YSZ (Y2O3-stabilized zirconia)-based ceramics have excellent mechanical properties, such as high strength and wear resistance. In the application, YSZ is utilized in the bead mill, a fine-grinding process. YSZ-based parts, such as the rotor and pin, can be easily damaged by continuous application with high rpm in the bead mill process. In that case, adding WC particles improves the tribological and mechanical properties. YSZ-30 vol.% WC composite ceramics are manufactured via hot pressing under different pressures (10/30/60 MPa). The hot-pressed composite ceramics measure the physical properties, such as porosity and bulk density values. In addition, the phase formation of these composite ceramics is analyzed and discussed with those of physical properties. For the increased applied pressure of hot pressing, the tetragonality of YSZ and the crystallinity of WC are enhanced. The mechanical properties indicate an improved tendency with the increase in the applied pressure of hot pressing.

The engineered barrier system (EBS) for deep geological disposal of high-level radioactive waste requires a buffer material that can prevent groundwater infiltration, protect the canister, dissipate decay heat effectively, and delay the transport of radioactive materials. To meet those stringent performance criteria, the buffer material is prepared as a compacted block with high-density using various press methods. However, crack and degradation induced by stress relaxation and moisture changes in the compacted bentonite blocks, which are manufactured according to the geometry of the disposal hole, can critically affect the performance of the buffer. Therefore, it is imperative to develop an adequate method for quality assessment of the compacted buffer block. Recently, several non-destructive testing methods, including elastic wave measurement technology, have been attempted to evaluate the quality and aging of various construction materials. In this study, we have evaluated the compressive wave velocity of compacted bentonite blocks via the ultrasonic velocity method (UVM) and free-free resonant column method (FFRC), and analyzed the relationship among compressive wave velocity, dry density, thermal conductivity, and strength parameter. We prepared compacted bentonite block specimens using the cold isostatic pressure (CIP) method under different water content and CIP pressure conditions. Based on multiple regression analysis, we suggest a prediction model for dry density in terms of manufacturing conditions. Additionally, we propose an empirical model to predict thermal conductivity and unconfined compressive strength based on compressive wave velocity. The database and suggested models in this study can contribute to the development of quality assessment and prediction techniques for compacted buffer blocks used in the construction of a disposal repository.

Among the Additive Manufacturing (AM) technologies, the Binder-Jetting printing technology is a method of spraying an adhesive on the surface of powder and laminate layer by layer. Recently, this technique has become a major issue in the production of large casting products such as ship-building, custom vehicles and so on. In this study, we performed research to make actual mold castings and increase mechanical property by using special sand and water-based binders. For use as a mold, it has a strength of more than 3MPa and permeability. Various experiments were carried out to obtain suitable them. The major process parameters were binder jetting volume, binder types, layer thickness and heat treatment condition. As a result of this study, the binder drop quantity was measured to be about 60 pico-liter, layer thickness was 100μm and the heat treatment condition was measured about 1,000℃ and compressive strength were measured to be more than 5MPa. The optimum condition of this experiment was established through actual casting of aluminum. The equipment used in this study was a Freeforms T400 model (SFS Co., Ltd.), and the printing area of 420 * 300 * 250mm and resolution of 600dpi can be realized.

Novel Ni- and Fe-based alloys are developed to impart improved mechanical properties and corrosion resistance. The designed alloys are manufactured as a powder and deposited on a steel substrate using a high-velocity oxygen-fuel process. The coating layer demonstrates good corrosion resistance, and the thus-formed passive film is beneficial because of the Cr contained in the alloy system. Furthermore, during low-temperature heat treatment, factors that deteriorate the properties and which may arise during high-temperature heat treatment, are avoided. For the heattreated coating layers, the hardness increases by up to 32% and the corrosion resistance improves. The influence of the heat treatment is investigated through various methods and is considered to enhance the mechanical properties and corrosion resistance of the coating layer.

Transition metal carbides (TMCs) are used to process difficult-to-cut materials due to the trend of requiring superior wear and corrosion properties compared to those of cemented carbides used in the cutting industry. In this study, TMC (TiC, TaC, Mo2C, and NbC)-based cermets were consolidated by spark plasma sintering at 1,300 oC (60 oCmin) with a pressure of 60 MPa with Co addition. The sintering behavior of TMCs depended exponentially on the function of the sintering exponent. The Mo2C-6Co cermet was fully densified, with a relative density of 100.0 %. The Co-binder penetrated the hard phase (carbides) by dissolving and re-precipitating, which completely densified the material. The mechanical properties of the TMCs were determined according to their grain size and elastic modulus: TiC-6Co showed the highest hardness of 1,872.9 MPa, while NbC-6Co showed the highest fracture toughness of 10.6 MPa*m1/2. The strengthened grain boundaries due to high interfacial energy could cause a high elastic modules; therefore, TiC-6Co showed a value of 452 ± 12 GPa.

In this study, binderless-WC, WC-6 wt%Co, WC-6wt% 1 and 2.5 B4C materials are fabricated by spark plasma sintering process (SPS process). Each fabricated WC material is almost completely dense, with a relative density up to 99.5 % after the simultaneous application of pressure of 60 MPa. The WC added Co and Co-B4C materials resulted in crystalline growth. The WC with HCP crystal structure has respective interfacial energy (basal facet direction: 1.07 ~ 1.34 J·m−2, prismatic direction: 1.43 ~ 3.02 J·m−2) that depends on the grain growth direction. It is confirmed that the continuous grain growth, biased by the basal facet, which has relatively low energy, is promoted at the WC/Co interface. As abnormal grain growth takes place, the grain size increases more than twice from 0.37 to 0.8 um. It is found through analysis that the hardness property also greatly decreases from about 2661.4 to 1721.4 kg/mm2, along with the grain growth.

Expensive PCBN or ceramic cutting tools are used for processing of difficult-to-cut materials such as Ti and Ni alloy materials. These tools have the problem of breaking easily due to their high hardness but low fracture toughness. To solve these problems, cutting tools that form various coating layers are used in low-cost WC-Co hard material tools, and research on various tool materials is being conducted. In this study, binderless-WC, WC-6 wt%Co, WC-6 wt%Co-1 wt% Mo2C, and WC-6 wt%Co-2.5 wt% Mo2C hard materials are densified using horizontal ball milled WC-Co, WC-Co-Mo2C powders, and spark plasma sintering process (SPS process). Each SPSed Binderless-WC, WC-6 wt%Co-1 wt% Mo2C, and WC-6 wt%Co- 2.5 wt% Mo2C hard materials are almost completely dense, with relative density of up to 99.5 % after the simultaneous application of pressure of 60 MPa and almost no significant change in grain size. The average grain sizes of WC for Binderless- WC, WC-6 wt%Co-1 wt% Mo2C, and WC-6 wt%Co-2.5 wt% Mo2C hard materials are about 0.37, 0.6, 0.54, and 0.43 μm, respectively. Mechanical properties, microstructure, and phase analysis of SPSed Binderless-WC, WC-6 wt%Co-1 wt% Mo2C, and WC-6 wt%Co-2.5 wt% Mo2C hard materials are investigated.

The penetration depth, bead height, width, and internal porosity were analyzed to select the perfect penetration conditions for the STS316L tube material with an outer diameter of 38.1mm and a thickness of 3.4 mm. The welding conditions to secure a penetration depth of 3.4mm or more were selected. In addition, a welding range in which underfill does not occur was selected. The range of the selected conditions is the condition of a welding speed of 0.75 to 1.25m/min with an output of 2.0kW. The selected welding conditions were applied to STS316L tube orbital welding, and as a result of cross-sectional inspection after welding, a welded part of less than 4% of complete penetration and porosity was secured. The strength of the weld was measured to be more than 800kgf, and the hardness of the weld was found to decrease compared to the base material. The decrease in the hardness of the weld is judged by the annealing effect of the heat treated base material.

Ti-based alloys are widely used in biomaterials owing to their excellent biocompatibility. In this study, Ti- Mn-Cu alloys are prepared by high-energy ball milling, magnetic pulsed compaction, and pressureless sintering. The microstructure and microhardness of the Ti-Mn-Cu alloys with variation of the Cu addition and compaction pressure are analyzed. The correlation between the composition, compaction pressure, and density is investigated by measuring the green density and sintered density for samples with different compositions, subjected to various compaction pressures. For all compositions, it is confirmed that the green density increases proportionally as the compaction pressure increases, but the sintered density decreases owing to gas formation from the pyrolysis of TiH2 powders and reduction of oxides on the surface of the starting powders during the sintering process. In addition, an increase in the amount of Cu addition changes the volume fractions of the α-Ti and β-Ti phases, and the microstructure of the alloys with different compositions also changes. It is demonstrated that these changes in the phase volume fraction and microstructure are closely related to the mechanical properties of the Ti-Mn-Cu alloys.

Martensitic stainless steel is commonly used in the medical implant instrument. The alloy has drawbacks in terms of strength and wear properties when applied to instruments with sharp parts. 440C STS alloy, with improved durability, is an alternative to replace 420 J2 STS. In the present study, the carbide precipitation, and mechanical and corrosion properties of STS 440C alloy are studied as a function of different heat treatments. The STS 440C alloy is first austenitized at different temperatures; this is immediately followed by oil quenching and sub-zero treatment. After sub-zero treatment, the alloy is tempered at low temperatures. The microstructures of the heat treated STS 440C alloy consist of martensite and retained austenite and carbides. Using EDX and SADP with a TEM, the precipitated carbides are identified as a Cr23C6 carbide with a size of 1 to 2 μm. The hardness of STS 440C alloy is improved by austenitization at 1,100 oC with sub-zero treatment and tempering at 200 oC. The values of Ecorr and Icorr for STS 440C increase with austenitization temperature. Results can be explained by the dissolution of Cr-carbide and the increase in the retained austenite. Sub-zero treatment followed by tempering shows a little difference in the properties of potentiodynamic polarizations.

Aluminum High Vacuum Die-casting process has become more prevalent in automotive manufacturing industry which require high productive rate, weldable process and heat treatment process. However, high pressure die castings usually contain gas porosity due mainly to the entrapment of air or gas in the die during the high speed injection of the molten metal into the die cavity. Vacuum block system with disk spring was developed and vacuum chanel was optimized with numerical flow analysis. The porosity of die castings was analyzed by X-ray CT, and the effect of porosity on the mechanical properties was analyzed by hardness and tensile test. Tensile strength was improved 49.5% for 50mbar high vacuum die-casting process compare then 300mbar. And then, Surface property was analyzed with plunger velocity and fast shot set point.

본 연구에서는 그래핀 함량에 따른 고분자 나노섬유의 물리적 특성 변화에 대해 연구하였다. 전기방사법으로 GO PAN 나노섬유 복합체 막을 제조하였으며, 접촉각⋅SEM⋅인장강도에 관한 실험을 진행하였다. GO+계면활성제를 이용 하여 나노섬유에 존재하는 GO의 함량을 증가시켰다. 제조한 나노섬유의 경우 기존의 나노섬유보다 강한 기계적 강도를 나타내었다. 이러한 결과를 바탕으로 수처리 분리막의 연구 기초자료로 활용될 수 있을 것으로 기대된다.

The microstructural evolution and modulation of mechanical properties were investigated for a Ti65Fe35 hypereutectic alloy by addition of Bi53In47 eutectic alloys. The microstructure of these alloys changed with the additional Bi- In elements from a typical dendrite-eutectic composite to a bimodal eutectic structure with primary dendrite phases. In particular, the primary dendrite phase changed from a TiFe intermetallic compound into a β-Ti solid solution despite their higher Fe content. Compressive tests at room temperature demonstrated that the yield strength slightly decreased but the plasticity evidently increased with an increasing Bi-In content, which led to the formation of a bimodal eutectic structure (β-Ti/TiFe + β- Ti/BiIn containing phase). Furthermore, the (Ti65Fe35)95(Bi53In47)5 alloy exhibited optimized mechanical properties with high strength (1319MPa) and reasonable plasticity (14.2%). The results of this study indicate that the transition of the eutectic structure, the type of primary phases and the supersaturation in the β-Ti phase are crucial factors for controlling the mechanical properties of the ultrafine dendrite-eutectic composites.

In this study, Fe-Cu-C alloy is sintered by spark plasma sintering (SPS). The sintering conditions are 60 MPa pressure with heating rates of 30, 60 and 9oC/min to determine the influence of heating rate on the mechanical and microstructure properties of the sintered alloys. The microstructure and mechanical properties of the sintered Fe-Cu-C alloy is investigated by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM). The temperature of shrinkage displacement is changed at 450oC with heating rates 30, 60, and 90oC/min. The temperature of the shrinkage displacement is finished at 650oC when heating rate 30oC/min, at 700oC when heating rate 60oC/min and at 800oC when heating rate 90oC/min. For the sintered alloy at heating rates of 30, 60, and 90oC/min, the apparent porosity is calculated to be 3.7%, 5.2%, and 7.7%, respectively. The hardness of the sintered alloys is investigated using Rockwell hardness measurements. The objective of this study is to investigate the densification behavior, porosity, and mechanical properties of the sintered Fe-Cu-C alloys depending on the heating rate.

In this study, H13 tool steel sculptures are built by a metal 3D printing process at various laser scan speeds. The properties of commercial H13 tool steel powders are confirmed for the metal 3D printing process used: powder bed fusion (PBF), which is a selective laser melting (SLM) process. Commercial H13 powder has an excellent flowability of 16.68 s/50 g with a Hausner ratio of 1.25 and a density of 7.68 g/cm3. The sculptures are built with dimensions of 10 × 10 × 10 mm3 in size using commercial H13 tool steel powder. The density measured by the Archimedes method is 7.64 g/cm3, similar to the powder density of 7.68 g/cm3. The hardness is measured by Rockwell hardness equipment 5 times to obtain a mean value of 54.28 HRC. The optimum process conditions in order to build the sculptures are a laser power of 90 W, a layer thickness of 25 μm, an overlap of 30%, and a laser scan speed of 200 mm/s.

본 연구에서는 복합막의 물성향상을 위해 clay를 도입한 polysulfone 나노섬유 복합막을 제조하였다. Polysulfone/clay 복합막은 clay가 들어간 N,N-dimethyl acetamide와 acetone 혼합용매에 polysulfone을 첨가한 후 전기방사법 을 이용하여 제조하였으며, 제조된 나노섬유 복합막은 적층수를 변화해 기공크기를 조절한 후 사용하였다. 전반적인 분리막 의 특성은 SEM, contact angle, 기공특성, tensile strength, water flux 분석을 사용하여 고찰하였다. 특히 SEM image로 clay의 도입을 확인하였으며 contact angle 측정을 통해 표면이 개질된 결과를 확인할 수 있었다. 그리고 clay의 도입량에 따른 복합 막의 기계적 물성을 확인하였다. 따라서 본 연구에서 제조된 분리막은 수처리용 분리막으로 충분히 활용 가능할 것으로 판단 된다.

본 연구에서는 clay를 고분자와 복합하여 전기방사법을 이용해 나노섬유 복합막을 제조하였다. 다양한 친·소수성 고분자에 균일하게 clay를 nanofiller로 첨가함으로서 일반적으로 나노섬유 자체가 보여주는 취약한 물리적 기계적 특성을 증가시켜 수처리 막으로의 활용 가능성을 확인하였다. 그리고 고분자와 clay간의 interaction이 제조된 복합막들의 특성에 어떤 영향을 나타내는지 고찰해보았다. 이러한 결과를 바탕으로 nanofiller를 활용한 다양한 나노섬유 복합막의 제조 및 나노섬유의 물리적 특성을 보완 하는 연구의 기초자료로 활용할 수 있을 것이라 생각된다.

In this study, the curvature FSW experiments were performed with the 2 mm thickness of Al 5083-O using by the 5 axis(X/Y/Z/A/C) position control system. For the mechanical test of the butt joints, the tungsten heavy alloy as the tool material without necessary after finishing the heat treatment such as quenching was used. In particular, the insertion depth and the welding speed was changed at the constant rotation speed in order to select the optimum FSW condition. The test results were visually satisfactory for the approximate joint length of 300 mm. Sound joint was formed at the condition of 1.9 mm-1000 rpm-100 mm/min and its tensile strength of joint was the most high almost the same as that of the base material.

기체 분리막 소재에 있어서, 자유체적 및 기계적 특성은 기체투과 성능 및 소재 응용에 있어서 필수적인 요소 들이다. 따라서, 기체 투과 성능의 핵심인 자유체적 비율을 최대한 높이면서도, 동시에 높은 연신율을 가질 수 있는 고분자 구조의 설계가 필수적이며, 이를 위해서는 각각의 특성을 분자 수준에서 이해하고 분석을 할 수 있어야 한다. 본 연구에서는 분자전산모사(molecular simulation) 기술을 이용하여, 기존에 실험적으로 밝혀진 TR-polymer와 spiro-group이 도입된 TR-PBO 간의 차이를 분자수준에서 밝혀냄으로서, 고분자 구조내의 특정 작용기가 최종 고분자 소재의 자유체적 및 기계적 특성에 어떻게 작용하는지를 규명하고자 한다.