In-Yong Ko

Rapid synthesis and consolidation of nanostuctured Al2O3-MgSiO3 composites by high frequency induction heated sintering

Nanopowders of MgO, Al2O3 and SiO2 were made by high energy ball milling. The rapid sintering of nanostuctured Al2O3-MgSiO3 composites was investigated by the high-frequency induction heating sintering process. The advantage of this process is that it allows very quick densification to near theoretical density and inhibits grain growth. Highly dense nanostructured Al2O3-MgSiO3 composites were produced with the simultaneous application of 80 MPa pressure and the induced output current of total power capacity (15 kW) within 2 min. The sintering behavior, grain size and mechanical properties of Al2O3-MgSiO3 composites were investigated.

Rapid Sintering and Synthesis of Nanostuctured FeCrAlSi-Al_2O_3 Composite by High-Frequency Induction Heating

Nanopowder of Fe2O3, Al, Cr and Si was fabricated by high energy ball milling. A dense nanostuctured A2O3 and 6.06Fe0.33Cr0.16Al0.23Si0.29 composite was simultaneously synthesized and consolidated using high frequency induction heated sintering method within 1 minute from mechanically activated powders of Fe2O3, Al, Cr and Si. The grain sizes of Al2O3 and Fe0.33Cr0.16Al0.23Si0.29 in composite are 80 and 18 nm, respectively. (Received December 1, 2010)

Fabrication of Nanostructured MoSi2-TaSi2 Composite by High-Frequency Induction Heating and its Mechanical Properties

Nanopowders of Mo, Ta and Si were made by high-energy ball milling. A dense nanostructured MoSi2-TaSi2 composite was sintered by the high-frequency induction heated combustion method within 2 minutes from mechanically activated powder of Mo, Ta and Si. A highly dense MoSi2-TaSi2 composite was produced under simultaneous application of a 80 MPa pressure and the induced current. Mechanical properties and microstucture were investigated. The hardness and fracture toughness of the MoSi2-TaSi2 composite were 1200 kg/mm and 3.5 MPa.m, respectively. The mechanical properties were higher than those of monolithic MoSi2. (Received January 3, 2012)

Mechanical Properties and Fabrication of Nanostructured (Ti,Mo)Si2 by Pulsed Current Activated Combustion

Nanopowders of Mo, Ti and Si were made by high-energy ball milling. A dense nanostructured (Ti,Mo)Si2 compound was sintered by the pulsed current activated combustion method within two minutes from mechanically activated powder of Mo, Ti and Si. A highly dense (Mo,Ti)Si2 compound was produced under simultaneous application of 80 MPa pressure and a pulsed current. The mechanical properties and micorostructure were investigated. The hardness and fracture toughness of the (Mo,Ti)Si2 were 1030 kg/mm 2 and 4.9 MPa· m, respectively. The mechanical properties were higher than monolithic TiSi2. (Received February 17, 2011)

Rapid Sintering of Nanostuctured Tungsten Carbide by High-Frequency Induction Heating and its Mechanical Properties

Extremely dense WC with a relative density of up to 99% was obtained within five minutes under a pressure of 80 MPa using the High-Frequency Induction Heated Sintering method. The average grain size of the WC was about 71 nm. The advantage of this process is not only rapid densification to obtain a neartheoretical density but also the prohibition of grain growth in nano-structured materials. The hardness and fracture toughness of the dense WC produced by HFIHS were 2660 kg·mm and 7.2 MPa·m, respectively. (Received September 6, 2010)

Mechanochemical synthesis and rapid consolidation of nanocrystalline 3NiAl-Al 2 O 3 composites

Nanopowders of 3NiAl and Al2O3 were synthesized from 3NiO and 5Al powders by high-energy ball milling. Nanocrystalline Al2O3 reinforced composite was consolidated by high-frequency induction-heated sintering within 3 minutes from mechanochemically synthesized powders of Al2O3 and 3NiAl. The advantage of this process is that it allows very quick densification to near theoretical density and inhibition grain growth. Nanocrystalline materials have received much attention as advanced engineering materials with improved physical and mechanical properties. The relative density of the composite was 97%. The average Vickers hardness and fracture toughness values obtained were 804 kg/mm2 and 7.5MPa ċ m1/2, respectively.

Effect of Al and Cr on Oxidation of Fe-Al and Fe-Cr Alloys

The effects of Cr and Al contents in Fe-Al and Fe-Cr alloys on oxidation resistance, hardness, and the thermal expansion coefficient were investigated. Fe-Al and Fe-Cr alloys above 10wt.%Al and 20wt.%Cr contents have a high oxidation resistance. The hardness of the Fe-Al and Fe-Cr alloys increased with an increase in Al and Cr contents due to solid solution or formation of an intermetallic compound. The coefficients of thermal expansion of the Fe-Al alloys were higher than those of the Fe-Cr alloys because the coefficient of thermal expansion of Al was higher than that of Fe and Cr. (Received May 20, 2010)