• 한국분말재료학회지
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• 제19권4호
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• pp.264-270
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• 2012

In this study, we mainly focus on the study of densification of gas-atomized Cu-50 wt.%In-13 wt.%Ga alloy powder without occurrence of crack during the forming process. Cu-50 wt.%In-13 wt.%Ga alloy powder was consolidated by sintering and rolling processes in order to obtain high density. The phase and microstructure of formed materials were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and optical microscopy (OM), respectively. Warm rolling using copper can result in the improvement of density. The specimen obtained with 80% of rolling reduction ratio at $140^{\circ}C$ using cooper can have the highest density of $8.039g/cm^3$.

• 한국분말재료학회지
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• 제19권3호
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• pp.189-195
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• 2012

A novel PM (powder metallurgy) steel for automotive power-train gear components was developed to reduce manufacturing cost, while meeting application requirements. The high-density PM steel was manufactured by mixing using special Cr-Mo atomized iron powders, high-pressure compaction, and sintering. Tensile strength, charpy impact, bending fatigue, and contact fatigue tests for the PM steel were carried out and compared to conventional forged steel. Pinion gears for auto-transmission were also manufactured by helical pressing, sintering, and surface densification process. In order to evaluate the durability of the PM parts, auto-transmission durability tests were performed using dynamometer tests. Results showed that the PM steel fulfilled the requirements for pinion gears indicating suitable tensile, bending fatigue, contact fatigue strengths and improved gear tooth profile. The PM gears also showed good performance during the transmission durability tests. As a result, the PM gears showed significant potential to replace the conventional forged steel gears manufactured by tooth machining (hobbing, shaving, and grinding) processes.

• 한국세라믹학회지
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• 제43권12호
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• pp.839-845
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• 2006

Graphite has hexagonal closed packing structure with two bonding characteristics; (1) van der waals bonding between c axis, and (2) covalent bonding in the a and b axis. The weak van der waals bonds cause self-lubricant property, and the strong covalent bonds cause excellent electric and thermal conductivity. Furthermore, graphite is chemically very inert because of the material composed of only carbon elements. Thus, graphite is very useful for mechanical sealing materials. However, Graphite have porous microstructure because starting materials of graphite produce many volatile during the manufacturing processes. This causes low density of graphite, which is unsuitable for the mechanical sealing materials. Thus, further impregnation process is generally needed to enhance the graphite density. In this work, high density graphite is prepared with the principle of densification when coke and pitch binder, prepared from thermal treatment of coal tar pitch, become dehydrogenation during graphitization or carbonization.

• 한국재료학회지
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• 제30권11호
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• pp.573-580
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• 2020

YAG (Yttrium Aluminum Garnet, Y₃Al₅O₁₂) has excellent plasma resistance and recently has been used as an alternative to Y₂O₃ as a chamber coating material in the semiconductor process. However, due to the presence of an impurity phase and difficulties in synthesis and densification, many studies on YAG are being conducted. In this study, YAG powder is synthesized by an organic-inorganic complex solution synthesis method using PVA polymer. The PVA solution is added to the sol in which the metal nitrate salts are dissolved, and the precursor is calcined into a porous and soft YAG powder. By controlling the molecular weight and the amount of PVA polymer, the effect on the particle size and particle shape of the synthesized YAG powder is evaluated. The sintering behavior of the YAG powder compact according to PVA type and grinding time is studied through an examination of its microstructure. Single phase YAG is synthesized at relatively low temperature of 1,000 ℃ and can be pulverized to sub-micron size by ball milling. In addition, sintered YAG with a relative density of about 98 % is obtained by sintering at 1,650 ℃.

• Journal of Ceramic Processing Research
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• 제19권5호
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• pp.383-387
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• 2018

Highly transparent $Y_2O_3$ ceramics were produced using spark plasma sintering (SPS) at $1600^{\circ}C$ and 30 MPa for 5 min. When the SPS process was applied with various amounts of $La_2O_3$ as dopant. The specimen doped with 3 mol% $La_2O_3$ showed the highest density, and rapid particle growth and pore growth occurred, exhibiting that the relative density and average grain size are 99.2% and $17.2{\mu}m$, respectively. The specimen showed excellent transmittance of 79.44% in the visible light region (600 nm), resulting that $La_2O_3$ would be a useful dopant for improving the transmittance and mechanical properties of transparent $Y_2O_3$ ceramics produced with SPS.

• 한국분말재료학회지
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• 제5권1호
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• pp.57-63
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• 1998

The densification behaviors of rapidly solidified Al-Si alloys under high temperature processing were investigated. In general, it was difficult to establish optimum process variables for forging condition through experimentation, because this was costly and time consuming. In this paper, to overcome these problems, we compared the experimental result to the finite element analysis for forging processes of rapidly solidified Al-Si alloys. The results of these simulations helped understand the distribution of relative density during various forging processes. This information is expected to assist in improving rapidly solidified Al-Si alloys forging operations.

• 한국세라믹학회지
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• 제31권1호
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• pp.69-73
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• 1994

Si3N4 ceramics could be densified above 3.2g/㎤ with pressureless sintering at below 178$0^{\circ}C$ by coating Si3N4 and Y2O3 powder with an alumina sol. Substitution a portion of Al2O3 with AlN improved densification. Additional milling of the coated powder in large improvement in bending strength greater than 800 MPa (4-point).

• 한국분말재료학회지
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• 제4권4호
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• pp.283-290
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• 1997

$Ti_5Si_3$ intermetallics containing 0-6 wt% of Cu were made by reactive sintering (RS) under vacuum using elemental powder mixtures (Process 1), electro-pressure sintering (EPS) using RS'ed materials (Process2), and EPS using elemental powder mixtures (Process 3). Relatively low dense titanium silicides were gained by process 1, in which porosity decreased with increasing Cu content. For example, porosity changed from 42 to 19.4% with the increase in Cu content from 0 to 6 wt%, indicating that Cu is a useful sintering aid. The titanium silicides fabricated by Process 2 had a higher density than those by Process 1 at given composition, and porosity decreased with increasing Cu content. For example, porosity decreased from 38 to 6.8% with the change in Cu content from 0 to 6 wt%. A high dense titanium silicides were obtained by Process 3. In this Process, porosity decreased a little by Cu addition, and was almost insensitive to Cu content. Namely, about 9 or 7% of porosity was shown in 0 or 1-6 wt% Cu containing silicides, respectively. The hardeness increased by Cu addition, and was not changed markedly with Cu content for the silicides fabricated by Process 3. This tendency was considered to be resulted from porosity, hardening of grain interior by Cu addition, and softening of grain boundary by Cu-base segregates. All these results suggested that EPS using elemental powder mixtures (Process 3) is an effective processing method to achieve satisfactorily dense titanium silicides.

• 한국분말재료학회지
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• 제3권2호
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• pp.104-111
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• 1996

In order to obtain homogeneous and high quality products in powder compaction forging process, it is very important to control stress, strain, density and density distributions. Therefore, it is necessary to understand quantitatively the elasto-plastic deformation and densification behaviors of porous metals and metal powders. In this study, elasto-plastic finite element method using Lee-Kim's pressure dependent porous material yield function has been used for the analysis of three dimensional indenting process. The analysis predicts deformed geometry, stress, strain and density distribution and load. The calculated load is in good agreement with experimental one. The calculated results do not show axisymmetric distributions because of the edge effect. The core part which is in contact with the indentor and the outer diagonal edge part are in compressive stress states and the middle part is in tensile stress state. As a results, it can be concluded that three dimensional analysis is more realistic than axisymmetric assumption approach.

• 전자공학회논문지A
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• 제33A권7호
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• pp.171-175
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• 1996

Gate insulator for Si field emitter is usually formed by e-beam evaporation. However, the evaported oxide requires densification for a stable process and a reduction of gate leakage which results from its Si-rich and nonstoicheiometric structure. In this study, we have developed the process technology able to densify the evaporated oxide in H$_{2}$O ambient. Using this process, we have fabricted thefield emitter array with 625 emitters per pixel, of which gate hole diameter is 1.4.mu.m, for the pixel, anode current of 14.3.mu.A was extracted at a gate bias of 100V and gate leakage was about 0.27% of the total emission current.