• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.10
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• pp.3234-3242
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• 1996

This paper describes experimental results of modified small punch( MSP) test conducted to evaluate the fracure characteristics and mechanical properties of plasma sparayed zirconia ($ZrO_2$ stabilized with 8wt. % $Y_20_3$ : YSZ) NiCrAlY composite. The mixing ratios of YSZ/NiCrAlY were 0/100, 25/75, 50/50, 100/0 v.%. Test temperatures ranged from 293K to 1473K. This study is directed at development of thermal barrrier coating(TBC) system with superior heat resistance and mechanical properties. The microstructure and fracture process of the composite were examined by SEM and AE method. The mechanical properties of 100% YSZ were nearly independent of the temperatures tested in this study. In contrast, the NiCrAlY-containing composites showed a significant decrease of the mechanical properties above 1273K, showing a ductile- brittle transition behavior up to the temperature. Furthermore, it can seen that 25% YSZ/75% NiCrAlY composite gave the highest fracure strength and fracture energy among the mixing ratio tested over the temperature range.

• Journal of Korea Foundry Society
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• v.20 no.1
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• pp.21-28
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• 2000

Ni and Ni-Cr porous metals which are estimated to be easy to fabricate by squeeze casting are used as strengtheners for composite materials. As a matrix material, Al-7%wtSi-0.3 wt%Mg(AC4C) has been used. In case of Ni/AC4C and Ni-Cr/AC4C composite, $750^{\circ}C$ melt temperature and minimum 25 MPa squeezing pressure are needed to produce sound composite materials. The observation of interfacial reaction zone at various heat treatment condition showed that solutionizing temperature of above 520^{\circ}C$, the interfacial reaction zone increased proportionally with increasing heat treatment tim and reaction products formed by interfacial reaction are mainly composed of $Al_3Ni$ and $Al_3Ni_2$ phases. The tensile strength of Ni/AC4C and Ni-Cr/AC4C composite is lower than the matrix metal and this can be explained by the brittle intermetallic compounds formed at the interface of Ni and Ni-Cr reinforcements. But the properies of hardness, wear resistance and thermal expansion are better than the matrix due to the strengthening effect of Ni-Cr porous metals.

• Journal of the Korean institute of surface engineering
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• v.29 no.3
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• pp.163-175
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• 1996

Flame-sprayed Ni-based coatings are investigated in order to improve the thermal fatigue properties of gray cast iron in the presence of water spraying. The results of thermal cycling tests from room temperature to $1100^{\circ}C$ indicate that thermal fatigue endurance is increased in the order of Ni-20%Cr, NiCr-6%Al, and Ni-5%Al. The thermal fatigue failure is caused by the formation of iron oxides between the coating and the substrate and then the thermal fatigue cracks have propagated either along the brittle iron oxide layer resulting in the spatting of the coatings in case of Ni-5%Al and NiCr-6%Al coatings or to the substrate resulting in the whole specimen fracture in case of Ni-20%Cr coating. It seems that the most governing factor for thermal fatigue resistance is the thermal expansion coefficient difference between the coating and the substrate. Microstructural variations before and after the tests are also discussed.

• Resources Recycling
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• v.16 no.6
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• pp.3-9
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• 2007

Although the ferrous material was separated by the magnetic separation before the incineration process, the municipal solid waste incineration bottom ash generated during incinerator in metropolitan area consists of many iron products which account for about $3{\sim}11%$ as well as ceramics and glasses. The formation of $NiFe_2O_4$ and $FeCr_2O_4$ with a $Fe_3O_4-Fe_2O_3$ (similar to pure Fe) on the surface of iron product was found during air-annealing in the incinerator at $1000^{\circ}C$, because Ni and Cr has a chemical attraction about iron is using to coat with Ni and Cr metals for poish or to prevent corrosion. Therefore, Fe-Ni Cr oxide can be formed on durface of the iron product and it can be separated from bottom ash through the magnetic separation. So, in this study, the separation ratio of heavy metals as magnetic separation and mineralogical formation of Fe-ion(heavy metal) in ferrous metals corroded were investigated. As the result, the separation ratio of Ni and Cr based on particle sizes accounted for about $45{\sim}50%$, and Cu and Pb accounted for below 20%. Also, the leaching concentration of Ni and Cr in bottom ash separated by magnetic separation was lower than that in fresh bottom ash.

• Korean Journal of Materials Research
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• v.28 no.6
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• pp.324-329
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• 2018

Needle-like NiO protecting layers on NiCrAl alloy foam, used as support for hydrogen production, are introduced through electroplated Ni and subsequent microwave annealing. To improve the stability of the NiCrAl alloy foam, oxygen concentration of microwave annealing to form a needle-like NiO layer with good chemical stability and corrosion resistance is controlled in a range of 20 and 50 %. As the oxygen concentration increases to 50 %, needle-like NiO forms a dense coating layer on the NiCrAl alloy foam; this layer formation can be attributed to accelerated growth of the (200) plane. In addition, the increased oxygen concentration causes increased NiO/Ni ratio of the resultant coating layer on NiCrAl alloy foam due to improved rate of the oxidation reaction. As a result, the introduction of dense needle-like NiO layers formed at 50 % oxygen concentration improves the chemical stability of the NiCrAl alloy foam by protecting the direct electrochemical reaction between the electrolyte and the foam. Thus, needle-like NiO can be proposed as a superb protecting layer to improve the chemical stability of NiCrAl alloy form.

• Proceedings of the KIEE Conference
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• 2001.11a
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• pp.168-170
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• 2001

The NiCr is an important material for present thin-film resistor application owing to its low TCR and thermal stability. In this work, the NiCr thin films were deposited on corning glass substrate by reactive magnetron sputtering and the annealing at temperatures range from 300 to $500^{\circ}C$ for 20 min in vacuum. X-ray, AFM, $R_s$(surface leakage current) have been used to study the structural and electrical properties of the NiCr thin films. The high precision NiCr thin films resistor with TCR(temperature coefficient of resistance) of less then 10 ppm/$^{\circ}C$ was obtained under in in-situ annealing at $300^{\circ}C$ on Cr buffer layer substrate. It is clear that the NiCr thin-films resistor electrical properties are low TCR related with it's annealing and buffer layer condition. NiCr thin film resistor having a good thermal stability and low TCR properties are expected for the application to the dielectric material of passive component.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.81-84
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• 2004

The NiCr is an important material for present thin-film resistor application owing to its low TCR and thermal stability. In this work, the NiCr thin films were deposited on coming glass substrate by reactive magnetron sputtering and the annealing at temperatures range from 300 to $500^{\circ}C$ for 20 min in vacuum. X-ray, AFM, $R_s$(surface leakage current) have been used to study the structural and electrical properties of the NiCr thin films. The high precision NiCr thin films resistor with TCR(temperature coefficient of resistance) of less then $10\;ppm/^{\circ}C$ was obtained under in in-situ annealing at $300^{\circ}C$ on Cr buffer layer substrate. It is clear that the NiCr thin-films resistor electrical properties are low TCR related with it's annealing and buffer layer condition. NiCr thin film resistor having a good thermal stability and low TCR properties are expected for the application to the dielectric material of passive component.

• Proceedings of the KWS Conference
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• 1996.10a
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• pp.3-15
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• 1996

The formation of a thicker hard alloyed layer have been investigated on the surface of aluminum cast alloy (AC2B) by PTA overlaying process with Cr, Cu and Ni motel powders under the condition of overlaying current 125-200A. overlaying speed 150 mm/min and different powder feeding rate 5-20 g/min. In addition the characteristics of hardening and wear resistance of alloyed layer here been examined in relation to the microstructure of alloyed layer. Main results obtained were summarized as follows: 1) There was an optimum overlaying condition to get a good alloyed layer with smooth surface. This good layer became easy to be formed as increasing overlaying current and decreasing powder feeding rate under a constant overlaying speed. 2) Cu powder was the most superior one in metal powders used due to a wide optimum overlaying condition range, uniform hardness distribution of Hv250-350, good oar resistance and freedom from cracking in alloyed layer with fine hyper-eutectic structure. 3) On the contrary, irregular hardness distribution was usually obtained in Cr ar Ni alloyed layers of which hardness was increased as Cr or Ni contents and reached to maximum hardness of about Hv400-850 at about 60wt%cr or 40wt%Ni in alloyed layer. 4) Cracking occurred in Cr or Ni alloyed layers with higher hardness than Hv250-300 at mere than 20-25wt% of Cr or Ni contents in alloyed layer. Porosity was observed in all alloyed layers but decreased by usage of spherical powder with smooth surface.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2004.04a
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• pp.42-43
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• 2004

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2002.11a
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• pp.41-42
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• 2002