• The Korean Journal of Ceramics
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• 제7권2호
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• pp.74-79
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• 2001

Alumina composite reinforced by chopped alumina fiber was fabricated by filter-pressing the fiber slurry followed by the infiltration of alumina slurry. The chopped fiber was coated with nickel by electroless plating method. The green samples were densified by hot-pressing. Microstructures were studied by SEM and the mechanical properties such as bending strength and fracture toughness were measured. The resulting mechanical properties were analyzed in relation with processing parameters such as preform density and resulting microstructures. The load-displacement curve of the specimen with Ni interlayer but without Ni inclusion showed brittle fracture mode due to the direct contact between matrix and fiber. The load-displacement curve of the specimen with Ni interlayer and Ni inclusion in the matrix which is introduced by high applied pressure during specimen preparation showed non-brittle fracture mode due to the fiber pull-out and dutile phases in the matrix.

• 한국분말재료학회지
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• 제9권1호
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• pp.43-49
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• 2002

Microstructural and mechanical characteristics of P/M 6061 Al alloy subjected to equal channel angular pressing (ECAP) were investigated. The P/M 6061 Al alloy had an intial grain size of approximately $20\mutextrm{m}$. An equiaxed ultra-fine grained structure with the mean grain size of $~50 \mutextrm{m}$ was obtained by four repetitive ECAP at 473 K. The microhardness of P/M 6061 Al alloy was drastically increased from about 40 Hv to 80 Hv by two repetitive ECAP at 373 K. However, the microhardness decreased with increasing ECAP temperature. The tensile stength of as-hot-pressed P/M 6061 Al alloy before ECAP was 95 MPa, whereas it increased to both 248 MPa after two repetitive ECAP at 373 K and 130 MPa after four repetitive ECAP at 473 K. The tensile properties of the ECAPed sample were compared with those of commercial cast 6061-O and 6061-T4 Al alloys.

• 한국분말재료학회지
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• 제9권1호
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• pp.11-18
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• 2002

The 6061 Al alloy based composites reinforced with 10 vol% SiC whiskers were prepared by powder metallurgy with the powders having the different sizes, i.e. < $30{\mu}m$ and > $30{\mu}m$ The composites were subjected to equal channel angular pressing (ECAP) at various conditions and the microstructural changes during ECAP were examined In the composites SiC whiskers were clustered and randomly aligned. The clusters were relatively well distributed in the composite with the smaller initial powder size. After ECAP, the clusters were aligned parallel to flow direction and became smaller. In addition, the shape of clusters was changed from irregular to round. The microstructure of the ECAPed samples were compared with those of the conventionally hot-extruded composites. The uniform microstructure and enhanced microhardness could be obtained by using the powders having the smaller size, decreasing ECAP temperature and repeating ECAP.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.1301-1302
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• 2006

Sintered composites of Al-8wt%Cu-10vol%SiCp were deformed by repressing or equal channel angular pressing(ECAP) at room temperature, $500^{\circ}C$ and $600^{\circ}C$. Repressing produced more densification than ECAP but resulted in much lower transverse rupture strengths. In both cases, deformation at room temperature and $500^{\circ}C$, resulted in much lower strengths than deformation at $600^{\circ}C$, and also caused the fracturing of some SiC particles. The higher bend strengths and less SiC fracturing at $600^{\circ}C$ are attributable to the presence of an Al-Cu liquid phase during deformation. The employment of copper coated SiC instead of bare SiC particles for preparing the composites was found not improving the properties.

• 한국세라믹학회지
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• 제26권2호
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• pp.267-275
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• 1989

YBa2Cu3O7-x oxide superconductors were fabricated by sintering and hotisostatic pressing (HIP), and their microstructures and properties were compared with each other. Thougha part of the second phase was observed along grain boundaries, their structures were consisted of single (123) phase and they had many porosities. But, porosities were remakably reduced by Hiping and the densification was brought about. The structure of (123) compound also showed a number of twins, which are typical of high Tc superconductors. The on-set temperature of YBa2Cu3O7-x compound sintered at 96$0^{\circ}C$ in oxygen and hipped at 88$0^{\circ}C$ was highest, but that shwoed 0 resistance at 87$^{\circ}$K, which is a little lower than the compound sintered at 96$0^{\circ}C$. HIP treatment also increased the critical current density of as-sintered compound. However, its value was low, which may be ascribed to the many pores of starting-sintered compact and partially to the second phase along grain boundaries.

• Journal of the Korean Wood Science and Technology
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• 제25권3호
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• pp.96-104
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• 1997

The objective of this research project was to develop the wooden footpath block to reuse of wood waste. Some physical and mechanical properties of the wooden block such as water absorption, thickness swelling, modulus of rupture, internal bond, density profile and impact resistance were studied. Water absorption and thickness swelling of the wooden block were greatly reduced when the wooden block was pressed inside the forming device than by conventional hot pressing. Also, Modulus of rupture and internal bond of the wooden block were increased greatly when the pressing was completed inside the forming device. The density profile of the wooden block was improved up to 93.5%, minimum to average density ratio. The wooden block manufactured in this study have excellent physical and mechanical prperties in comparison with existing wood based materials. So, these wooden blocks are applicable to footpth block or other exterior members.

• 펄프종이기술
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• 제46권4호
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• pp.62-68
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• 2014

The application of conifer leave to the papermaking process as a functional organic filler was investigated in this study. The powder of the conifer leave after hot water extraction for the functional extract, such as phytoncide, was applied to OCC stock. The comparison between the commercial wood flour and the conifer leave powder as organic filler for OCC paper were conducted with various wet pressing conditions. The amount of the water removal by the wet pressing process and the bulk of handsheet were increased by the addition of the wood flour and the conifer leave powder, although the tensile strength was decreased. At the higher pressure condition of the wet pressing, the wet pressing efficiency was greatly increased by the wood flour and the conifer leave powder. There was a little difference in the performance of the wood flour and the conifer leave powder as an organic filler. Those results showed the conifer leave powder could be an alternative resource to the wood powder for papermaking organic filler.

• 한국재료학회지
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• 제9권8호
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• pp.817-824
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• 1999

$Al_2$$O_3$-SiC 화합물 분말이 $SiO_2$, A1 그리고 C 분말들을 원료분말로 하여 SHS(self-propagating High-temperature Synthesis)법에 의해 제조되었다. 원료 분말에서의 몰비, 성형압력, 반응물의 초기온도의 영향이 생성물과 연소과정에 대해 연구되었다. $SiO_2$/A1/C계의 자전연소합성은 낮은 연소온도 때문에 $400^{\circ}C$ 이상으로 예열되어야 한다. 연소반응의 결과로서 최종생성물의 순도는 반응물의 순도보다 높았다. 이 계에서 $SiO_2$:Al:C의 적당한 몰비는 3.0:4.0:6.0이었고, free carbon은 30min 동안 $650^{\circ}C$에서 배소함으로써 제거되었다. 본 연구에서 상압소결은 $1700^{\circ}C$에서 powder bed를 사용한 표본의 분해를 제어하고 치밀한 소결체를 얻는데 매우 효과적이었다. hot-pressing으로 생성된 소결체는 이론비교밀도의 약 98%이었다.

• 한국재료학회지
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• 제10권4호
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• pp.312-316
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• 2000

HIP처리가 가스터빈 고정익 등 고온부품에 적용되는 열차폐 코팅층의 접착강도 및 고온특성에 미치는 영향을 조사하였다. 시편은 IN738LC 초합금 표면에 8wt%Y$_2$O$_3$-$ZrO_2$분말을 플라즈마 용사법으로 코팅한 후 $1200^{\circ}C$, 100MPa의 고온, 고압에서 4시간 동안 HIP 처리하여 준비하였다. 실험결과 HIP 처리된 코팅의 경우 미세균열과 기공이 상당량 감소하였으며 EDX분석을 통해 계면에서 원자간 상호확산이 발생한 것을 확인하였다. 이러한 코팅층의 치밀화 및 상호확산으로 인해 HIP처리된 코팅층의 접착강도는 48% 이상 크게 증가하였으며 조직 또한 균질화 되었다. 반면 가열과 냉각이 반복되는 환경에서 코팅층의 내구력은 HIP 처리된 경우가 다소 저하되었다. 이는 코팅과 모재와의 열팽창 차이로 인한 변형을 완화시켜주는 기공과 미세균열이 감소되었기 때문으로 판단된다.

• 한국세라믹학회지
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• 제29권5호
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• pp.410-418
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• 1992

Si3N4, AlN and Y2O3 powder mixtures of the Y0.1(Si, Al)12(N, O)16 composition were hot-pressed at 1900℃ for 0 to 60 min under 30 MPa in order to fabricate the partially-stabilized α-Sialon ceramics (X=0.1). Room and high temperature flexural strengths of the specimens were compared with those of Si3N4-5 wt%Y2O3, Si3N4-5 wt%Y2O3-2 wt%Al2O3, and β-Sialon (Z=0.5) ceramics. The flexural strength of the α-Sialon ceramics which was hot-pressed for 15 min showed the highest value of 820 MPa at 1400℃ that is relatively higher temperature. It is guessed that a little amount of glassy phase existed in grain boundary because Y2O3 and AlN components were incoperated in Si3N4 grains, or transient liquid phase sintering, and microstructure with the smaller grain size and the interlocked grains of α'-and β-Si3N4 was obtained by the hot-pressing at high temperature of 1900℃ for the short time (15 min).