Insight into microstructure evolution on anti-corrosion property of Al_(x)CoCrFeNiC_(0.01) high-entropy alloys using scanning vibration electrode technique

The effect of micro structure on the corrosion resistance of Al_(x)CoCrFeNiC_(0.01)(x=0.2,0.7,and 1.2)high-entropy alloys(HEAs) was systematically studied in this work.The microstructure evolution by regulating the Al content was analyzed in detail.Corrosion behavior was in situ monitored using the scanning vibration electrode technique,as well as some traditional electrochemical measurements.It is interesting to find that the compositions of body-centered cubic(bcc) and face-centered cubic(fcc)phases changed with the rising Al content,while the corresponding electrochemical responses for both phases were discriminated using the scanning Kelvin probe force microscopy method.Cr element was mainly distributed in the bcc phase for Al0.2(x=0.2) alloy,while its distribution changed to the fcc phase for the A10.7 and Al1.2alloys.The micro-galvanic corrosion cells formed between Cr-depleted and Cr-rich phases,resulting in the localized corrosion behaviors for the Al_(x)CoCrFeNiC_(0.01) HEAs,and the order for anti-corrosion property was Al0.2>Al1.2> Al0.7 HEAs.

Effect of scratch on corrosion resistance of calcium phosphate conversion coated AZ80 magnesium alloy

In order to analyze the effect of scratch on the corrosion behaviour of a calcium phosphate conversion coating(CPCC)on AZ80,the electrochemical testing,scanning vibrating electrode technique(SVET),immersion test and hydrogen evolution experiment were performed to study the corrosion resistance of AZ80,AZ80 with CPCC and coated AZ80 with scratch.The results show that the coating improves the corrosion resistance of the AZ80 from a current density of(85±4)to(4±1)μA/cm^(2).When the coating was damaged,its protection on substrate would be reduced.The scratch with a length of around 12 mm on the coating reduced the corrosion resistance to a current density of(39±1)μA/cm^(2).In addition,the corrosion occurred initially in the scratch area and the corrosion site first occurred at the junction of the scratch and the coating.Besides,the micro corrosion mechanism of the specimen containing scratch was clarified.

Relationship between La and Ce additions on microstructure and corrosion resistance of hot-dip galvanized steel

Scanning electron microscopy,X-ray diffraction,a neutral salt spray test,and electrochemical methods were applied to observe the microstructure and test the corrosion resistance of hot-dip galvanized steel before and after the addition of La and Ce.La/Ce mixture existed in the form of(La,Ce)Zn13 on the coated surface,decreased the coating thickness and accelerated the zinc dendritic growth.The corrosion current density of Zn-0.1La-0.1Ce coating was 63%less than that of pure Zn coating.This phenomenon can be explained that La/Ce mixture inhibited the transformation of Zn5(OH)8Cl2·H2O into Zn5(CO3)2(OH)6 or ZnO,reduced the time for appearance of red rust,and thus enhanced the stability of corrosion products and delayed the oxidation and corrosion processes of galvanized coating.La/Ce mixture improved the corrosion resistance compared to a single La or a single Ce addition.A competitive relationship between La and Ce was observed in the corrosion resistance improvement of hot-dip galvanized steel.

Galvanic Corrosion Behavior of Copper-Drawn Steel for Grounding Grids in the Acidic Red Soil Simulated Solution

The influence of pH and metallographic structure on the corrosion behavior of copper-drawn steel is studied with the simulated system.The effect of pH on the corrosion behavior of copper-drawn steel has been investigated using open-circuit potential,potentiodynamic polarization,galvanic current measurement,scanning electron microscopy and scanning vibrating electrode technique techniques.The steel is corroded as anode,while the corrosion of copper plate is protected as cathode.All the results revealed that pH and metallographic structure had a significant influence on the corrosion behavior of copper-drawn steel.With the decrease in pH value from 6 to 2.4,the corrosion rate of copper-drawn steel galvanic couple(Cu-Fe GC)obviously increased in the simulated solution of acidic red soil.The electric field formed by the Cu-Fe GC changes the direction of ion migration between the copper and drawn steel electrodes,which impacts the composition and microstructure of corrosion products formed on the electrode surface.

Initiation and propagation of localized corrosion induced by(Zr,Ti,Al)-O_(x) inclusions in low-alloy steels in marine environment

The effects of inclusions on localized corrosion of Zr–Ti deoxidized low-alloy steels in marine environment were investigated by various analytical techniques including scanning electron microscopy with X-ray microanalysis(SEM/EDS),confocal Raman microscopy(CRM),and in situ scanning vibrating electrode technique(SVET).It was found that complex(Zr,Ti,Al)-O_(x)inclusions were responsible for the initiation of localized corrosion.Localized corrosion pref-erentially occurred at Fe matrix adjacent to these inclusions and formed micro-gaps.In the early stage of corrosion,catalytic-occluded cells and the diffusion of chloride ions played a major role in the propagation of corrosion,further accelerating the dissolution of Fe matrix and(Zr,Ti,Al)-O_(x)inclusions.Combining SVET and CRM results,it revealed that the maximum anodic current density in local area gradually decreased with prolonged exposure time,indicating that corrosion products covered the steel surface and lowered the propagation rate of corrosion.In the later stage of corrosion,the barrier effect of corrosion products played an important role in inhibiting localized corrosion.

Inhibition of galvanic corrosion in Al/Cu coupling model by synergistic combination of 3-Amino-1,2,4-triazole-5-thiol and cerium chloride

Asynergistic inhibition study was carried out on an aluminium/copper galvanic coupling model in neutral aerated NaCl solution using scanning vibrating electrode technique(SVET).The approach allows the simulation of the local micro-galvanic cells of AA2024-T3 obtained from the potential difference between the intermetallic particles(IMPs)and the aluminium matrix.The inhibition effect of CeCl3 and 3-Amino-1,2,4-triazole-5-thiol(ATAT)was demonstrated by the reduction in the galvanic current density over Al and Cu surfaces.An improved inhibition from positive synergistic effect was revealed by the combination of the two inhibitors after 24 h of immersion,with the best inhibition recorded for Ce1.5ATAT3.5.Scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS)and time of flight secondary ion mass spectrometry(ToF-SIMS)were used to characterize the Ce-and ATAT-based complex film formed and to illustrate the mechanism of inhibition.

Effects of chloride on electrochemical and stress corrosion cracking behavior of 9Cr ferritic-martensitic steel

The electrochemical and stress corrosion cracking behavior of 9Cr ferritic-martensitic steel is investigated in the chloride environment by using the traditional electrochemical method, the scanning vibrating electrode technique and the slow strain rate test (SSRT). Results of the static corrosion tests and corrosion morphology show that the prior austenite grain boundaries and martensite lath boundaries are the preferred sites for pit nucleation and growth in chloride environment. Results of SSRT coupled with insitu electrochemical test show that the transition from pitting corrosion to uniform corrosion, as well as the nucleation of stress corrosion crack, is the synergistic effects of the chloride and applied load. Stress corrosion cracking of the steel in the chloride environment can be divided into three different regions as follows: fast and uniform corrosion activ-ity, microcrack nucleation and propagation, and active crack growth regions.