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The emergence of ferrous-medium entropy alloys (FeMEAs) with excellent tensile properties represents a potential direction for designing alloys based on metastable engineering. In this study, an FeMEA is successfully fabricated using laser powder bed fusion (LPBF), a metal additive manufacturing technology. Tensile tests are conducted on the LPBF-processed FeMEA at room temperature and cryogenic temperatures (77 K). At 77 K, the LPBF-processed FeMEA exhibits high yield strength and excellent ultimate tensile strength through active deformation-induced martensitic transformation. Furthermore, due to the low stability of the face-centered cubic (FCC) phase of the LPBF-processed FeMEA based on nano-scale solute heterogeneity, stress-induced martensitic transformation occurs, accompanied by the appearance of a yield point phenomenon during cryogenic tensile deformation. This study elucidates the origin of the yield point phenomenon and deformation behavior of the FeMEA at 77 K.
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In this study, we evaluated the effects of acid leaching on the properties of Cr powder synthesized using self-propagating high-temperature synthesis (SHS). Cr powder was synthesized from a mixture of Cr2O3 and magnesium (Mg) powders using the SHS Process, and the byproducts after the reaction were removed using acid leaching. The properties of the recovered Cr powder were analyzed via X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), particle size analysis (PSA), and oxygen content analysis. The results show that perfect selective leaching of Cr is challenging because of various factors such as incomplete reaction, reaction kinetics, the presence of impurities, and incompatibility between the acid and metal mixture. Therefore, this study provides essential information on the properties under acidic conditions during the production of high-quality Cr powder using a self-propagating high-temperature synthesis method.
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 900°C. The dominant mass transport mechanism seemed to be grain-boundary diffusion during heat treatment at 900°C, 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.
Tungsten carbide is widely used in carbide tools. However, its production process generates a significant number of end-of-life products and by-products. Therefore, it is necessary to develop efficient recycling methods and investigate the remanufacturing of tungsten carbide using recycled materials. Herein, we have recovered 99.9% of the tungsten in cemented carbide hard scrap as tungsten oxide via an alkali leaching process. Subsequently, using the recovered tungsten oxide as a starting material, tungsten carbide has been produced by employing a self-propagating high-temperature synthesis (SHS) method. SHS is advantageous as it reduces the reaction time and is energy-efficient. Tungsten carbide with a carbon content of 6.18 wt % and a particle size of 116 nm has been successfully synthesized by optimizing the SHS process parameters, pulverization, and mixing. In this study, a series of processes for the highefficiency recycling and quality improvement of tungsten-based materials have been developed.
Oxide dispersion-strengthened (ODS) steel has excellent high-temperature properties, corrosion resistance, and oxidation resistance, and is expected to be applicable in various fields. Recently, various studies on mechanical alloying (MA) have been conducted for the dispersion of oxide particles in ODS steel with a high number density. In this study, ODS steel is manufactured by introducing a complex milling process in which planetary ball milling, cryogenic ball milling, and drum ball milling are sequentially performed, and the microstructure and high-temperature mechanical properties of the ODS steel are investigated. The microstructure observation revealed that the structure is stretched in the extrusion direction, even after the heat treatment. In addition, transmission electron microscopy (TEM) analysis confirmed the presence of oxide particles in the range of 5 to 10 nm. As a result of the room-temperature and high-temperature compression tests, the yield strengths were measured as 1430, 1388, 418, and 163 MPa at 25, 500, 700, and 900°C, respectively. Based on these results, the correlation between the microstructure and mechanical properties of ODS steel manufactured using the composite milling process is also discussed.
The effects of drying temperature on the microstructure of porous W fabricated by the freeze-casting process of tert-butyl alcohol slurry with WO3 powder was investigated. Green bodies were hydrogen-reduced at 800°C for 1 h and sintered at 1000°C for 6 h. X-ray diffraction analysis revealed that WO3 powders were completely converted to W without any reaction phases by hydrogen reduction. The sintered body showed pores aligned in the direction of tertbutyl alcohol growth, and the porosity and pore size decreased as the amount of WO3 increased from 5 to 10v ol%. As the drying temperature of the frozen body increased from -25°C to -10°C, the pore size and thickness of the struts increased. The change in microstructural characteristics based on the amount of powder added and the drying temperature was explained by the growth behavior of the freezing agent and the degree of rearrangement of the solid powder during the solidification of the slurry.
In this study, the high-temperature oxidation properties of austenitic 316L stainless steel manufactured by laser powder bed fusion (LPBF) is investigated and compared with conventional 316L manufactured by hot rolling (HR). The initial microstructure of LPBF-SS316L exhibits a molten pool ~100 μm in size and grains grown along the building direction. Isotropic grains (~35 μm) are detected in the HR-SS316L. In high-temperature oxidation tests performed at 700°C and 900°C, LPBF-SS316L demonstrates slightly superior high-temperature oxidation resistance compared to HR-SS316L. After the initial oxidation at 700°C, shown as an increase in weight, almost no further oxidation is observed for both materials. At 900°C, the oxidation weight displays a parabolic trend and both materials exhibit similar behavior. However, at 1100°C, LPBF-SS316L oxidizes in a parabolic manner, but HR-SS316L shows a breakaway oxidation behavior. The oxide layers of LPBF-SS316L and HR-SS316L are mainly composed of Cr2O3, Febased oxides, and spinel phases. In LPBF-SS316L, a uniform Cr depletion region is observed, whereas a Cr depletion region appears at the grain boundary in HR-SS316L. It is evident from the results that the microstructure and the hightemperature oxidation characteristics and behavior are related.
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Zinc selenide (ZnSe) nanoparticles were synthesized in aqueous solution using glutathione (GSH) as a ligand. The influence of the ligand content, reaction temperature, and hydroxyl ion concentration (pH) on the fabrication of the ZnSe particles was investigated. The optical properties of the synthesized ZnSe particles were characterized using various analytical techniques. The nanoparticles absorbed UV-vis light in the range of 350-400 nm, which is shorter than the absorption wavelength of bulk ZnSe particles (460 nm). The lowest ligand concentration for achieving good light absorption and emission properties was 0.6 mmol. The reaction temperature had an impact on the emission properties; photoluminescence spectroscopic analysis showed that the photo-discharge characteristics were greatly enhanced at high temperatures. These discharge characteristics were also affected by the hydroxyl ion concentration in solution; at pH 13, sound emission characteristics were observed, even at a low temperature of 25°C. The manufactured nanoparticles showed excellent light absorption and emission properties, suggesting the possibility of fabricating ZnSe QDs in aqueous solutions at low temperatures.
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In the present study, we investigated the austenite stability of a sintered Fe-based nanocrystalline alloy. The volume fraction of austenite was measured based on the X-ray diffraction data of sintered Fe-based nanocrystalline alloys, which were prepared by high-energy ball milling and spark plasma sintering. The sintered alloy samples showed a higher volume fraction of austenite at room temperature as compared to the equilibrium volume fraction of austenite obtained using thermodynamic calculations, which resulted from the nanosized crystalline structure of the sintered alloy. It was proved that the austenite stability of the sintered Fe-based alloy increased with a rise in the amount of austenite stabilizing elements such as Mn, Ni, and C; however, it increased more effectively with a decrease in the actual grain size. Furthermore, we proposed a new equation to predict the martensite starting temperature for sintered Fe-based alloys.
Nano-sized ZnSe particles are successfully synthesized in an aqueous solution at room temperature using sodium borohydride (NaBH4) and thioglycolic acid (TGA) as the reducing agent and stabilizer, respectively. The effects of the mass ratio of the reducing agent to Se, stabilizer concentration, and stirring time on the synthesis of the ZnSe nanoparticles are evaluated. The light absorption/emission properties of the synthesized nanoparticles are characterized using ultraviolet-visible (UV-vis) spectroscopy, photoluminescence (PL) spectroscopy, and particle size analyzer (PSA) techniques. At least one mass ratio (NaBH4/Se) of the reducing agent should be added to produce ZnSe nanoparticles finer than 10 nm and to absorb UV–vis light shorter than the ZnSe bulk absorption wavelength of 460 nm. As the ratio of the reducing agent increases, the absorption wavelengths in the UV-vis curves are blue-shifted. Stirring in the atmosphere acts as a deterrent to the reduction reaction and formation of nanoparticles, but if not stirred in the atmosphere, the result is on par with synthesis in a nitrogen atmosphere. The stabilizer, TGA, has an impact on the Zn precursor synthesis. The fabricated nanoparticles exhibit excellent photo-absorption/discharge characteristics, suggesting that ZnSe nanoparticles can be alloyed without the need for organic solutions or high-temperature environments.
Bismuth vanadate (BiVO4) is considered a potentially attractive candidate for the visible-light-driven photodegradation of organic pollutants. In an effort to enhance their photocatalytic activities, BiVO4 nanofibers with controlled microstructures, grain sizes, and crystallinities are successfully prepared by electrospinning followed by a precisely controlled heat treatment. The structural features, morphologies, and photo-absorption performances of the asprepared samples are systematically investigated and can be readily controlled by varying the calcination temperature. From the physicochemical analysis results of the synthesized nanofiber, it is found that the nanofiber calcines at a lower temperature, shows a smaller crystallite size, and lower crystallinity. The photocatalytic degradation of rhodamine-B (RhB) reveals that the photocatalytic activity of the BiVO4 nanofibers can be improved by a thermal treatment at a relatively low temperature because of the optimization of the conflicting characteristics, crystallinity, crystallite size, and microstructure. The photocatalytic activity of the nanofiber calcined at 350°C for the degradation of RhB under visible-light irradiation exhibits a greater photocatalytic activity than the nanofibers synthesized at 400°C and 450°C.
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ZrB2 ceramic and ZrB2 ceramic composites with the addition of SiC, WC, and SiC/WC are successfully synthesized by a spark plasma sintering method. During high-temperature oxidation, SiC additive form a SiO2 amorphous outer scale layer and SiC-deplete ZrO2 scale layer, which decrease the oxidation rate. WC addition forms WO3 during the oxidation process to result in a ZrO2/WO3 liquid sintering layer, which is known to improve the antioxidation effect. The addition of SiC and WC to ZrB2 reduces the oxygen effective diffusivity by one-fifth of that of ZrB2. The addition of both SiC and WC shows the formation of a SiO2 outer dense glass layer and ZrO2/WO3 layer so that the anti-oxidation effect is improved three times as much as that of ZrB2. Therefore, SiC- and WC-added ZrB2 has a lower two-order oxygen effective diffusivity than ZrB2; it improves the anti-oxidation performance 3 times as much as that of ZrB2.
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Piezoelectric ceramic specimens with the Pb(Mg1/3Nb2/3)0.65Ti0.35O3 (PMN-PT) composition are prepared by the solid state reaction method known as the “columbite precursor” method. Moreover, the effects of the Li2O-Bi2O3 additive on the microstructure, crystal structure, and piezoelectric properties of sintered PMN-PT ceramic samples are investigated. The addition of Li2O-Bi2O3 lowers the sintering temperature from 1,200°C to 950°C. Moreover, with the addition of >5 wt.% additive, the crystal structure changes from tetragonal to rhombohedral. Notably, the sample with 3 wt.% additive exhibits excellent piezoelectric properties (d33 = 596 pC/N and Kp = 57%) and a sintered density of 7.92 g/cm3 after sintering at 950°C. In addition, the sample exhibits a curie temperature of 138.6°C at 1 kHz. Finally, the compatibility of the sample with a Cu electrode is examined, because the energy-dispersive X-ray spectroscopy data indicate the absence of interdiffusion between Cu and the ceramic material.
In this study, ultrasonic spray pyrolysis combined with salt-assisted decomposition, a process that adds sodium nitrate (NaNO3) into a titanium precursor solution, is used to synthesize nanosized titanium dioxide (TiO2) particles. The added NaNO3 prevents the agglomeration of the primary nanoparticles in the pyrolysis process. The nanoparticles are obtained after a washing process, removing NaNO3 and NaF from the secondary particles, which consist of the salts and TiO2 nanoparticles. The effects of pyrolysis temperature on the size, crystallographic characteristics, and bandgap energy of the synthesized nanoparticles are systematically investigated. The synthesized TiO2 nanoparticles have a size of approximately 2–10 nm a bandgap energy of 3.1–3.25 eV, depending on the synthetic temperature. These differences in properties affect the photocatalytic activities of the synthesized TiO2 nanoparticles.
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Over the last decade, the next generation’s ultra-high-temperature materials as an alternative to Nickel-based superalloys have been highlighted. Ultra-high-temperature materials based on refractory metals are one of several potential candidates. In particular, molybdenum alloys with small amounts of silicon and boron (Mo-Si-B alloys) have superior properties at high temperature. However, research related to Mo-Si-B alloys were mainly conducted by several developed countries but garnered little interest in Korea. Therefore, in this review paper, we introduce the development history of Mo-Si-B alloys briefly and discuss the properties, particularly the mechanical and oxidation properties of Mo-Si-B alloys. We also introduce the latest research trends of Mo-Si-B alloys based on the research paper. Finally, for domestic research related to this field, we explain why Mo-Si-B alloys should be developed and suggest the potential directions for Mo-Si-B alloys research.
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The impact of different mixing methods and sintering temperatures on the microstructure and piezoelectric properties of PZNN-PZT ceramics is investigated. To improve the sinterability and piezoelectric properties of these ceramics, the composition of 0.13Pb((Zn0.8Ni0.2)1/3Nb2/3)O3-0.87Pb(Zr0.5Ti0.5)O3 (PZNN-PZT) containing a Pb-based relaxor component is selected. Two methods are used to create the powder for the PZNN-PZT ceramics. The first involves blending all source powders at once, followed by calcination. The second involves the preferential creation of columbite as a precursor, by reacting NiO with Nb2O5 powder. Subsequently, PZNN-PZT powder can be prepared by mixing the columbite powder, PbO, and other components, followed by an additional calcination step. All the PZNNPZT powder samples in this study show a nearly-pure perovskite phase. High-density PZNN-PZT ceramics can be fabricated using powders prepared by a two-step calcination process, with the addition of 0.3 wt% MnO2 at even relatively low sintering temperatures from 800°C to 1000°C. The grain size of the ceramics at sintering temperatures above 900°C is increased to approximately 3 μm. The optimized PZNN-PZT piezoelectric ceramics show a piezoelectric constant (d33) of 360 pC/N, an electromechanical coupling factor (kp) of 0.61, and a quality factor (Qm) of 275.
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We report the feasibility of TaC production via self-propagating high temperature synthesis, and the influence of the initial green compact density on the final composite particle size. Experiments are carried out from a minimum pressure of 0.3 MPa, the pressure at which the initial green body becomes self-standing, up to 3 MPa, the point at which no further combustion occurs. The green density of the pellets varies from 29.99% to 42.97%, as compared with the theoretical density. The increase in green density decreases the powder size of TaC, and the smallest particle size is observed with 1.5 MPa, at 10.36 μm. Phase analysis results confirm the presence of the TaC phase only. In the range of 0.3-0.5 MPa, traces of unreacted Ta and C residues are detected. However, results also show the presence of only C residue in the matrix within the pressure range of 0.6-3.0 MPa.
In this study we manufacture a Ni-Cr-B-Si +WC/12Co composite coating layer on a Cu base material using a laser cladding (LC) process, and investigate the microstructural and mechanical properties of the LC coating and Ni electroplating layers (reference material). The initial powder used for the LC coating layer is a powder feedstock with an average particle size of 125 μm. To identify the microstructural and mechanical properties, OM, SEM, XRD, room and high temperature hardness, and wear tests are implemented. Microstructural observation of the initial powder and LC coating layer confirm the layer is composed mainly of γ-Ni phases and WC and Cr23C6 carbides. The measured hardness of the LC coating and Ni electroplating layers are 653 and 154 Hv, respectively. The hardness measurement from room up to high temperatures of 700°C result in a hardness decrease as the temperature increases, but the hardness of the LC coating layer is higher for all temperature conditions. Room temperature wear results show that the wear loss of the LC coating layer is 1/12 of the wear level of the Ni electroplating layer. The measured bond strength is also greater in the LC coating than the Ni electroplating.
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Synthesized monocrystalline nanodiamond (nD) particles are heat-treated at various temperatures to produce highly structured diamond crystals. The heat-treated nDs show different weight loss ratios during thermogravimetric analysis. The crystallinities of the heat-treated nDs are analyzed using Raman spectroscopy. The average particle sizes of the heat-treated nDs are measured by a dynamic light scattering (DLS) system and direct imaging observation methods. Moreover, individual dispersion behaviors of the heat-treated nD particles are investigated based on ultrasonic dispersion methods. The average particle sizes of the dispersed nDs according to the two different measurement methods show very similar size distributions. Thus, it is possible to produce highly crystallized nD powder particles by a heattreatment process, and the nD particles are relatively easy to disperse individually without any dispersant. The heattreated nDs can lead to potential applications such as in nanocomposites, quantum dots, and biomedical materials.
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This study investigates the oxidation properties of Fe-14Cr ferritic oxide-dispersion-strengthened (ODS) steel at various high temperatures (900, 1000, and 1100°C for 24 h). The initial microstructure shows that no clear structural change occurs even under high-temperature heat treatment, and the average measured grain size is 0.4 and 1.1 μm for the as-fabricated and heat-treated specimens, respectively. Y–Ti–O nanoclusters 10–50 nm in size are observed. High-temperature oxidation results show that the weight increases by 0.27 and 0.29 mg/cm2 for the asfabricated and heat-treated (900°C) specimens, and by 0.47 and 0.50 mg/cm2 for the as-fabricated and heat-treated (1000°C) specimens, respectively. Further, after 24 h oxidation tests, the weight increases by 56.50 and 100.60 mg/cm2 for the as-fabricated and heat-treated (1100°C) specimens, respectively; the latter increase is approximately 100 times higher than that at 1000°C. Observation of the surface after the oxidation test shows that Cr2O3 is the main oxide on a specimen tested at 1000°C, whereas Fe2O3 and Fe3O4 phases also form on a specimen tested at 1100°C, where the weight increases rapidly. The high-temperature oxidation behavior of Fe-14Cr ODS steel is confirmed to be dominated by changes in the Cr2O3 layer and generation of Fe-based oxides through evaporation.
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In this study, we report the microstructure and the high-temperature oxidation behavior of Fe-Ni alloys by spark plasma sintering. Structural characterization is performed by scanning electron microscopy and X-ray diffraction. The oxidation behavior of Fe-Ni alloys is studied by means of a high-temperature oxidation test at 1000°C in air. The effect of Ni content of Fe-Ni alloys on the microstructure and on the oxidation characteristics is investigated in detail. In the case of Fe-2Ni and Fe-5Ni alloys, the microstructure is a ferrite (α) phase with body centered cubic (BCC) structure, and the microstructure of Fe-10Ni and Fe-20Ni alloys is considered to be a massive martensite (α’) phase with the same BCC structure as that of the ferrite phase. As the Ni content increases, the micro-Vickers hardness of the alloys also increases. It can also be seen that the oxidation resistance is improved by decreasing the thickness of the oxide film.
This study investigates the thermal shock property of a polycrystalline diamond compact (PDC) produced by a high-pressure, high-temperature (HPHT) sintering process. Three kinds of PDCs are manufactured by the HPHT sintering process using different particle sizes of the initial diamond powders: 8-16 μm (D50 = 4.3 μm), 10-20 μm (D50 = 6.92 μm), and 12-22 μm (D50 = 8.94 μm). The microstructure observation results for the manufactured PDCs reveal that elemental Co and W are present along the interface of the diamond particles. The fractions of Co and WC in the PDC increase as the initial particle size decreases. The manufactured PDCs are subjected to thermal shock tests at two temperatures of 780°C and 830°C. The results reveal that the PDC with a smaller particle size of diamond easily produces microscale thermal cracks. This is mainly because of the abundant presence of Co and WC phases along the diamond interface and the easy formation of Co-based (CoO, Co3O4) and W-based (WO2) oxides in the PDC using smaller diamond particles. The microstructural factors for controlling the thermal shock property of PDC material are also discussed.
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In this study, we investigate the effect of the diffusion barrier and substrate temperature on the length of carbon nanotubes. For synthesizing vertically aligned carbon nanotubes, thermal chemical vapor deposition is used and a substrate with a catalytic layer and a buffer layer is prepared using an e-beam evaporator. The length of the carbon nanotubes synthesized on the catalytic layer/diffusion barrier on the silicon substrate is longer than that without a diffusion barrier because the diffusion barrier prevents generation of silicon carbide from the diffusion of carbon atoms into the silicon substrate. The deposition temperature of the catalyst and alumina are varied from room temperature to 150°C, 200°C, and 250°C. On increasing the substrate temperature on depositing the buffer layer on the silicon substrate, shorter carbon nanotubes are obtained owing to the increased bonding force between the buffer layer and silicon substrate. The reason why different lengths of carbon nanotubes are obtained is that the higher bonding force between the buffer layer and the substrate layer prevents uniformity of catalytic islands for synthesizing carbon nanotubes.
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The organic binder-free paste for dye-sensitized solar cell (DSSC) has been investigated using peroxo titanium complex. The crystal structure of TiO2 nanoparticles, morphology of TiO2 film and electrical properties are analyzed by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Electrochemical Impedance Spectra (EIS), and solar simulator. The synthesized TiO2 nanopowders by the peroxo titanium complex at 150, 300, 400°C, and 450°C have anatase phase and average crystal sizes are calculated to be 4.2, 13.7, 16.9, and 20.9 nm, respectively. The DSSC prepared by the peroxo titanium complex binder have higher Voc and lower Jsc values than that of the organic binder. It can be attributed to improvement of sintering properties of TCO/TiO2 and TiO2/TiO2 interface and to formation of agglomerate by the nanoparticles. As a result, we have investigated the organic binder-free paste and 3.178% conversion efficiency of the DSSC at 450°C.
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MgB2 bulk superconductors are synthesized by the solid state reaction of (MgB4+xMg) precursors with excessive Mg compositions (x=1.0, 1.4, 2.0 and 2.4). The MgB4 precursors are synthesized using (Mg+B) powders. The secondary phases (MgB4 and MgO) present in the synthesized MgB4 are removed by HNO3 leaching. It is found that the formation reaction of MgB2 is accelerated when Mg excessive compositions are used. The magnetization curves of Mg1+xB2 samples show that the transition from the normal state to the superconducting state of the Mg excessive samples with x=0.5 and x=0.7 are sharper than that of MgB2. The highest
The GaN-powder scrap generated in the manufacturing process of LED contains significant amounts of gallium. This waste can be an important resource for gallium through recycling of scraps. In the present study, the influence of annealing temperatures on the structural properties of GaN powder was investigated when the waste was recycled through the mechanochemical oxidation process. The annealing temperature varied from 200°C to 1100°C and the changes in crystal structure and microstructure were studied. The annealed powder was characterized using various analytical tools such as TGA, XRD, SEM, and XRF. The results indicate that GaN structure was fully changed to Ga2O3 structure when annealed above 900°C for 2 h. And, as the annealing temperature increased, crystallinity and particle size were enhanced. The increase in particle size of gallium oxide was possibly promoted by powder-sintering which merged particles to larger than 50 nm.
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In this study, ternary compound Max Phase Ti2AlC material was mixed by 3D ball milling as a function of ball milling time. More than 99.5 wt% pure Ti2AlC was synthesized by using spark plasma sintering method at 1000, 1100, 1200, and 1300°C for 60 min. The material characteristics of synthesized samples were examined with relative density, hardness, and electrical conductivity as a function of sintering temperature. The phase composition of bulk was identified by X-ray diffraction. On the basis of FE-SEM result, a terraced structures which consists of several laminated layers were observed. And Ti2AlC bulk material obtained a vickers hardness of 5.1 GPa at the sintering temperature of 1100°C.
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The porous metals are known as relatively excellent characteristic such as large surface area, light, lower heat capacity, high toughness and permeability. The Fe-Cr-Al alloys have high corrosion resistance, heat resistance and chemical stability for high temperature applications. And then many researches are developed the Fe-Cr-Al porous metals for exhaust gas filter, hydrogen reformer catalyst support and chemical filter. In this study, the Fe-Cr-Al porous metals are developed with Fe-22Cr-6Al(wt) powder using powder compaction method. The mean size of Fe-22Cr-6Al(wt) powders is about 42.69 μm. In order to control pore size and porosity, Fe-Cr-Al powders are sintered at 1200~1450°C and different sintering maintenance as 1~4 hours. The powders are pressed on disk shapes of 3 mm thickness using uniaxial press machine and sintered in high vacuum condition. The pore properties are evaluated using capillary flow porometer. As sintering temperature increased, relative density is increased from 73% to 96% and porosity, pore size are decreased from 27 to 3.3%, from 3.1 to 1.8 μm respectively. When the sintering time is increased, the relative density is also increased from 76.5% to 84.7% and porosity, pore size are decreased from 23.5% to 15.3%, from 2.7 to 2.08 μm respectively.
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Silicon carbide(SiC) layer is particularly important tri-isotropic (TRISO) coating layers because it acts as a miniature pressure vessel and a diffusion barrier to gaseous and metallic fission products in the TRISO coated particle. The high temperature deposition of SiC layer normally performed at 1500-1650°C has a negative effect on the property of IPyC layer by increasing its anisotropy. To investigate the feasibility of lower temperature SiC deposition, the influence of deposition temperature on the property of SiC layer are examined in this study. While the SiC layer coated at 1500°C obtains nearly stoichiometric composition, the composition of the SiC layer coated at 1300-1400°C shows discrepancy from stoichiometric ratio(1:1). 3-7 μm grain size of SiC layer coated at 1500°C is decreased to sub-micrometer (<1 μm) -2 μm grain size when coated at 1400°C, and further decreased to nano grain size when coated at 1300- 1350°C. Moreover, the high density of SiC layer (≥3.19 g/cm3) which is easily obtained at 1500°C coating is difficult to achieve at lower temperature owing to nano size pores. the density is remarkably decreased with decreasing SiC deposition temperature.
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A high temperature dilatometer attached to a graphite furnace is built and used to study the sintering behavior of B4C. Pristine and carbon doped B4C compacts are sintered at various soaking temperatures and their shrinkage profiles are detected simultaneously using the dilatometer. Carbon additions enhance the sinterability of B4C with sintering to more than 97% of the theoretical density, while pristine B4C compacts could not be sintered above 91% due to particle coarsening. The shrinkage profiles of B4C reveal that the effect of carbon on the sinterability of B4C can be seen mostly below 1950°C. The high temperature dilatometer delivers very useful information which is impossible to obtain with conventional furnaces.
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Fe-Cr-Al powder porous metal was manufactured by using new electro-spray process. First, ultra-fine fecralloy powders were produced by using the submerged electric wire explosion process. Evenly distributed colloid (0.05~0.5% powders) was dispersed on Polyurethane foam through the electro-spray process. And then degreasing and sintering processes were conduced. In order to examine the effect of cell size (200 μm, 450 μm, 500 μm) in process, pre-samples were sintered for two hours at temperature of 1450°C, in H2 atmospheres. A 24-hour thermo gravimetric analysis test was conducted at 1000°C in a 79% N2 + 21% O2 to investigate the high temperature oxidation behavior of powder porous metal. The results of the high temperature oxidation tests showed that oxidation resistance increased with increasing cell size. In the 200 μm porous metal with a thinner strut and larger specific surface area, the depletion of the stabilizing elements such as Al and Cr occurred more quickly during the high-temperature oxidation compared with the 450, 500 μm porous metals.
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