• Journal of Powder Materials
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• v.15 no.1
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• pp.23-30
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• 2008

Ni-20Cr-20Fe-5Nb alloy with or without $Y_2O_3$ was manufactured by mechanical alloying process and consolidated by spark plasma sintering (SPS). The grain size of the alloy with $Y_2O_3$ was smaller than that of alloy without $Y_2O_3$ which results from the effect of $Y_2O_3$ suppressing grain growth. The tensile strength at room temperature was increased by the addition of $Y_2O_3$ but decreased abruptly at temperature above $600^{\circ}C$. It seems to result from the change of deformation mechanism due to fine grain size, that is, grain boundary sliding is predominant at above $600^{\circ}C$ while internal dislocation movement is predominant at below $600^{\circ}C$. After conventional heat treatment process of solution treatment and aging, a small amount of ${\delta}(Ni_3Nb)$ phase was formed in Ni-20Cr-20Fe-5Nb alloy while a large amount of ${\gamma}"(Ni_3Nb)$ was formed in Inconel 718 in the previous report. This is due to exhaustion of Nb content by the formation of NbC during consolidation.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2003.10a
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• pp.65-66
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• 2003

1. The oxidation resistance of $Y_{2}O_{3}$ containing Ni-base alloy is superior to that of the alloy without $Y_{2}O_{3}$. 2. The appearance of oxides of Ni-20Cr-20Fe-5Nb-$1Y_{2}O_{3}$ alloy is similar to that of oxides in commercial PM1000 and MA754 alloy. 3. The oxides in ODS alloy are grown mainly at particle boundaries.

• Journal of Powder Materials
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• v.30 no.1
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• pp.1-6
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• 2023

High-entropy alloys (HEAs) are attracting attention because of their excellent properties and functions; however, they are relatively expensive compared with commercial alloys. Therefore, various efforts have been made to reduce the cost of raw materials. In this study, MIM is attempted using coarse equiatomic CoCrFeMnNi HEA powders. The mixing ratio (powder:binder) for HEA feedstock preparation is explored using torque rheometer. The block-shaped green parts are fabricated through a metal injection molding process using feedstock. The thermal debinding conditions are explored by thermogravimetric analysis, and solvent and thermal debinding are performed. It is densified under various sintering conditions considering the melting point of the HEA. The final product, which contains a small amount of non-FCC phase, is manufactured at a sintering temperature of 1250℃.

• Proceedings of the KIEE Conference
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• 2001.11b
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• pp.106-108
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• 2001

As 3V cathode material, a new doping spinel material, LiMn1.6Se0.4O4 powder with a phase-pure polycrystalline was synthesized by a sol-gel method. In spite of Jahn-teller distortion in 3V region($2.4{\sim}3.5V$), the LiMn1.6Se0.4O4 electrode shows no capacity loss. The material in the 3V region initially delivers a discharge capacity of 100mAh/g which increase with cycling to reach 105mAh/g after 90cycles. And 5V cathode material LiNi0.5-xMxMn1.5O4(M=Cr, V, Fe) compounds have been synthesized by sol-gel method. a series of electroactive spinel compounds, LiNi0.5-xMxMn1.5O4(M=Cr, V, Fe) has been studied by crystallographic and electrochemical methods. The material presents only one plateau at around 4.5 V vs. Li/Li+ with a large discharge capacity of 152mAh/g and fairly good cyclability.

• Journal of Powder Materials
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• v.29 no.3
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• pp.240-246
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• 2022

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.

• Journal of Powder Materials
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• v.18 no.5
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• pp.430-436
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• 2011

Joining of NiO-YSZ to 316 stainless steel was carried out with B-Ni2 brazing alloy (3 wt% Fe, 4.5 wt% Si, 3.2 wt% B, 7 wt% Cr, Ni-balance, m.p. 971-$999^{\circ}C$) to seal the NiO-YSZ anode/316 stainless steel interconnect structure in a SOFC. In the present research, interfacial (chemical) reactions during brazing at the NiO-YSZ/316 stainless steel interconnect were enhanced by the two processing methods, a) addition of an electroless nickel plate to NiO-YSZ as a coating or b) deposition of titanium layer onto NiO-YSZ by magnetron plasma sputtering method, with process variables and procedures optimized during the pre-processing. Brazing was performed in a cold-wall vacuum furnace at $1080^{\circ}C$. Post-brazing interfacial morphologies between NiO-YSZ and 316 stainless steel were examined by SEM and EDS methods. The results indicate that B-Ni2 brazing filler alloy was fused fully during brazing and continuous interfacial layer formation depended on the method of pre-coating NiO-YSZ. The inter-diffusion of elements was promoted by titanium-deposition: the diffusion reaction thickness of the interfacial area was reduced to less than 5 ${\mu}m$ compared to 100 ${\mu}m$ for electroless nickel-deposited NiO-YSZ cermet.

• Journal of Powder Materials
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• v.20 no.6
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• pp.432-438
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• 2013

In this study, analysis on the oxidation behavior was conducted by a series of high-temperature oxidation tests at both $800^{\circ}C$, $900^{\circ}C$ and 1000 in the air with sintered STS 316L. The weight gain of each oxidized specimen was measured, the oxidized surface morphologies and composition of oxidation layer were analyzed with Scanning Electron Microscope-Energy Dispersive x-ray Spectroscopy (SEM-EDS), finally, the phase change and composition of the oxidized specimen were shown by X-Ray Diffraction (XRD). As a result, the weight gain increased sharply at $1000^{\circ}C$ when oxidation test was conducted for 210 hours. Also, a plentiful of pores were observed in the surface oxidation layers at $900^{\circ}C$ for 210 hours. In addition, the following conclusions on oxidation behavior of sintered STS 316L can be obtained: $Cr_2O_3$ can be formed on pores by influxing oxygen through open-pores, $(Fe_{0.6}Cr_{0.4})_2O_3$ can be generated on the inner oxidation layer, and $Fe_2O_3$ was on the outer oxidation layer. Also, $NiFe_2O_4$ could be precipitated if the oxidation time was kept longer.

• Journal of Powder Materials
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• v.29 no.3
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• pp.213-218
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• 2022

This study investigates the interfacial reaction between powder-metallurgy high-entropy alloys (HEAs) and cast aluminum. HEA pellets are produced by the spark plasma sintering of Al_0.5CoCrCu_0.5FeNi HEA powder. These sintered pellets are then placed in molten Al, and the phases formed at the interface between the HEA pellets and cast Al are analyzed. First, Kirkendall voids are observed due to the difference in the diffusion rates between the liquid Al and solid HEA phases. In addition, although Co, Fe, and Ni atoms, which have low mixing enthalpies with Al, diffuse toward Al, Cu atoms, which have a high mixing enthalpy with Al, tend to form Al-Cu intermetallic compounds. These results provide guidelines for designing Al matrix composites containing high-entropy phases.

• Journal of the Korean institute of surface engineering
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• v.42 no.5
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• pp.227-231
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• 2009

The niobium capacitor showed somewhat more unstable characteristics than the commercial tantalum capacitors, but is nonetheless considered applicable as a future substitute for tantalum capacitors. In this study, niobium powder was fabricated by metallothermic reduction process using $K_2NbF_7$ as the raw materials, KCl and KF as the diluents and Na as the reducing agent. The niobium particle size greatly decreased from 0.7um to 0.2 um as the amount of diluent increased. However if a higher surface area of powder is required, more diluents need to be used in the said method in order to produce niobium powder. The niobium powder morphology and particle size are very sensitive to a amount of sodium excess. The particle size of niobium powder increased with a increasing amount of sodium excess. When more diluent and sodium are used, the niobium powder will be contaminated with more impurities such as Fe, Cr, Ni so on.

• Journal of Powder Materials
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• v.17 no.6
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• pp.489-493
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• 2010

Nickel-based and iron-based alloys have been developed and commercialized for a wide range of high performance applications at severely corrosive and high temperature environment. This alloy foam has an outstanding performance which is predestinated for diesel particulate filters, heat exchangers, and catalyst support, noise absorbers, battery, fuel cell, and flame distributers in burners in chemical and automotive industry. Production of alloy foam starts from high-tech coating technology and heat treatment of transient liquid-phase sintering in the high temperature. These technology allow for preparation of a wide variety of foam compositions such as Ni, Cr, Al, Fe on various pore size of pure nickel foam or iron foam in order for tailoring material properties to a specific application.