• 한국분말재료학회지
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• 제10권2호
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• pp.103-107
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• 2003

Aluminum-based $Al/Al_2O_3$ composites were fabricated by a powder-in sheath rolling method. A stainless steel tube with outer diameter of 12 mm and wall thickness of 1 mm was used as a sheath. A mixture of aluminum powder and $Al_2O_3$ particles of which volume content was varied from 5 to 20%, was filled in the tube by tap filling and then rolled by 75% reduction in thickness at ambient temperature. The rolled specimen was then sintered at 56$0^{\circ}C$ for 0.5 h. The mixture of Al powders and $Al_2O_3$ particles was successfully consolidated by the sheath rolling. The $Al/Al_2O_3$ composite fabricated by the sheath rolling showed a recrystallized structure, while unreinforced Al powder compact fabricated by the same procedure showed a deformed structure. The unreinforced Al powder compact was characterized by a deformation (rolling) texture of which main component is {112}<111>, while the $Al/Al_2O_3$ composite showed a mixed texture oi deformation and recrystallization. The sintering resulted in recrystallization in Al powder compact and grain growth in the composite.

• 한국재료학회지
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• 제24권5호
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• pp.236-242
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• 2014

Fabrication of reaction-bonded $Al_2O_3$ (RBAO) ceramics using Al-Zn-Mg alloy powder was studied in order to improve traditional RBAO ceramic processing using Al powder. The influence on reaction-bonding and microstructure, as well as on physical and mechanical properties, of the particulate characteristics of the $Al_2O_3$-Al alloy powder mixtures after milling, was revealed. Variation of the particulate characteristics of this $Al_2O_3$-Al alloy powder mixture with milling time was reported previously. To start, the $Al_2O_3$-Al alloy powder mixture was milled, reaction-bonded, post-sintered, and characterized. During reaction-bonding of the $Al_2O_3$-Al alloy powder mixture compacts, oxidation of the Al alloy took place in two stages, that is, there was solid- and liquid-state oxidation of the Al alloy. The solid-state oxidation exhibited strong dependence on the density of surface defects on the Al-alloy particles formed during milling. Higher milling efficiency resulted in less participation of the Al alloy in reaction-bonding. This was because of its consumption by chemical reactions during milling, and subsequent powder handling, and could be rather harmful in the case of over-milling. In contrast to very little dependence of oxidation of the Al alloy on its particle size after milling, the relative density, microstructure, and flexural strength were strongly dependent on particle size after milling (i.e., on milling efficiency). The relative density and 4-point flexural strength of the RBAO ceramics in this study were ~98% and ~365 MPa, respectively, after post-sintering at $1,600^{\circ}C$.

• 한국세라믹학회지
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• 제32권3호
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• pp.331-340
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• 1995

Microwave (Hybrid) Heating (MHH) was used to oxidize and sinter Al-Al2O3 powder mixture. For 25 v/o Al specimen and 35 v/o Al specimen, the total processing to produce low-shrinkage reaction bonded alumina was carried out within 1 hour even though conventional furnace process took more than 10 hours. Compared with conventional fast firing process, MHH process increased more than 40% oxidation at the same temperature, and these high oxidation rates were thought to be caused by the surface ohmic current on Al particles.

• 한국세라믹학회지
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• 제32권2호
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• pp.227-233
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• 1995

By using homestyle microwave oven, Al-Al2O3 powder mixture could be oxidized and sintered into Al2O3 body. The differences in powder characteristics among the differently processed raw materials affect the oxidation and sintering behaviours, and these effects were more pronounced in case of microwave oven than of conventional furnace. Al-Al2O3 powder mixture was oxidized and sintered within 2hrs, which could save both processing time and energy.

• Advances in materials Research
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• 제5권4호
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• pp.263-277
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• 2016

Mechanical properties of $Al/Al_2O_3$ and $Al/B_4C$ composites prepared through powder metallurgy are estimated up to 50% $Al_2O_3$ and 35% $B_4C$ weight fractions using micromechanics models and experiments. The experimental Young's modulus up to 0.40 weight fraction of ceramic is found to lie closely between Ravichandran's/Hashin-Shtrikman lower/upper bounds, and close to self consistent method/Miller and Lannutti method/modified rule of mixture/fuzzy logic method single value predictions. Measured Poisson's ratio lies between rule of mixture/Ravichandran lower and upper bound/modified Ravichandran upper bounds. Experimental Charpy energy lies between Hopkin-chamis method/equivalent charpy energy/Ravichandran lower limit up to 20%, and close to the reciprocal rule of mixture for higher $Al_2O_3$ content. Rockwell hardness (RB) and Micro-hardness of $Al/Al_2O_3$ are closer to modified rule of mixture predictions.

• 한국세라믹학회지
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• 제34권1호
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• pp.1-6
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• 1997

가정용 전자 렌지를 사용하여, SiO2-Al 분말 성형체로 이루어진 시편을 질화분위기에서 점화시켰다. 연소파대가 전파되면서 미반응물없이 Si와 AIN와 Al2O3를 석출하였으며, 냉각과정을 거치지 않고 곧바로 석출물들이 마이크로파를 흡수하여 고온에서 가열되어서 사이알론상을 합성하였다. 전자렌지안에서 SiO2-Al 분말성형체로부터 사이알론상들의 합성율은 일반적인 로내에서의 합성율보다 높았고, 공정시간이 불과 1시간내외에 이어서 에너지와 제조경비를 절약할 수 있었다.

• 한국분말재료학회지
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• 제10권2호
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• pp.97-102
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• 2003

The powder-in sheath rolling was applied to the fabrication of $Al/Al_2O_3$ composite. A stainless steel tube with outer diameter of 12 mm and wall thickness of 1 mm was used as a sheath. Mixture of aluminum powder and $Al/Al_2O_3$ particles of which volume content was varied from 5 to 20 vol.% was filled in the tube by tap filling and then rolled to 75% reduction at ambient temperature. The re]]ed specimen was sintered at 56$0^{\circ}C$ for 0.5 hr. The $Al/Al_2O_3$ composite fabricated by the sheath rolling and subsequent sintering showed the relative density higher than 0.96. The tensile strength of the composite increased with the volume content of $Al_2O_3$ particles, and it reached a maximum of 90 MPa which is 1.5 times higher than unreinforced material. The elongation decreased with the volume content of $Al_2O_3$ particles. It is concluded that the powder-in sheath rolling is an effective method for fabrication of $Al/Al_2O_3$ composite.

• 한국분말재료학회지
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• 제7권1호
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• pp.35-41
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• 2000

Al2O3$.$SiC particle was prepared was prepared by the self-propagting high temperature sYthesis(SHS) process from a mixture of SiO2, Al and C powders, The fabricated Al2O3$.$SiC particle was applied to 2024Al/(Al2O3$.$SiC)pcomposite as a reinforcement. Aluminum matix composites were fabricares by the powder extrusion method using the synthesized Al2O3$.$SiC particle and commercial 2024Al powder. Theoptimum preparation conditions for Al2O3$.$SiC partticle by SHS process were described. The influence of the Al2O3$.$SiC voiume fraction on the mechanical was composite was also discussed. Despite adiabatic temperature was about 2367K, SHs reaction was completed not by itself, but by using pre-heating. Mean particle size of final particle synthesized was 0.73 ${\mu}$m and most of the particle was smaller than 2${\mu}$m. Elastic modulus and tensile strength of the composite increased with increase the volume fraction of reinforcement but, tensile strength depreciated at 30 vol% of reinforcement.

• 한국분말재료학회지
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• 제8권3호
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• pp.157-162
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• 2001

An optimum route to fabricate the ferrous alloy dispersed $Al_2O_3$ nanocomposites such as $Al_2O_3$/Fe-Ni and $Al_2O_3$/Fe-Co with sound microstructure and desired properties was investigated. The composites were fabricated by the sintering of powder mixtures of $Al_2O_3$ and nano-sized ferrous alloy, in which the alloy was prepared by solution-chemistry routes using metal nitrates powders and a subsequent hydorgen reduction process. Microstructural observation of reduced powder mixture revealed that the Fe-Ni or Fe-Co alloy particles of about 20 nm in size homogeneously surrounded $Al_2O_3$, forming nanocomposite powder. The sintered $Al_2O_3$/Fe-Ni composite showed the formation of Fe$Al_2O_4$ phase, while the reaction phases were not observed in $Al_2O_3$/Fe-Co composite. Hot-pressed $Al_2O_3$/Fe-Ni composite showed improved mechanical properties and magnetic response. The properties are discussed in terms of microstructural characteristics such as the distribution and size of alloy particles.

• 한국세라믹학회지
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• 제21권4호
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• pp.327-332
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• 1984

Proper amount of $Al_2O_3$ must be added to increase the yield of mullite which is formed from free silica decomposed from kaolin. The previous study has suggested that Al powder may be a good $Al_2O_3$ supply source at 1400~150$0^{\circ}C$. In this study the application of Al powder is discussed about its mullitization behavior in the higher temperature range of 1500~175$0^{\circ}C$ the results of which compared with those obtained from the reactive $Al_2O_3$ and activated $Al_2O_3$. The oxdation and reaction stages of Al powder were analyzed by DTA crystal growth andmorphology of the mullite were observed by SEM and the yields of the mullite were compared according to their solubilities in HF solution.