Corrosion Topography Research Articles

A hybrid corrosion-structural model for simulating realistic corrosion topography of maritime structures

A multiscale multiphysics model has been developed coupling nonlinear structural behaviour and the corrosion kinetics. This study develops a hybrid mechano-electrochemical corrosion model using finite element method to evaluate long-term topography evolution on carbon steel stiffened plates for marine applications. A parametric study is performed on a stiffened plate (1.5 m × 0.95 m) with different localised corrosion locations (0.75 m × 0.045 m) at different load levels. Stress-based anodic and cathodic surfaces are defined using a level-set function to solve the transport equation, facilitated by the moving boundary technique. Key model insights show broad-pitted corrosion features with benching, closely resembling those found in actual ship inspections and/or surveys.

Electrolytic accelerated corrosion morphology for structural steel based on an improved solution

Abstract Atmospheric corrosion degrades the mechanical properties of steel structures mainly because of stress concentrations caused by an uneven corrosion topography. Electrolytic corrosion is regarded as one of the most efficient indoor accelerated corrosion approaches, while, the uneven atmospheric corrosion topography usually cannot be well simulated by electrolytic corrosion. This study aims to introduce an electrolytic corrosion solution suitable for simulating atmospheric corrosion. The surface morphologies of the structural steel specimens after electrolytic corrosion in three different solutions under various electrification time and magnitude of the current were compared. The surface characteristics of the corroded steel plates were measured by a 3D noncontact surface topography scanner, and analyzed based on surface roughness theory and fractal theory. The results showed that the mixed solution of 0.5% CH3COONa and 0.2% NaCl will produce pitting corrosion on the steel surface, and the surface morphologies of the steel specimens after electrolytic corrosion were consistent with that of neutral salt spray accelerated corrosion test. It is verified that the electrolytic accelerated corrosion in such a solution can simulate actual atmospheric corrosion reasonably.

Corrosion Behavior of Al0.1CoCrFeNi High Entropy Alloy in Various Chloride-Containing Solutions

The present work investigates the corrosion behavior of Al0.1CoCrFeNi high entropy alloy (HEA) in various concentrations of chloride-containing solutions. Electrochemical tests exhibit overall excellent corrosion resistance of this alloy against the attack of Cl−-containing solutions. The main type of corrosion topography presents an intergranular feature. In addition, electrochemical impedance spectroscopy (EIS) investigation of the HEA samples under immersion test suggests chloride anion–containing environment leads to the decline of passivation film quality. Further analysis of XPS results reveals that significant amounts of elements exist with atomic states in the passive films.

Experimental and numerical investigation on the corrosion effects on the bonding behavior between CFRP and steel

This paper intends to investigate the corrosion effects on the bonding behavior between CFRP and steel. The corrosion parameters such as the pit density Pd, the average pit depth Dave and width Wave were acquired by using an immersion simulation algorithm. By conducting the shear tests of the CFRP/steel single lap specimens, the bonding parameters such as the ultimate load Fu, the shear strength τmax and the fracture energy G were obtained and their relationships with corrosion parameters were established. In addition, finite element models considering the corrosion topography were proposed to simulate the bonding behavior. Results showed that the Fu and the G increased first and then stabilized as the Pd increased, and increased slightly then decreased as the Dave and the Wave increased, indicating that the corroded surfaces distributed with a large number of pits of appropriate sizes may maximize the bonding strength and the fracture energy; the τmax increased with the Pd, and decreased as the Dave and the Wave increased, indicating that a larger pit number and a smaller pit sizes would lead to a higher shear strength; the Fu and the interfacial shear stress distribution in finite element analysis were similar to the experimental results.

Effect of Sol-Gel Film on the Corrosion Resistance of Low Carbon Steel Plate

To improve the corrosion resistance on Q235 low carbon steel, in this paper, tetraethyl orthosilicate (TEOS), N-dodecyl trimethoxysilane and γ-(2,3-epoxypropoxy) propytrimethoxysilane (KH560) were used to make organic-inorganic hybrid sol-gel film. Cross cut test adhesion method, neutral salt spray test, electrochemical test and film protective efficiency were taken to value the corrosion resistance property. The corrosion topography was studied by optical microscope. In addition, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) curves and equivalent electric circuit fitting were used to analyze the corrosion mechanism. The cross cut adhesion of sol-gel film can reach 1 class and the protection class can attain 5 class after 72 hours neutral salt spray test. According to the potentiodynamic polarization curve analysis, the corrosion potential of sol-gel film coating sample after 0.5 hours immersion was -0.46 V (vs. SCE) on the 0.1 Hz, and its corrosion current density was 4.74×10-7 A·cm-2. The corrosion potential of bare Q235 low carbon steel plate after 0.5 hours immersion was -0.78 V (vs. SCE) on the 0.1 Hz, and its corrosion current density was 4.75×10-6 A·cm-2. The impedance value on 0.1 Hz (|Z|0.1Hz) (1.27×106 Ω·cm2) of sol-gel film coating sample was more than three orders of magnitude higher than the value of the low carbon steel plate. Even dipping in 3.5 wt. % NaCl for 72 hours, the |Z|0.1Hz value of sol-gel coating sample was still one order of magnitude higher than the low carbon steel plate with 0.5 hours immersion. Sol-gel film with excellent adhesion can significantly improve the corrosion resistance of low carbon steel plate. Sol-gel film can increase the protection efficiency of low carbon steel plate by 90%.

Evolution Laws of 7B04 Aluminum Alloys Pitting Corrosion Topography Characteristics and Size Parameters

Evolution Laws of 7B04 Aluminum Alloys Pitting Corrosion Topography Characteristics and Size Parameters

Pitting Corrosion Topography Characteristics and Evolution Laws of LC4 Aluminum Alloy in Service Environment

Pitting Corrosion Topography Characteristics and Evolution Laws of LC4 Aluminum Alloy in Service Environment

Corrosion mechanisms of sintered Nd–Fe–B magnets in the presence of water as vapour, pressurised vapour and liquid

Corrosion behaviour of three commercial sintered Nd–Fe–B magnets exposed to environments containing water as vapour, pressurised vapour, and liquid was investigated in order to understand their overall corrosion performance under a range of conditions. Two types of heat humidity exposure tests, namely the 85/85 and pressure cooker test, and the immersion test combined with electrochemical measurements were used as corrosion tests. It was observed that varying the temperature, pressure, and the prevailing state of water in the exposure tests, different corrosion mechanisms were detected on the surface of Nd–Fe–B magnets. The surface finish of the magnet had an effect on the initiation of corrosion in mild heat-humidity exposure. Immersion in liquid water resulted in a corrosion topography where the Nd-rich grain-boundary phase did not corrode selectively as in the other accelerated corrosion tests but was retained intact while the matrix phase underwent corrosion. These results and the dominant corrosion mechanisms of sintered Nd–Fe–B magnets in different environments are presented and discussed in this paper.

Effect of Low Temperature on Fatigue Crack Formation and Microstructure-Scale Growth from Corrosion Damage in Al-Zn-Mg-Cu

The strong effect of cold temperature on the fatigue resistance of 7075-T651 is established. As temperature decreases from 296 K to 183 K (23 °C to −90 °C), the formation life for cracking about pit and EXCO corrosion perimeters increases, microstructure scale crack growth rates decrease in the range from 20 to 500 μm beyond the corrosion topography, and long crack growth rates similarly decline. Fatigue crack surface features correlate with reduced hydrogen embrittlement with decreasing temperature fed by localized H produced during precorrosion for pit and EXCO-proximate cracks, as well as by crack tip H produced by water vapor reaction during stressing for all crack sizes. The importance of the former H source increases with decreasing temperature for cracks sized below 200 μm. Decreasing temperature to 223 K (−50 °C) eliminates the contribution of environmental H through interaction of reduced water vapor pressure in equilibrium with ice and reduced H diffusion. The Knudsen flow model and exposure parameter, \( P_{{{\text{H}}_{2} {\text{O}}}}/f \), enables improved modeling of temperature dependent crack propagation, but does not fully describe low temperature fatigue behavior due to possible rate limitation by H diffusion. Further decreases in MSC da/dN to 183 K (−90 °C) are related to reduced mobility of the corrosion-precharged H which may associate with vacancies from dissolution. Crack formation, and growth rates correlate with either elastic stress intensity range or cyclic crack tip opening displacement, and are available to predict corrosion effects on airframe fatigue for the important low temperature regime.

Effect of initiation feature on microstructure-scale fatigue crack propagation in Al–Zn–Mg–Cu

High fidelity measurements of constituent particle or corrosion topography nucleated fatigue crack growth rates (da/dN) are established for 7075-T651 in humid air. Values of microstructure-scale da/dN are determined by microscopy of programmed load-induced crack surface markers, rather than surface-only measurements. Both pristine and corroded specimen da/dN from various applied stress levels are successfully correlated using continuum-elastic stress intensity (ΔK or ΔK and Kmax) or dislocation-based (Bilby–Cottrell–Swindon) crack tip opening displacement (cyclic ϕ and ϕmax), with the former accounting for the gradient of elastic stress concentration due to the initiating feature. Values of da/dN vary by an order of magnitude at each fixed driving force due to microstructural influences that result in a locally irregular crack front. Grain-scale models using stress intensity closure or slip-based crystal plasticity do not capture experimental da/dN variability. Due to an inadequate mechanistic basis, mechanics-inspired models of da/dN do not predict multiple growth regimes that are typical of environment enhanced cracking. An elastic ΔK-based description of long crack da/dN data for a given alloy-environment can be transformed to a continuum elastic–plastic ϕc basis to provide a mean crack growth rate description. Coupling mean rates with a statistical description of microstructure sensitive variability, and dislocation or crystal plasticity-finite element modeling of component ϕc for non-continuum cracking, will enhance prognosis in the MSC regime.

Effects of Temperature on Corrosion Behavior of X70 Steel in Halons

The corrosion behavior of X70 pipeline steel in 0.5% NaC1 solution in different temperature of 25°C、35°C and 55°C was studied by dynamic potential polarization curve and electrochemical impedance spectroscopy（EIS）method. The corrosion topography of X70 pipeline steel in normal temperature and 30°C was also compared in immersion corrosion test after 25 days. The results show that when the temperature rises, the corrosion current density Icorr increases, the linear polarization resistance reduces, cathode polarization curve right shift, caused corrosion rate increases which primarily by the increasing the transmission of reactant in the cathode reaction. Pitting corrosion developed after 25 days immersion corrosion in 30°C solution which proved the promoter action of temperature to pit corrosion, and which is agreed with the electrochemical corrosion test results.

Fatigue crack formation and growth from localized corrosion in Al–Zn–Mg–Cu

The effect of precorrosion on the fatigue life of aluminum alloy 7075-T6511 was measured, physical characteristics of corrosion topography plus fatigue damage were established by microscopy, and a corrosion modified equivalent initial flaw size (CM-EIFS) was established using fracture mechanics modeling. Fatigue life is reduced by clustered corrosion pits on the L–S surface from laboratory-EXCO exposure. Cracks initiate from pits clustered as a semi-elliptical surface micronotch rather than the deepest pits, consistent with shape-dependent stress intensity. Marker band analysis establishes that the number of cycles to form a crack about a pit cluster can be a significant fraction of total fatigue life. The CM-EIFS, back-calculated from fracture mechanics analysis of measured fatigue life, equals measured initiating-pit cluster size provided that important inputs are provided; such favorable comparison validates this approach to corrosion-fatigue interaction. Calculated CM-EIFS provides a metric to characterize alloy corrosion damage, and can be used to forward-model the effects of stress and loading environment on fatigue life distribution, critical for efficient alloy development. Use in prognosis of the fatigue performance of a service-corroded surface is hindered by uncertain non-destructive characterization of corrosion topography.

Development of an Aircraft Lap Joint Simulant Environment

Abstract The aging of aircraft fleet has led to significant concern about the development of corrosion. Occluded regions such as lapsplice joints, which are difficult to inspect, are of particular importance. By analyzing the corrosion products found in these joints, a simulant solution has been developed. The lap joint simulant solution (LJSS) contains 20 mM sodium chloride (NaCl), 4 mM sodium bicarbonate (NaHCO3), 4 mM sodium nitrite (NaNO2), and 2 mM sodium fluoride (NaF) at pH 9. Exposure of AA2024-T3 (UNS A92024) to the LJSS results in a similar corrosion topography to that found on aircraft in the field.