반응 금속 침투법에 의한 $Al/Al_2O_3$복합체의 제조 및 기계적 특성

윤영훈,홍상우,최성철 한국결정성장학회 2001 한국결정성장학회지 Vol.11 No.6

뮬라이트 preform과 비정질 실리카를 알루미늄 용융체에서 $1100^{\circ}C$, 5시간 동안 반응시켜 $Al/Al_2O_3$복합체가 제조되었다. 뮬라이트 preform과 알루미늄 용융체 간의 화학적 반응은 상호 연결된 미세구조를 형성하였다. $Al/Al_2O_3$복합체의 금속의 양은 뮬라이트 preform의 소결 온도($1600^{\circ}C$, $1625^{\circ}C$, $1650^{\circ}C$, $1700^{\circ}C$)에 따른 겉보기 기공율의 변수로서 조절되었으며, 복합체의 기계적 특성들은 알루미늄 양에 따라 조사되었다. $1600^{\circ}C$ 이상의 온도에서 소결된 뮬라이트 preform은 침투된 알루미늄 용융체와 화학반응을 이루었으나, $1600^{\circ}C$에서 소결된 뮬라이트 소결체는 알루미늄 용융체에 대해 젖음이 이루어지지 않아 화학반응이 진행되지 않았다. 알루미늄 용융체의 침투 방향에 따른 복합체의 기계적 특성에 대한 영향은 알루미늄 용융체의 수직, 평행한 침투 방향 패턴의 두 가지 다른 모델들에 의해 고려되었다. $Al/Al_2O_3$복합체에서 알루미늄의 양의 증가에 따라 파괴강도는 감소하였으며, 파괴인성은 증가하는 경향을 나타냈다.$ Al/Al_2O_3$복합체의 미세구조는 금속의 침투 방향에 의해 결정되었지만, 복합체의 파괴강도와 파괴인성은 금속 침투 방향에 대한 의존성은 나타내지 않았다. $Al/Al_2O_3$composites were prepared from the reaction of mullite preforms and amorphous silica in aluminum melt at $1100^{\circ}C$ for 5 hrs. The chemical reaction between mullite preform and aluminum melt has formed the interconnected microstructure. The metal content of $Al/Al_2O_3$composite was controlled with the variable of the apparent porosity according to the sintering temperature of mullite preforms; $1600^{\circ}C$,$ 1625^{\circ}C$, $1650^{\circ}C$ and $1700^{\circ}C$, the mechanical properties of $Al/Al_2O_3$composite were investigated upon the content of Al. The mullite preform sintered above $1600^{\circ}C$ showed the chemical reaction with the penetrated Al melt, but the mullite sintered at $1600^{\circ}C$ didnt react with aluminum melt owing to the non-wetting of Al melt/mullite preform. The influences of penetration direction on the mechanical properties of composites were considered with the two different models of the perpendicular pattern and the parallel pattern to the direction of Al melt penetration. With the increase of Al metal penetration content, the fracture strength of $Al/Al_2O_3$composite decreased and the fracture toughness of composite increased. The microstructure of $Al/Al_2O_3$composite was determined by the direction of metal penetration, but the fracture strength and fracture toughness of composite didnt show the dependence on metal penetration direction.

방전 플라즈마 소결법에 의한 다공성 육티탄산 칼륨 휘스커 프리폼의 제조

이장훈,조동철,조원승,이지환,Lee, Chang-Hun,Cho, Dong-Choul,Cho, Won-Seung,Lee, Chi-Hwan 한국세라믹학회 2002 한국세라믹학회지 Vol.39 No.12

방전 플라즈마 소결법을 이용하여 건전한 강도를 갖는 다공성 육티탄산 칼륨 휘스커 프리폼을 제조하기 위해서, 여러 소결온도 조건하에서 휘스커 프리폼을 제조한 후 기공률과 압축강도 등을 조사하였다. 그 결과, 소결 온도 900∼950${\circ}C$, 유지시간 10분, 압축하중 40 MPa, 승온속도 50${\circ}C$/min, on-off pulse type 12:2의 조건에서 높은 기공률을 갖는 프리폼을 제조할 수 있었다. 이상의 최적조건에서 제조한 프리폼은 기공률이 15∼37% 범위임에도 불구하고 174∼266 MPa의 비교적 높은 압축강도를 나타내었다. 이와 같은 강도의 향상은 휘스커간의 스파크 플라즈마 방전 및 자기 발열작용의 영향에 기인한 것으로 생각된다. 900${\circ}C$ 이하에서 제조한 휘스커 프리폼의 강도 레벨은 80∼100MPa로 900∼950${\circ}C$의 온도조건에서 제조한 프리폼에 비해 2배 이하의 낮은 값을 나타내었다. 1000 ${\circ}C$에서의 압축강도는 523 MPa로 가장 높은 강도값을 나타내었으나, 약 5%의 낮은 기공률을 나타내었다. 이상의 결과로부터, 비교적 강도가 높고 다공성의 티탄산 칼륨 휘스커를 제조하는데 있어 방전 플라즈마 소결법이 효과적인 것으로 생각된다. In order to develope the porous $K_2Ti_6O_13$ whisker preform with good strength, the pore characteristics and compressive strength were investigated as a function of spark plasma sintering temperature. As a result, high porous whisker preform were successfully fabricated by sintering at 900∼950${\circ}C$ for 10 min under a pressure of 40 MPa, heating rate of 50${\circ}C$/min and on-off pulse type of 12:2. The whisker preform prepared under above optimum condition showed relatively high compressive strength of 174∼266 MPa, despite of high porosity ranging from 15% to 37%. This improvement in strength was considered to be mainly due to the spark-plasma discharges and the self-heating action between whiskers. The compressive strength of whisker preform, fabricated at sintering temperature less than 900${\circ}C$, showed 80∼100 MPa. This is low strength level less than one half times compared with whisker preform fabricated at 900∼950${\circ}C$. The whisker preform fabricated at 1000${\circ}C$ showed the highest compressive strength of 523 MPa, but resulted in low porosity of ∼5%. Based on above results, it was considered that spark plasma sintering was an effective method for developing high strength and porosity of whisker preform.

TR단존 공정의 적정 예비성형체 설계에 관한 연구

송민철(M. C. Song),김대순(D. S. Kim) 한국소성가공학회 2012 한국소성가공학회 학술대회 논문집 Vol.2012 No.5

The purpose of this study is to design the proper preform for TR forging, a closed-die forging process in order to secure the dimensional accuracy of the forged crank throw under the same material volume, die and forging load. Considering the kinematic characteristics of TR device and the target forged shape of crank throw, the analytical design of preform could have a various choice of geometry variables such as the pin diameter of preform, volumeallo cation and angle between pin and web of preform. The effect of the geometry variables on the dimensions of the crank throw was evaluated by using FEA in order to determine the geometry detail of the preform. According to FEA results, it can be concluded that the pin of the preform should be controlled as same as volume of the pin of the final product. The web diameter of preform should be also maximized as far as the web length of the preform should be controlled smaller than the web thickness of the target forged crank throw.

광섬유 생산공정용 퍼니스 내의 모재 가열 및 유리섬유 인출에 대한 열전달 해석

김경진(K. Kim),김동주(D. Kim),곽호상(H.S. Kwak) 한국전산유체공학회 2011 한국전산유체공학회 학술대회논문집 Vol.2011 No.5

Glass fiber drawing from a silica preform is one of the most important processes in optical fiber manufacturing. High purity silica preform of cylindrical shape is fed into the graphite furnace, and then a very thin glass fiber of 125 micron diameter is drawn from the softened and heated preform. A computational analysis is performed to investigate the heat transfer characteristics of preform heating and the glass fiber drawing in the furnace. In addition to the dominant radiative heating of preform by the heating element in the furnace, present analysis also includes the convective heat transport by the gas flowing around the preform that experiences neck-down profile and the freshly drawn glass fiber at high fiber drawing speed. The computational results present the effects of gas flow on the temperature of preform and glass fiber as well as the neck-down profile of preform.

High-toughness natural polymer nonwoven preforms inspired by silkworm cocoon structure

Kwak, Hyo Won,Eom, Jungju,Cho, Se Youn,Lee, Min Eui,Jin, Hyoung-Joon Elsevier 2019 INTERNATIONAL JOURNAL OF BIOLOGICAL MACROMOLECULES Vol.127 No.-

<P><B>Abstract</B></P> <P>As the interest in environmentally friendly materials and concerns regarding depletion of petroleum resources has increased, the research on natural polymers is being actively pursued. Among the various materials based on natural polymeric resources, the interest in using natural fibers in bio-composites has grown due to their lightweight, non-toxicity, low cost, and abundance. However, the lack of interfacial adhesion between filaments and poor water resistance make the use of natural fiber-based polymer composites less attractive. To overcome these drawbacks, formaldehyde-based synthetic binders have been used. However, this requires an additional synthesis of the binder, and potential toxicity problems exist. In this work, robust and rigid natural polymer nonwoven preforms were prepared by mixing jute fibers with silk sericin (SS). SS was employed as a natural facile binder and the strong binding between jute fibers and SS resulted in remarkable enhancements in tensile strength, elongation, and toughness, which increased up to 539.1, 385.7, and 1943.8%, respectively, compared with the pristine jute nonwoven. In addition, the dense and rigid structure obtained through SS coating ensured the structural stability of the nonwoven preforms in moisture environments. Silkworm cocoon-structured natural polymer nonwoven preforms with excellent mechanical strength and higher physical stability may have more potential utilization in the composite material fields.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Silkworm cocoon-like natural fiber-based nonwoven preforms were fabricated. </LI> <LI> Sericin strongly bonded interface between each jute filament. </LI> <LI> Sericin dramatically improves the mechanical properties of jute nonwoven preforms. </LI> <LI> The water resistance of nonwoven preforms was obtained by sericin binder. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

An Evaluation on Preform Process and Compressive Strength of Whisker reinforcement

Huawei Rong,HyunJun Lee,SunChul Huh,WonJo Park 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5

Nowadays, many components in aerospace and automobile industry require lightness and high strength. And existent metal is confronted by limitation. Accordingly, there are many studies on Metal Matrix Composite (MMC) taking more excellent characteristics than existent metal material. MMC can obtain mechanical characteristics of application purposes that a single material is difficult to obtain. MMC is manufactured from preform by pressure casting. The pressure causes deformation or fault of manufactured MMC and preform. Accordingly, in order to maintain the preform shape enduring infiltration pressure, preform manufacture have to consider influence of binder and sintering temperature. This study manufactured preform by Aluminum Borate Whisker and researched effect of compressive strength on binder and sintering temperature of preform.

파워 소자의 고속 다이 접합을 위한 5 μm Cu@Sn 입자 기반 프리폼의 천이액상 소결접합 특성

한병조,조상호,전강록,이종현 대한금속·재료학회 2024 대한금속·재료학회지 Vol.62 No.1

To ensure the high-temperature stability of a bondline under next-generation power devices suchas SiC semiconductors, a die bonding test was performed by transient liquid-phase (TLP) sinter-bonding usinga Sn-coated Cu (Cu@Sn) particle-based preform. Compared to the existing 20 min-bonding result using a 30μm Cu@Sn particle-based preform, a 5 μm Cu@Sn particle-based preform was used to significantly reducethe bonding time to 5 min, and the optimal levels of the amount of Sn in the Cu@Sn particles, the thicknessesof Sn surface finish layers on the chip and substrate, and compression pressure during the bonding wereinvestigated. The Sn content in the Cu@Sn particles significantly changed the microstructure, including theporosity of the prepared preform. The preform porosity of 0.01% was confirmed after the formation of sufficientSn shells with an average thickness of about 602 nm at Sn 30 wt%. In addition, in the preform with Sn 30wt% content, the Sn phase was almost depleted after 3 min after annealing at 250 °C. The Sn finish layerwas evaluated in the thickness range of 0.63−4.12 μm, and it was observed that the shear strength of theformed bondline tended to increase with increasing pressure for all Sn layer thicknesses. In particular, whenthe bonding was carried out at a pressure of 2 MPa using a dummy Cu chip and substrate coated with a 1.53μm thick Sn layer, the best shear strength value of 36.89 MPa was achieved. In this case, all the Sn phasestransformed into intermetallic compound phases of Cu6Sn5 and Cu3Sn, and all the phases formed within thebondline, including Cu, exhibited high melting-point characteristics. Therefore, it was determined that therewould be no remelting of the bondline or a drastic decrease in mechanical properties in a high-temperatureenvironment below 300 oC, as initially intended. By increasing the content of the Sn shell up to 30 wt%, itwas possible to achieve a nearly full density (porosity: 0.3%) bondline structure, due to the rearrangementbehavior of particles, by maintaining liquid Sn for a long time during the bonding process. In conclusion, theoptimal Sn finish thickness was determined to be at the level of 1.5 μm, and the optimal pressure was at thelevel of 2 MPa. The short bonding time of 5 min represents a significant advance in TLP bonding processes,and it is expected to contribute to a substantial improvement in the die bonding of future SiC power devices.

광섬유 생산용 유리섬유 인출공정에 대한 복사 열전달 해석

김경진(K. Kim),김동주(D. Kim),곽호상(H.S. Kwak) 한국전산유체공학회 2011 한국전산유체공학회지 Vol.16 No.1

In this study, the glass fiber drawing from a silica preform in the furnace for the optical fiber manufacturing process is numerically simulated by considering the radiative heating of cylindrically shaped preform. The one-dimensional governing equations of the mass, momentum, and energy conservation for the heated and softened preform are solved as a set of the boundary value problems along with the radiative transfer approximation between the muffle tube and the deformed preform shape, while the furnace heating is modeled by prescribing the temperature distribution of muffle tube. The temperature-dependent viscosity of silica plays an important role in formation of preform neck-down profile when the glass fiber is drawn at high speed. The calculated neck-down profile of preform and the draw tension are found to be reasonable and comparable to the actual results observed in the optical fiber industry. This paper also presents the effects of key operating parameters such as the muffle tube temperature distribution and the fiber drawing speed on the preform neck-down profile and the draw tension. Draw tension varies drastically even with the small change of furnace heating conditions such as maximum heating temperature and heating width, and the fine adjustment of furnace heating is required in order to maintain the appropriate draw tension of 100~200 g.

Radial flow advancement in multi-layered preform for resin transfer molding

윤재륜,Y. S. Song,K. S. Shin 한국유변학회 2006 Korea-Australia rheology journal Vol.18 No.4

Rapid flow advancement without void formation is essential in the liquid composite molding (LCM) such as resin transfer molding (RTM) and vacuum assisted resin transfer molding (VARTM). A highly permeable layer in multi-layered preform has an important role in improvement of the flow advancement. In this study, a multi-layered preform which consists of three layers is employed. Radial flow experiment is carried out for the multi-layered preform. A new analytic model for advancement of flow front is proposed and effective permeability is defined. The effective permeability for the multi-layered preform is obtained analytically and compared with experimental results. Compaction test is performed to determine the exact fiber volume fraction of each layer in the multi-layered preform. Transverse permeability employed in modeling is measured experimentally unlike the previous studies. Accurate prediction of flow advancement is of great use for saving the processing time and enhancing product properties of the final part.

Radial flow advancement in multi-layered preform for resin transfer molding

Shin, K.S.,Song, Y.S.,Youn, J.R. The Korean Society of Rheology 2006 Korea-Australia rheology journal Vol.18 No.4

Rapid flow advancement without void formation is essential in the liquid composite molding (LCM) such as resin transfer molding (RTM) and vacuum assisted resin transfer molding (VARTM). A highly permeable layer in multi-layered preform has an important role in improvement of the flow advancement. In this study, a multi-layered preform which consists of three layers is employed. Radial flow experiment is carried out for the multi-layered preform. A new analytic model for advancement of flow front is proposed and effective permeability is defined. The effective permeability for the multi-layered preform is obtained analytically and compared with experimental results. Compaction test is performed to determine the exact fiber volume traction of each layer in the multi-layered preform. Transverse permeability employed in modeling is measured experimentally unlike the previous studies. Accurate prediction of flow advancement is of great use for saving the processing time and enhancing product properties of the final part.