We investigated the microstructure of an FeCrMnNiCo alloy fabricated by spark plasma sintering under different sintering temperatures (1000–1100°C) and times (1–600 s). All sintered alloys consisted of a single face-centered cubic phase. As the sintering time or temperature increased, the grains of the sintered alloys became partially coarse. The formation of Cr7C3 carbide occurred on the surface of the sintered alloys due to carbon diffusion from the graphite crucible. The depth of the layer containing Cr7C3 carbides increased to ~110 μm under severe sintering conditions (1100°C, 60 s). A molten zone was observed on the surface of the alloys sintered at higher temperatures (>1060°C) due to severe carbon diffusion that reduced the melting point of the alloy. The porosity of the sintered alloys decreased with increasing time at 1000°C, but increased at higher temperatures above 1060°C due to melting-induced porosity formation.

Pure SnO2 has proven very difficult to densify. This poor densification can be useful for the fabrication of SnO2 with a porous microstructure, which is used in electronic devices such as gas sensors. Most electronic devices based on SnO2 have a porous microstructure, with a porosity of > 40%. In pure SnO2, a high sintering temperature of approximately 1300°C is required to obtain > 40% porosity. In an attempt to reduce the required sintering temperature, the present study investigated the low-temperature sinterability of a current system. With the addition of TiO2, the compositions of the samples were Sn1-xTixO2-CoO(0.3wt%)-CuO(2wt%) in the range of x ≤ 0.04. Compared to the samples without added TiO2, densification was shown to be improved when the samples were sintered at 950°C. The dominant mass transport mechanism appears to be grain-boundary diffusion during heat treatment at 950°C.

In this study, a core-shell powder and sintered specimens using a mechanically alloyed (MAed) Ti-Mo powder fabricated through high-energy ball-milling are prepared. Analysis of sintering, microstructure, and mechanical properties confirms the applicability of the powder as a sputtering target material. To optimize the MAed Ti-Mo powder milling process, phase and elemental analyses of the powders are performed according to milling time. The results reveal that 20 h of milling time is the most suitable for the manufacturing process. Subsequently, the MAed Ti-Mo powder and MoO3 powder are milled using a 3-D mixer and heat-treated for hydrogen reduction to manufacture the core-shell powder. The reduced core-shell powder is transformed to sintered specimens through molding and sintering at 1300 and 1400oC. The sintering properties are analyzed through X-ray diffraction and scanning electron microscopy for phase and porosity analyses. Moreover, the microstructure of the powder is investigated through optical microscopy and electron probe microstructure analysis. The Ti-Mo core-shell sintered specimen is found to possess high density, uniform microstructure, and excellent hardness properties. These results indicate that the Ti-Mo core-shell sintered specimen has excellent sintering properties and is suitable as a sputtering target material.

Molybdenum-tungsten (Mo-W) alloy sputtering targets are widely utilized in fields like electronics, nanotechnology, sensors, and as gate electrodes for TFT-LCDs, owing to their superior properties such as hightemperature stability, low thermal expansion coefficient, electrical conductivity, and corrosion resistance. To achieve optimal performance in application, these targets’ purity, relative density, and grain size of these targets must be carefully controlled. We utilized nanopowders, prepared via the Pechini method, to obtain uniform and fine powders, then carried out spark plasma sintering (SPS) to densify these powders. Our studies revealed that the sintered compacts made from these nanopowders exhibited outstanding features, such as a high relative density of more than 99%, consistent grain size of 3.43 μm, and shape, absence of preferred orientation.

The influence of MgO addition on the densification and microstructure of alumina (Al2O3) was studied. Compacted alumina specimens were manufactured using ball-milling and one-directional pressing followed by sintering at temperatures below 1700oC. Relative density, shrinkage, hardness, and microstructure were investigated using analytical tools such as FE-SEM, EDS, and XRD. When the MgO was added up to 5.0 wt% and sintered at 1500oC and 1600oC, the relative density exhibited an average value of 97% or more at both temperatures. The maximum density of 99.2% was with the addition of 0.5 wt% MgO at 1500oC. Meanwhile, the specimens showed significantly lower density values when sintered at 1400oC than at 1500oC and 1600oC owing to the relatively low sintering temperature. The hardness and shrinkage data also showed a similar trend in the change in density, implying that the addition of approximately 0.5 wt% MgO can promote the densification of Al2O3. Studying the microstructure confirmed the uniformity of the sintered alumina. These results can be used as basic compositional data for the development of MgOcontaining alumina as high-dielectric insulators.

A mixture of elemental Co50Si50 powders was subjected to mechanical alloying (MA) at room temperature to prepare a CoSi thermoelectric compound. Consolidation of the Co50Si50 mechanically alloyed powders was performed in a spark plasma sintering (SPS) machine using graphite dies up to 800 °C and 1,000 °C under 50 MPa. We have revealed that a nanocrystalline CoSi thermoelectric compound can be produced from a mixture of elemental Co50Si50 powders by mechanical alloying after 20 hours. The average grain size estimated from a Hall plot of the CoSi intermetallic compound prepared after 40 hours of MA was 65 nm. The degree of shrinkage of the consolidated samples during SPS became significant at about 450 °C. All of the compact bodies had a high relative density of more than 94 % with a metallic glare on the surface. X-ray diffraction data showed that the SPS compact produced by sintering mechanically alloyed powders for 40-hours up to 800 °C consisted of only nanocrystalline CoSi with a grain size of 110 nm.

Metal-additive manufacturing techniques, such as selective laser sintering (SLS), are increasingly utilized for new biomaterials, such as cobalt-chrome (Co-Cr). In this study, Co-Cr gas-atomized powders are used as charge materials for the SLS process. The aim is to understand the consolidation of Co-Cr alloy powder and characterization of samples sintered using SLS under various conditions. The results clearly suggest that besides the matrix phase, the second phase, which is attributed to pores and oxidation particles, is observed in the sintered specimens. The as-built samples exhibit completely different microstructural features compared with the casting or wrought products reported in the literature. The microstructure reveals melt pools, which represent the characteristics of the scanning direction, in particular, or of the SLS conditions, in general. It also exposes extremely fine grain sizes inside the melt pools, resulting in an enhancement in the hardness of the as-built products. Thus, the hardness values of the samples prepared by SLS under all parameter conditions used in this study are evidently higher than those of the casting products.

In this study, an Al82Ni7Co3Y8 (at%) bulk metallic glass is fabricated using gas-atomized Al82Ni7Co3Y8 metallic glass powder and subsequent spark plasma sintering (SPS). The effect of powder size on the consolidation of bulk metallic glass is considered by dividing it into 5 m or less and 20–45 m. The sintered Al82Ni7Co3Y8 bulk metallic glasses exhibit crystallization behavior and crystallization enthalpy similar to those of the Al82Ni7Co3Y8 powder with 5 m or less and it is confirmed that no crystallization occurred during the sintering process. From these results, we conclude that the Z-position-controlled spark plasma sintering process, using superplastic deformation by viscous flow in the supercooled liquid-phase region of amorphous powder, is an effective process for manufacturing bulk metallic glass.

Recently, research on MAX phase materials has been actively conducted. M of MAX phase is made of early transition metal element, A is A-group (IIIA or IVA) element, and X is Carbon or Nitrogen. It has the chemical formula of MnAXn-1, and is called the 211, 312, and 413 groups according to the indices(n=1,2,3). MXene material is characterized by having a layered structure of 2D structure like graphene by etching the element corresponding to A-gruop in the MAX phase. So far, MXene materials have been reported to be applied in various fields. In particular, research is being actively conducted as anode material for Li secondary batteries, electromagnetic wave shielding material, and hydrogen storage alloy material. In the pulse energization active sintering method, the surface of the powder particles is cleaned and activated more easily than the conventional electrical sintering process and material transfers at both the macro and micro level, so that a high-quality sintered body can be obtained at low temperature and fast time. In this study, the MAX phase was synthesized in a short time by using a pulse current active sintering apparatus, and the MXene material was prepared from the synthesized MAX phase and the structure was analyzed.

We investigate the austenite stability in nanocrystalline Fe-7%Mn-X%Mo (X = 0, 1, and 2) alloys fabricated by spark plasma sintering. Mo is known as a ferrite stabilizing element, whereas Mn is an austenite stabilizing element, and many studies have focused on the effect of Mn addition on austenite stability. Herein, the volume fraction of austenite in nanocrystalline Fe-7%Mn alloys with different Mo contents is measured using X-ray diffraction. Using a disk compressive test, austenite in Fe–Mn–Mo alloys is confirmed to transform into strain-induced martensite during plastic deformation by a disk d. The variation in austenite stability in response to the addition of Mo is quantitatively evaluated by comparing the k-parameters of the kinetic equation for the strain-induced martensite transformation.

Recently, the necessity of designing and applying tool materials that perform machining of difficult-to-cut materials in a cryogenic treatment where demand is increasing. The objective of this study is to evaluate the performance of cryogenically treated WC-5 wt% NbC hard materials fabricated by a pulsed current activated sintering process. The densely consolidated specimens are cryogenically exposed to liquid nitrogen for 6, 12, and 24 h. All cryogenically treated samples exhibit compressive stress in the sintered body compared with the untreated sample. Furthermore, a change in the lattice constant leads to compressive stress in the specimens, which improves their mechanical performance. The cryogenically treated samples exhibit significant improvement in mechanical properties, with a 10.5 % increase in Vickers hardness and a 60 % decrease in the rupture strength compared with the untreated samples. However, deep cryogenic treatment of over 24 h deteriorates the mechanical properties indicating that excessive treatment causes tensile stress in the specimens. Therefore, the cryogenic treatment time should be controlled precisely to obtain mechanically enhanced hard materials.

본 연구에서는 용제를 전혀 사용하지않고 UV경화가 가능한 나노 실버 페이스트를 개발하였다. 무용제(solvent-free) 타입으로 개발한 나노 실버 페이스트의 점도 및 점탄성 측정하였다. 그리고 스크린인쇄로 패턴을 인쇄한 후에 UV 경화로 전극도막을 형성시켰다. 형성된 전극도막의 전도성, 연필경도, 접착력에 대해서 평가하였다. 또한 전극 도막 을 광 소결하여 전도성을 평가하였다. 마지막으로 전극도막의 경화특성은 TGA 및 FT-IR로 평가하였다. 이러한 결 과를 정리하면 UV경화만 시켰을 경우에는 전도성, 접착력, 경화특성에 대해서는 Paste(3)이 가장 우수하였다. 그러 나 광소결 후에는 Paste(1)이 가장 우수한 전도성을 얻을수있었다. 그 이유는 10nm 실버 파우더를 사용한 것이 소 결 특성이 가장 우수했기 때문이라고 판단된다.

The low-temperature sinterability of TiO2-CuO systems was investigated using a solid solution of SnO2. Sample powders were prepared through conventional ball milling of mixed raw powders. With the SnO2 content, the compositions of the samples were Ti1-xSnxO2-CuO(2 wt.%) in the range of x  0.08. Compared with the samples without SnO2 addition, the densification was enhanced when the samples were sintered at 900oC. The dominant mass transport mechanism seemed to be grain-boundary diffusion during heat treatment at 900oC, where active grain-boundary diffusion was responsible for the improved densification. The rapid grain growth featured by activated sintering was also obstructed with the addition of SnO2. This suggested that both CuO as an activator and SnO2 dopant synergistically reduced the sintering temperature of TiO2.

3Y-TZP ceramics obtained by doping 3 mol.% of Y2O3 to ZrO2 to stabilize the phase transition are widely used in the engineering ceramic industry due to their excellent mechanical properties such as high strength, fracture toughness, and wear resistance. An additional increase in mechanical properties is possible by manufacturing a composite in which a high-hardness material such as oxide or carbide is added to the 3Y-TZP matrix. In this study, composite powder was prepared by dispersing a designated percentage of WC in the 3Y-TZP matrix, and the results were compared after manufacturing the composite using the different processes of spark plasma sintering and HP. The difference between the densification behavior and porosity with the process mechanism was investigated. The correlation between the process conditions and phase formation was examined based on the crystalline phase formation behavior. Changes to the microstructure according to the process conditions were compared using field-emission scanning electron microscopy. The toughness-strengthening mechanism of the composite with densification and phase formation was also investigated.

Changes in the mechanical properties and microstructure of an IN 939 W alloy according to the sintering heating rate were evaluated. IN 939 W alloy samples were fabricated by spark plasma sintering. The phase fraction, number density, and mean radius of the IN 939W alloy were calculated using a thermodynamic calculation. A universal testing machine and micro-Vickers hardness tester were employed to confirm the mechanical properties of the IN 939W alloy. X-ray diffraction, optical microscopy, field-emission scanning electron microscopy, Cs-corrected-field emission transmission electron microscopy, and energy dispersive X-ray spectrometry were used to evaluate the microstructure of the alloy. The rapid sintering heating rate resulted in a slightly dispersed γ' phase and chromium oxide. It also suppressed the precipitation of the η phase. These helped to reinforce the mechanical properties.

This study demonstrates the effect of the compaction pressure on the microstructure and properties of pressureless-sintered W bodies. W powders are synthesized by ultrasonic spray pyrolysis and hydrogen reduction using ammonium metatungstate hydrate as a precursor. Microstructural investigation reveals that a spherical powder in the form of agglomerated nanosized W particles is successfully synthesized. The W powder synthesized by ultrasonic spray pyrolysis exhibits a relative density of approximately 94% regardless of the compaction pressure, whereas the commercial powder exhibits a relative density of 64% under the same sintering conditions. This change in the relative density of the sintered compact can be explained by the difference in the sizes of the raw powder and the densities of the compacted green body. The grain size increases as the compaction pressure increases, and the sintered compact uniaxially pressed to 50 MPa and then isostatically pressed to 300 MPa exhibits a size of 0.71 m. The Vickers hardness of the sintered W exhibits a high value of 4.7 GPa, mainly due to grain refinement.

An alternative fabrication method for carburizing steel using spark plasma sintering (SPS) is investigated. The sintered carburized sample, which exhibits surface modification effects such as carburizing, sintered Fe, and sintered Fe–0.8 wt.%C alloys, is fabricated using SPS. X-ray diffraction and micro Vickers tests are employed to confirm the phase and properties. Finite element analysis is performed to evaluate the change in hardness and analyze the carbon content and residual stress of the carburized sample. The change in the hardness of the carburized sample has the same tendency to predict hardness. The difference in hardness between the carburized sample and the predicted value is also discussed. The carburized sample exhibits a compressive residual stress at the surface. These results indicate that the carburized sample experiences a surface modification effect without carburization. Field emission scanning electron microscopy is employed to verify the change in phase. A novel fabrication method for altering the carburization is successfully proposed. We expect this fabrication method to solve the problems associated with carburization.

수처리 및 의약바이오 분야에서 유효물질 분리에 활용되고 있는 알루미나 중공사 분리막은 얇은 두께로 인해 취 급 및 적용시 쉽게 파괴되는 단점이 있기 때문에 분리막의 강도를 100 MPa 이상으로 향상시키기 위한 연구가 필요하다. 본 연구에서는 나노입자의 함량을 0, 1, 3, 5 wt%로 증가시켰을 때 제조된 중공사 분리막의 특성을 평가하였다. 그 결과, 나노입 자의 함량이 증가함에 따라 중공사 분리막의 강도는 79 MPa에서 115 MPa로 증가하였으며, 밀도는 1.76 g/m3에서 1.88 g/m3 으로 증가하였고 기공률과 평균기공크기는 각각 51%에서 48%로, 416 nm에서 352 nm로 감소한 것을 확인하였다. 스폰지구 조가 발달하고 스폰지구조의 기공크기가 향상된 알루미나 중공사 분리막은 100 MPa 이상으로 기계적 강도가 향상되었으며, 약 100000 GPU의 높은 질소 투과도 및 약 3000 L/m2h의 높은 물 투과도를 나타내었다. 따라서, γ-알루미나 나노입자를 소 결조제로 첨가하는 것은 α-알루미나 중공사 분리막의 기계적 강도를 효과적으로 증진시키고 높은 투과성능을 유지할 수 있 는 매우 유효한 방법임을 확인하였다.

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.