Effect of Sn and Mo on Microstructure and Electrochemical Property of TiZrTaNb High Entropy Alloys

The effects of Sn and Mo alloying elements on the microstructure and electrochemical properties of TiZrTaNb high entropy alloys were studied by optical microscope (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and electrochemistry. TiZrTaNb, TiZrTaNbMo and TiZrTaNbSn alloys with equal atomic ratio were prepared by the arc melting method. The results showed that the microstructure of the high entropy alloys was dendritic structure with single BCC structure. The addition of Mo and Sn elements promoted the growth of the dendritic structure and accelerated the interdendritic segregation of the TiZrTaNb alloy. The TiZrTaNbMo alloy exhibited excellent corrosion properties compared to TiZrTaNb and TiZrTaNbSn alloys based on corrosion parameters Icorr, φcorr, Ipass. The corrosion mechanism is discussed based on the corrosion morphology. The alloying elements have an important effect on the microstructure and electrochemical properties of a high entropy alloy.

Study of SCC of X70 Steel Immersed in Simulated Soil Solution at Different pH by EIS

An electrochemical study of stress corrosion cracking (SCC) of API X70 steel in a simulated soil solution at different pH values (3, 8 and 10) was carried out. The stress conditions were implemented by slow strain rate stress test (SSRT) and the SCC process was simultaneously monitored by electrochemical impedance spectroscopy (EIS). Fracture surface analysis and corrosion product analysis were performed by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The results show that the susceptibility to SCC was higher as the pH decreases. In the acid solution, hydrogen evolution can occur by H+ and H2CO3 reduction, and more atomic hydrogen can diffuse into the steel, producing embrittlement. EIS results indicated that the anodic dissolution contributed to SCC process by reducing the charge transfer resistances during the SSRT test. While SEM micrographs shown a general corrosion morphology on the longitudinal surface of samples. At higher pH (pH 8 and pH 10), the SCC susceptibility was lower, which it is attributed to the presence of corrosion products film, which could have limited the process. Using the angle phase (φ) value it was determined that the cracking process started at a point close to the yield strength (YS).

Corrosion behavior of X80 pipeline steel local defect pits under static liquid film

In this work, the corrosion electrochemical information under different thicknesses of liquid film was tested. The local corrosion development process of X80 steel under different thicknesses of liquid film was studied by combining the detection and analysis of scale and the matrix corrosion morphology. The corrosion was studied by EIS. The composition and microstructures of corrosion scale at different locations were detected by EDS and SEM, and the metal matrix was detected by 3D topography technology to analyze the local corrosion. The results show that a liquid film with a thickness greater than or equal to 1 mm has no effect on the mechanism of the corrosion process, but has a control effect on the corrosion rate and the time of each stage in corrosion. The corrosion process can be divided into two stages: in the early stage, the concentration of ions inside and outside ADP is the same, so the corrosion is uniform; in the later stage, due to the influence of CO2 dissolution and mass transfer distance, the cathodic reaction is mainly outside ADP and the anodic reaction is mainly inside ADP. In addition, corrosion acidification occurs in ADP, which enhances the corrosion process in ADP.

Corrosion Law of Metal Pipeline in Tahe Oilfield and Application of New Materials

Frequent corrosion perforation of metal pipes severely restricts oil and gas fields’ safety production and increases maintenance costs. Therefore, it is imminent to change the characteristics of metal materials fundamentally. In this paper, taking the metal pipe of Northwest Oil and Gas Field in China as an example, for the corrosion environment with high concentrations of H2S, CO2, H2O, Cl−, and O2, the main factors leading to corrosion are analyzed, the corrosion rules and optical materials of the pipe under different environmental and operating conditions are figured out, and the corrosion resistance of new pipes materials is evaluated. The main conclusions are as follows: (1) In the environment of the CO2–H2O–Cl− strong scouring system, electrochemical corrosion dominates, and the corrosion morphology is mainly groove-like corrosion and ulcer-like corrosion; (2) The H2S content affects the incubation period and development period of pipe corrosion; (3) Through the two optimization directions of 20# steel refining and material alloying, BX245-1Cr pipe material has been developed. At present, the application of this pipe material has relatively better results.

Modelling Strategies for the Numerical Simulation of the Behaviour of Corroded RC Columns under Cyclic Loads

Rebars corrosion phenomena can modify the structural behaviour of reinforced concrete (RC) members and consequently the seismic performance of RC structures. Since many existing RC structures are affected by this phenomenon, the influence of the reinforcement corrosion on the seismic performance is still under examination, especially when the corrosive attack is localized in the dissipative areas of the plastic hinges. In this work, the effect of localized corrosion is numerically investigated, through the adoption of a suitable finite element model, object of validation with the outcomes of an experimental campaign carried out in the Laboratory of the University of Rome “Tor Vergata”, on un-corroded and corroded RC columns subjected to axial load and cyclic horizontal actions. Particular attention has been paid to the definition of the three-dimensional model and to the modelling of the corroded rebars and their corrosion morphology. Indeed, different modelling strategies are proposed with the aim to properly simulate the cyclic behaviour of the corroded columns. The main results show how more refined strategies taking into account the morphological aspects of the corrosion phenomenon produce a better fit with the experimental results for both Damage Control and Life Safety limit states performance.

Corrosion Characterization at Surface and Subsurface of Iron-Based Buried Water Pipelines

Water pipe surface deterioration is the result of continuous electrochemical reactions attacking the surface due to the interaction of the pipe surface with environments through the time function. The study presents corrosion characterization at the surface and sub-surface of damaged ductile iron pipe (DIP) and galvanized steel (GS) pipes which served for more than 40 and 20 years, respectively. The samples were obtained from Addis Ababa city water distribution system for the analysis of corrosion morphology patterns at different surface layers. Mountains 8.2 surface analysis software was utilized based on the ISO 25178-2 watershed segmentation method to investigate corrosion features of damaged pipe surface and to evaluate maximum pit depth, area, and volume in-situ condition. Based on the analysis maximum values of pit depth, area and volume were 380 μ m, 4000 μm2, and 200,000 μm3, respectively, after 25% loss of the original 8 mm thickness of DIP. Similarly, the pit depth of the GS pipe was 390 μm whereas the maximum pit area and volume are 4000 μm2 and 16,000 μm3, respectively. In addition, characterizations of new pipes were evaluated to study microstructures by using an optical microscope (OM), and a scanning electron microscope (SEM) was used to analyze corrosion morphologies. Based on the SEM analysis, cracks were observed at the sub-surface layer of the pipes. The results show that uniform corrosion attacked the external pipe surface whereas pitting corrosion damaged the subsurface of pipes. The output of this study will be utilized by water suppliers and industries to investigate corrosion phenomena at any damage stage.

Corrosion of Longquan celadons in the marine environment: study on the celadons from the Dalian Island shipwreck of the Yuan Dynasty

The Dalian ("Image missing") Island shipwreck of the Yuan Dynasty (1271–1368 CE) was located in the sea area of Pingtan ("Image missing"), Fujian ("Image missing") Province, China. A total of 603 Longquan ("Image missing") celadon wares were excavated, some of which have been severely corroded. In this study, two celadon specimens with severe corrosion were selected to investigate the corrosion mechanism in the marine environment. Optical microscopy (OM), scanning electron microscopy equipped with energy dispersive X-ray spectrometry (SEM–EDS), X-ray diffraction analysis (XRD), Micro-Raman spectroscopy, and thermal expansion analysis were applied to analyze the microstructure of the glaze, corrosion morphology, and composition of corrosion products, and the corrosion mechanism was discussed in depth. The results showed that these two celadon wares are opaque matt glaze, in which the anorthite crystallization-phase separation structure with low chemical stability was found, which was more likely to be corroded. There are three possible stages in the corrosion process of the glaze. The first stage is mainly the long-term cation exchange reaction. Then, because of the corrosion of the CaO-rich droplet phase and the crystal-glass phase interface layer, the porous structure and many microcracks may be formed, promoting the corrosion process. Finally, many corrosion craters, caused by the shedding of anorthite crystals, may appear on the glaze surface. The quintinite group minerals in the glaze were probably formed during the corrosion process, which may be related to the marine buried environment and the corrosion of the glaze. This study discussed the influencing factors of the corrosion process of celadon wares in the marine environment from the perspective of microstructure for the first time, which is of great significance to the study of the corrosion mechanism of ancient ceramics.

Comparative Study of Chloride and Fluoride Induced Aluminum Pad Corrosion in Wire-Bonded Device Packaging Assembly

The introduction of copper as wire bonding material brings about a new challenge of aluminum bond pad bimetallic corrosion at the copper/aluminum galvanic interface. Aluminum is well known to undergo pitting corrosion under halide-contaminated environments, even in slightly acidic conditions. This paper aims to study the corrosion morphology and progression of aluminum influenced by different halide contaminations in the presence and absence of galvanic contact with copper. We used a new corrosion characterization platform of the micropattern corrosion screening to simulate the copper wire bonding on the aluminum bond pad. The corrosion screening data and subsequent SEM–EDX analyses showed a striking difference in morphology and progression between chloride-induced and fluoride-induced aluminum corrosion. The corrosion products formed play a vital role in the resulting morphology and in sustaining further aluminum corrosion.