• Nuclear Engineering and Technology
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• v.45 no.2
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• pp.265-276
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• 2013

Pressure tubes made of Zr-2.5 wt% Nb alloy are important components consisting reactor coolant pressure boundary of a pressurized heavy water reactor, in which unanticipated through-wall cracks and rupture may occur due to a delayed hydride cracking (DHC). The Canadian Standards Association has provided deterministic and probabilistic structural integrity evaluation procedures to protect pressure tubes against DHC. However, intuitive understanding and subsequent assessment of flaw behaviors are still insufficient due to complex degradation mechanisms and diverse influential parameters of DHC compared with those of stress corrosion cracking and fatigue crack growth phenomena. In the present study, a deterministic flaw assessment program was developed and applied for systematic integrity assessment of the pressure tubes. Based on the examination results dealing with effects of flaw shapes, pressure tube dimensional changes, hydrogen concentrations of pressure tubes and plant operation scenarios, a simple and rough method for effective cooldown operation was proposed to minimize DHC risks. The developed deterministic assessment program for pressure tubes can be used to derive further technical bases for probabilistic damage frequency assessment.

• Journal of Ocean Engineering and Technology
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• v.19 no.5 s.66
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• pp.65-70
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• 2005

Fracture behavior and pipe strength are very important to the integrity of energy plants, ocean structures, and so forth. The pipes of energy plants and ocean structures are subject to local wall thinning, resulting from severe erosion-corrosion damage. Recently, the effects of local wall thinning on fracture strength and fracture behavior of piping systems have been the focus of many studies. In this paper, the elasto-plastic analysis is performed by FE code ANSYS on straight pipes with wall thinning. We evaluated the failure mode, fracture strength and fracture behavior, using FE analysis. Also, the effect of the axial strain on deformations and failure modes was estimated by FE analysis.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2011.05a
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• pp.58-58
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• 2011

Nickel-ceramics nanocomposite coatings can be applied as the wear resistance coating, corrosion protection of underlying materials, and decorative coatings. Hence, Nickel based nanocomposite coatings, especially Ni-SiC, have been extensively studied in recent years. However, more often agglomeration problem of the nanoparticles in the nickel matrix can cause deterioration of the mechanical properties rather than improvement. The homogeneous distribution of the nanoparticles in the matrix coating is still being challenging. In this experiment, electrochemical deposition of Ni-SiC composite coating was done in presence of ultrasound. The effects of different ultrasonic powers and frequencies on the nanoparticle dispersion were studied. The electrodeposition was carried out in nickel sulfamate bath by applying pulse current technique. Compared to the conventional mechanical stirring technique to prevent nanoparticles agglomeration and sedimentation during composite electrodeposition, the aid of ultrasonic dispersion along with mechanical stirring has been found to be more effective not only for the nanoparticles dispersion, but also for the mechanical properties of the electrodeposited coatings. Nanoparticles were found to be distributed homogeneously with reduced agglomeration. The microstructure of the composite coating has also been changed, allowing some random orientations of the nickel crystallite grain growths, smooth surface, and finer grains. As a consequence, better mechanical properties of the composites were observed.

• Journal of Surface Science and Engineering
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• v.49 no.2
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• pp.119-124
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• 2016

Plasma electrolytic oxidation (PEO) is a promising coating process to produce ceramic oxide on valve metals such as Al, Mg and Ti. The PEO coating is carried out with a dilute alkaline electrolyte solution using a similar technique to conventional anodizing. The coating process involves multiple process parameters which can influence the surface properties of the resultant coating, including power mode, electrolyte solution, substrate, and process time. In this study, ceramic oxide coatings were prepared on commercial Al alloy in electrolytes with different KOH concentrations (0.5 ~ 4 g/L) by plasma electrolytic oxidation. Microstructural and electrochemical characterization were conducted to investigate the effects of electrolyte concentration on the microstructure and electrochemical characteristics of PEO coating. It was revealed that KOH concentration exert a great influence not only on voltage-time responses during PEO process but also on surface morphology of the coating. In the voltage-time response, the dielectric breakdown voltage tended to decrease with increasing KOH concentration, possibly due to difference in solution conductivity. The surface morphology was pancake-like with lower KOH concentration, while a mixed form of reticulate and pancake structures was observed for higher KOH concentration. The KOH concentration was found to have little effect on the electrochemical characteristics of coating, although PEO treatment improved the corrosion resistance of the substrate material significantly.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.275-278
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• 2005

INCONEL 718, nickel based superalloy, has good formability, high strength, excellent corrosion resistance and mechanical properties at high temperature. Owing to theses attractive properties, it finds use in applications such as combustion system, turbine engines and nuclear reactors. In such applications, components are typically required to be tolerant of high stress impact loading. This may cause material degradation and lead to catastrophic failure during service operation. In order to design optimal structural parts made of INCONEL 718, accurate understanding of material's mechanical properties, dynamic behavior and fracture characteristic as a function of strain rates are required. This paper concerned with the dynamic material properties of the INCONEL 718 for the various strain rates. The dynamic response of the INCONEL 718 at intermediate strain rate is obtained from the high speed tensile test machine test and at the high strain rate is from the split Hopkinson pressure bar test. Based on the experimental results, the effects of strain rate on dynamic flow stress, work hardening characteristics, strain rate sensitivity and elongation to the failure are evaluated. Experimental results from both quasi-static and high strain rate up to the 5000/sec are interpolated in order to construct the Johnson-Cook model as the constitutive relation that should be applied to simulate and design the structural parts made of INCONEL 718.

• Korean Journal of Materials Research
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• v.9 no.6
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• pp.622-629
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• 1999

Effects of the fluorination in the $K_2$TiF\ulcorner solution and in-situ KF+ KOH electrolyte on the electrochemical charge-discharge properties of CaNi\ulcorner and the Mg-CaNi\ulcorner electrodes were investigated. In-situ fluorination in the KF+ KOH electrolyte compared with pre-fluorination in the$ K_2$TiF\ulcorner solution could improve the electrochemical cycling durability of CaNi\ulcorner and MG-CaN\ulcorner electrodes. The fluorinated layer on the alloy surface by pre-fluorination to improve the activity and anti-corrosion of the electrodes was dissolved in the pure KOH electrolyte during the cycling. The fluorinated layer was formed continuously on the surface of the electrode by thee2N KF addition in the 6N KOH electrolyte. The excess F\ulcorner ion addition in KOH electrolyte could improve the electrochemical cycling durability of CaNi\ulcorner and Mg-CaNi\ulcorner electrode. But, in case of MG-CaNi\ulcorner electrode, the discharge capacity of the electrode was reduced and the poor cycling property was shown with increasing of the MG process times.

• Korean Journal of Materials Research
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• v.16 no.10
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• pp.639-646
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• 2006

Over the last two decades, microbiologically influenced corrosion (MIC) of metallic materials has received considerable attention due to its serious effects on industrial field. In this context, it is important to devise control methods which inhibit biofilm formation on various metallic compounds and are compatible with environment. It was change of various conditions (duty cycle, current density, $AgNO_3$ concentration and pH) for injection of Ag particles in anodized Aluminum alloy pore using pulsed current. Optimal condition was obtained by means of FE-SEM, ICP analysis etc. The antibacterial metal's specimen were manufactured under optimal condition and this specimen were tested the antibacterial characterization and anticorrosion characterization. In result of test, we can confirmed that the antibacterial characterization and anticorrosion characterization of the specimens of injected Ag particles in anodized Aluminum alloy pore using pulsed current were better than the anodized Aluminum alloy specimens.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.5
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• pp.901-910
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• 1989

Corrosion fatigue crack propagation behavior of duplex stainless steel weldments in substitute ocean water was investigated to evalulate effects of micro-structural change and residual stresses. Fatigue crack propagation rate was found influenced markedly .alpha./.gamma. phase ratio but little by residual stresses. Fatigue crack propagation rate is higher in the corrosive environment than in room atmosphere. The crack propagation rate estimated by the measurement of striation spacing was higher than that, obtained by crack length measurement in low .DELTK.K region. At hight .DELTK.K region, however, both crack propagation rates were found to be identical.

• Journal of Surface Science and Engineering
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• v.31 no.3
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• pp.142-150
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• 1998

Stainless steel is being used widely for various purposes due to its good corrosion resistance. There has been much research to produce colored stainless steel by several methods such as anodizing and ion plating. In this experiment, we coated TiN(C,O,H)films SUS304 substraate with the DC magnetron spttering system made by Leybold Heraeus and studied the interlater structure and abhesive strength of the films as a function of additional gases, acetylene, hydrogen and oxygen. When the acetylene gas was added into the chamber, the specimen with the interlayer phase had good adhesion due to the toughness of the $\gamma'-Fe_4N$ plase induced from a solid solution of carbon atoms, while low adhesion appeared on the specimen of the non interlayer phase. The formation of the interlayer phase($\gamma'-Fe_4N$) was due to hydrogen embrittlement and internal stress induced by $\gamma'-Fe_4N$ formation in the interlayer. We could fine the interlayer phase ($\gamma'-Fe_4N$) at the interface between the film and the substrate of the TEM image when $\gamma'-Fe_4N$ was detected by the X-ray duffraction metheod.

• Advances in concrete construction
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• v.10 no.3
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• pp.221-236
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• 2020

To reduce the CO₂ emissions associated with the manufacture of portland cement (PC), an efficient alternative like an alkali-activated binder (AAB) is the requirement of the industry. To promote the use of AAB in construction activities, a practically implementable mix proportion is required. Owing to the several raw ingredients of AAB concrete and their associated uncertainties, partial replacement of PC by AAB may be adopted instead of complete replacement as per industrial requirements. Hence, the present study aims to determine an optimal proportion for partial replacement of PC with AAB and recommend a technique for it based on site conditions. Three modes of partial replacement are followed: combining all the dry ingredients for AAB and PC followed by the addition of the requisite liquids (PAM); combining the PC and the AAB concrete in two horizontal layers (PAH); and two vertical layers (PAV). 28-day old specimens are exposed to 10% v/v solutions of HCl, H₂SO₄, and HNO₃ to evaluate changes in mechanical, physical, and microstructural characteristics through compressive strength, corrosion depth, and microscopy. Based on deterioration in strength and integrity, PAH or PAV can be adopted in absence of acid attack, whereas PAM is recommended in presence of acid attack.