High-strength low-alloy steel is one of the widely used materials in onshore and offshore plant engineering. We investigated the alloying effect of solute atoms in α-Fe based alloy using ab initio calculations. Empirical equations were used to establish the effect of alloying on the Vicker’s hardness, screw energy coefficient, and edge dislocation energy coefficient of the steel. Screw and edge energy coefficients were improved by the addition of V and Cr solute atoms. In addition, the addition of trace quantities of V, Cr, and Mn enhanced abrasion resistance. Solute atoms and contents with excellent mechanical properties were selected and their thermal conductivity and thermal expansion behavior were investigated. The addition of Cr atom is expected to form alloys with low thermal conductivity and thermal expansion coefficient. This study provides a better understanding of the state-of-the-art research in low-alloy steel and can be used to guide researchers to explore and develop α-Fe based alloys with improved properties, that can be fabricated in smart and cost-effective manners.

This study focused on improving the phase stability and mechanical properties of yttria-stabilized zirconia (YSZ), commonly utilized in gas turbine engine thermal barrier coatings, by incorporating Gd2O3, Er2O3, and TiO2. The addition of 3-valent rare earth elements to YSZ can reduce thermal conductivity and enhance phase stability while adding the 4-valent element TiO2 can improve phase stability and mechanical properties. Sintered specimens were prepared with hot-press equipment. Phase analysis was conducted with X-ray diffraction (XRD), and mechanical properties were assessed with Vickers hardness equipment. The research results revealed that, except for Z10YGE10T, most compositions predominantly exhibited the t-phase. Increasing the content of 3-valent rare earth oxides resulted in a decrease in the monoclinic phase and an increase in the tetragonal phase. In addition, the t(400) angle decreased while the t(004) angle increased. The addition of 10 mol% of 3-valent rare-earth oxides discarded the t-phase and led to the complete development of the c-phase. Adding 10 mol% TiO2 increased hardness than YSZ.

This research investigated the effect of Si addition on the microstructure, mechanical properties, electric and thermal conductivity of as-extruded Al 6013 alloys. As the content of Si increased, the area fraction of the second phase increased. As the Si content increased, the average grain size decreased remarkably, from 182 (no Si addition) to 142 (1.5Si), 78 (3.0Si) and 77 μm (4.5Si) due to dynamic recrystallization by the dispersed second particles in the aluminum matrix during the hot extrusion. As the Si content increased, the yield strength and ultimate tensile strength increased. The maximum values of yield strength and ultimate tensile strength were 224 MPa and 103 MPa for the 6013-4.5Si alloy. As the amount of Si added increased, the electrical and thermal conductivity decreased. The electrical and thermal conductivity of the Al6013-4.5Si alloy were 44.0% IACS and 165.0 W/mK, respectively. The addition of Si to Al 6013 alloy had a significant effect on its thermal conductivity and mechanical properties.

A Cu-15Ag-5P filler metal (BCuP-5) is fabricated on a Ag substrate using a high-velocity oxygen fuel (HVOF) thermal spray process, followed by post-heat treatment (300oC for 1 h and 400oC for 1 h) of the HVOF coating layers to control its microstructure and mechanical properties. Additionally, the microstructure and mechanical properties are evaluated according to the post-heat treatment conditions. The porosity of the heat-treated coating layers are significantly reduced to less than half those of the as-sprayed coating layer, and the pore shape changes to a spherical shape. The constituent phases of the coating layers are Cu, Ag, and Cu-Ag-Cu3P eutectic, which is identical to the initial powder feedstock. A more uniform microstructure is obtained as the heat-treatment temperature increases. The hardness of the coating layer is 154.6 Hv (as-sprayed), 161.2 Hv (300oC for 1 h), and 167.0 Hv (400oC for 1 h), which increases with increasing heat-treatment temperature, and is 2.35 times higher than that of the conventional cast alloy. As a result of the pull-out test, loss or separation of the coating layer rarely occurs in the heat-treated coating layer.

Diamond reinforced silicon carbide matrix composites (diamond/SiC) with high thermal conductivity were prepared by tape casting combined with Si vapor infiltration for thermal management application. The effects of the mixing mode of bimodal diamond particles on the microstructure, thermal and mechanical properties of the composites were analyzed. The results reveal that the thermal conductivity of composites is affected significantly by mixing mode of diamond. In general, when the content of large diamond remains constant, adding a slight amount of small diamond was found to be effective in improving the thermal conductivity of the composite. However, excess small diamonds added will decrease thermal conductivity due to its high interfacial thermal resistance. The maximum thermal conductivity of obtained diamond/SiC is 469 W/(m K) when 38 vol% large diamond and 4 vol% small diamond were added. Such a result can be attributed to the formation of efficient heat transfer channels within the composite and sound interfacial bonding between diamond and SiC phase. Diamond/SiC with high thermal conductivity are expected to be the next generation of electronic packaging substrate.

We investigate the effects of Yb2O3 and calcium aluminosilicate (CAS) glass as sintering additives on the sintering behavior of AlN. The AlN specimens are sintered at temperatures between 1700oC and 1900oC for 2 h in a nitrogen atmosphere. When the Yb2O3 content is low (within 3 wt.%), an isolated shape of secondary phase is observed at the AlN grain boundary. In contrast, when 3 wt.% Yb2O3 and 1 wt.% CAS glass are added, a continuous secondary phase is formed at the AlN grain boundary. The thermal conductivity decreases when the CAS glass is added, but the sintering density does not decrease. In particular, when 10 wt.% Yb2O3 and 1 wt.% CAS glass are added to AlN, the flexural strength is the highest, at 463 MPa. These results are considered to be influenced by changes in the microstructure of the secondary phase of AlN.

Effects of Sc addition on microstructure, electrical conductivity, thermal conductivity and mechanical properties of the as-cast and as-extruded Al-2Zn-1Cu-0.3Mg-xSc (x = 0, 0.25, 0.5 wt%) alloys are investigated. The average grain size of the as-cast Al-2Zn-1Cu-0.3Mg alloy is 2,334 μm; however, this value drops to 914 and 529 μm with addition of Sc element at 0.25 wt% and 0.5 wt%, respectively. This grain refinement is due to primary Al3Sc phase forming during solidification. The as-extruded Al-2Zn-1Cu-0.3Mg alloy has a recrystallization structure consisting of almost equiaxed grains. However, the asextruded Sc-containing alloys consist of grains that are extremely elongated in the extrusion direction. In addition, it is found that the proportion of low-angle grain boundaries below 15 degree is dominant. This is because the addition of Sc results in the formation of coherent and nano-scale Al3Sc phases during hot extrusion, inhibiting the process of recrystallization and improving the strength by pinning of dislocations and the formation of subgrain boundaries. The maximum values of the yield and tensile strength are 126 MPa and 215 MPa for the as-extruded Al-2Zn-1Cu-0.3Mg-0.25Sc alloy, respectively. The increase in strength is probably due to the existence of nano-scale Al3Sc precipitates and dense Al2Cu phases. Thermal conductivity of the as-cast Al-2Zn-1Cu-0.3Mg-xSc alloy is reduced to 204, 187 and 183 W/MK by additions of elemental Sc of 0, 0.25 and 0.5 wt%, respectively. On the other hand, the thermal conductivity of the as-extruded Al-2Zn-1Cu-0.3Mg-xSc alloy is about 200 W/Mk regardless of the content of Sc. This is because of the formation of coherent Al3Sc phase, which decreases Sc content and causes extremely high electrical resistivity.

Ti0.5Al0.5N/CrN nano-multilayers, which are known to exhibit excellent wear resistances, were prepared using the unbalanced magnetron sputter for various periods of 2–7 nm. Ti0.5Al0.5N and CrN comprised a cubic structure in a single layer with different lattice parameters; however, Ti0.5Al0.5N/CrN exhibited a cubic structure with the same lattice parameters that formed the superlattice in the nano-multilayers. The Ti0.5Al0.5/CrN multilayer with a period of 5.0 nm exceeded the hardness of the Ti0.5Al0.5N/CrN single layer, attaining a value of 36 GPa. According to the low-angle X-ray diffraction, the Ti0.5Al0.5N/CrN multilayer maintained its as-coated structure up to 700oC and exhibited a hardness of 32 GPa. The thickness of the oxidation layer of the Ti0.5Al0.5N/CrN multilayered coating was less than 25% of that of the single layers. Thus, the Ti0.5Al0.5N/CrN multilayered coating was superior in terms of hardness and oxidation resistance as compared to its constituent single layers.

Herein, we report significantly enhanced mechanical properties and thermal conductivity of polyimide (PI) by incorporating a small amount (0.01 wt %) of individualized boron-doped high-quality graphene as a filler. The boron-doped expandable graphite (B-EG) was synthesized by mixing boric acid ( H3BO4) with expandable graphite (EG) and thermally treating the mixture at 2450 °C for 30 min using a graphite furnace in an argon atmosphere. The boron-doped graphene (B-g) was prepared by the solution-phase exfoliation of B-EG with an ultrasonication process, which is a method to obtain individualized graphene as well as few-layer graphene. The PI nanocomposites were prepared using the obtained graphene. The PI nanocomposites synthesized with high-quality B-graphene (B-g) showed enhanced mechanical properties and thermal conductivity compared to those of pure PI due to the doping effects and strong interfacial interactions between graphene and the PI matrix.

In this study, epoxy composites were reinforced with multi-walled carbon nanotubes and fused silica particles, dispersing the fillers within the epoxy resin based on a simple physical method using only shear mixing and ultrasonication. The hybrid composite specimens with 0.6 wt% of carbon nanotubes and 50 wt% of silica particles showed improved mechanical properties, with increase in tensile strength and Young’s modulus up to 12 and 37%, respectively, with respect to those of the baseline specimens. The experimental results showed that the low thermal expansion of the silica particles improved the thermal stability of the composites compared with that of the baseline specimen, whereas the thermal expansion slightly increased, due to the increased heat transfer from the exterior to the interior of specimens by the carbon nanotube filler. The coefficient of thermal expansion of the hybrid composite specimen reinforced with 0.6 wt% of carbon nanotubes and 50 wt% of silica particles was decreased by 25%, and the thermal conductivity was increased by about 84%, compared with those of the baseline specimen.

Aluminum nitride (AlN) has excellent electrical insulation property, high thermal conductivity, and a low thermal expansion coefficient; therefore, it is widely used as a heat sink, heat-conductive filler, and heat dissipation substrate. However, it is well known that the AlN-based materials have disadvantages such as low sinterability and poor mechanical properties. In this study, the effects of addition of various amounts (1-6 wt.%) of sintering additives Y2O3 and Sm2O3 on the thermal and mechanical properties of AlN samples pressureless sintered at 1850oC in an N2 atmosphere for a holding time of 2 h are examined. All AlN samples exhibit relative densities of more than 97%. It showed that the higher thermal conductivity as the Y2O3 content increased than the Sm2O3 additive, whereas all AlN samples exhibited higher mechanical properties as Sm2O3 content increased. The formation of secondary phases by reaction of Y2O3, Sm2O3 with oxygen from AlN lattice influenced the thermal and mechanical properties of AlN samples due to the reaction of the oxygen contents in AlN lattice.

TiO2-particles containing Co grains are fabricated via thermal hydrogenation and selective oxidation of Ti- Co alloy. For comparison, TiO2-Co composite powders are prepared by two kinds of methods which were the mechanical carbonization and oxidation process, and the conventional mixing process. The microstructural characteristics of the prepared composites are analyzed by X-ray diffraction, field-emission scattering electron microscopy, and transmission electron microscopy. In addition, the composite powders are sintered at 800℃ by spark plasma sintering. The flexural strength and fracture toughness of the sintered samples prepared by thermal hydrogenation and mechanical carbonization are found to be higher than those of the samples prepared by the conventional mixing process. Moreover, the microstructures of sintered samples prepared by thermal hydrogenation and mechanical carbonization processes are found to be similar. The difference in the mechanical properties of sintered samples prepared by thermal hydrogenation and mechanical carbonization processes is attributed to the different sizes of metallic Co particles in the samples.

한국원자력연구원 부지 내에 위치한 지하처분연구시설(KAERI Underground Research Tunnel, KURT) 에서는 선진핵주기 고준위폐기물처분시스템(A-KRS)을 기반으로 고준위방사성폐기물을 처분하였을때, 예상되는 공학적방벽(Engineered Barrier System, EBS)과 자연방벽(Natural Barrier System, NBS)에서의 열-수리-역학적 복합거동(Thermo-Hydro-Mechanical coupled behavior)의 특성을 규명하고자 현장시험(In-situ Demonstration of Engineered Barrier System, In-DEBS)을 2012년부터 계획 및 설계를 시작하여, 2016년 5월부터 지하처분연구시설 3번 연구 갤러리(Research gallery 3)에서 진행하고 있다. 현장시험의 데이터를 분석하고 열-수리-역학적 복합거동 특성을 명확히 규명하기 위해서는 경주 벤토나이트와 KURT 암석 및 암반의 열적, 수리적, 그리고 역학적 물성 특성을 반드시 파악하고 있어야만 한다. 이에 본 연구에서는 지금까지 수행된 KURT 부지 특성과 KURT 화강암 및 경주 벤토나이트의 열적, 수리적, 그리고 역학적 특성을 정리하고, 열적, 수리적, 그리고 역학적 모델을 제시하였다. 특히, 온도에 따른 암석의 열팽창계수 변화, 응력에 따른 암석의 투수계수 변화, 포화도에 따른 벤토나이트 및 암석의 열전도도 변화, 포화도에 따른 벤토나이트의 비열 및 흡입력 변화와 같은 열-수리-역학적 복합물성에 대한 다양한 모델을 도출함으로써, In-DEBS 현장시험 결과 분석과 열-수리-역학적 복합거동 특성 평가를 위해 수행 될 수치시험에 필요한 벤토나이트와 암석 및 암반의 입력자료를 제시하고자 하였다.

PVA 부직포의 방염성을 향상시키기 위하여 POCl3로 방염처리하였다. POCl3로 처리한 PVA 부직포의 물리적 및 열적 특성을 측정하고 분석하였다. 개질한 PVA 부직포는 대부분 물에 용해하지 않았으나 수축과 스웰링 특성을 보 였다. POCl3로 방염처리한 PVA 부직포의 열적 특성이 우수하고 방염특성이 원시료 보다 많이 우수한 것을 확인하였다. 그라프트 비와 염색성 사이의 선형관계는 PVA 부직포의 히드록시기와 POCl3가 공유결합으로 연결된 것에 기인하는 것 으로 분석되었다.

RBSC (reaction-bonded silicon carbide) represents a family of composite ceramics processed by infiltrating with molten silicon into a skeleton of SiC particles and carbon in order to fabricate a fully dense body of silicon carbide. RBSC has been commercially used and widely studied for many years, because of its advantages, such as relatively low temperature for fabrication and easier to form components with near-net-shape and high relative density, compared with other sintering methods. In this study, RBSC was fabricated with different size of SiC in the raw material. Microstructure, thermal and mechanical properties were characterized with the reaction-sintered samples in order to examine the effect of SiC size on the thermal and mechanical properties of RBSC ceramics. Especially, phase volume fraction of each component phase, such as Si, SiC, and C, was evaluated by using an image analyzer. The relationship between microstructures and physical properties was also discussed.

Multi-walled carbon nanotube (MWCNT)/epoxy composites are prepared by a vacuum assisted resin transfer molding (VARTM) method. The mechanical properties, fracture surface morphologies, and thermal stabilities of these nanocomposites are evaluated for epoxy resins with various amounts of MWCNTs. Composites consisting of different amounts of MWCNTs displayed an increase of the work of adhesion between the MWCNTs and the matrix, which improved both the tensile and impact strengths of the composites. The tensile and impact strengths of the MWCNT/epoxy composite improved by 59 and 562% with 0.3 phr of MWCNTs, respectively, compared to the epoxy composite without MWCNTs. Thermal stability of the 0.3 phr MWCNT/epoxy composite increased compared to other epoxy composites with MWCNTs. The enhancement of the mechanical and thermal properties of the MWCNT/epoxy nanocomposites is attributed to improved dispersibility and strong interfacial interaction between the MWCNTs and the epoxy in the composites prepared by VARTM.

The amorphization process and the thermal properties of amorphous TiCuNiAl powder during milling by mechanical alloying were examined by X-ray diffractometry (XRD), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). The chemical composition of the samples was examined by an energy dispersive X-ray spectrometry (EDX) facility attached to the scanning electron microscope (SEM). The as-milled powders showed a broad peak (2 = 42.4) with crystalline size of about 5.0 nm in the XRD patterns. The entire milling process could be divided into three different stages: agglomeration (0 < t 3 h), disintegration (3 h < t 20 h), and homogenization (20 h < t 40 h) (t: milling time). In the DSC experiment, the peak temperature T and crystallization temperature T were 466.9 and 444.3, respectively, and the values of T, and T increased with a heating rate (HR). The activation energies of crystallization for the as-milled powder was 291.5 kJ/mol for T.