• Korean Journal of Materials Research
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• v.8 no.6
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• pp.538-544
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• 1998

The spallation of a thermal barrier coating layer depends on the formation of brittle spinels. thermal expansion mismatch between ceramic and metal. the phase transformation of a ceramic layer and residual stress of coating layer. In this work. the formation mechanism of oxide scale formed by oxidation treatment at 90$0^{\circ}C$ was investigated in order to verify oxidation behavior at the interface between E-beam coated $Zr0_2$-7wt.% $Y_20_3$ and plasma sprayed CoNiCrAIY. Some elements distributed in the bond coating layer were selectively oxidized after oxidation. At the initial time of oxidation. AI-depletion zone and $\alpha$-$Al_O_3$,O, were formed at the bond coating layer by the AI-outward diffusion. After layer grew until critical thickness. spinels. $Cr_20$, and $C0_2CrO_4$ by outward diffusion of Co. Cr, Ni were formed. It was found that the formation of spinels may be related to the spallation of $Zr0_2$-7wt.% $Y_20_3$ during isothermal oxidation.

• Journal of Welding and Joining
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• v.19 no.1
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• pp.75-81
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• 2001

The metallurgical study of microconstituents in transient liquid phase bonded joints of Ni-base single crystal superalloys, CMSX-2 and CMSX-4 was investigated employing MBF-80 insert metal. TLP bonding of specimens was carried out at 1,373~1,523K for 0~19.6ks in vacuum. Three types of microconstituents ; needle-like constituent, dot-like constituent and abnormal shape constituent were formed in the bonded interlayer during TLP bonding operation. All these microconstituents were identified as boride. Microconstituents contain a large percentage of Cr in the early stage of bonding. As increasing the holding time, the amount of Cr was decreased and the amount of W, Co and Re were increased. From the analysis results of electron diffraction pattern by TEM, composition of elements in microconstituents were into MBlongrightarrowM$_{5}$B$_3$longrightarrowM$_2$B type with the increased in holding time. It can be explained by the fact that the relative amount of boron in microconstituents was decreased when the holding time was increased.d.

• Journal of the Korean institute of surface engineering
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• v.34 no.5
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• pp.499-502
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• 2001

Functionally gradient NiCrAlY/$ZrO_2$-$Y_2$$O_3$ and NiCrAlY/$ZrO_2$- $CeO_2$-$Y_2$$O_3$ coatings were prepared by APS. The as-sprayed microstructure consisted of metal-rich and ceramic-rich regions, between which $Al_2$$O_3$-rich layers existed owing to the oxidation during APS. During oxidation between 900 and $1100^{\circ}C$ in air, the pre-existing $Al_2$$O_3$-rich scales grew, due mainly to the preferential reaction of Al with inwardly transporting oxygen along the heterogeneous phase boundaries. As the amount of ceramics in the coating increased, the oxidation resistance increased.

• Analytical Science and Technology
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• v.6 no.2
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• pp.197-205
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• 1993

Blends of elemental Ni and 20 weight % Cr powder were milled for different period in a laboratory attritor. Powder size distribution, microstructure and X-ray diffraction characteristics were investigated as a function of processing period. Saturated magnetization, Ms and coercive force, Hc we also measured and compared with plasma melted ingot to confirm the mechanically alloyed states. Mechanical alloying occurred as a consequence of the partition of powders and the increase of interfacial area driving diffusing of Cr into Ni. However, magnetic properties of chemically homogeneous solid solution like melted ingot has not been observed even though steady state of submicron grain size has been achieved after milling over 15 hrs. Further mechanical alloying period gave refinement of grain size, which resulted in the increase of alloyed layer. It is concluded that homogenization should be controlled by the increase of interfacial area between constitutive powders caused by plastic particle deformation and by the diffusion of Cr within the alloyed phase into Ni-rich phase through lattice defects.

• Journal of the Korean institute of surface engineering
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• v.32 no.1
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• pp.67-77
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• 1999

The Ni base superalloy Mar-M247 substrate was aluminized or aluminized after boronizing by the pack cementation under Ar atmosphere. The hot corrosion resistance and after-heat-treatment effect of aluminized specimens were studied by the cyclic hot corrosion test in $Na_2SO_4$-NaCl molten salt. XRD analysis showed that the $Ni_2Al_3$ phase was formed between the coated layer and substrate below 1273K but the NiAl phase above 1273K. The peak of the NiAl phase was developed after heat treatment. Corrosion test showed that corrosion resistance of the specimen with the NiAl phase was better than that with the $Ni_2Al_3$ phase. Corrosion resistance could be improved by heat treatment to form ductile NiAl phase, where cracks were not formed by thermal shock on coating layer. Moreover, it appeared that heat treatment played a role to improve corrosion resistance of Al diffusion coating above 1273K. The existence of boron in the Al diffusion coating layer obstructed outwared diffusion of Cr from the substrate, and it influenced on corrosion resistance of the coating layer by weakening adherence of the oxide scale.

• Journal of the Korean Ceramic Society
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• v.32 no.11
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• pp.1219-1226
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• 1995

Creep behaviors of Cr3C2 composites containing 90 wt% Cr3C2 and 10 wt% Ni were studied at high temperature. Compression tests at 100$0^{\circ}C$ and bending tests at 100$0^{\circ}C$ and 105$0^{\circ}C$ were done in argon environment. In all test conditions primary and steady-state creep behaviors were observed. Stress exponent and activatiion energy were determined from the experimental data. By microstructural analysis of Cr3C2 composites after creep test, the separate agglomerations of Ni phase were observed. Numerical analysis was also studied to analyze bending creep behaviors of Cr3C2 by assumming different tensile and compressive creep behavior in a bending sample. From the analysis, it was found that the stress state at the compressive region as applied stress increased. The observed creep rates were compared with the predicted creep rates by estimating power-law creep parameters from bending test data.

• Journal of the Korean institute of surface engineering
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• v.50 no.2
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• pp.91-97
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• 2017

The aim of this paper is to investigate the characteristics of electrochemical corrosion with the plasma ion nitriding temperature for 16Cr-10Ni-2Mo stainless steel. The corrosion behavior was analyzed by means of galvanostatic experiment in natural seawater that applied various current density with plasma ion nitriding temperature parameters. In result of galvanostatic experiment, relatively less surface damage morphology and the less damage depth was observed at a nitrided temperature of $450^{\circ}C$ that measured the thickest nitrided layer(S-phase). On the other hand, the most damage depth and unified corrosion behavior presented at a temperature of $500^{\circ}C$.

• Journal of Korea Foundry Society
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• v.17 no.3
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• pp.258-266
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• 1997

The purpose of this study is to improve hardness and wear resistance of high strength yellow brass by adding Fe, Cr, Mn, Si and Ni. Results showed that NiO, $FeCr_2O_4$ and intermetallic compound $Mn_5Si_3$ were produced when Ni, Fe-Cr and Mn-Si were added to the yellow brass. The hardness and wear tests showed the best results with the presence of the product precipitates and intermetallic compound. The calculation of relative wear resistance by volume fraction of each phases showed that the relative wear resistance of $Mn_5Si_3$ had the highest value, that of ${\beta}$ phase had the lowest. Observation of the worn surface showed that the main wear mechanism were found to be the abrasive wear, and also showed that the wear is caused by mechanical failure at the early stage.

• Journal of Welding and Joining
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• v.17 no.4
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• pp.53-59
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• 1999

Amorphous alloys have also been called glassy alloys or non-crystalline alloys. They are made by the rapid solidification. The solidification occurs so rapid that the atoms are frozen in their liquid configuration. There are unique magnetic, mechanical, electrical and corrosive behaviors which result form their amorphous structure. In the study. amorphous coatings were manufactured with Ni-Cr-B-Si powders by flame spray. Measurement of hardness, were resistance, corrosion resistance and observation of microstructures and XRD, DSC were performed to investigate characteristics of amorphous coatings. The experimental results obtained as follow: 1) Amorphous powders could not be manufactured with the spraying in the spraying in the liquid nitrogen. But, amorphous coatings could be manufactured with the rotation cooling method by liquid nitrogen. In the fabrication of amorphous coatings, major factor was the rapid cooling by rotation of the substrate. 2) Hardness of coatings was obtained Hv 960 by formation of amorphous phase. But, wear resistance decreased. That was due to porosity in the coatings by the rapid cooling. 3) In the case of corrosion resistance, amorphous coatings were superior to air-cooled coatings. That was due to formation of amorphous phase. 4) After amorphous coatings were heat-treated at 520℃ for 1hr. hardness increased 80% and wear resistance increased 30% comparing with air cooled coatings. These were due to crystallization of amorphous phase and decrease of porosity by heat-treatment.

• Journal of the Korean Magnetics Society
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• v.3 no.1
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• pp.7-12
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• 1993

The effects of Mn, Cr or Co addItion on the magnetic properties of Fe-Ni Invar alloys were investigated. The composition range of the three additives is up to 5wt%. In the temperature range of room temperature-$250^{\circ}C$, the variation of specific magnetization with the addition of Mn, Cr or Co in the Fe-Ni alloys except for 5wt% Co shows the phenomenon characteristics of the Invar effect, viz., the specific magnetization decreases very abrubtly with the temperature and the dependence of temperature on the specific magnetization is in the mixed form of $T^{3/2}$ and $T^{2}$. In the room temperature, the amount of increase in the specific magnetization, Curie temperature and coercivity is in order of Co > Cr > Mn. In the case of 5wt% Co an anomalous phenomena were observed due to the occurrance of ferromagnetic $\alpha$ phase which reduces the invar effect.