Journal of Powder Materials

Abnormal Grain Growth During the Liquid-Phase Sintering: Kyoon Choi, Doh-Yeon Kim; J Korean Powder Metall Inst. 1998;5(3):171-177.

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A Study of UltraRne WC-l0wt.%Co Cemented Carbides Powders Properties Fabricated by direct Carburization: J Korean Powder Metall Inst. 1998;5(3):178-183.

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Abstract PDF: 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 °C with heating rate of 8.2°C/min and held for various times in flowing H_2. For carbon addition of 140%, the carburization was completed by heating at 800°C for 4 hours. The carburization time decreased with increasing amount of carbon and carburization was completed by heating at 800 °C for 2 hours with carbon addition of 150%. WC-10 wt%Co cemented carbides powders fabricated by direct carburization have nanoscale WC(/leqq100 nm) size.

Fabrication Processes and Properties of High Volume Fraction SiC Particulate Preform for Metal Matrix Composites: J Korean Powder Metall Inst. 1998;5(3):184-191.

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Abstract PDF: The fabrication process and properties of SiC particulate preforms with high volume fraction above 50% were investigated. The SiC particulate preforms were fabricated by vacuum-assisted extraction method after wet mixing of SiC particulates of 48 µm in diameter, SiO_2 as inorganic binder, cationic starch as organic binder and polyacrylamide as dispersant in distilled water. The SiC particulate preforms were consolidated by vacuum-assisted extraction, and were followed by drying and calcination. The drying processes were consisted with natural drying at 25°C for 36 hrs and forced drying at 100°C for 12 hrs in order to prevent the micro-cracking of SiC particulates preform. The compressive strengths of SiC particulate preforms were dependent on the inorganic binder content, calcination temperature and calcination time. The compressive strength of SiC preform increased from 0.47 MPa to 1.79 MPa with increasing the inorganic binder content from 1% to 4% due to the increase of SiO_2 flocculant between the interfaces of SiC particulates. The compressive strength of SiC preform increased from 0.90 MPa to 3.21 MPa with increasing the calcination temperatures from 800 to 1200°C under identical calcination time of 4hrs. The compressive strength of SiC preform increased from 0.92 to 1.95 MPa with increasing the calcination time from 2 hrs to f hrs at calcination temperature of 1100°C. The increase of compressive strength of SiC preform with increasing the calcination temperature and time is due to the formation of crystobalite SiO_2 phase at the interfaces of SiC particulates.

Microstructure and High Temperature Strength of Rapidly Solidified Al-8wt%Fe Alloy: J Korean Powder Metall Inst. 1998;5(3):192-198.

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Abstract PDF: Microstructure and mechanical properties were examined on rapidly solidified Al-8wt%Fe alloy. High temperature strength test was also undertaken, and it is shown that the refinement in microstructure resulting from extremely rapid cooling rates gives rise to improved high temperature strength, but the elongation to fracture of this material decreases with increasing temperature, particularly in the temperature range up to 300°C. Specimens heat-treated for 100 hrs were analyzed with TEM micrographs to understand the thermal stability of this material.

Selective Laser Sintering of Alumina Using an Inorganic Binder Monoclinic HBO_2 and Post-Processing: J Korean Powder Metall Inst. 1998;5(3):199-209.

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Abstract PDF: A new low melting inorganic binder, monoclinic HBO_2, has been developed for Selective Laser Sintering (SLS) of alumina powder by dehydration process of boron oxide powder in a vacuum oven at 120°C. It led to better green SLS parts and higher bend strength far green and fired parts compared to other inorganic binders such as aluminum and ammmonium phosphate. This appeared to be due to its low viscosity and better wettability of the alumina particle surface. A low density single phase ceramic, aluminum borate (Al_18B_4O_33), and multiphase ceramic composites, A_12O_3-A_14B_2O_9, were successfully developed by laser processing of alumina-monoclinic HBO_2 powder blends followed by post-thermal processing; both Al_18B_4O_33 and A_14B_2O_9 have whisker-like grains. The physical and mechanical properties of these SLS-processed ceramic parts were correlated to the materials and processing parameters. Further densification of the A_12O_3-A_14B_2O_9 ceramic composites was carried out by infiltration of colloidal silica, and chromic acid into these porous SLS parts followed by heat-treatment at high temperature (1600°C). The densities obtained after infiltration and subsequent firing were between 75 and 80% of the theoretical densities. The bend strengths are between 15 and 33 MPa.

Microstructural Change and Sintering Behavior of W-Cu Composite Powders Milled by 3-Dimensional Mixer: J Korean Powder Metall Inst. 1998;5(3):210-219.

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Abstract PDF: The W-Cu composite powders were synthesized from W and Cu elemental powders by ball-milling process, and their microstructural changes and sintering behaviors were evaluated. The ball milling process was carried out in a 3-dimensional mixer (Turbula mixer) using zirconic (ZrO_2) ball and alumina (Al_2O_3) vial up to 300 hrs. The ball-milled W-Cu powders revealed nearly spherical shape. Microstructure of the composite powders showed onion-like structure which consists of W and Cu shells due to the moving characteristic of Turbula mixer. The W and Cu elements in the composite powders milled for 300 hrs were homogeneously distributed, and W grain size in the ball-milled powder was smaller than 0.5 mutextrmm. Fe impurity introduced during ball milling process was very low as of 0.001 wt%. The relative sintered density of ball-milled W-Cu specimens reached about 94% after sintering at 1100°C.

Mechanical Alloying Behavior of Immiscible W-Cu-Pb Ternary System: J Korean Powder Metall Inst. 1998;5(3):220-226.

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Abstract PDF: W-12.8wt%Cu-7.2%Pb powders were milled at room temperature and -100°C to investigate the mechanical alloying behavior of immiscible W-Cu-Pb system and the effect of milling temperature on the extent of alloying and microstructural refinement. W-Cu-Pb powder reached steady state after further extended milling due to Pb addition, compared to the W-Cu system. The cryomilling at -100°C caused the more refinement of powder particle size, and enhanced the solubility of Cu or Pb in W, compared with milling at room temperature. In W-12.8wt%Cu-7.2%Pb powder cryomilled at -100°C, the monotectic temperature of Cu-Pb as well as the melting temperature of Cu was decreased by refinement of Cu crystalline size, and the most amorphization was occurred after milling for 150 h.

텅스텐 중합금에서 미세조직 변화에 따른 재료의 특성변화: J Korean Powder Metall Inst. 1998;5(3):227-235.

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