Papers by Keyword: Alloy 600

Abstract: Alloy 600 (UNS N06600) is an austenitic nickel-based alloy with superior corrosion resistance and high-temperature endurance, which determines its widespread applications in aeronautical, aerospace, marine and nuclear industries. Particularly, a number of nuclear components used Alloy 600 as their structure materials due to their high corrosion resistance, high-temperature endurance and excellent fabricant characteristics. Many failures have occurred in Alloy 600 with various forms of environmental degradations during long-term operation. In this study, an ultrasonic nanocrystal surface modification (UNSM) technique was applied to Alloy 600 at a room and a high temperature of 500 ^OC. The effects of UNSM treatment temperature on the microstructure and wear behavior including a compressive residual stress were investigated. The hardness, compressive residual stress with respect to depth from the top surface were measured. Also, the wear behavior of UNSM-treated at a room and a high temperature Alloy 600 specimen was compared to that of the untreated specimen. The increase in wear resistance by UNSM technique was discussed in terms of increased hardness, refined grain size and induced compressive residual stress.

Abstract: Alloy 600 was studied from three aspects including corrosion behaviour experiment in high temperature, metallurgy element dissolving experiment and water chemistry optimization analysis. Experimental results showed that there was not obvious corrosion velocity for Alloy 600 in local concentrated NaOH solution; high ratio of iron dissolving concentration was found after high P,T experiment, which indicated that Alloy 600 experienced de-alloy corrosion in localized concentrated environment.

Abstract: Alloy 600 was studied in different Na2SO4 solutions with three approaches including Tafel curve method, AC impedance curve and high temperature experiment. Experimental results showed that interface electric transfer process was the control step of whole electrochemistry process; and selective corrosion of Alloy 600 would not happen in high temperature process

Abstract: Abstract: Alloy 600 was studied in different acidic environments with three approaches including Tafel curve method, linear polarization method and AC impedance curve. Experimental results showed that there was greatest corrosion velocity when pH was 4 for preventing film factor; and it was possibly caused by elements corrosion dissolving with different proportional compared with Alloy 600 metallurgical contents.

Abstract: Alloy 600 was studied in NaCl solution for its pitting corrosion behavior in this paper. According to Tafel polarization, impedance analysis, specimen morphological analysis and metal dissolving analysis by AAS, there must be selective de-alloy corrosion happened in localized concentrated environment; corrosion velocity reaches maximum when Cl^- concentration was 100mmol/L.

Abstract: Corrosion-resistant nickel-based Alloy 600 is susceptible to a lead-induced stress corrosion cracking (PbSCC) in aqueous solutions. The lead species incorporated into the oxide at the alloy surface degraded the passivity, and caused the PbSCC. Effects of lead on the properties of the surface passive films were investigated. The cross sections of the surface films were examined by the transmission electron microscopy and the species present in the films were analyzed with the energy dispersive x-ray spectroscopy and the x-ray photoelectron spectroscopy. In-depth concentration profiles of the species were analyzed by using an ion sputtering technique. The electrochemical impedance spectroscopy technique was used to characterize the electrochemical behaviors. Effectiveness of a nickel boride inhibitor was evaluated. The boride inhibitor altered the properties of the passive film, and significantly reduced the susceptibility to the PbSCC.

Abstract: Alloy 600(74wt% Ni, 15wt% Cr, 9wt% Fe) is used as a material for steam generator tubing in pressurized water reactors(PWR) due to its high corrosion resistance under a PWR environment whose primary side and secondary side are operated under 340oC, 150bar and 290oC, 50bar, respectively. However, in spite of its outstanding corrosion resistance, a stress corrosion cracking(SCC) which has been one of the most important degradation issues, has occurred occasionally owing to the severe high temperature and pressure condition of a PWR. It is expected that a SCC is deeply related to an electrochemical property of a passive film formed under a high temperature and pressure condition. Therefore an understanding of the basic electrochemical behaviors regarding an anodic dissolution and a passivation of the bare surface of metals and alloys provides important information about a SCC mechanism and control. In the present work, the passive oxide films on Alloy 600 were investigated as a function of the dissolved oxygen content and the pH by using a potentiodynamic polarization, electrochemical impedance spectroscopy(EIS) and a depth profiling by Auger electron spectroscopy(AES). For this purpose, 0.5M H3BO3, 0.5M Na2SO4 and 0.1M NaOH aqueous solutions with/without dissolved oxygen at 300oC were used as the test solutions. The resistance of an oxide formed in an aerated solution was smaller than that in a deaerated solution while the oxide film in the aerated solution was thicker than the oxide film in the deaerated solution.

Abstract: Alloy 600 is used as a material for a steam generator tubing in pressurized water reactors(PWR) due to its high corrosion resistance under a PWR environment. In spite of its corrosion resistance, a stress corrosion cracking(SCC) has occurred on the primary side as well as the secondary side of a tubing. It is known that a SCC is related to the electrochemical behaviors of an anodic dissolution and a passivation of a bare surface of metals and alloys. Therefore in the present work, the passive oxide films on Alloy 600 have been investigated as a function of the solution temperature by using a potentiodynamic polarization, electrochemical impedance spectroscopy and a TEM, equipped with EDS. Moreover the semiconductive property was evaluated by using the Mott-Schottky relation. It was found that the passivity depends on the chemical composition and the densification of the oxide film rather than the oxide thickness. As the solution temperature of 0.5M H3BO3 increased, the thickness of the passive film increased but the oxide resistance of the passive film was decreased, indicating that the measured current in the passive region of the potentiodynamic curve is closely related to the stability of the passive film rather than the oxide thickness. It was found that the oxide films were composed of an outer oxide layer with a lower resistance and an inner oxide layer with a relatively higher resistance. From the Mott-Schottky relation, the oxide formed at 300oC showed a p-type semiconductor property unlike the n-type oxide films up to 250oC.

Abstract: The precipitates in the base metal and the fusion zone of an Alloy 600/182 weld were characterized through a transmission electron microscopy. Precipitates in the Alloy 600 base metal were identified as Cr7C3. On the other hand, (Nb,Ti)C, Al-rich and Ti-rich oxides were found on the dendritic interfaces, and tiny Cr-rich M23C6 were distributed on the grain boundaries in the Alloy 182 fusion zone.

Abstract: Alloy 600 tubing can be repaired by using a Ni electroplating to have 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 the applied current density and the duty cycle(Ton / (Ton + Toff)) of the pulse current on the material properties of the Ni electrodeposit obtained from a Ni sulphamate bath by analyzing the current efficiency, the potentiodynamic curve, the hardness and the stress-strain curve. Hardness, YS(yield strength) and TS(tensile strength) decreased whereas the elongation increased as the applied current density increased. This was due to a concentration depletion of the nickel ion 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 of the nickel ion could not be sufficiently recovered and the fraction of the hydrogen evolution reaction which is kinetically faster than the nickel ion reduction decreased, which contributed to a coarse grain sized electrodeposit. The experimental results of the hardness and the stress-strain curves were supplemented by the results of the potentiodynamic curve.