• Transactions of the Korean Society of Mechanical Engineers
• /
• v.9 no.2
• /
• pp.140-149
• /
• 1985

Fully reversed push-pull low cycle fatigue tests under strain control of trapezoid cyclic mode have been conducted in air at temperature of 550.deg. C and with frequency of 0.5 cpm on the domestic stainless steel STS 316 after solution treatment for 1 hour at 1100.deg. C. As an experimental equipment for high temperature fatigue tests, an electric servo-hydraulic fatigue machine(Instron model 1350) was used. This paper presents the effects of creep hold time and plastic strain range on push-pull high temperature low cycle fatigue life and fracture behavior. The fracture surfaces were observed by means of the scanning electron microscope. The results are as follows. (1) The fatigue life decreases with increase of the plastic strain range equal hold time and also decreases as the hold time is getting longer. (2) The frequency modified damage function can predict fatigue life by incorporating a variation of Coffin's frequency modified approach into damage function. (3) The ratios of creep damage and fatigue damage can be calculated by using he linear accumulation damage concept and the ratio of creep damage increases as the hold time is getting longer. (4) At the creep hold time of 5 minutes and the strain range of 2.0%, the fracture mode was intergranular fracture and striations were hardly observed. In this case, the intergranular cracking was originated in void type('.gamma.' type) cracking.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
• /
• v.20 no.1
• /
• pp.43-63
• /
• 2022

The aim of this review is to communicate some essential knowledge of the underlying mechanism of the corrosion of structural containment alloys during molten salt reactor operation in the context of prospective online monitoring in future MSR installations. The formation of metal halide species and the progression of their concentration in the molten salt do reflect containment corrosion, tracing the depletion of alloying metals at the alloy salt interface will assure safe conditions during reactor operation. Even though the progress of alloying metal halides concentrations in the molten salt do strongly understate actual corrosion rates, their prospective 1^st order kinetics followed by near-linearly increase is attributed to homogeneous matrix corrosion. The service life of the structural containment alloy is derived from homogeneous matrix corrosion and near-surface void formation but less so from intergranular cracking (IGC) and pitting corrosion. Online monitoring of corrosion species is of particular interest for molten chloride systems since besides the expected formation of chromium chloride species CrCl₂ and CrCl₃, other metal chloride species such as FeCl₂, FeCl₃, MoCl₂, MnCl₂ and NiCl₂ will form, depending on the selected structural alloy. The metal chloride concentrations should follow, after an incubation period of about 10,000 hours, a linear projection with a positive slope and a steady increase of < 1 ppm per day. During the incubation period, metal concentration show 1^st order kinetics and increasing linearly with time^1/2. Ideally, a linear increase reflects homogeneous matrix corrosion, while a sharp increase in the metal chloride concentration could set a warning flag for potential material failure within the projected service life, e.g. as result of intergranular cracking or pitting corrosion. Continuous monitoring of metal chloride concentrations can therefore provide direct information about the mechanism of the ongoing corrosion scenario and offer valuable information for a timely warning of prospective material failure.

• Korean Journal of Materials Research
• /
• v.12 no.6
• /
• pp.436-441
• /
• 2002

Effect of Sn addition on the stress corrosion cracking(SCC) resistance of the Al-Cu-Mn cast alley was investigated by C-ring teat and electrical conductivity measurement, The electrical conductivity and SCC resistance increased by Sn addition. The alley containing 0,10%Sn showed maximum electrical conductivity and the best SCC resistance. At the same composition, the electrical conductivity and SCC resistance increased from peak aged condition to ever aged condition. The PFZ and coarse precipitates along the grain boundary were observed from TEM micrographs. The fracture mode of the alloy was confirmed as intergranular type and showed brittle fracture surface. The SCC mechanism of the alloy was concluded as the anodic dissolution model, The maximum hardness was increased from 130Hv in the Sn-free alloy to 156Hv in the 0.10%Sn added alloy.

• Korean Journal of Materials Research
• /
• v.11 no.4
• /
• pp.266-271
• /
• 2001

Effect of Cd addition on the stress corrosion cracking(SCC) resistance of Al-Cu-Mn cast alloy was investigated by C-ring test and electrical conductivity measurement. With increasing Cd contents, the electrical conductivity and the SCC resistance were increased. The PFZ and coarse precipitates along the grain boundary were observed from TEM micrographs. The fracture made of the alloys was confirmed as intergranular type and showed brittle fracture surface. As a result, it was concluded that the SCC mechanism of these alloys is the anodic dissolution model. The maximum hardness was increased from 127Hv in the Cd-free alloy to 138∼145Hv in the Cd addition alloys.

• Journal of the Microelectronics and Packaging Society
• /
• v.17 no.3
• /
• pp.33-41
• /
• 2010

Crack propagation mechanisms of Sn-3.0Ag-0.5Cu solder were studied in strain controlled push-pull creepfatigue conditions using the fast-fast (pp) and the slow-fast (cp) strain waveforms at 313 K. Transgranular cracking was found in the pp strain waveform which led to the cycle-dominant crack propagation and intergranular cracking in the cp strain waveform that led to the time-dominant crack propagation. The time-dominant crack propagation rate was faster than the cycle-dominant crack propagation rate when compared with J-integral range which resulted from the creep damage at the crack tip in the cp strain waveform. Clear recrystallization around the crack was found in the pp and the cp strain waveforms, but the recrystallized grain size in the cp strain waveform was smaller than that in the pp strain waveform. The cycle-dominant crack propagated in the normal direction to the specimen axis macroscopically, but the time-dominant crack propagated in the shear direction which was discussed in relation with shear micro cracks formed at the crack tip.

• Korean Journal of Materials Research
• /
• v.4 no.3
• /
• pp.329-333
• /
• 1994

A large number of grain boundaries were seen to crack in near-eutectic solder joints of leadless ceramic chip carriers (LLCC's) during thermal cycling at temperature ranges from -$35^{\circ}C$ to +$125^{\circ}C$ with lhr time period. One potential explanation for this type of cracking might be the presence of embrittling species on the boundary. Although there do not appear to be any instances reported in the literature of solders being embrittled by small amounts of contaminating species, the possibility of such an occurrence exists. The potential presence of impurities located at crack surfaces was inspected using Scanning Auger Microprobe(SAM) and it was found that intergranular cracking could be accomplished by the oxidation of the grain boundary. A physical model for fatigue crack growth was introduced, in which grain boundary separation took place under oxidation facilitated by sliding.

• Corrosion Science and Technology
• /
• v.17 no.1
• /
• pp.6-11
• /
• 2018

Outdoor exposure tests using of 7B04 aluminium alloy samples including plate, tensile and various SCC samples were carried out in Tuandao station, Shandong province (East of China) and Wanning station, Hainan province (South of China). Corrosion characteristics including weight loss, microstructure, tensile strength and SCC susceptibility were investigated. The corrosion rates in Tuandao and Wanning showed high to low and the corrosion rates changed to the following equation of $w=at^b$ (b<1). The corrosion of 7B04 aluminium alloy in Wanning was more serious than that in Tuandao. Pitting appeared at early stage of expose test, and it can be changed to general corrosion with test time extension. The 7B04 aluminium alloy of which specimen shapes are forging and thick plate also showed SCC (Stress corrosion cracking) in the marine atmosphere. The higher SCC sensitivity was observed in Wanning station than in Tuandao station. The 7B04 aluminium alloy with a high stress level was more sensitive to SCC. Intergranular and transgranular or a mixed mode of cracking can be observed in different marine exposure.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.27 no.6
• /
• pp.541-549
• /
• 2007

This work describes an investigation into the feasibility of using an acoustic emission (AE) technique to evaluate the integrity of a composite actuator with a PZT ceramic under electromechanical cyclic loading. AE characteristics have been analyzed in terms of the behavior of the AE count rate and signal waveform in association with the performance degradation of the composite actuator during the cyclic tests. The results showed that the fatigue cracking of the composite actuator with a PZT ceramic occurred only in the PZT ceramic layer, and that the performance degradation caused by the fatigue damage varied immensely depending on the existence of a protecting composite bottom layer. We confirmed the correlations between the fatigue damage mechanisms and AE signal types for the actuators that exhibited multiple modes of fatigue damage; transgranular micro damage, intergranular fatigue cracking, and breakdown by a short circuiting were related to a burst type signal showing a shortly rising and slowly decaying waveform with a comparably low voltage, a continuous type signal showing a gradual rising and slowly decaying waveform with a very high voltage and a burst and continuous type signal with a high voltage, respectively. Results from the present work showed that the evolution of fatigue damage in the composite actuator with a PZT ceramic can be nondestructively identified via in situ AE monitoring and microscopic observations.

• Nuclear Engineering and Technology
• /
• v.55 no.9
• /
• pp.3183-3193
• /
• 2023

The water radiolysis in-core at light water reactors (LWRs) produces various radicals with other ionic species/molecules and radioactive nitrogen species in the reactor coolant. Nitrogen species can exist in many different chemical forms and recirculate in water and steam, and consequently contribute to what extent the environmental safety at nuclear power plants. Therefore, a clear understanding of formation kinetics and chemical behaviors of nitrogen species under irradiation is crucial for better insight into the characteristics of major radioactive species released to the main steam or relevant coolant systems and eventually development of advanced processes/methodologies to enhance the environmental safety at nuclear power plants. This paper thus focuses on basic principles on electrochemical interaction kinetics of radiolytic molecules and various nitrogen species in high temperature water, fundamental approaches for calculating thermodynamic values to predict their stability and domain in LWRs, and the effect of nitrogen species on crevice chemistry/corrosion and intergranular stress corrosion cracking (IGSCC) susceptibility of structure materials in high temperature water.

• Corrosion Science and Technology
• /
• v.23 no.4
• /
• pp.266-277
• /
• 2024

Due to its good corrosion and heat resistance with excellent mechanical properties, 304L stainless steel is commonly used in the fabrication of spent nuclear fuel dry storage canisters. However, welds are sensitive to stress corrosion cracking (SCC) due to residual stress generation. Although SCC resistance can be improved by stress relieving the weld and changing the chloride environment, it is difficult to change corrosion environment for certain applications. Stress control in the weld can improve SCC resistance. Ultrasonic shot peening (USP) needs further research as compressive residual stresses and microstructure changes due to plastic deformation may play a role in improving SCC resistance. In this study, 304L stainless steel was welded to generate residual stresses and exposed to a chloride environment after USP treatment to improve SCC properties. Effects of USP on SCC resistance and crack growth of specimens with compressive residual stresses generated more than 1 mm from the surface were studied. In addition, correlations of compressive residual stress, grain size, intergranular corrosion properties, and pitting potential with crack propagation rate were determined and the improvement of SCC properties by USP was analyzed.