Microstructure and electrochemical corrosion behavior of selective laser melted Ti−6Al−4V alloy in simulated artificial saliva

Ti−6Al−4V alloy was fabricated via selective laser melting(SLM)to improve its corrosion resistance for implant.The microstructure and electrochemical corrosion behavior were investigated using scanning electron microscopy(SEM),electron backscatter diffraction(EBSD),transmission electron microscopy(TEM),electrochemical test and contact angle test.It can be found that the as-selective laser melted(as-SLMed)Ti−6Al−4V alloys showβcolumnar microstructure in building direction and nearly circular checkerboard microstructure in scanning direction,while the wrought and wrought+HT samples exhibit equiaxed microstructure.The as-SLMed Ti−6Al−4V alloy exhibits better corrosion resistance than the wrought and wrought+HT samples due to hydrophobicity,high grain boundary density and uniform distribution of alloying elements in simulated artificial saliva at 37℃.

Comparative study on microstructure and electrochemical corrosion resistance of Al7075 alloy prepared by laser additive manufacturing and forging technology

Al7075 alloy is a typical aviation aluminum with good mechanical properties and anodic oxidation effect.Laser engineered net shaping technology has unique advantages in the integrated forming of high-performance large aircraft structural parts.The manufacturing of 7075 aluminum alloy structural parts by laser engineered net shaping technology has become an important development direction in the future aerospace field.Electrochemical corrosion resistance of aluminum alloys is of vital importance to improve reliability and life-span of lightweight components.A comparative study on microstructure and anti-corrosion performance of Al7075 alloy prepared by laser additive manufacturing and forging technology was conducted.There are hole defects in LENS-fabricated Al7075 alloy with uniformly distributedηphase.No defects are observed in Al7075 forgings.The large S phase particles and small ellipsoidalηphase particles are found in Al matrix.The corrosion mechanisms were revealed according to the analysis of polarization curves and corrosion morphology.It was found that compared with that prepared by forgings,the additive manufactured samples have lower corrosion tendency and higher corrosion rate.Corrosion occurred preferentially at the hole defects.The incomplete passivation film at the defects leads to the formation of a local cell composed of the internal Al,corrosion solution and the surrounding passive film,which further aggravates the corrosion.

Effect of Mo_2C on electrochemical corrosion behavior of Ti(C,N)-based cermets

The electrochemical corrosion behavior of Ti（C,N）-based cermets with different Mo2C additions was investigated in freely aerated 10% H2SO4 and potentiodynamic polarization of all the materials was conducted from -0.5 to 1.5 V. There are two passive regions for all polarization curves. The first should be attributed to passive film formation due to Ti（C,N）, while the second may be due to the presence of Ni. Corrosion current density increases with M02C content increasing, from 2.06×10^-3 to 6.70×10^-3 mA/cm2. It is indicated that the corrosion resistance of Ti（C,N）-based cermets decreases with the increase of Mo2C addition. A skeleton of Ti（C,N） gains is observed after dissolution of Ni. The inner rim of cermets, rich in Mo2C, is corroded along with Ni binder and is more serious with the increase of Mo2C content. The secondary carbide Mo2C can be oxidized and dissolved in sulphuric acid.

Effects of Mg content on pore structure and electrochemical corrosion behaviors of porous Al-Mg alloys

Porous Al-Mg alloys with different nominal compositions were successfully fabricated via elemental powder reactive synthesis, and the phase composition, pore structure, and corrosion resistance were characterized with X-ray diffractometer, scanning electron microscope and electrochemical analyzer. The volume expansion ratio, open porosity and corrosion resistance in 3.5%(mass fraction) Na Cl aqueous solution of the alloys increase at first and then decrease with the increase of Mg content. The maxima of volume expansion ratio and open porosity are 18.3% and 28.1% for the porous Al-56%Mg(mass fraction) alloy, while there is the best corrosion resistance for the porous Al-37.5% Mg(mass fraction) alloy. The pore formation mechanism can be explained by Kirkendall effect, and the corrosion resistance can be mainly affected by the phase composition for the porous Al-Mg alloys. They would be of the potential application for filtration in the chloride environment.

Electrochemical corrosion failure mechanism of M152 steel under a salt-spray environment

The corrosion failure mechanism of M152 was studied using the neutral salt-spray test to better understand the corrosion behavior of 1Cr12Ni3Mo2VN（M152）, provide a basis for the optimization of material selection, and prevent the occurrence of failure. Moreover, the mechanism was investigated using the mass loss method, polarization curves, electrochemical impedance spectroscopy（EIS）, stereology microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy（EDS）. The results show that M152 steel suffers severe corrosion, especially pitting corrosion, in a high-salt-spray environment. In the early stage of the experiment, the color of the corrosion products was mainly orange. The products then gradually evolved into a dense, brown substance, which coincided with a decrease of corrosion rate. Correspondingly, the EIS spectrum of M152 in the late test also exhibited three time constants and presented Warburg impedance at low frequencies.

Electrochemical Hydrogen Charging on Corrosion Behavior of Ti-6Al-4V Alloy in Artificial Seawater

This study employs advanced electrochemical and surface characterization techniques to investigate the impact of electrochemical hydrogen charging on the corrosion behavior and surface film of the Ti-6Al-4V alloy.The findings revealed the formation ofγ-TiH andδ-TiH_(2) hydrides in the alloy after hydrogen charging.Prolonging hydrogen charging resulted in more significant degradation of the alloy microstructure,leading to deteriorated protectiveness of the surface film.This trend was further confirmed by the electrochemical measurements,which showed that the corrosion resistance of the alloy progressively worsened as the hydrogen charging time was increased.Consequently,this work provides valuable insights into the mechanisms underlying the corrosion of Ti-6Al-4V alloy under hydrogen charging conditions.

Electrochemical Corrosion,Wear,and Tribocorrosion Behavior of Novel Ti-19Zr-10Nb-1Fe Alloy

The electrochemical corrosion,wear,and tribocorrosion behavior of the novel Ti-19Zr-10Nb-1Fe alloy were investigated.The electrochemical corrosion analysis results show that the corrosion resistance of the Ti-19Zr-10Nb-1Fe alloy is better than that of the Ti-6Al-4V alloy under the test conditions in this research.Compared with the static electrochemical corrosion,the corrosion resistance of Ti-19Zr-10Nb-1Fe alloy during tribocorrosion decreases significantly,because the wear accelerates corrosion.The wear volume of Ti-19Zr-10Nb-1Fe alloy is increased with the increase in applied load whether the electrochemical corrosion occurs or not.Due to the acceleration effect of electrochemical corrosion,the wear volume caused by electrochemical corrosion is larger than that without electrochemical corrosion.The results of Wa/Wc are much greater than 10,indicating that during the tribocorrosion process,the material loss caused by mechanical wear is much larger than that caused by electrochemical corrosion.Through SEM observation of the wear morphologies of Ti-19Zr-10Nb-1Fe alloy after tribocorrosion,it can be inferred that the micro-abrasion is the main wear mechanism.The above results show that during the tribocorrosion process,the corrosion accelerates wear,and the wear accelerates corrosion.

Electrochemical Corrosion Behavior and Mechanical Response of Selective Laser Melted Porous Metallic Biomaterials

The porous metallic biomaterials have attracted significant attention for implants because their lower young's modulus matches the human bones, which can eliminate the stress shielding effect and facilitate the growth of bone tissue cells. The porous metallic biomaterials fabricated by selective laser melting (SLM) have broad prospects, but the surface of the SLM-built porous structure has been severely adhered with unmelted powders, which affects the forming accuracy and surface quality. The porous metallic biomaterials face the corrosion problem of complex body fluid environments during service, so their corrosion resistance in the human body is extremely important. The surface quality will affect the corrosion resistance of the porous metallic biomaterials. Therefore, it is necessary to study the effect of post-treatment on the corrosion resistance of SLMed samples. In this work, the mechanical response and the electrochemical corrosion behavior in simulated body fluid of diamond and pentamode metamaterials Ti-6Al-4V alloy fabricated by SLM before and after sandblasting were studied. After sandblasting, the mechanical properties of the two porous metallic biomaterials were slightly improved, and the self-corrosion potential and pitting potential were more negative;meanwhile, the self-corrosion current density and passive current density increased, indicating that its corrosion performance decreased, and the passive film stability of sandblasted samples got worse.

Electrochemical corrosion resistance of CeO_2-Cr/Ti coatings on 304 stainless steel via pack cementation

The pack cementation was employed to improve the electrochemical corrosion resistance of 304 stainless steel via CeO2- Cr modified Ti coatings. Continuous coatings were formed on 304 stainless steel surface by this method. A series of electrochemical experiments were carried out to investigate the corrosion resistance of 304 stainless steel, Ti coating and CeO2-Cr/Ti coatings. The sample surface was investigated by scanning electron microscopy （SEM）. The phases of sample surface were detected by X-ray diffraction （XRD）. It was concluded from all the outcomes that the Corrosion resistance of the samples could be sorted in the following sequence： CeO2-Cr/Ti coatings〉Ti coating〉304 stainless steel.

Electrochemical Corrosion Behavior of Nanocrystalline Materials-a Review

Nanocrystallization significantly influences the electrochemical corrosion behaviors of metals/alloys in liquid system. In active dissolution, nanocrystallization accelerates the corrosion reactions. If the corrosion products are dissoluble, the corrosion rate is increased by nanocrystallization; if the corrosion products are insoluble, the corrosion rate is decreased on the contrary because the corrosion products act as a block layer to delay the dissolution. In passivation, nanocrystallization changes the composition of the passive film, and results into different morphology and growth process of the passive film, both of which improves the formation of compact film and influences the semiconductor property. It influences the passivation depending on fast element diffusion and special adsorbed ability. The small grain size improves the element diffusion, which leads to the different composition of passive film （passive elements enrichment such as Cr, Ti）. The small grain size also changes the surface condition, which influences the ions adsorption. All increase the corrosion resistance of materials. In local corrosion, nanocrystallization increases the unstable points on the surface of the materials, which increases the possibility of local corrosion. However, the excellent ability of element diffusion helps heal the local corrosion points, which inhibits the growth of the local corrosion.

Electrochemical corrosion behavior of 300M ultra high strength steel in chloride containing environment

The electrochemical corrosion behavior of 300M ultra high strength steel in chloride containing environment was investigated by potentiodynamic polarization technique, electrochemical impedance spectroscopy （EIS） and scanning electron microscopy （SEM）. The results show that uniform corrosion occurs on 300M steel during the elec- trochemical measurements because no anodic passivation phenomenon is observed on polarization curves within the measurement range. The tests also show that 300M steel is highly susceptible to chloride containing solution, which is characterized by corrosion current density increasing with the addition of chlorides, and corrosion potential shifting towards positive direction and corrosion resistance decreasing, pos- itively suggesting that chloride ions speed up the corrosion rate of 300M steel. Mean- while corrosion products on the 300M steel surface formed during the salt spray test are too loose and porous to effectively slow down the corrosion rate. Additionally, a schematic structure of uniform corrosion mechanism can explain that 300M steel has better property of stress corrosion cracking （SCC） resistance than stainless steels.

Electrochemical corrosion and oxidation resistances of Zr_(60)Ni_(21)Al_(19) bulk amorphous alloys

Electrochemical corrosion and oxidation resistances of Zr 60 Ni 21 Al 19 amorphous alloy were studied. The ternary amorphous alloy exhibits greater positive potential than its crystalline counterpart and 0Cr19Ni9Ti stainless steel. Its weight loss result measured in 2 mol/L HCl solution is in agreement with the potentiodynamic curve. But there is no obvious difference in the oxidation resistances between Zr 60 Ni 21 Al 19 amorphous and its crystalline alloys. They both exhibit high oxidation resistance.

Microstructure design of C/C composites through electrochemical corrosion for brazing to Nb

Surface structure of C/C composites has been regulated through electrochemical corrosion at room temperature to modify the residual stress and improve the joining strength when brazed to Nb.The unique crevice corrosion in C/C composites is investigated to reveal the change of corrosion depth and fiber size.The interlacing zone of carbon fiber reinforced brazing alloy replaces the reaction layer in the original joint.Joining area is increased dramatically and the continuous crack will be hindered.The interlacing zone eliminates the stress concentration and relieves the residual stress through reducing the property mismatch.All advantages contribute to the joining quality of C/C–Nb.Shear strength of C/C–Nb joint with 80μm depth reached 37.7 MPa,which was 1.2 times higher than that of original joint.Surface structure design of C/C composites not only expands the application in structure component,but also exhibits the promising application in energy field.

Hydrogen trapping and electrochemical corrosion behavior of V–N microalloyed X80 pipeline steels consisting of acicular ferrite and polygonal ferrite

Hydrogen trapping behavior of V–N microalloyed X80 pipeline steels was studied by means of hydrogen permeation and hydrogen induced cracking(HIC)tests.In addition,the electrochemical performance of the steels in 3.5 wt.%NaCl solution was investigated.Results indicated that the microstructure of experimental steels mainly consisted of acicular ferrite and polygonal ferrite(PF).When the fraction of PF was 9.1%and 30.4%,hydrogen effective diffusion coefficient was 1.624×10^(−6) and 3.121×10^(−6) cm^(2)/s,respectively.The pipeline steels were not susceptible to HIC.Numerous potential hydrogen traps distributed in homogeneous dispersion were conducive to high HIC resistance.With increasing the fraction of PF from 9.1%to 30.4%,the corrosion current density increased from 5.39×10^(−6) to 9.49×10^(−6) A cm^(−2),the corrosion potential decreased from−0.48 to−0.57 V,and the charge transfer resistance decreased from 2301 to 2068Ωcm^(2),respectively.Increased fraction of PF was disadvantageous for corrosion resistance because of galvanic corrosion.

Microstructure and Electrochemical Corrosion Behavior of Fe-Cr System Alloys as Substitutes for Ni-Based Brazing Filler Metal

Two new Fe-Cr system alloys,Fe-20Cr-43Ni-10P（mass%）and Fe-20Cr-20Ni-8P-5Si-2Mo（mass%）,have been developed as substitutes for the expensive Ni-based brazing filler metal used in brazing exhaust gas recirculation coolers.The microstructures and melting properties of the alloys were analyzed by electron probe X-ray microanalyzer and differential scanning calorimetry.The electrochemical characteristics of the alloys were investigated by potentiodynamic polarization testing in an electrolyte solution made in accordance with the standards of the Automobile Manufacturers Association of Germany.Furthermore,the corrosion behaviors of the alloys were investigated by constant-potential polarization testing and surface characterization.It is found that both alloys are composed of solid-solution phases and phosphide phases.The solid-solution phases serve as the anode,and the phosphide phases serve as the cathode in the corrosion reaction for both alloys.Fe-20Cr-43Ni-10 P exhibits galvanic corrosion on the entire surface.In contrast,Fe-20Cr-20Ni-8P-5Si-2Mo is attacked at a few localized areas so that the cavities form on the surface.The corrosion potential（E_（corr）） is lower than that of Ni-29Cr-6P-4Si（mass%）for both alloys.This means that the Fe-Cr system alloys are more easily corroded than Ni-29Cr-6P-4Si.The corrosion rate and corrosion resistance cannot be investigated by the corrosion current density（i_（corr）） and polarization resistance（R_p）,respectively,because of localized corrosion of the two alloys.

Tribological and Electrochemical Corrosion Properties of CNT-Incorporated Plasma Electrolytic Oxidation(PEO)Coatings on AZ80 Magnesium Alloy

Plasma electrolytic oxidation(PEO)coatings were carried out in silicate-based electrolyte embedded with various amounts of carbon nanotube(CNT)additives(0,0.5,1,2 and 4 g/L)on AZ80 magnesium alloy substrate.Microstructure,tribological and electrochemical corrosion properties of the coated specimens were investigated.The results demonstrated that the increasing CNT additions into the electrolyte resulted in a gradual increase in the thickness of PEO-coating layer.The CNT addition to the electrolyte by 0.5 g/L resulted in a slight decrease in the roughness of PEO-coating above which it continually increased.Wear resistance of the PEO-coated specimens showed a gradual improvement with increasing CNT-incorporation within the coating.The electrochemical corrosion tests revealed that the best corrosion resistance was found after the CNT addition into the electrolyte by 0.5 g/L due to the better roughness values,more homogenous coating layers and less pore formation.

Microstructure Characteristic and Electrochemical Corrosion Behavior of Surface Nano-crystallization Modified Carbon Steel

The surface nano-crystallization （SNC） of carbon steel was achieved via a high-speed rotating wire-brush- ing process. Microstructure characteristics of SNC steel were systematically studied. The SNC steel surface exhibited marked deformed plastic flows and high surface roughness. Due to the accumulated strains, a deformed gradient lay er with thickness of 40-50 μm was produced, and the grain size of the topmost zone was about 50-100 nm. X-ray photoelectron spectroscopy （XPS） analysis indicated that enhanced Fe oxides and Cr oxides were generated. Electrochemical corrosion tests, including open circuit potential （OCP）, electrochemical impendence spectroscopy （EIS）, potentiodynamic polarization （PDP） and potentiostatic polarization （PP） were conducted to study the corrosion be- havior of SNC steel in 3.5 mass% NaC1 solution, where an improved corrosion resistance was observed. The resulted improvement resulted from the dominated positive effects （the attached Cr alloying element and enhanced oxide film） against the negative effects （the higher roughness and the improved corrosion activity of surface microstructure）.

Effect of surface layer softening from previous electrochemical corrosion on electrochemical cold drawing of Q235 steel bar

The effects of H_(2)SO_(4)concentration and current in electrochemical corrosion on surface layer softening or plasticizing of Q235 steel bar and their effects on subsequent electrochemical cold drawing(ECD)were investigated.The results indicate that the electrochemical corrosion can soften or plasticize the surface layer of Q235 steel bar and then make the subsequent ECD be conducted more easily.The softening degree and thickness of the surface layer are continuously enhanced with increasing corrosion rate,i.e.,increasing H_(2)SO_(4)concentration or current,due to the generation of more vacancy clusters in deeper regions of surface layer.These vacancy clusters then relax dislocations through being absorbed during ECD,and the formation and movement of additional dislocation flux are thereby enhanced,resulting in the further obvious decrease in the drawing force.It is also due to the enhanced formation and movement of additional dislocation flux that the dislocation density and thus the hardness of the surface layer are decreased,as well as that the texture structure is weakened.These behaviors are enhanced as the corrosion rate increases.

Numerical Simulation of Fretting Fatigue Damage Evolution of Cable Wires Considering Corrosion and Wear Effects

In this paper,a numerical model of fretting fatigue analysis of cablewire and the fretting fatigue damage constitutive model considering the multi-axis effect were established,and the user material subroutine UMAT was written.Then,the constitutive model of wear morphology evolution of cable wire and the constitutive model of pitting evolution considering the mechanical-electrochemical effect were established,respectively.The corresponding subroutines UMESHMOTION_Wear and UMESHMOTION_Wear_Corrosion were written,and the fretting fatigue lifewas further predicted.The results showthat the numerical simulation life obtained by the programin this paper has the same trend as the tested one;the error is only about 0.7%in the medium life area;When the normal contact force increases from 120 to 240 N,the fretting life of cable wire decreases by 25%;When the evolution of wear morphology and corrosion effect are considered simultaneously,the depth of the wear zone exceeds 0.08mm after 600,000 loads,which ismuch larger than 0.04 mmwhen only the evolution of wear morphology is considered.When the evolution of wear morphology and corrosion morphology is considered simultaneously,the damage covers the whole contact surface after 300,000 loads,and the penetrating damage zone forms after 450,000 loads,which is obviously faster than that when only the wearmorphology evolution is considered.Themethod proposed in this paper can provide a feasible numerical simulation scheme for the visualization of the damage process and accurate life prediction of cable-supported bridges.

Prevention of Q235 Steel Corrosion using Waterborne Rust Inhibitor

Sorbitol,triethanolamine,sodium benzoate,boric acid,and sodium carbonate were mixed to prepare a waterborne rust inhibitor.A temperature and humidity accelerated corrosion test was applied to investigate the corrosion behaviour of waterborne rust inhibitor coated Q235 steel and original Q235 steel,which was carried out in a temperature and humidity test chamber(WSHW-1000)at a temperature of 80℃and humidity of 95%.Compared with the original Q235,waterborne rust inhibitor coated Q235 has better resistance to corrosion in hot and humid ambient conditions.Electrochemical impedance spectroscopy and potentiodynamic polarization were measured with a three-electrode cell in 3.5%NaCl aqueous solution on a CHI760E potentiostat/galvanostat.Molecular dynamics was simulated to verify the synergistic corrosion inhibitory mechanism of sodium carbonate and triethanolamine.The test shows that the prepared waterborne rust inhibitor can reduce the tendency of Q235 to corrosion and can also effectively reduce the corrosion rate.