• Journal of Powder Materials
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• v.9 no.1
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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.

• Journal of Powder Materials
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• v.9 no.1
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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.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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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.

• Journal of the Korean Ceramic Society
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• v.26 no.2
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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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• v.25 no.3
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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.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.46 no.4
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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.

• Korean Journal of Materials Research
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• v.9 no.8
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• pp.817-824
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• 1999

The $Al_2$$O_3$-SiC composite powder was prepared by Self-propagating High-Temperature Synthesis(SHS) process using $SiO_2$Al and C powders as raw material. The effects of the molar ratio in raw material, compaction pressure, initial temperature of reactants on the products and combustion process were studied. Self-propagating high temperature synthesis of $SiO_2$/Al/C system should be preheated above $400^{\circ}C$ owing to the low combustion temperature. As the result of the combustion reaction, the purity of final product became better than that of reactants. In this system, the optimum molar ratio of $SiO_2$:Al:C was 3.0:4.0:6.0. The free carbon was removed by roasting at $650^{\circ}C$ for 30min. In this study, pressureless sintering was very dffective both for controlling the disintegration of specimen with powder bed and for obtaining dense sintered-body at $1700^{\circ}C$. The sintered-body produced with hot-pressing was about 98% of the theoretical relative density.

• Korean Journal of Materials Research
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• v.10 no.4
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• pp.312-316
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• 2000

A study has been made to investigate the effects of hot isostatic pressing(HIP ping) on bond strength and elevated temperature characteristics of thermal barrier coating(TBC). The specimens were prepared by HIPping of TBC which is composed of the ceramic top coat(8wt%$Y_2$$O_3$-$ZrO_2$) and the metallic bond coat on the matrix of IN738LC superalloy. The results showed that the porosity and microcracks in the ceramic top coat of TBC were significantly decreased by HIP. As a result, the bond strength of the HIPped coating was increased above 48% compared to that of as-coated specimen and microstructure was homogenized. It was found that the thermal cycle resistance of HIPped coating was inferior to that of as-coated specimen. It was considered that this result was mainly caused by the reduction of internal defects in the top coat layer which could play a role in relaxing the thermal stress due to a large difference in thermal expansion between TBC and matrix.

• Journal of the Korean Ceramic Society
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• v.29 no.5
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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).

• Transactions of Materials Processing
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• v.23 no.7
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• pp.425-430
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• 2014

The aim of the current study was to predict the plastic deformation behavior of a heated slab during hot rough rolling. FE-simulations were performed to investigate the metal flow and to locate the position of surface material from the slab through the rough rolling and onto the strip, using a material point tracking technique. In addition, experimental hot rolling trials were conducted where artificial defects were impressed onto a heated slab in order to validate the FE-simulation results. The simulated results show the same tendency of deformation behavior as the experimental measurements. The movement of slab defects from the side surface towards the strip center is directly linked to the extent of lateral spread during the rolling.