• Journal of the Korean Ceramic Society
• /
• v.35 no.9
• /
• pp.939-944
• /
• 1998

The formation microstructure and properties of novel ceramic composite materials by active filler con-trolled polymer pyrolysis were investigated. Polymethlsiloxane filled with W is of particular interested be-cause of the formation of ceramic bonded hard materials (WC-$W_{2}C$-$S_{1}OC$) for wear resistant applications. Highly metal-filled polymer suspensions were prepared and their conversion to ceramic composites by an-nealing in $N_{2}C$ atmosphere at 1000-$1600^{\circ}C$ were studied. Dimensional change porosity and phase distribution (filler network) were analyzed and correlated to the resulting material properties. Microcrystalline com-posites with the filler reaction products embedded to the resulting material properties. Microcrystalline com-posites with the filler reaction products embedded in a silicon oxycarbide glass matrix were produced. De-pending on the pyrolysis conditions ceramic composites with a density up to 95 TD% a hardness of 7-8.8GPa Yong's modulus of 220-230 GPa a fracture toughness of 6-6.8$MPam^{1/2}$ and a flexual strength of 380-470 MPa were obtained.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.13 no.5
• /
• pp.235-240
• /
• 2003

The development of large area GaN substrates is one of important issues in expanding of GaN-based applications. In order to investigate the possibility, GaN thick films were grown by a sublimation technique, using MOCVD-GaN films grown on a sapphire as a seed-crystal substrate and a commercial GaN powder as a source material. The pressure in chamber under the fixed flow rate of $N_2$ gas and $NH_3$ gas was kept at 1 atmosphere and the effects of the various processing parameters such as the distance between source material and seed crystal, the temperature of top- and bottom heater and the growth time during the growth of GaN thick film were investigated. The growth feature and microstructure of the GaN thick films were observed by SEM and XRD. The optical bandgap properties and the defects were evaluated by the PL measurement. By these results, the growth conditions such as the distance between the GaN source and the seed substrate, the growth temperature and the growth time were determined for the satisfied growth of GaN thick films.

• Korean Journal of Materials Research
• /
• v.21 no.5
• /
• pp.263-267
• /
• 2011

The present study was carried out to evaluate the microstructural and mechanical properties of cross-roll rolled pure copper sheets, and the results were compared with those obtained for conventionally rolled sheets. For this work, pure copper (99.99 mass%) sheets with thickness of 5 mm were prepared as the starting material. The sheets were cold rolled to 90% thickness reduction and subsequently annealed at $400^{\circ}C$ for 30 min. Also, to analyze the grain boundary character distributions (GBCDs) on the materials, the electron back-scattered diffraction (EBSD) technique was introduced. The resulting cold-rolled and annealed sheets had considerably finer grains than the initial sheets with an average size of 100 ${\mu}M$. In particular, the average grain size became smaller by cross-roll rolling (6.5 ${\mu}M$) than by conventional rolling (9.8 ${\mu}M$). These grain refinements directly led to enhanced mechanical properties such as Vickers micro-hardness and tensile strength, and thus the values showed greater increases upon cross-roll rolling process than after conventional rolling. Furthermore, the texture development of <112>//ND in the cross-roll rolling processed material provided greater enhancement of mechanical properties relative to the case of the conventional rolling processed material. In the present study, we systematically discuss the enhancement of mechanical properties in terms of grain refinement and texture distribution developed by the different rolling processes.

• Korean Journal of Materials Research
• /
• v.23 no.9
• /
• pp.501-509
• /
• 2013

To evaluate the development of the microstructure and mechanical properties on surface modified and post-heattreated Inconel 718 alloy, this study was carried out. A friction stir process as a surface modification method was employed, and overlap welded Inconel 718 alloy as an experimental material was selected. The friction stir process was carried out at a tool rotation speed of 200 rpm and tool down force of 19.6-39.2 kN; post-heat-treatment with two steps was carried out at $720^{\circ}C$ for 8 h and $620^{\circ}C$ for 6 h in vacuum. To prevent the surface oxidation of the specimen, the method of using argon gas as shielding was utilized during the friction stir process. As a result, applying the friction stir process was effective to develop the grain refinement accompanied by dynamic recrystallization, which resulted in enhanced mechanical properties as compared to the overlap welded material. Furthermore, the post-heat-treatment after the friction stir process accelerated the formation of precipitates, such as gamma prime (${\gamma}^{\prime}$) and MC carbides, which led to the significant improvement of mechanical properties. Consequently, the microhardness, yield, and tensile strengths of the post-heat-treated material were increased more than 110%, 124% and 85 %, respectively, relative to the overlap welded material. This study systematically examined the relationship between precipitates and mechanical properties.

• Journal of Advanced Marine Engineering and Technology
• /
• v.29 no.8
• /
• pp.891-898
• /
• 2005

Inertia welding is a solid-state welding process in which butt welds in materials are made in bar and in ring form at the joint race, and energy required lot welding is obtained from a rotating flywheel. The stored energy is converted to frictional heat at the interface under axial load. The quality of the welded joint depends on many parameters, including axial force, initial revolution speed and energy amount of upset. working time, and residual stresses in the joint. Inertia welding was conducted to make the large exhaust valve spindle for low speed marine diesel engine. superalloy Nimonic 80A for valve head of 540mm and high alloy SNCrW for valve stem of 115mm. Due to different material characteristics such as, thermal conductivity and flow stress. on the two sides of the weld interface, modeling is crucial in determining the optimal weld geometry and Parameters. FE simulation was performed by the commercial code DEFORM-2D. A good agreement between the Predicted and actual welded shape is observed. It is expected that modeling will significantly reduce the number of experimental trials needed to determine the weld parameters. especially for welds for which are very expensive materials or large shaft. Many kinds of tests, including macro and microstructure observation, chemical composition tensile , hardness and fatigue test , are conducted to evaluate the qualify of welded joints. Based on the results of the tests it can be concluded that the inertia welding joints of the superalloy exhaust valve spindle are better properties than the material specification of SNCrW.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.18 no.7
• /
• pp.39-45
• /
• 2017

In this study, permeable repair materials mainly composed of silicate - based inorganic materials(SIM), which are easily available domestically, were prepared as a basic study for the development of permeable repair materials using SIM. SIM were compared and examined for their performance as repair materials by selecting a product group which has many cases of use in foreign countries. The SIM used were mainly composed of sodium, potassium and lithium silicate. Performance evaluation of SIM was performed by absorption and penetration, compression and adhesion, rapid chloride ion penetration, rapid freezing and thawing, and chemical resistance test. According to the test results, SIM showed effective performance in all areas, mainly because SIM permeates into the interior of the capillary and has a dense internal microstructure. Therefore, it can be used variously to improve the durability of concrete based on the results of this experiment.

• Journal of Korean Society of Environmental Engineers
• /
• v.37 no.7
• /
• pp.412-417
• /
• 2015

This study investigated to recycle geobond and ash produced in thesewage sludge incinerator using reduction/stabilization. Nonsintering process was performed by binding cement (High Early Strength Portland cement, Micro cement), geobond and sand mixed with sewage sludge ash (SSA). Chemical ingradients of the sewage sludge ash was mainly composed of $SiO_2$, $Al_2O_3$, $Fe_2O_3$, CaO and others, which were similar to those of the each binders consisting High Early Strength Portland cement, Micro cement and geobond. Results showed that unconfined the long term compressive strength could be obtained components of sewage sludge ash. It exceeded more than double score 64.6 MPa of the Korean standard ($22.54MPa=229.7kg/cm^2$). Microstructure of solidified block for the different admixture was related to the compressive strength according to SEM analysis. Optimum mixing range of the sewage sludge ash to each binders were found to be 10~40% which can widly safely regulate the confined a long term compressive strength. The best binder of long term compressive strengh was revealed Geobond more than High Early Strength Portland cement and Micro cement. This study revealed the sewage sludge ash can be partial replacement of the inorganic binder & application block for recycling.

• Journal of the Korean Applied Science and Technology
• /
• v.29 no.2
• /
• pp.317-322
• /
• 2012

The microstructures were examined by SEM, FT-IR spectra, tensible properties mole % of [NCO/OH], and particle size analyzer. Growing concerns in the environment-friendly industries have led to the development of solvent-free formulations that can be cured. We had synthesized the polyurethane resin having the ability to protect stainless steel against corrosion. Compared with general packing materials and coatings, this resin is highly stronger in intensity and longer durability. Polyurethane resins were composed of polyols, IPDI, silicone surfactant, catalyst and crosslink agent. Moreover, thermal fillers such as $Al_2O_3$, fume silica and $ZrO_2$ not only accelerated the curing rate but also improved the physical property as thermal barriers. The rigid segments of polyurethane in mechanical properties were due to crosslink agent and the increase of [NCO/OH]. In conclusion, the polyurethane microstructure with crosslink agent can be good material for themoset coating of metal substrates such as stainless steel.

• Journal of Korean Society of Environmental Engineers
• /
• v.36 no.12
• /
• pp.843-850
• /
• 2014

This study investigated to recycle ash produced in the sewage sludge incinerator using reduction/stabilization. Nonsintering process was performed by binding cement, geobond and sand mixed with sewage sludge ash (SSA). Results showed that unconfined compressive strength could be obtained components of sewage sludge ash. it exceeded more than double score of the 22.54 Mpa ($229.7kg/cm^2$) Korean standard. chemical ingradients of the sewage sludge ash was mainly composed of $SiO_2$, $Al_2O_3$, $Fe_2O_3$, CaO and others, which were similar to those of the each binders consisting cement and geobond. microstructure of solidified speceimen for the different admixture was related to the compressive strength according to SEM analysis. optimum mixing range of the sewage sludge ash to inorganic binder was found to be 10~40% which can widly safely regulate the confined compressive strength. This study revealed the sewage sludge ash can be partial replacement of the inorganic binder for recycling.

• Progress in Superconductivity
• /
• v.6 no.1
• /
• pp.64-68
• /
• 2004

We fabricated cube-textured Ni and Ni-W alloy substrates for coated conductors and characterized the effects of W addition on microstructure, mechanical strength, and magnetic properties of the substrate. Pure Ni and Ni-(2, 3, 5at.%)W alloys were prepared by plasma arc melting, heavily cold rolled and then annealed at various temperatures of $600-1300^{\circ}C$. The texture was evaluated by pole-figure and orientation distribution function (ODF) analysis. Mechanical properties were investigated by micro Vickers hardness and tension test. Ferromagnetism of the substrate was measured by physical property measurement system (PPMS). It was observed that Ni-W substrates had sharp cube texture, and the full-width at half-maximums (FWHMs) of in-plane texture was $^{\circ}$-5.57$4.42^{\circ}$, which is better than that of pure Ni substrate. In addition cube texture of Ni-W substrates was retained at higher temperature up to $1300^{\circ}C$. Microstructural observation showed that the Ni-W substrates had fine grain size and higher mechanical properties than the pure Ni substrate. These improvements are probably due to strengthening mechanisms such as solid solution hardening and/or grain size strengthening. PPMS analysis showed that addition of W effectively reduced saturation magnetization in applied magnetic field and Curie temperature.