Structure and corrosion behavior of FeCoCrNiMo high-entropy alloy coatings prepared by mechanical alloying and plasma spraying

FeCoCrNiMox composite powders were prepared using the mechanical alloying technique and made into high-entropy alloy(HEA)coatings with the face-centered cubic phase using plasma spraying to address the element segregation problem in HEAs and pre-pare uniform HEA coatings.Scanning electron microscopy,transmission electron microscopy,and X-ray diffractometry were employed to characterize these coatings’microstructure and phase composition.The hardness,elastic modulus,and fracture toughness of coatings were tested,and the corrosion resistance was analyzed in simulated seawater.Results show that the hardness of the coating is HV0.1606.15,the modulus of elasticity is 128.42 GPa,and the fracture toughness is 43.98 MPa·m^(1/2).The corrosion potential of the coating in 3.5wt%NaCl solution is-0.49 V,and the corrosion current density is 1.2×10^(−6)A/cm^(2).The electrochemical system comprises three parts:the electrolyte,the adsorption and metallic oxide films produced during immersion,and the FeCoNiCrMo HEA coating.Over in-creasingly long periods,the corrosion reaction rate increases first and then decreases,the corrosion product film comprising metal oxides reaches a dynamic balance between formation and dissolution,and the internal reaction of the coating declines.

Corrosion behavior of 2A97 Al-Cu-Li alloys in different thermomechanical conditions by quasi-in-situ analysis

As a promising material in the aircraft industry,2A97 Al-Cu-Li alloy exhibits high corrosion susceptibility that may limit its application.In the present work,to illustrate the influences of precipitate and grain-stored energy on localized corrosion evolution in 2A97 Al-Cu-Li alloy,cold working and artificial aging were carried out to produce 2A97 Al-Cu-Li alloys under different thermomechanical conditions.Quasi-in-situ analysis,traditional immersion test and electrochemical measurement were then conducted to examine the corrosion behavior of 2A97 alloys.It is revealed that precipitate significantly affects Cu enrichment at corrosion fronts,which determines corrosion susceptibility of alloys,whereas grain-stored energy distribution is closely associated with localized corrosion propagation.It is also indicated that quasi-in-situ analysis exhibits a consistent corrosion evolution with traditional immersion tests,which is regarded as a proper method to explore localized corrosion mechanisms by providing local microstructural information with enhanced time and spatial resolutions.

Galvanic corrosion behavior of AZ91D alloy/45 steel couple under magnetic field

Galvanic corrosion behavior of AZ91D alloy/45 steel couple in 3.5 wt.%NaCl solution under 0,0.2 and 0.4 T magnetic field were studied by microstructure observation,immersion test and electrochemical measurement.The mixed potential theory was used to estimate the galvanic current density and the mixed potential of the galvanic corrosion between AZ91D alloy and 45 steel.The results indicated that magnetic field could accelerate the corrosion of AZ91D alloy,and impede the corrosion process of 45 steel.The effect of magnetic field on corrosion sensibility and corrosion rate of these two alloys increased as the intensity rising.The galvanic corrosion rate of the couple was accelerated by magnetic field.With the magnetic field intensity rising,the galvanic corrosion sensibility and corrosion rate of the couple increased.The effects of magnetic field on the galvanic corrosion performance of the couple and the corrosion behavior of AZ91D alloy and 45 steel were due to the appearance of field gradient force and magnetohydrodynamic(MHD)force.The mixed potential theory has a certain accuracy to estimate the Ecouple and icouple values in this work.

Influence of deformation on the corrosion behavior of LZ91 Mg-Li alloy

The effect of rolling and forging on the microstructure and corrosion behavior of LZ91 alloy was investigated using an electron probe micro-analyzer,immersion and electrochemical tests.Results showed that the area fraction of theβ-Li phase remained unchanged,and the grain size of theβ-Li phase decreased after forging.The as-rolled forged alloy(FR-LZ91)exhibited the highest area fraction of theβ-Li phase and the longest grains.The corrosion resistance of the forged LZ91 alloy increased due to grain refinement that prevented further corrosion during the immersion test.Among the experimental alloys,FR-LZ91 showed the highest resistance of corrosion film and charge transfer resistance values due to its protective film caused by the high area fraction of theβ-Li phase.

Corrosion behavior of composite coatings containing hydroxyapatite particles on Mg alloys by plasma electrolytic oxidation: A review

Mg and its alloys have been introduced as promising biodegradable materials for biomedical implant applications due to their excellent biocompatibility, mechanical behavior, and biodegradability. However, their susceptibility to rapid corrosion within the body poses a significant challenge and restricts their applications. To overcome this issue, various surface modification techniques have been developed to enhance the corrosion resistance and bioactivity of Mg-based implants. PEO is a potent technique for producing an oxide film on a surface that significantly minimizes the tendency to corrode. However, the inevitable defects due to discharges and poor biological activity during the coating process remain a concern. Therefore, adding suitable particles during the coating process is a suitable solution. Hydroxyapatite(HAp)has attracted much attention in the development of biomedical applications in the scientific community. HAp shows excellent biocompatibility due to its similarity in chemical composition to the mineral portion of bone. Therefore, its combination with Mg-based implants through PEO has shown significant improvements in their corrosion resistance and bioactivity. This review paper provides a comprehensive overview of the recent advances in the preparation, characterization, corrosion behavior and bioactivity applications of HAp particles on Mg-based implants by PEO.

Impressive strides in amelioration of corrosion behavior of Mg-based alloys through the PEO process combined with surface laser process: A review

The unsatisfactory corrosion properties of Mg-based alloys pose a significant obstacle to their widespread application. Plasma electrolytic oxidation(PEO) is a prevalent and effective coating method that produces a ceramic-like oxide coating on the surface of Mg-based alloys,enhancing their resistance to corrosion. Research has demonstrated that PEO treatment can substantially improve the corrosion performance of alloys based on magnesium in the short term. In an effort to enhance the corrosion resistance of PEO coatings over an extended period of time, researchers have turned their attention to the use of laser processes as both pre-and post-treatments in conjunction with the PEO process. Various laser processes, such as laser shock melting(LSM), laser shock adhesion(LSA), laser shock texturing(LST), and laser shock peening(LSP), have been investigated for their potential to improve PEO coatings on Mg substrates and their alloys. These laser melting processes can homogenize and alter the microstructure of Mg-based alloys while leaving the bulk material unchanged, thereby modifying the substrate surface. However, the porous and rough structure of PEO coatings, with their open and interconnected pore structure, can reduce their long-term corrosion resistance. As such, various laser processes are well-suited for surface modification of these coatings. This study will first examine the PEO process and the various types of laser processes used in this process, before investigating the corrosion behavior of PEO coatings in conjunction with laser pre-and post-treatment processes.

Corrosion behavior of micro-arc oxidation coating on AZ91D magnesium alloy in NaCl solutions with different concentrations

Ceramic oxide coatings were prepared on AZ91D magnesium alloys in alkaline silicate solution using micro-arc oxidation（MAO） technique.The corrosion behavior of MAO coating on AZ91D magnesium alloys in NaCl solutions with different concentrations（0.1%,0.5%,1.0%,3.5% and 5.0% in mass fraction） was evaluated by electrochemical measurements and immersion tests.The results showed that the corrosion rate of the MAO coated AZ91D increased with increasing chloride ion concentration.The main form of corrosion failure was localized corrosion for the MAO coated AZ91D immersed in higher concentration NaCl solutions（1.0%,3.5% and 5.0%）,while it was general corrosion in dilute NaCl solutions（0.1% and 0.5%）.Two different stages of the failure process of the MAO coated AZ91D could be identified：1） occurrence of the metastable pits and 2） growth of the pits.Different equivalent circuits were also proposed based on the results of electrochemical impedance spectroscopy（EIS） for the MAO coated AZ91D immersed in different concentrations of NaCl solutions for 120 h.

Corrosion behavior of tinplate in NaCl solution

The corrosion process of tinplate in 0.5 mol/L NaCl solution was investigated using the electrochemical impedance spectroscopy（EIS）,and the morphology and structure of the corrosion products were characterized by scanning electron microscope（SEM）,scanning probe microscopy（SPM）,X-ray diffraction（XRD） and X-ray photoelectron spectroscopy（XPS）.The results showed that the resistance of tin coating,Rc,was essentially constant but the charge transfer resistance,Rct,decreased by 2 orders of magnitude,which indicated that the tin coating was not seriously corroded while the carbon steel substrate was corroded continuously.The corrosion of tinplate in 0.5 mol/L NaCl solution was mainly the dissolution of carbon steel substrate because of the defects in the tin layer and the corrosion product was mainly γ-FeOOH.

Fabrication, tribological and corrosion behaviors of detonation gun sprayed Fe-based metallic glass coating

A metallic glass coating with the composition of Fe51.33Cr14.9Mo25.67Y3.4C3.44B1.26 （mole fraction, %） on the Q235 stainless steel was developed by the detonation gun （D-gun） spraying process. The microstructure and the phase aggregate were analyzed by scanning electron microscopy and X-ray diffractometry, respectively. Microhardness, wear resistance and corrosion behavior were assessed using a Vickers microhardness tester, a ball-on-disk wear testing machine and the electrochemical measurement method, respectively. Microstructural studies show that the coatings possess a densely layered structure with the porosity less than 2.1%. The tribological behavior of the coatings examined under dry conditions shows that their relative wear resistance is five times higher than that of the substrate material. Both adhesive wear and abrasive wear contribute to the friction, but the former is the dominant wear mechanism of the metallic glass coatings. The coatings exhibit low passive current density and extremely wide passive region in 3.5% NaCl solution, thus indicating excellent corrosion resistance.

Electrochemical corrosion behavior of arc sprayed Al-Zn-Si-RE coatings on mild steel in 3.5% NaCl solution

Al-Zn-Si-RE coating with high Al content was deposited on mild steel by arc spraying. The electrochemical behavior of Al-Zn-Si-RE coating in 3.5%NaCl solution was systematically studied by potentiodynamic polarization, corrosion potential (φcor ) and electrochemical impedance spectroscopy techniques (EIS). The impedance data were fitted to appropriate equivalent circuits to explain the different electrochemical processes occurring at the electrode-electrolyte interface. The results indicate that Al-Zn-Si-RE coating reveals the similar polarization behavior as Zn-15Al coating. The coating has no passive region in the anodic polarization, but far lower corrosion current and much higher corrosion potential. Al-Zn-Si-RE coating provides effective sacrificial protection for steel substrate and the sacrificial anodic protection plays dominant role during the immersion process. In addition, theφcor evolution and EIS plots indicate that the corrosion process can be divided into five stages: pitting-dissolution-redeposition, activation corrosion, cathodic protection, physical barriers and the coating failure.

Corrosion behavior of T2 copper in 3.5% sodium chloride solution treated by rotating electromagnetic field

Copper is susceptible to producing corrosion problems in corrosive environments, which leads to serious safety problems. Thus, investigating the corrosion behavior of copper is of great significance. The effects of rotating electromagnetic field on corrosion behavior of T2 copper in 3.5% sodium chloride solution with electrochemical measurements were investigated. The results showed that rotating electromagnetic field changed properties of 3.5% sodium chloride solution by increasing the values of temperature and pH and decreasing the values of conductivity and dissolved oxygen. The rotating electromagnetic field improved the corrosion resistance of T2 copper. The corrosion products of T2 copper in treated 3.5% sodium chloride solution were composed of Cu20 and CuCl. The low corrosion rate of T2 copper was resulted from the decrease of dissolved oxygen in 3.5% sodium chloride solution treated by rotating electromagnetic field.

Corrosion behavior of Ti-Nb-Ta-Zr-Fe alloy for biomedical applications in Ringer's solution

The corrosion resistance of Ti？25Nb？10Ta？1Zr？0.2Fe （mass fraction, %） （TNTZF） alloy in Ringer’s solution at 37 °C was investigated by potentiodynamic polarization measurement. Ti？6Al？4V ELI （Extra low interstitial） alloy was also investigated to make a comparison. The results show that TNTZF alloy has higher corrosion potential, lower corrosion current density, more stable passive current density and wider passive region compared with Ti–6Al–4V ELI alloy, which indicates that TNTZF alloy has better corrosion resistance. In addition, pitting corrosion is observed on the surface passive film of Ti–6Al–4V ELI alloy but is not found on that of TNTZF alloy. The XPS analysis results reveal that the passive film formed on TNTZF alloy is composed of Nb2O5, NbO2, Ta2O5, ZrO2, TiO and Ti2O3oxides in the matrix of TiO2, which makes the passive film more stable and protective than that formed on Ti？6Al？4V ELI alloy and contributes much to its superior corrosion resistance.

Growth and corrosion behaviors of thin anodic alumina membrane on AA5083 Al-Mg alloy in incalescent medium

A self-ordered porous film was fabricated on aluminum alloy in a ternary boric-sulfuric-oxalic acid electrolyte system. By means of voltage–time response, the oxidation process as well as the growth efficiency was studied. Field emission scanning electron microscopy（FE-SEM） was adopted to reveal the morphological and microstructural features of as-fabricated oxide layers. The corrosion protection properties of the films were investigated by electrochemical impedance spectroscopy and potentiodynamic polarization measurements. The results showed that increasing the concentration of the double ionic layer located at the oxide interface could accelerate the film growth rate. The anodic oxidative layer with thickness of 8-9 μm and pore diameter of 10-14 nm maintains the pattern and topography of workpieces, compared with the overall closed film with hierarchical structure. Both samples exhibited much lower corrosion current density after boil water sealing. Meanwhile, a superior stability could be achieved through raising the ambient temperature.

Influence of casting module on corrosion behavior of Mg-11Gd-3Y alloy

The influences of two kinds of casting modules of metal casting （MC） and expandable pattern casting （EPC） on the corrosion behavior of Mg-11Gd-3Y alloy were studied by electrochemical measurements, scanning electron microscopy （SEM） observation, X-ray diffractometry （XRD） and X-ray photoelectron spectroscopy （XPS） analysis. It is found that the quantity of the Mg 24 （Gd, Y） 5 phase in MC is more than that in EPC due to the cooling rate. There is more alloying element dissolved in the matrix compared with MC. For EPC, the galvanic corrosion effect between the matrix and the Mg 24 （Gd, Y） 5 phase decreases and the corrosion resistance increases compared with the MC. The chief corrosion mode for Mg-11Gd-3Y alloy is pitting corrosion because most of the alloying elements are transformed into intermetallic phases. The average corrosion rate of the MC alloy in the immersion test is five times higher than that of EPC alloy and yttrium is present in the product film, which will provide increased protection for Mg-11Gd-3Y alloy. The electrochemical measurements and immersion test show that the EPC process increases the corrosion resistance compared with the MC Mg-11Gd-3Y alloy.

Effect of ageing time on corrosion behavior of Mg-10Gd-4.8Y-0.6Zr extruded-alloy

The corrosion behaviors of Mg-10Gd-4.8Y-0.6Zr extruded-alloys with various ageing time were investigated by immersion test and electrochemical measurements.The results show that the corrosion rate of the experimental alloy decreases with the increase of ageing time from 0 to 108 h.The corrosion resistance of the experimental alloy was found to increase with the increase of the size of the precipitate phases.The open circuit potential of the experimental alloy increases with the increase of the ageing time.The potentiodynamic polarization curves show that the cathodic over-potential increases with the increase of ageing time,leading to a decrease in the current density of anodic current plateau with the increase of ageing time.

Corrosion behavior and surface treatment of superlight Mg-Li alloys

Mg-Li alloy,as a superlight metallic engineering material,shows great potential in the fields of aerospace and militarydue to its high specific strength,better formability,and excellent electromagnetic shielding performance.The research process ofMg-Li alloys is reviewed and three main problems are pointed out.Aimed at the poor corrosion resistance of Mg-Li alloys,thecorrosion behavior is mainly summarized.The surface treatment technologies,including electroplating,electroless plating,plasmaspraying,molten salt replacement,conversion coating,anodizing,micro-arc oxidation,organic coating,and organic-inorganic hybridcoating,are introduced in detail.Finally,the future development of corrosion and protection of Mg?Li alloys is discussed.

Effects of Ag contents in Sn-xAg lead-free solders on microstructure,corrosion behavior and interfacial reaction with Cu substrate

The effects of Ag on the microstructure and corrosion behavior of pre-soldering Sn-xAg lead-free solders,and on the formation of intermetallic layer of the solders with Cu substrate were investigated.The Ag contents(x)were 0,3.0,3.5,4.0,and5.0 wt.%.The Ag content played a role in the morphology of Ag3 Sn phase in the solders.The microstructure analysis showed that theβ-Sn phase was surrounded by eutectic networks in the 3.0 Ag and 3.5 Ag solders and large plate-like Ag3 Sn formed in the 4.0 Ag and5.0 Ag solders.Nonetheless,the Ag content slightly impacted the corrosion behavior of the as-cast solders as characterized using potentiodynamic polarization test.After soldering,only a single layer of a Cu6 Sn5 intermetallic compound formed at the Sn-xAg/Cu interface.By comparison,the Cu6 Sn5 intermetallic layer of the Ag-doped solders was thinner than that of the 0Ag solder.The fine Ag3 Sn particles in the eutectic networks precipitating in the 3.0 Ag and 3.5 Ag solders effectively hindered the growth of Cu6 Sn5 grains compared to large plate-like Ag3 Sn in the 4.0 and 5.0Ag solders.

Effect of lithium content on the mechanical and corrosion behaviors of HCP binary Mg–Li alloys

The microstructure,crystallographic texture,mechanical properties and corrosion resistance of as-extruded HCP Mg-x Li(x=1,3,5;in wt%)alloys were investigated.The results indicated that the HCP Mg-5 Li alloy with high lithium content exhibited a low degree of dynamic recrystallization(DRX)compared with Mg-1 Li and Mg-3 Li alloys.Besides,the 45°base(0001)texture of Mg-1 Li alloy could turn into(11–20)and(10–10)prismatic texture of Mg-3 Li and Mg-5 Li alloys with c-axis approximately parallel to transverse direction(TD).As a result,the strong prismatic texture resulted in the mechanical anisotropy of as-extruded Mg-3 Li and Mg-5 Li alloys with higher mechanical strength and low elongation along extrusion direction(ED)(reverse for TD sample).Regarding of corrosion behaviors,filiform corrosion occurred in the three Mg–Li alloys,whilst the high lithium content could mitigate the groove-like corrosion and improve the corrosion resistance of Mg-5 Li alloy,which was ascribed to the refined grains,prismatic texture and surface film.

Influence of grain refinement on the corrosion behavior of metallic materials:A review

Grain refinement can strengthen the mechanical properties of materials according to the classical Hall-Petch relationship but does not always result in better corrosion resistance.During the past few decades,various techniques have been dedicated to refining grain,along with relevant studies on corrosion behavior,including general corrosion,pitting corrosion,and stress corrosion cracking.However,the funda-mental consensus on how grain size influences corrosion behavior has not been reached.This paper reviews existing literature on the beneficial and detrimental effects of grain refinement on corrosion behavior.Moreover,the effects of microstructural changes(i.e.,grain boundary,dislo-cation,texture,residual stress,impurities,and second phase)resulting from grain refinement on corrosion behavior are discussed.The grain re-finement not only has an impact on the corrosion performance,but also results in microstructural changes that have a non-negligible effect on corrosion behavior or even outweigh that of grain refinement.Grain size is not the only factor affecting the corrosion behavior of metallic ma-terials;thus,the overall influence of microstructures on corrosion behavior should be understood.

Corrosion behavior of Mg−Li alloys:A review

It has been known that the lack of excellent corrosion resistance is the key problem restricting the wide application of Mg−Li alloys.Based on a quantity of literature about corrosion behavior of Mg−Li alloys,this review elaborates the factors affecting the corrosion behavior of Mg−Li alloys and the processing methods for improving corrosion resistance.The corrosion characteristics of Mg−Li alloys are described firstly.Then,it is explained that the grain size,orientation,second phase,and surface film strongly influence corrosion performance,which can be tailored by alloying,plastic deformation,and heat treatment.Further in-depth discussion about the corrosion mechanisms for Mg−Li alloys was also presented.Finally,important points of improving corrosion resistance are suggested.