Sung-Soo Ryu

Dilatometric analysis on the sintering behavior of nanocrystalline W-Cu prepared by mechanical alloying

Abstract Unlike conventional W–Cu powder, the sintering of nanocrystalline W–Cu powder was significantly enhanced at solid phase sintering temperature. In the present study, in order to clarify this enhanced sintering behavior of nanocrystalline W–Cu powder prepared by mechanical alloying, the sintering behavior during heating stage was analyzed by dilatometry with various heating rates. The sintering of the nanocrystalline W–Cu powder was characterized by the densification of two stages, having two peaks in shrinkage rate curves. The temperature at which the first peak appeared was well below the Cu melting point and significantly dependent on the heating rate. On the basis of dilatometric data and microstructural observation, the possible mechanism for the enhanced sintering of the nanocrystalline W–Cu powder in the solid phase was attributable to the coupling effect of the sintering occurring inside as-milled powder and the sintering between powder particles.

Densification behavior of mechanically alloyed W-Cu composite powders by the double rearrangement process

Department of Materials Engineering, Hanyang University, Seoul 133-791, Korea(Received January 22, 1998)(Accepted in revised form May 25, 1998)IntroductionTungsten-copper(W-Cu) composites are promising materials for thermal managing applications such asmicroelectronic devices because of the low thermal expansion coefficient of tungsten and the highthermal conductivity of copper (1–3). These materials have been produced by conventional Cu-infiltration sintering or by liquid-phase sintering (4, 5). The full densification of W-Cu composites byliquid-phase sintering is attained mainly by the tungsten particle rearrangement due to the capillaryforce and surface tension of Cu-liquid phase (6, 7) as well as solid-state sintering, because W and Cuhave no solubility under equilibrium condition (8). If the constituent phases are extremely finehomogeneous state, the fully dense parts with the homogeneous microstructure can be attained at thestage of particle rearrangement. To promote homogeneity, much works such as the coreduction methodof the raw oxide powders (9, 10) or mechanical alloying of the element powders (11, 12) have beenstudied. The mechanical alloying method is the attractive one from the engineering viewpoint becausethe nanostructured(NS) materials can be easily synthesized in large quantities. Nevertheless, the studiesof nanostructured W-Cu alloys have been focused only on the formation and the fabrication ofcomposite powders by mechanical alloying (11–13). And there were few researches of liquid-phasesintering behavior of NS W-Cu composite powders compared to nanostructure characteristic study.The authors have recently reported on the characteristics of nanostructured W-Cu alloys producedby mechanical alloying method (14, 15). In this study, the new concept of nanosintering was suggestedto explain the drastic grain growth of mechanically alloyed NS W-Cu powders during the solid-statesintering. The high sinterabilty of these mechanically alloyed NS W-Cu alloys was also obtained byliquid-phase sintering. In this present work, the enhanced sinterabilty of mechanically alloyed NS W-Cucomposite powders with sintering temperature is investigated and evaluated by the combination ofnanosintering and conventional liquid-phase sintering.ExperimentalElemental W (99.9% purity, 4.28mm) and Cu(99.5% purity, 50.42mm) powders were used for rawpowders in this experiment. The mechanical alloying was carried out in an attrition mill using a stainlesssteel vial and balls with a speed of 400 rpm. The powder charge was 20g, with balls to powders weightratio of 60:1. The W-20wt%Cu and W-30wt%Cu composite powders were prepared by milling for 100

CaO-ZnO-B₂O₃-Al₂O₃-SiO₂ 계 유리가 적용된 질화알루미늄 기판용 RuO₂계 친환경 후막저항의 전기적 특성 연구

The objective of this study is to prepare lead-free thick film resistor (TFR) paste compatible with AlN substrate for hybrid microelectronics. For this purpose, CaO-ZnO-B₂O₃-Al₂O₃-SiO₂ glass system was chosen as a sintering aid of RuO₂. The effects of the weight ratio of CaO to ZnO in glass composition, the glass content and the sintering temperature on the electrical properties of TFR were investigated. RuO₂ as a conductive and glass powder were dispersed in an organic binder to obtain printable paste and then thick-film was formed by screen printing, followed by sintering at the range between 750℃ and 900℃ for 10 min with a heating rate of 50℃/min in an ambient atmosphere. The addition of ZnO to glass composition and sintering at higher temperature resulted in increasing sheet resistance and decreasing temperature coefficient of resistance. Using RuO₂-based resistor paste containing 40 wt%glass of CaO-20.5%ZnO-25%B₂O₃-7%Al₂O₃-15%SiO₂ composition, it is possible to produce thick film resistor on AlN substrate with sheet resistance of 10.6Ω/□ and the temperature coefficient of resistance of 702ppm/℃ after sintering at 850℃.

Effect of heat-treatment on the nanostructural change of W-Cu powder prepared by mechanical alloying

W-30wt.%Cu powder prepared by mechanical alloying (MA) was annealed at various temperatures to investigate the structural change of MA W-Cu powder. From differential scanning calorimeter analysis and transmission electron microscope observation, it was revealed that the recovery of W in MA W-30wt.%Cu powder occurred at 700°C and the W grain started growing also at this temperature. The W grain had grown significantly after annealing at 900°C, and the Cu phase in the MA powder was found to act as liquid melt near 900°C. The microstructure of the sintered specimen was similar to that of the W-Cu alloy via liquid phase sintering. This microstructure, even at temperatures below Cu melting, was the new feature observed in the MA W-Cu powder. This suggests that such a microstructure is closely related to the inherent high diffusivity of the nanosized W crystallites as well as the liquid-like behavior of the Cu phase.

Effects of Li 2 O Addition and Heat-Treatment on Formability of FeS 2 Powder for Cathode of Thermal Battery

has been widely used for cathode materials in thermal battery because of its high stability and current capability at high operation temperature. Salts such as a LiCl-KCl were added as a binder for improving electrical performance and formability of cathode powder. In this study, the effects of the addition of in LiCl-KCl binder on the formability of powder compact were investigated. With the increasing amount of addition to LiCl-KCl binder salts, the strength of the pressed compacts increased considerably when the powder mixture were pre-heat-treated above . The heat-treatment resulted in promoting the coating coverage of particles by the salts as was added. The observed coating as addition might be attributed to the enhanced wettability of the salt rather than its reduced melting temperature. The high strength of compacts by the addition and pre-heat-treatment could improve the formability of raw materials.

고에너지 볼밀링된 BaCO3와 TiO2 혼합분말의 고상반응에 의한 나노결정 BaTiO3 분말 합성

【Nanocrystalline

Sintering Behavior of Ag-Ni Electrode Powder with Core-shell Structure

BaTiO_3

Effects of Particle Size and Binder Phase Addition on Formability of Li-Si Alloy Powder for Thermal Battery Anode

powder could be synthesized by solid-state reaction using the mixture which was prepared by a high energy milling process in a bead mill for

Facile Synthesis of Highly Dispersed Ultra-fine ZrC Powders by Carbothermal Reduction Method Using Nanosized ZrO 2 and Nanosized Graphite Powder Mixtures

BaCO_3

Thermo-Mechanical Properties of Al 2 TiO 5 Ceramics Stabilized with MgO and ZrO 2 Additives

and nanocrystalline