• Journal of Korea Foundry Society
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• v.12 no.2
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• pp.131-138
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• 1992

The effects of B additions, alone or in combination with Si, on the microstructure, $DO_3{\rightleftharpoons}B2$ transition temperature($T_c$) and corrosion behavior of Fe-25at%Al alloys were investigated. The raw materials were arc-melted in vacuum and then subjected to the following heat treatments to maximize the $DO_3$ order : homogenized at $1000^{\circ}C$ for 48hrs, slowly cooled to $500^{\circ}C$, and held at that temperature for 24hours. Results showed that the B addition to Fe-25at%Al alloys does indeed refine the grain and change from intergranular to transgranular fracture mode at room temperature, indicating a strengthening of grain boundaries. The Fe-25at% Al-1at% B-3at% Si alloy showed the highest $T_c$(${\Delta}T_c=150^{\circ}C$) in this work. However, the effectiveness of Si in raising $T_c$ decreased with more than 5at% Si additions combined with B. Since the preferential corrosion occurs at the precipitates, the corrosion resistance decreased due to the increased amount of precipitates with alloying additions.

• Journal of Surface Science and Engineering
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• v.52 no.5
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• pp.251-257
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• 2019

Fe-9Cr-2W steels were corroded at $600-800^{\circ}C$ for up to 100 hr in ($Na_2SO_4-K_2SO_4-Fe_2O_3$)-($CO_2-0.3%SO_2-6%O_2$) mixed gas. The poor condition samples formed thick oxide scales that consisted primarily of $Fe_2O_3$ as the major oxide and $Fe_3O_4$, FeO as the minor one through preferential oxidation of Fe. Fe-9Cr-2W steels corroded fast, forming thick and non-protective scale. The scale divided into the outer and inner layer, which consisted of the outer Fe-O layer and the inner (Fe,Cr)-O layer containing some (Fe,Cr)-S.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.525-528
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• 2008

For well-constructed concrete, its service life is a long term and it has an enough durability performance. However, for cracked concrete, it is clear that cracks should be preferential channel for the penetration of aggressive substance such as chloride ions according to author's previous researches. In order to enhance the lifetime of cracked concrete, critical issues in the performance of the concrete is the risk of chloride-induced corrosion. Even though crack width can be reduced due to the high reinforcement ratio, the question is to which extend these cracks may jeopardize the durability of cracked concrete. If the size of crack is small, surface treatment system can be considered as one of the best options to extend the service life of concrete structures exposed to marine environment simply in terms of cost effectiveness versus durability performance. Thus, it should be decided to undertake an experimental study on the effect of different types of surface treatment system, which are expected to seal the concrete and the cracks to chloride-induced corrosion in particular. In this study, it is examined the effect of surfaced treated systems on chloride penetration through microcracks. Single surface treatments of penetrant or coating and double application were considered as an experimental variation. RCM (Rapid Chloride Migration) testing is accomplished to visualize chloride penetration via cracks.

• Journal of the Korean Society for Heat Treatment
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• v.14 no.2
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• pp.89-95
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• 2001

The 7175Al alloy is particularly interesting for its high strength and sufficient ductility, fracture toughness and corrosion resistance. Currently vigorous efforts have been made to develop large rockets usable for various purposes in the space. This has created the demand of big size of 7175Al billet which would be applied to heavy forgings. The aim of this study is to investigate the quality level of big billet and the effect of billet size on the mechanical properties of large 7175Al ring roll forgings. The billets range from 370 mm to 720 mm in diameter were homogenized and forged after direct chill casting. The size and volume fraction of second phase particles In ${\Phi}720$ mm billet are larger than those of ${\Phi}370$ mm billet, and its ductility is lower for the condition of homogenization and T6 treatment. The Cu-rich phases formed in interdendritic sites are considered to provide the preferential crack path during cold upsetting. The fracture toughness of ring roll forgings which are made by ${\Phi}370$ mm billet is higher than those of ${\Phi}720$ mm billet.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.7
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• pp.890-899
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• 2014

Austenitic stainless steel is widely used in various industries due to its excellent corrosion resistance. However, Cr carbides precipitation along the grain boundaries after heat treatment or welding may develop Cr depleted zone, which acts as a preferential site for intergranular corrosion attack. To resolve this, carbon stabilizing element such as Ti or Nb are added to suppress formation of Cr carbides. However, there are few reports on corrosion characteristics under seawater environment of the stabilized stainless steel. This study investigated the effects of alloying contents on the electrochemical characteristics in seawater of stainless steel containing stabilizing element(Ti and Nb). To achieve this, the changes on the microstructure due to alloying were observed with microscope, and the electrochemical characteristics were determined by measurement of natural potential and potentiodynamic polarization experiments. The microscopic observation revealed that all specimens had inclusions other than the austenite matrix phase due to the addition of alloying elements. Such inclusions are considered to have different electrochemical characteristics from those of the matrix, and thus a clear distinction was found according to the type of stabilizers and the contents. The results of this study suggest that it is important to consider the effects of alloying contents on the electrochemical characteristics in seawater with the addition of Ti or Nb into austenitic stainless steel.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.3
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• pp.23-30
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• 2012

For cracked concrete, it is obvious that cracks should be preferential channel for the penetration of aggressive substances such as chloride ions according to the previous researches. In order to extend the lifetime of cracked concrete, critical issues in the performance of the concrete is the risk of chloride-induced corrosion. Even though crack width can be reduced due to the high reinforcement ratio, the question is to which extend these cracks may jeopardize the durability of cracked concrete. If the size of crack is small, surface treatment system can be considered as one of the best options to extend the service life of concrete structures exposed to marine environment simply in terms of cost effectiveness versus durability performance. Thus, it should be decided to undertake an experimental study on the effect of surface coating system, which can be able to seal the concrete and the cracks to aggressive substances-induced corrosion in particular. In this study, it is excuted to examine the effect of surfaced treated systems on chloride penetration and carbonation through compressive stress induced cracks. Experimental results have showed conclusively that critical stress linked with deterioration, should be existed in compressive stress ratio 50 ~ 70% for chloride penetration and 70 ~ 80% for carbonation, respectively. When the critical stress is exceeded in concrete, a comparatively large deterioration was measured where the critical stress in concrete, the increase in the mass transportation is marginal in spite of the large increase in micro-cracks. As for the effect of surface coating system on crack-sealing, it can be seen conclusively that cracks can be healed.

• Korean Journal of Materials Research
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• v.29 no.1
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• pp.1-6
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• 2019

Recent industrialization has led to a high demand for the use of fossil fuels. Therefore, the need for producing hydrogen and its utilization is essential for a sustainable society. For an eco-friendly future technology, photoelectrochemical water splitting using solar energy has proven promising amongst many other candidates. With this technique, semiconductors can be used as photocatalysts to generate electrons by light absorption, resulting in the reduction of hydrogen ions. The photocatalysts must be chemically stable, economically inexpensive and be able to utilize a wide range of light. From this perspective, cuprous oxide($Cu_2O$) is a promising p-type semiconductor because of its appropriate band gap. However, a major hindrance to the use of $Cu_2O$ is its instability at the potential in which hydrogen ion is reduced. In this study, gold is used as a bottom electrode during electrodeposition to obtain a preferential growth along the (111) plane of $Cu_2O$ while imperfections of the $Cu_2O$ thin films are removed. This study investigates the photoelectrochemical properties of $Cu_2O$. However, severe photo-induced corrosion impedes the use of $Cu_2O$ as a photoelectrode. Two candidates, $TiO_2$ and $SnO_2$, are selected for the passivation layer on $Cu_2O$ by by considering the Pourbaix-diagram. $TiO_2$ and $SnO_2$ passivation layers are deposited by atomic layer deposition(ALD) and a sputtering process, respectively. The investigation of the photoelectrochemical properties confirmed that $SnO_2$ is a good passivation layer for $Cu_2O$.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.5A
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• pp.729-735
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• 2008

For well-constructed concrete, its service life is a long period and it has an enough durability performance. For cracked concrete, however, it is clear that cracks should be a preferential channel for the penetration of aggressive substance such as chloride ions accoding to author's previous researches. Even though crack width can be reduced due to the high reinforcement ratio, the question is to which extend these cracks may jeopardize the durability of cracked concrete. If the size of crack is small, surface treatment system can be considered as one of the best options to extend the service life of concrete structures exposed to marine environment simply in terms of cost effectiveness versus durability performance. Thus, it should be decided to undertake an experimental study to deal with the effect of different types of surface treatment system, which are expected to seal the concrete and the cracks to chloride-induced corrosion in particular. In this study, it is examined the effect of surfaced treated systems such as penetrant, coating, and their combination on chloride penetration through microcracks. Experimental results showed that penetrant can't cure cracks. However, coating and combined treatment can prohibit chloride penetration through cracks upto 0.06 mm, 0.08 mm, respectively.