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Acoustic emission (AE) technique was used to study the oxide film formation of 316LN stainless steel (SS) in high temperature aqueous environment. The morphology and chemical compositions of oxide films of 316LN SS base metal and weld were also investigated by using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). The results indicated that 316LN SS weld had a higher oxidation resistance than that of base metal due to higher amount of chromium and nickel in the weld material. AE activity and intensity were high during the oxide film formation and decreased gradually with increasing immersion time. The evolution of AE hits was consistent with the oxidation kinetics of 316LN SS base metal and weld. The formation of Cr-enrichment layer and Ni(OH)2 contributed to the enhancement of oxidation resistance, leading to a continuous decrease of AE activity and intensity. Two types of AE waveforms were detected and the frequency spectra of both types mainly ranged from 0.3 to 0.6 MHz. According to the analyses of AE based b-values and parameters, it could be deduced that AE sources during oxide film formation were the plastic deformation of base metal/weld and oxide film. [ABSTRACT FROM AUTHOR]

The electrochemical behavior and oxide film structure of the weld of 316L/52M/A508 dissimilar metal welded joints were investigated via scanning electron microscopy (SEM), potentiodynamic polarization measurements, electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS). The electrochemical measurements revealed that the weld materials could be arranged in descending order of protectiveness of the oxide film formed on their surface; that is, Alloy52Mw>Alloy52Mb>C52M>C308. The results of EIS and XPS analyses showed that the oxide films formed on these materials were duplex-structured; this duplex structure consisted of a Cr-rich (in 52M nickel-based weld materials) or Cr/Fe-rich (in C308 stainless steel weld materials) inner layer and a Ni/Fe-rich (in 52M nickel-based weld materials) or Fe-rich (in 308 stainless steel weld materials) porous outer layer. [ABSTRACT FROM AUTHOR]

Many failures in nuclear safe-end dissimilar metal weld joint (DMWJ) have revealed that stress corrosion cracking (SCC) is mainly located in the weld metal (WM). Since the oxide film formed on the stainless steel during service plays an important role in SCC, this research focuses on the short time oxidation behavior of 308 L WM with different surface state in the simulated primary water of pressurized water reactors (PWRs) with 0.1 mg/L dissolved oxygen (DO). In the meanwhile, the oxidation behavior of the 316 L stainless steel with different surface state under the same environmental condition is also studied. Surface state and oxide films are analyzed using various methods. The results show that a dual layered oxide film is formed on 308L WM and 316 L surfaces. Both the cold-worked layer and the surface topography should be considered together when discussing the effects of the surface state on the morphologies of the oxide films. [ABSTRACT FROM AUTHOR]

Oxidation behavior on intersecting and longitudinal surfaces of directionally solidified cobalt-base superalloy DZ40M was studied respectively at 1050 °C for 0.1 h, 1 h and 10 h and electrochemical property before and after oxidation on two orientations in 3.5% sodium chloride solution at room temperature was investigated. Grain boundaries of DZ40M are conducive to ion diffusion at elevated temperature and the higher area fraction of grain boundaries on intersecting surface results in higher oxidation rate and more CoO in the oxide layers. Carbides with Cr depletion zone around vulnerable to corrosion are located in grain boundaries, and unoxidized intersecting surface with higher area fraction of grain boundaries is prone to more serious uneven general corrosion. After oxidation, the corrosion resistance of the alloy is enhanced because oxide layer preferentially covers the grain boundaries and relieves the unevenness of corrosion. The protective effect of oxide layer is mainly provided by the innermost compact and continuous chromium oxide (Cr2O3). The intersecting surface has lower Ecorr and higher icorr, for the protective Cr2O3 layer on this orientation is largely consumed by excessive cobalt oxide to form CoCr2O4. [ABSTRACT FROM AUTHOR]

The corrosion inhibition behaviors of 2′-hydroxy-acetophenone for AZ91D magnesium alloy in ASTM D1384-87 corrosive water (model water) were investigated using weight loss and electrochemical measurements. The surface morphologies and composition of films formed on magnesium alloy in solutions with and without 2′-hydroxy-acetophenone were examined by scanning electron microscope and Fourier transform infrared spectrum. The results show that inhibition efficiency first increases and then decreases with the increasing 2′-hydroxy-acetophenone concentration, its maximum value is at 50 ppm. It is considered that 2′-hydroxy-acetophenone anions can chelate with the Mg2+ and form a 2′-hydroxy-acetophenone-Mg complex on the magnesium alloy surface, hindering the corrosion development of magnesium alloy. [ABSTRACT FROM AUTHOR]

High velocity arc spraying (HVAS) process was used to deposit Al-Ni-Y-Co amorphous and nanocrystalline composite coating on AZ91 magnesium alloy substrate. The microstructure of the coating was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy dispersive spectrometer (EDS) and transmission electron microscopy (TEM). The results show that the coating with thickness of 500 µm presents a dense layered structure with low porosity (1.8%). The coating consists of amorphous, nanocrystalline, and crystalline phases. The microhardness was measured by a microhardness tester. The average values of Vickers hardness for the Al-Ni-Y-Co coating, pure Al coating and AZ91 alloys are about HV0.1 310, HV0.1 70, and HV0.1 60, respectively. The electrochemical corrosion resistance of the coating in 5 wt% NaCl aqueous solution was also investigated, and the results showed that the Al-Ni-Y-Co coating exhibits better corrosion resistance than pure Al coating and AZ91 magnesium alloy. [ABSTRACT FROM AUTHOR]

Characteristics of the deposits and oxide films formed on 316L stainless steel in situ tested on a boiler of 1000 MW pulverized coal-fired power plant for 150 h were examined. The results show that the deposits are mainly composed of outer fly ash, middle sulfate, and chloride and fluoride in the inner layer. Oxide films are mainly Fe2O3 and Fe3O4. Two models of coupling mechanism of dew point corrosion and viscous ash deposits at different temperature ranges are proposed to instruct engineering application. [ABSTRACT FROM AUTHOR]

Anodizing of AZ91D magnesium alloy in the alkaline borate-potassium hydrogen tartrate (PHT) environmental friendly electrolyte was studied. The effect of PHT on the anodizing process and anodic film properties was investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrometry (EDS), and potentiodynamic polarization. The results showed that the anodizing parameters, surface morphology, thickness, phase structure, and corrosion resistance of the anodic film were strongly dependent on the concentration of PHT. Moreover, the anodizing mechanism of the AZ91D magnesium alloy in the presence of PHT was also studied. That is, by adsorption on the surface of magnesium alloy, PHT decreases the anodizing current density and make the anodizing condition moderate, which is conducive to the performance improvement of the anodic film. [ABSTRACT FROM AUTHOR]

Thermal barrier coatings of nanostructured and microstructured yttria stabilized zirconia (YSZ) were deposited on GH4049 substrate by air plasma spray, respectively. Hot corrosion behaviors of both coatings were evaluated in comparative aspects. Results revealed that the nanostructured YSZ displayed higher resistance to the hot corrosion attack by Na2SO4 and V2O5. It was also shown, through X-ray diffraction quantitative phase analysis, that the nanostructured YSZ had good resistance to the tetragonal-monoclinic phase transformation during the hot corrosion process. [ABSTRACT FROM AUTHOR]

The intercrystalline corrosion, exfoliation corrosion (EXCO), and stress corrosion cracking (SCC) of Al-Zn-Mg-Sc-Zr alloy were investigated by means of constant temperature immersion corrosion method, optical microscopy, transmission electron microscopy (TEM), and electrochemical impedance spectroscopy (EIS). The results show that intercrystalline corrosion, and EXCO susceptibility of Al-Zn-Mg-Sc-Zr alloy decrease gradually with increasing of aging time. Corrosion susceptibility order from low to high is as follows: OA > PA > UA > NA. The SCC susceptibility index of PA temper is more than OA temper at the same strain rate. According to TEM observation, with aging time prolonging, a part of η′ phases transform to η equilibrium phases, which become coarse gradually. The distribution discontinuity of the grain boundary precipitates increases. In addition, for Al-Zn-Mg-Sc-Zr alloy without EXCO, the EIS is comprised by a capacitive impedance arc at high frequency and an inductive impedance arc at low frequency. Once EXCO occurs, the EIS is composed of two capacitive impedance arcs at high frequency and at low frequency, respectively. [ABSTRACT FROM AUTHOR]

Ni-Si3N4 nanocomposite films with both the consecutive Ni crystallites and dispersed Si3N4 particles in the nanometer range have been fabricated using DC electroplating technique, and characterized by scanning electron microscopy (SEM), transmission electron microscope (TEM), and X-ray diffraction (XRD). The corrosion resistance of the Ni-Si3N4 nanocomposite film has been compared to that of pure Ni coating through polarization. Meanwhile, the corrosion process of Ni-Si3N4 nanocomposite film in neutral 3.5% NaCl solution has been investigated using electrochemical impedance spectroscopy (EIS). The results show that the Ni-Si3N4 nanocomposite film is more resistant to corrosion than the pure Ni coating. The corrosion of Ni-Si3N4 nanocomposite film is controlled by electrochemical step, and the whole corrosion process is divided into two sequential stages. The main corrosion type of Ni-Si3N4 nanocomposite films in neutral 3.5% NaCl solution is pitting. [ABSTRACT FROM AUTHOR]

Interference of alternative current (AC) on corrosion of X65 steel was investigated in soil. It was observed that the unfavorable effect of interfering AC was able to be effectively inhibited by increasing the direct current density of the cathodic protection (CP) system. A clear correlation was established between the CP current density and the tolerable AC current density. This led to a new criterion for assuring the effectiveness of CP of buried pipelines being interfered with AC. Field experimental results on a buried pipeline running below a 500 kV transmission line showed that the criterion could satisfactorily predict the risk of AC interfering on the CP system. [ABSTRACT FROM AUTHOR]