Pitting Corrosion Tests Research Articles

Microstructure and Corrosion Study on Friction Surfaced Aluminum Alloy Coatings over Mild Steel

In this study, the low-carbon steel (AISI 1018 mild steel) substrate is coated with the aluminum alloys AA6082-T6, Al-20Zn, and Al-2Si-15SiC to improve its corrosion resistance by the friction surfacing (FS) technique. To produce a high-quality coating, friction surfacing process variables including spin speed, speed of travel, and the rate of feed are crucial. This experiment examines twelve friction-surfaced plates with different parameter combinations. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) examinations were carried out in order to comprehend the microstructure and chemical composition of the coating deposits and the area in contact between the coated surface and the substrate. Microstructure investigation reveals that the intermetallic combination of Fe-Al at the coating interface region is an effect of the elemental diffusion of Fe to aluminum at the contact interface. Then a uniform and fine-grained coating deposit is observed as a result of the continuous recrystallization of the consumable rod under frictional stress and heat generation. According to the outcomes of the microhardness test, the coated surface is roughly 15–16% harder than the consumable rod. The coating bond strength was measured using a ram tensile test, and it ranged from 102 MPa to 135 MPa. Finally, evaluation of corrosion behavior through immersion testing and pitting corrosion testing reveals that the coatings made of Al-20Zn and Al-2Si-15SiC exhibit good corrosive resistance in an alkaline environment.

Mechanism of improving corrosion resistance in heat affected zone of duplex stainless steel by tantalum addition

The effect of tantalum addition on corrosion resistance in HAZ of duplex stainless steel was investigated by pitting corrosion test and material characterizations (SEM, TEM, APT). The Ta addition improved corrosion resistance of HAZ simulating welding at low heat input and rapid cooling rate since Ta segregated in the Cr nitrides and suppressed formation of Cr-depleted zone. The Ta addition also improved corrosion resistance in HAZ subjected to isothermal aging heat treatment assuming welding at high heat input and low cooling rate because Ta promotes the formation of χ phase and delays the formation of σ phase and Cr-depleted zone.

Corrosion studies on friction stir spot welded dissimilar AZ31-C27200 Cu joints

In this investigation, corrosion studies were conducted on dissimilar friction stir spot welded AZ31 Mg-C27200 Cu joints using pitting corrosion tests. Mechanical characteristics of the joints were also evaluated. By conducting tensile testing, the tensile shear failure load value of AZ31 Mg-C27200 Cu joints were 62.36% of the value of similar AZ31 Mg – AZ31 Mg joints and 51.9% of the values of C27200 Cu– C27200 Cu joints, respectively. The joint interface hardness of the dissimilar combination such as AZ31 Mg– C27200 Cu joints were 22.03 % and 35.84% greater than the interface hardness values of similar AZ31 Mg–AZ31 Mg and C27200 Cu–C27200 Cu joints, respectively. Bend tests revealed that similar joints broke with interfacial tear and the dissimilar joints broke with nugget pullout. By conducting pitting corrosion tests on the joints, potentiodynamic polarization curves were developed. The corroded samples were subjected to microstructural evaluation using scanning electron microscopy. The variations in corrosion pit density were also identified.

Failure analysis of the leakage in girth weld of bimetal composite pipe

A bimetal mechanically-composite pipe leaked at the entrance of processing station. The failure location was the 6o'clock direction of the girth weld connecting the gathering pipe and pipe in the station. In order to figure out the root cause of the failure, a series of experiments were carried out. The macroscopic analysis and metallographic test results show that the leakage point is located at the 6o'clock direction of the girth weld, the root welding and the base pipe of the bimetallic composite pipe are corroded, resulting in perforation. The end of the bimetallic composite pipe is not seal-welded, the girth weld has misalignment and at 6o'clock, the root weld was concave, and the wall thickness of the root weld and the lining is<1.5 mm. The FeCl3 pitting corrosion test results of the girth weld show that the pitting corrosion resistance of the root weld is lower than that of the liner and pure stainless-steel pipe. The galvanic corrosion test shows that the galvanic corrosion grades of weld-pure material, weld-liner, carbon steel-weld, carbon steel-liner are all severe corrosion, and the galvanic corrosion of carbon steel-weld is the most serious. The root cause of the failure of girth weld puncture leakage: the end of the bimetallic composite pipe is not seal-welded. At 6o’clock, the girth weld has misalignment, and the root weld is concave, resulting in that the thickness connecting the root weld and the liner being small. In the medium environment containing Cl- and CO2, local corrosion occurs, and then the medium enters the base pipe and the liner interlayer, and the galvanic corrosion aggravates the corrosion of the base pipe. To avoid the reoccurrence of such failure, the mitigation measures were proposed.

Technical Note: Low-Cost Sample Holder with Flooded Gasket Prevents Crevice Corrosion in Pitting Corrosion Tests

This work describes an inexpensive holder for corrosion experiments, developed to avoid crevice corrosion during pitting corrosion tests of corrosion-resistant alloys. It is based on a flooded gasket, incorporated in a Stern-Makrides sample holder. Unlike the Avesta cell designed by Qvarfort, the proposed sample holder does not require a pump. The sample holder attaches to prismatic or cylindrical specimens cut from bars, plates, or any other component with a thickness greater than 10 mm. The sample holder is versatile and with no limitations on chloride concentration, solution composition, or temperature. The testing solution can be deaerated or saturated with any gas if needed. The sample holding method was validated by cyclic potentiodynamic polarization experiments on Types 304, 316 stainless steel, and C-22HS nickel-based alloy. Crevice corrosion was not evident in any of the specimens tested with the proposed method.

Pitting corrosion studies on functionally graded Inconel 825-SS316L wall manufactured by wire arc additive manufacturing

This research article addresses the pitting corrosion resistance of FGM walls fabricated by the Wire Arc Additive Manufacturing (WAAM). The wall is created by layer-by-layer transfer of molten metal in an uninterrupted manner with little heat input using the CMT process. Pitting corrosion tests were carried out as per the ASTM G48-11 standard on the specimens extracted from Inconel 825, FGM interfaces, and SS316L regions of the wall. The specimens were immersed in the ferric chloride hexahydrate solution for 24, 48, and 72 h. It was found that the FGM interface and the specimens made of Inconel 825 were more resistant to corrosion than the SS316L specimens. The weight loss is measured as 0.462 g, 0.1087 g, and 0.1349 g for the SS316L, FGM interface, and Inconel 825 specimens, respectively. Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) were used to analyze the corrosion products at the corrosion pit. The order of the pitting corrosion resistance of the specimens extracted from the FGM wall was: FGM interface > Inconel 825 > SS316L.

Estimating Pitting Corrosion Depth and Density on Carbon Steel (C-4130) using Artificial Neural Networks

The purpose of this research is to investigate the impact of corrosive environment (corrosive ferric chloride of 1, 2, 5, 6% wt. at room temperature), immersion period of (48, 72, 96, 120, 144 hours), and surface roughness on pitting corrosion characteristics and use the data to build an artificial neural network and test its ability to predict the depth and intensity of pitting corrosion in a variety of conditions. Pit density and depth were calculated using a pitting corrosion test on carbon steel (C-4130). Pitting corrosion experimental tests were used to develop artificial neural network (ANN) models for predicting pitting corrosion characteristics. It was found that artificial neural network models were shown to be quite effective; the results were validated by the experimental agreement with those acquired from laboratory tests. Specifically, the correlation coefficient, R = 0.9944.

Evaluation of Physicochemical and Electrochemical Properties of Surface Modified Pure Titanium Grade II

The paper contains the results of surface modification on the properties of the pure titanium Grade II, obtained by the SLM procedure. In the paper, the analysis of the results of physicochemical properties, such as pitting corrosion test and contact angle measurements and Surface Free Energy calculated were performed. Additionally, the microscopic observation with microchemical analysis, surface topography analysis using Atomic Force Microscopy, surface roughness measurements and wear test were performed too. The studies were carried out on three groups of samples in an initial state (1) (after mechanical treatment - mechanical grinding and polishing) and after surface modification by PVD method using CrN layer (2) and TiN layer (3). Based on the obtained results it can be concluded that the samples with TiN layer were characterized by the optimum properties.

Physical Properties and Failure Analysis for Bolts in the Diaphragm Valve by Micro Morphology and Metallographic Test

The reasons leading to the fracture of 17-4PH stainless steel bolts in the isolation valve of a power plant was analysed by means of morphology analysis, chemical analysis, hardness test, metallographic test, pitting corrosion test and intergranular corrosion test, SEM and other detection means. The results show that there are many corrosion pits on the surface of the valve stem in the seawater system, the corrosion pits is extend and propagation in intergranular cracking. The main reasons to valve stem fracture are the low corrosion resistance of the material and the improper aging process of heat treatment.

Experimental and numerical analysis of Pitting Corrosion in CUSTOM 450 Stainless Steel

The present study aimed at the propagation of the pit in CUSTOM 450 Stainless Steel blades after the initiation stage. The depth of pits was measured by Eddy Current and the relationship between pitting corrosion time and pit depth was determined based on simulation and compared to the experimental results. Moreover, the electrolyte potential and the local strain distribution around the pit were displayed at different potentials and times. The pit growth increased rapidly for a certain period and then declined. For stressed and stress-free samples, the local strain distribution and pit depth growth were compared at 350 mVSCE potential. Based on the results, the presence of stress in the specimens accelerated the pitting corrosion growth in CUSTOM 450 stainless steel. To calculate the stresses on the blade surface, the model of the blade was constructed and two adjacent pits were created at the location of the fractured surface. The results show that the pits are turned into stress cracks after about 4 months corresponding to the result of the other references. To make a connection between accelerated pitting corrosion tests and the operating conditions of the gas turbine, the comparison of pitting time (simulation) was made for the stressed sample at 350 mVSCE potential and sample with real operating conditions.350 mVSCE potential and sample with real operating conditions.

Experimental studies on effect of post weld heat treatments on the pitting corrosion and impact toughness of GTA welded martensitic stainless steel joints

Objectives: The present experimental work investigates the effect of post weld heat treatments on the pitting, impact toughness and metallurgical properties of gas tungsten arc welded martensitic stainless steel joints. Methods/Statistical analysis: Martensitic stainless steel (AISI410 SS) cold rolled plates used as a base materials and welded using GTAW process with two filler materials (ER 304LSS and ER 410 SS for root pass and cover passes respectively). Three heat treatments namely annealing, quenching and plasma nitriding were given to the specimens. After the heat treatments the specimens were subjected to pitting corrosion test, impact toughness test, microhardness testing and microstructural examination. Findings: Pitting corrosion results under different heat treatments of the welds showed that the post weld heat treatment induces the significant variations in the pitting resistance. The maximum pitting resistance (minimum mass loss of 0.5108mg) was possessed by the weld with plasma nitriding treatment. The maximum energy absorption capacity of the welds of 62 Joules was obtained in the annealing treatment. The average microhardness values of 474VHN, 372 VHN, 492VHN and 559VHN was obtained in as welded condition, under annealing treatment, under quenching treatment and under plasma nitriding treatment respectively of the welded joints. Based on the micro-structural studies of the welded joint in as received and post weld heat treated conditions, the significant microstructural changes were observed in weld metal zones. Novelty/Applications: The present experimental study can beneficially be adopted for welding of martensitic stainless steel (AISI 410 SS) as it suggests the processing conditions to forecast the adequate pitting resistance, impact toughness and microhardness behaviour in similar service conditions. Keywords Pitting corrosion, impact toughness, post weld heat treatments, microhardness, microstructure, GTAW

Electrochemical testing of thermal spray coatings using gel electrolytes

The use of electrochemical methods allows fast and inexpensive corrosion measurements of bulk materials with high significance. In the case of thermal spray coatings, electrolyte penetration into open pores up to the substrate material can cause undesired mixed potentials. Furthermore, the implementation of complex geometries or rough surfaces remains a problem. Preconditioning of the surface or the use of the electrochemical cell is required to eliminate leakage. Therefore, reliably measuring corrosion is still a challenging task. This undermines fast monitoring of corrosion performance as a part of the production process. Gelling agents are investigated to increase the viscosity of many electrolytes. A procedure has been developed to determine the concentration level and the mixing conditions. Passivation and pitting-corrosion testing are performed on thermal spray AISI 316L coatings. The electrochemical potential curves as well as the corroded surface layers were studied in comparison to a liquid electrolyte. The suitability of the test on rough surfaces in the sprayed condition was investigated. The results prove the novel approach as an alternative to established electrochemical test methods with extended application range.

Effects of Laser Glazed Surface on Pitting Corrosion of Nickel Alloy 718 in Acidic and Seawater Environments

Studies on the effects of laser glazed and unglazed sample surfaces on the pitting corrosion resistance of nickel alloy 718 have been carried out. Both sample surfaces of nickel alloy 718 were cut to different dimensions for pitting corrosion tests using potentiostatic polarization process. The alloy samples used for electrochemical testing were connected to a flexible wire joined by spot weld process. The alloy samples were coated with low viscous polymeric wax leaving the surface areas to be tested exposed to seawater and one mole concentration of hydrochloric acid environments. These samples which are working electrodes have electrical connection between reference electrode and counter electrode and the entire system were connected to computer with PSTrace software that stands as potentiostat. Pre and post morphological examination of the sample surfaces were done using confocal laser scanning microscopy and scanning electron microscopy respectively. The results of pitting corrosion tests showed that the glazed and unglazed alloy sample surfaces immersed in seawater environment suffered from pitting corrosion as a result of the presence of pit initiation sites developed during surface laser treatment and also the presence of some aggressive anions like Cl^-, SO₄^- etc in the environment which migrated into the pits due to electrostatic balance and escalated pitting corrosion; while the samples of both surfaces immersed in 1MHCl suffered more from general corrosion. Post pitting corrosion examinations revealed that corrosion oxide films formed on the sample surfaces in acidic and alkaline environments were not protective as they flaked and exposed the sample surfaces to more corrosion attack.

Electrochemical corrosion tests of Nd-Fe-B-based magnetic materials with modified structure

The wide application of Nd-Fe-B permanent magnets in addition to the rare-earth metal resource constrains determine the necessity of their recycling. One of approaches to magnet-to-magnet recycling consists in using the grain boundary modification of sintered magnet material, which includes the grain-boundary diffusion (GBD) and grain-boundary structuring (GBS). The preparation of magnets with the modified structure determines a need for research their corrosion resistance. The corrosion resistance of magnets prepared by powder blending techniques, namely, magnets, which were recycled from hard-disk drivers, in using Dy/NdH2 additions in the powder mixture and magnets, which were prepared from strip-casting alloy, in using TbH2 hydride in the powder mixture, is studied. The corrosion potential and polarization resistance were measured, and the average corrosion rate was estimated based on polarization measurements of the magnet samples in the aqueous solution 0.1 M NaCl. Furthermore, a pitting resistance corrosion test was conducted and the values of pitting and repassivation potential were determined. The corrosive properties of the magnet samples are discussed from the viewpoint of the phase compositions of the material.

Atomic layer deposited ZnO films on stainless steel for biomedical applications

The main goal of carried out tests were the impact of physicochemical properties of surface layers on the course of processes taking place on the surface of implants made of metallic biomaterials used in the bone system. As a precursor of ZnO, diethylzinc (DEZ) has been used, which reacted with water enabling the deposition of thin films. The chamber temperature was as follows—T = 200°–300 °C. The number of cycles was 500, 1000, and 1500. In the first stage, pitting corrosion test was carried out. Corrosion resistance has been tested under conditions simulating tissue environment. Moreover, the created layers were tested using electrochemical impedance spectroscopy (EIS). The conducted electrochemical tests showed the beneficial effect of the ZnO layer on the substrate made of 316 LVM steel, as evidenced by the obtained parameters describing the corrosion resistance. Furthermore, tests were performed on mechanical properties (scratch test), surface morphology (SEM and AFM method), and physical properties (wettability and thickness layers) for samples with different surface treatments. The investigations of the surface morphology of the applied ZnO layer using the ALD method showed a tendency to inherit the substrate independently of the used application parameters. On the other hand, the tests of adhesion to the substrate showed that the number of cycles of the application process has a fundamental impact on the adhesion of the applied layer to the substrate. Summarizing tests have clearly shown that the number of cycles and temperature in the case of the ZnO coating is significant and positively influences the increase of electrochemical, mechanical, and physical properties of layers.

Influence of inhibitors on the corrosion behavior of the X5CrNi18 10 stainless steel‐welded joint

AbstractThis study considers the corrosion behavior of the X5CrNi18 10 stainless steel‐welded joint in NaCl solution, with and without the presence of several corrosion inhibitors (NaNO3, Ce(NO3)3, and CeCl3). The degree of sensitization of the welded joint to intergranular corrosion is determined using the electrochemical potentiokinetic reactivation method with a double‐loop method. Pitting corrosion tests are performed by the potentiodynamic method. Resistance to general corrosion and the stability of the passive film is assessed based on the results of electrochemical impedance spectroscopy measurements, as well as on the values of the corrosion and passivation current. The main goal of this study is to determine the relation of the welded joint microstructure to general and pitting corrosion in the presence of the corrosion inhibitors. The value of pitting potential for the base metal and weld metal in the presence of the NaNO3 or Ce(NO3)3 inhibitor is shifted to potentials in the transpassive area. The pitting potential for the heat‐affected zone also possesses a noticeable higher value. However, nitrate ions do not increase the general corrosion resistance of any part of the welded joint. CeCl3 does not increase resistance to general or pitting corrosion.

Relationship between the microstructure and local corrosion properties of weld metal in austenitic stainless steels

The purpose of this study is to evaluate the corrosion resistance of weld metal by electrochemical methods and discuss the relationship between microstructure and corrosion resistance. Intergranular and pitting corrosion resistances were measured using electrochemical potentiokinetic reactivation (EPR) test and pitting potential measurement respectively. The reactivation ratio and pitting potential corresponded to its chemical composition. The specimens containing more Cr and Mo showed higher resistance. In the EPR test, the dendrite core with a relatively low Cr content was corroded. In the pitting corrosion test, Nb carbide became the initiation site of pitting corrosion which propagated along the cell structure.

The Surface Morphology and Electrochemical Properties of Pure Titanium Obtained by Selective Laser Melting Method

High requirements in biomedical application are associated with biocompatibility and high corrosion resistance of metal biomaterials, which are used equally in joint and bon substitution and the healing and renewal of bone weaknesses. In this paper the surface morphology and electrochemical properties of samples manufactured by Selective Laser Melting SLM method using pure titanium Grade II powder material are explored. The tested samples were produced divided into four group, depended on the values of basic process parameters – laser power P, scanning speed SP and point distance PD. The value of energy density E delivered to the sintered material was constants and was an approximately E = 75 ± 2 J/mm3. In the paper, the pitting corrosion test by recording anodic polarization curves and electrochemical spectroscopy test were carried out. Additionally the microscopic observation and microchemical analysis by SEM/EDS analysis and material density measurements were performed too. Based on the obtained results it can be concluded that the laser power P and scanning speed SP have a significant affect on the obtained full density defect free material with high corrosion resistance.

Enhancing corrosion resistance of A-TIG welded UNS S32750 joints by optimizing its technological parameters

In this paper, an attempt was made to improve the corrosion resistance of activated tungsten inert gas welded super duplex stainless steel such as UNS S 32750. Joints were fabricated by fluctuating the important process parameters such as welding speed, shielding gas flow rate and welding current, using NiO as activation flux. A central composited design model was developed for identification of the Activated Tungsten Inert Gas welding process parameter values for fabricating twenty joints. The welded joints were subjected to pitting corrosion test using an electrochemical corrosion testing system and salt spray testing was done for 48 h. Empirical relationships were developed for the process parameters with variations in the pitting potential and the rate of mass loss. The significance of the developed model was ascertained using analysis of variance method and optimization was done using response surface methodology. The joints fabricated at welding speed of 54.26 mm/min, welding current of 157 A and gas flow rate of 14.8 L/min, were found to have maximum pitting potential of -252.36 eV and minimum mass loss of 0.0108 g. Using validation experiments, the error was identified within three percentage which indicated that the optimization model was developed with very high predictability.

Corrosion behaviour of AA2024 aluminium alloy in different tempers in NaCl solution and with the CeCl3 corrosion inhibitor

AbstractThe paper analyses the corrosion behaviour of naturally and artificially aged AA2024 alloy in NaCl solution and in the presence of an environment‐friendly corrosion inhibitor, CeCl3. On the basis of the values of polarisation resistance and corrosion current density, the corrosion resistance of the protective inhibitor film is established as well as the general corrosion resistance of this aluminium alloy. Resistance to pit formation is determined based on the difference in pitting and corrosion potentials while resistance to pit growth is determined based on the amount of charge consumed during pit growth. A scanning electron microscope is used to examine the morphology of the pits formed during the pitting corrosion testing, as well as to determine the cerium content on intermetallic particles and the matrix AA2024 alloy. The corrosion behaviour of AA2024 alloy is investigated after different test periods in NaCl solution and in the same solution with the CeCl3 inhibitor. The corrosion resistance of both tempers of AA2024 alloy is more than one order of magnitude higher in the presence of CeCl3. An explanation of the observed differences in the corrosion behaviour of the naturally and artificially aged AA2024 alloy is proposed. Different corrosion behaviour of the alloy after different test periods is also explained.