Papers by Author: In Jin Shon

Abstract: A dense nanostuctured Fe3Al was consolidated by high frequency induction heated sintering method within 2 minutes from mechanically synthesized powders of Fe3Al and milled powders of 3Fe+Al. The consolidation was accomplished under the combined effects of a induced current and mechanical pressure. The grain size, sintering behavior and hardness of Fe3Al sintered from horizontally milled Fe+Al powders and high energy ball milled Fe3Al powder were compared. Keywords: Combustion synthesis; Nanomaterials; Mechanical properties; Rapid sintering

Abstract: The rapid sintering of nanostuctured SiC hard materials was investigated with high-frequency induction heating sintering process. The advantage of this process is that it allows very quick densification to near theoretical density and prohibition of grain growth in nanostuctured materials. A dense nanostructured SiC hard material was produced with simultaneous application of 500 MPa pressure and induced current within 2 minutes. The effect of the ball milling times on the sintering behavior, grain size and mechanical properties of binderless SiC was investigated.

Abstract: A dense nanostructured 5NbSi2-SiC-Si3N4 composite was synthesized by the high-frequency induction-heated combustion synthesis (HFIHCS) method within 1 minute in one step from mechanically activated powders of 4NbN, NbC and 14Si. A highly dense 5NbSi2-SiC-Si3N4 composite with relative density of up to 98% was produced under the simultaneous application of a pressure of 80 MPa and the induced current. The average grain size and mechanical properties (hardness and fracture toughness) of the composite were investigated.

Abstract: Nanopowders of Cr and Al2O3 was fabricated from CrO3 and 2Al by high energy ball milling. Dense nanocrystalline Cr-Al2O3 composite was consolidated by pulsed current activated sintering (PCAS) method within 1 min from mechanically alloyed powders. Highly dense Cr-Al2O3 with relative density of up to 99% was produced under simultaneous application of a 80 MPa pressure and the pulsed current. The average grain size and mechanical properties of the composite were investigated.

Abstract: High frequency induction heated sintering (HFIHS) method is one of the rapid sintering methods. The advantage of rapid sintering method is that grain growth can be prevented during sintering at high temperature. Refinement of grains was known to increase the yield and flow stresses of crystals. The relation between the yield stress and the grain size is known as Hall-Petch relation. NbC-10vol.%Co, Ni and Fe composites were fabricated by HFIHS at 1060°C for 0 and 3 min as holding times under a pressure of 80MPa.The relative density of NbC-10vol.%Co, Ni and Fe composites which were sintered at 1060°C for 0min as holding time under 80MPa were 91.90%, 91.26% and 91.26%, respectively. These composites are difficult to use industrial parts due to low relative density. The longer sintering time was conducted for increasing relative density in this study. Nano-sized specimens, which were calculated grain size by full-width at half maximum (FWHM), can be obtained by HFIHS. The value of hardness and fracture toughness was investigated using 20kgf load Vickers indenter.

Abstract: The consolidation process of ultra fine Si powders, generated as by-product during the decomposition process of silane gases, was systematically investigated for use as economical solar-grade feedstock. Si powder compacts were tried to fabricate by a consolidation process without a binding agent and then their density ratio and strength were evaluated. The Si powders in as-received state were not pure enough to be used alone as solar grade feedstock material. After the adequate chemical treatments, a sufficiently high purity above solar-grade was able to be achieved.

Abstract: Two methods, High-Frequency Induction-Heated Sintering (HFIHS) and Pulsed Current Activated Sintering (PCAS), were utilized to consolidate WC-8wt.%Ni hard materials. The demonstrated advantages of these processes are rapid densification to near theoretical density in a relatively short time and with insignificant change in grain size. The hardness, fracture toughness, and the relative density of the dense WC–8Ni composites produced by HFIHS and PCAS were investigated. And the effect of variation in particle size of WC powder on the sintering behavior and mechanical properties were investigated.

Abstract: Dense nanostructured ZrSi2-SiC composite was synthesized by high frequency induction heated combustion synthesis (HFIHCS) method within 1 minute in one step from powders of ZrC and 3Si. Simultaneous combustion synthesis and densification were accomplished under the combined effects of an induced current and mechanical pressure. Highly dense ZrSi2-SiC with relative density of up to 98% were produced under simultaneous application of a 60MPa pressure and the induced current. The average grain size and mechanical properties (hardness and fracture toughness) of the composite were investigated.

Abstract: By the high frequency induction heated combustion synthesis (HFIHCS) method, dense nanostructured TaSi2-SiC composite was synthesized within 2 minutes and in a single step from powders of TaC and 3Si. Simultaneous combustion synthesis and densification were accomplished under the combined effects of an induced current and mechanical pressure. Highly dense TaSi2-SiC with relative density of up to 97% were produced under a 60MPa pressure and induced current. The average grain size and mechanical properties (hardness and fracture toughness) of the composite were investigated.

Abstract: Recrystallization behaviors have been investigated with respect to two different kinds of the initial structures, original austenite and martensite, in an Fe-32%Ni alloy. The recrystallized austenite grain size from the martensite is much smaller than that from the original austenite, and decreases linearly with increasing the initial hardness, independent of the initial structure. The recrystallization sequences are different between the two structures: only one step due to recrystallization appears in hardness-temperature curve of the original austenite, whereas two steps corresponding to reverse transformation of α’ to r’ and recrystallization are shown in that of the martensite.