mean size of WC particles in WC/Co composite powders was about 16 nm. The resultant powders were compacted and sintered at $1300{\sim}1360\;^{\circ}C$ for 0.5 hour. After sintering the mean size of WC particles was about 50 nm.

• Journal of Powder Materials
• /
• v.11 no.2
• /
• pp.124-129
• /
• 2004

Nanosized WC and WC-Co powders were synthesised by chemical vapor condensation(CVC) process using the pyrolysis of tungsten hexacarbonyl(W(CO)$_6$) and cobalt octacarbonyl(Co$_2$(CO)$_8$). The microstructural changes and phase evolution of the CVC powders during post heat-treatment were studied using the XRD, FE-SEM, TEM, and ICP-MS. CVC powders were consisted of the loosely agglomerated sub-stoichimetric WC$_{1-x}$ and the long-chain Co nanopowders. The sub-stochiometric CVC WC and WC-Co powders were carburized using the mixture gas of CH$_4$-H$_2$ in the temperature range of 730-85$0^{\circ}C$. Carbon content of CVC powder controlled by the gas phase carburization at 85$0^{\circ}C$ was well matched with the theoretical carbon sioichiometry of WC, 6.13 wt％. During the gas phase carburization, the particle size of WC increased from 20 nm to 40 nm and the long chain structure of Co powders disappeared.

• Journal of Welding and Joining
• /
• v.18 no.6
• /
• pp.102-107
• /
• 2000

It was attempted to improve the wear resistance of Al alloy under the load condition by making a formation of the thick surface hardening alloy layers. The thick surface hardening alloy layers were formed on 6061 Al alloys overlayed by MIG welding process with WC-12%Co powder addition. Effects of the dispersion of WE-12%Co powders on hardness and wear characteristics of alloys were investigated. The following results were obtained. Most of WE-12%Co powders are dispersed nearly uniform as unmelted particles in the matrix alloy. A part of WC-12%Co powders are melted in the molten pool, and during solidification {TEX}$Al_{9}Co_{2}${/TEX} appeared. With increasing addition of WC-12%Co powders, the hardness and specific wear resistance of the overlay weld alloys increased and reached Hv450 at WC-12%Co powder addition rate of 54g/min. It is considered that excellent wear resistance of the overlayed alloys was due to dispersed WC-12%Co powders and increased 10 times at WC-12%Co powder addition rate of 54 g/min than that of the WC-free overlaying layers.

• Journal of Powder Materials
• /
• v.5 no.3
• /
• pp.178-183
• /
• 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
• /
• v.15 no.2
• /
• pp.107-113
• /
• 2008

Ultrafine TiC-5%Co powders were synthesized by spray drying of aqueous solution of TiO$(OH)_2$ slurry and cobalt nitrate, followed by calcination and carbothermal reaction. The oxide powders with carbon powder was reduced and carburized at $900^{\circ}C{\sim}1250^{\circ}C$ under hydrogen atmosphere. During reduction, CO gas was mainly evolved by reducing reaction of oxides. Ultrafine TiC-5%Co powders were easily formed by carbothermal reaction at $1250^{\circ}C$ due to using ultrafine powders as raw materials. The ultrafine WC-TiC-Co alloy prepared by sintering of mixed powder of ultrafine WC-13%Co powder and ultrafine TiC-5%Co powder has higher sintered density and mechanical properties than WC-TiC-Co alloy prepared by commercial WC, TiC and Co powders.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09a
• /
• pp.642-643
• /
• 2006

Direct reduction and carburization process was thought one of the best methods to make nano-sized WC powder. The oxide powders were mixed with graphite powder by ball milling in the compositions of WC-5,-10wt%Co. The mixture was heated at the temperatures of $600{\sim}800^{\circ}C$ for 5 hours in Ar. The reaction time of the reduction and carburization was decreased as heating temperatures and cobalt content increased. The mean size of WC/Co composite powders was about 260 nm after the reactions. And the mean size of WC grains in WC/Co composite powders was about 38 nm after the reaction at $800^{\circ}C$ for 5 hours.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 1999.11a
• /
• pp.123-123
• /
• 1999

• Journal of Powder Materials
• /
• v.9 no.3
• /
• pp.167-173
• /
• 2002

A new approach to produce nanostructured WC/Co composite powders by a mechanochemical process was made to improve the mechanical properties of advanced hardmetals. Homogeneous spherical W-Co salt powders were made by spray drying of aqueous solution from ammonium metatungstate($(NH_4)_6(H_2W_{12}O_{40})\cdo4H_2O$,AMT) and cobalt nitrate hexahydrate (Co(NO$_3$)$_2$.6$H_2O$). spray dried W-Co salt powders were calcined for 1 hr at $700^{\circ}C$ in atmosphere of air. The oxide powder was mixed with carbon black by ball milling and this mixture was heated with various temperatures and times in $H_2$. The $WO_3/CoWO_4$ composite oxide powders were obtained by calcinations at $700^{\circ}C$. The primary particle size of W/Co composite oxide powders by SEM was 100 nm. The reduction/carburization time decreased with increasing temperatures and carbon additions. The average size of WC particle carburized at $800^{\circ}C$ by TEM was smaller than 50 nm.

• Journal of Powder Materials
• /
• v.10 no.1
• /
• pp.1-5
• /
• 2003

Nano-sized WC powders were synthesized by vapor phase reaction using the precusor of tungsten ethoxide under helium and hydrogen atmosphere. The phases of the powder were varied with reaction Bone and gas flow rate. The powder size was about 30nm in diameter, and the tungsten carbide powder was coated by carbon layer. The synthesis of nano-sized WC powders was promoted as the hydrogen gas flow rate became higher. Inversely, tungsten oxide was formed by increasing the flow rate of helium gas. The synthesized powders were analyzed by XRD, FE-SEM, carbon analyzer etc.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09a
• /
• pp.648-649
• /
• 2006

The dry-milling technique was used for mixing and crushing oxides and graphite powders. The ratio of ball-to-powder was 30:1 and argon gas was filled in jar. The excess carbon was $10{\sim}20wt%$ of the stoichiometric amount. The dry-milling was carried for 20 hours. The mixed powders were reduced and carburized at $900{\sim}980^{\circ}C$ for 3 hours flowing Ar gas in tube furnace. The dry-milled powders showed the wide diffraction patterns of X-ray. The reactions of reduction and carburization were completed in 3 hours at $980^{\circ}C$. After the reactions, the mean size of WC particles was about 200 nm. The content of free carbon in WC/Co mixed powders was less as the reaction temperature increased.