• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 1995.11a
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• pp.9-9
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• 1995

MATERIAL AND PROCESS VARIABLES THAT STRONGLY AFFECT THE CORROSION RESISTANCE OF PA4 STAINLESS STEELS, INCLUDE : ALLOY COMPOSITION, POWDER CLEANLINESS, NITROGEN, OXYGEN AND GARBON CONTENTS, CHROMIUM DEPLETION DUE TO SURFACE EVAPORATION AND SINTERED DENSITY. THE OPTIMUM PROCESS PARAMETERS FOR DELUBRICATION AND SINTERING THAT RESULT IN LOWEST LEVELS OF NITROGEN, OXYGEN AND CARBON AND MINIMUM LEVELS OF CHROMIUM DEPLETION WILL BE PRESENTED, FOR A NUMBER OF AUSTENTIC AND FERRITIC STAINLESS STEELS. THE EFFECT OF SINTERED DENSITY ON THE CORROSION RESISTANCE OF BOTH AUSTENITIC AND FERRITIC GRADES OF STAINLESS STEEL WILL ALSO BE COVERED.

• Journal of Korea Foundry Society
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• v.29 no.2
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• pp.59-63
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• 2009

Effects of Ti on damping capacity and mechanical properties are investigated in hot rolled Fe-17%Mn alloy. The existing damping alloy with Fe-Mn binary system was limited the use by high production cost, however in case of using scrap iron instead of pure iron although the content of carbon is higher it is possible to be applied wider field especially construction items because the production cost is lower. However, the excellent specific damping capacity is dropped due to the high content of carbon, we developed advanced type of damping alloy included Ti. TiC is formed with added Ti and it holds the specific damping capacity similar to existing damping alloy. The effect of Ti on damping capacity is found to be beneficial in carbon-containing alloy, which is attributed to the depletion of carbon solute due to the formation of TiC.

• Journal of Magnetics
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• v.18 no.3
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• pp.348-351
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• 2013

Inconel 600 alloy, Ni base alloy, is widely used for steam generator tubings where sensitization occurs at grain boundaries and sensitization will induce tubing failures. This alloy has usually paramagnetic property, however, it transforms into ferromagnetic property along grain boundaries when sensitization occurs: this means NDE using magnetism for sensitization is possible. Therefore, in this study, Inconel 600 alloys were heat treated at 873 K from 0 to 400 hours so as to generate sensitization and their magnetic properties were investigated in detail. The saturation and the residual magnetization increase with increasing heat treatment time and take a maximum. On the other hand, the coercive force decreases with the increase in time of heat treatment. We confirmed that characteristics at only grain boundaries change into ferromagnetic phase by a MFM observation. As a trial for industrial application, heat treated Inconel 600 alloy was scanned by a magnetic field sensor, and the variations in magnetization were obtained nondestructively. The results indicate a feasibility of magnetic NDE for sensitization of Inconel 600 alloy.

• Journal of the Korean Society for Heat Treatment
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• v.26 no.3
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• pp.105-112
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• 2013

The microstructural changes of Fe-20Mn-12Cr-1Cu alloy have been studied during high temperature gas nitriding (HTGN) at the range of $1000^{\circ}C{\sim}1150^{\circ}C$ in an atmosphere of nitrogen gas. The mixed microstructure of austenite and ${\varepsilon}$-martensite of as-received alloy was changed to austenite single phase after HTGN treatment at the nitrogen-permeated surface layer, however the interior region that was not affected nitrogen permeation remained the structure of austenite and ${\varepsilon}$-martensite. With raising the HTGN treatment temperature, the concentration and permeation depth of nitrogen, which is known as the austenite stabilizing element, were increased. Accordingly, the depth of austenite single phase region was increased. The outmost surface of HTGN treated alloy at $1000^{\circ}C$ appeared Cr nitride. And this was in good agreement with the thermodynamically calculated phase diagram. The grain growth was delayed after HTGN treatment temperature ranges of $1000^{\circ}C{\sim}1100^{\circ}C$ due to the grain boundary precipitates. For the HTGN treatment temperature of $1150^{\circ}C$, the fine grain region was shown at the near surface due to the grain boundary precipitates, however, owing to the depletion of grain boundary precipitates, coarse grain was appeared at the depth far from the surface. This depletion may come from the strong affinity between nitrogen and substitutional element of Al and Ti leading the diffusion of these elements from interior to surface. Because of the nitrogen dissolution at the nitrogen-permeated surface layer by HTGN treatment, the surface hardness was increased above 150 Hv compared to the interior region that was consisted with the mixed microstructure of austenite and ${\varepsilon}$-martensite.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.10
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• pp.806-813
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• 2018

The fracture of a turbine blade of aerospace engine is presented. Although there are a lot of causes and failure modes in blades, the main failure modes are two ways that fracture and fatigue. Degradation of blade material affects most failure modes. Total propagation of failure in this study specifies failure of fracture type. Some section appears fatigue mode. Especially since this study describes analysis of failure for blade in high temperature, it can be a case in point. Analysed blade is Ni super alloy. Investigations of blade are visual inspection, material, microstructure, high temperature stress rupture creep test, analysis and fracture surface, etc. The root cause for fracture was stress rupture due to abnormal thermal environment. Thermal property of Ni super alloy is excellent but if each chemical composition of alloys are different due to change mechanical properties, selection of material is very important.

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05b
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• pp.66-71
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• 1998

A study of treatment effects on laser surface melted Ni-base alloy 600, especially on precipitation behavior ad chemical composition changes on the grain boundary were conducted with microscopic equipments. Long-term aging treatment at 40$0^{\circ}C$ caused no considerable effects on the grain boundary properties. Cr-rich M$_2$$_3$C$_{6}$ and Cr$_{7}$C$_3$ carbides were precipitated and the resultant Cr depletion below 12 wt pct on some high angle grain boundaries was occurred by heat treatment at $600^{\circ}C$ for 24 hours. These results can imply that the resistance of intergranular stress corrosion cracking of heat treated alloy 600 might not be changed considerably in comparion with the as-LSM one.e.e.

• Journal of the Korean institute of surface engineering
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• v.29 no.6
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• pp.607-614
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• 1996

Yttrium(Y) coating was incorporated by ion-plating method either directly on the TiAl substrate or after pack aluminizing on TiAl to improve the oxidation resistance of TiAl alloy. After Y-coating, heat treatment at low oxygen partial pressure was carried out. Performance of various coating was evaluated by isothermal and cyclic oxidation tests. A simple Y-coating without pack aluminizing can give a detrimental effect on the. oxidation resistance of TiAl alloy, because it enhances formation of $TiO_2$. On the other hand, a composite coating of aluminide-yttrium has shown excellent oxidation resistance. A continuous protective $Al_2O_3$ scale is formed on the aluminized TiAl, and Y-coating improves $Al_2O_3$ scale adherence and substantially prevents depletion of Al in the aluminide-coating layer.

• Corrosion Science and Technology
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• v.3 no.4
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• pp.131-139
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• 2004

Effects of PbO on the repassivation kinetics and characteristics of passive film of Alloy 690 were examined to elucidate the influences of PbO on the SCC resistance of that alloy. The repassivation kinetics of the alloy was analyzed in terms of the current density flowing from the scratch, i(t), as a function of the charge density that has flowed from the scratch, q(t). Repassivation on the scratched surface of the alloy occurred in two kinetically different processes; passive film initially nucleated and grew according to the place exchange model in which log i(t) is linearly proportional to q(t), and then grew according to the high field ion conduction model in which log i(t) is linearly proportional to 1/q(t) with a slope of cBV. The cBV is found to be a parameter representing repassivation rate and hence SCC susceptibility of the alloy. The lower the value of cBV, the faster the repassivation rate and the higher the SCC resistance of an alloy. Addition of PbO to pH 4 and 10 solutions increased the value of cBV of alloy 690, reflecting slower repassivation rate than without PbO. The change in the value of cBV was grater in pH 10 than in pH 4. The increase in SCC susceptibility of alloy 690 with the addition of PbO to solution was presumably due to the Cr-depletion in the outer parts of passive film of the alloy with an incorporation of Pb compounds in the film, which was revealed by Mott-Schottky, AES and XPS analyses.

• Corrosion Science and Technology
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• v.5 no.5
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• pp.168-172
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• 2006

Alloy 600 having a superior resistance to a corrosion is used as a steam generator tubing in nuclear power plants. In spite of its high corrosion resistance, there are many tubings which experience corrosion problems such as a SCC under the high temperature and high pressure environments of nuclear power plants. The Alloy 600 tubing can be repaired by using a Ni electroplating having an excellent SCC resistance. In order to carry out a successful Ni electrodeposition inside a steam generator tubing, the effects of various parameters on the material properties of the electrodeposit should be elucidated. Hence this work deals with the effects of an applied current density, duty cycle($T_{on}/(T_{on}+T_{off})$) of a pulse current, bath temperature and solution pH on the material properties of Ni electrodeposit obtained from a Ni sulphamate bath by analyzing the current efficiency, potentiodynamic curve, hardness and stress-strain curve. Hardness, YS(yield strength) and TS(tensile strength) decreased whereas the elongation increased as the applied current density increased. This was thought to be by a concentration depletion at the interface of the electrodeposit/solution, and a fractional decrease of the hydrogen reduction reaction. As the duty cycle increased, the hardness, YS and TS decreased while the elongation increased. During an off time at a high duty cycle, the concentration depletion could not be recovered sufficiently enough to induce a coarse grain sized electrodeposit. With an increase of the solution temperature and pH, the YS and TS increased while the elongation decreased. The experimental results of the hardness and the stress-strain curves can be supplemented by the results of the potentiodynamic curve.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.65-69
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• 2002

An Al film deposited on the Kovar alloy substrate was anodically-bonded to the borosilicate glass, and the bond interfaces was closely investigated by transmission electron microscopy. Al oxide was found to form a layer ~l0 nm thick at the bond interface, and fibrous structure of the same oxide was found to grow epitaxially in the glass from the oxide layer. The fibrous structure grew with the bonding time. The mechanism of the formation of this fibrous structure is proposed on the basis of the migration of Al ions under the electric field. Penetration of Al into glass beyond the interfacial Al oxide was not detected. The comparison of the amount of excess oxygen ions generated in the alkali depletion layer with that incorporated in the Al oxide suggests that the growth of the alkali-ion depletion layer is controlled by the consumption of excess oxygen to form the interfacial Al oxide.