Increase In Corrosion Potential Research Articles

Preparation of a nickel-cobalt-zinc alloy coating as SOFC connection material in deep eutectic solvent

The Ni-Co-Zn alloy coating is prepared in a deep eutectic solvent system using pulse power supply technology, and the feasibility of the deep eutectic solvent system as an electrolyte is confirmed through infrared spectroscopy and cyclic voltammetry. The microscopic morphology analysis shows that the plating layer is uniform and dense, and the grains are spherical particles, and it is detected that the oxidized weight gain rate of the plating layer is 7.6842 × 10−8 g2 cm−4·h−1 at 900 °C, which is 3 orders of magnitude different from the oxidation rate constant of the substrate. The corrosion potential increases to −0.281 V in 3.5 % NaCl solution, and the corrosion current density decreases to 3.259 × 10−7 (A/cm2), with an ASR of 43.64 mΩ cm2 at 800 °C. The results indicate that the Ni-Co-Zn coating can meet the requirements for an SOFC connector material.

Effect of Al2O3 on Microstructure and Corrosion Characteristics of Al/Al2O3 Composite Coatings Prepared by Cold Spraying

Cold spraying was used to prepare Al/Al2O3 composite coatings. The Al2O3 content was controlled to increase the mechanical property and corrosion resistance of the composite coating. The inclusion of Al2O3 particles results in considerable plastic deformation of Al particles and grain size refinement in the coating. Additionally, the coating’s surface roughness decreased from 24.63 μm to 9.02 μm, and the porosity decreased from 6.34% to 2.07%. The increase in microhardness of the composite coatings was attributed to the combined effect of residual compressive stress, second phase strengthening of Al2O3, and plastic hardening of Al particles. The electrochemical test results indicate that the mass fractions of Al2O3 significantly affected the corrosion resistance of the Al/Al2O3 composite coating. Compared to the Al coating, the composite coating exhibited improved corrosion resistance, with a reduction in corrosion current density from 1.09 × 10−3 A/cm2 to 2.67 × 10−6 A/cm2 and an increase in corrosion potential from −1.57 V to −1.14 V. However, when the alumina particle content exceeded 17.7%, it led to more Al2O3 particle breakage, increasing the weak bonding interfaces in the composite coating, and consequently reducing its corrosion resistance.

Corrosion behavior of 700 MPa grade weathering steel with 4.0 wt% Ni and 5.0 wt% Cr in simulated marine atmospheric environment

The dry-wet cycle corrosion behavior of low alloy steel (Q355B) and 700 MPa grade Ni, Cr composite weathering steel (4 wt% Ni-5 wt% Cr) in 2 wt% NaCl solutions was studied. The distribution characteristics of elements and phases in the corrosion products after 360 h corrosion cycle were analyzed by SEM and Raman spectroscopy. The formation mechanism of protective rust layer of Ni, Cr composite weathering steel in simulated marine environment was briefly described. The results show that the corrosion products of Q355B appear obvious stratification, and the rust layer of Ni, Cr composite weathering steel has no longer stratified. The Ni, Cr composite weathering steel forms a cationic selective rust layer during the corrosion process, which effectively prevents the penetration of Cl- and exhibits excellent corrosion resistance, the corrosion rate of Ni, Cr composite weathering steel after 72 h-360 h corrosion cycle is 1/8–1/3 of that of Q355B. The value of α/γ * increases with the extension of corrosion cycle, which is reach to 1.0 after 360 h corrosion cycle. The corrosion potential increases with the extension of corrosion cycle, the corrosion current density fluctuates slightly around 100 × 10−6 A/cm2.

Tribocorrosion behavior of low-temperature plasma-carburized AISI 420 martensitic stainless steel: Investigating the synergy between corrosion and erosion in slurry and liquid impingement environments

Erosion-corrosion is a significant concern across industries, impacting equipment lifespan and efficiency. When erosion-corrosion occurs, the resulting damage becomes complex, often leading to greater mass loss than that observed with erosion or corrosion alone. Martensitic stainless steels (MSSs) are commonly used in such environments due to their favorable combination of mechanical and corrosion resistance. However, under severe tribocorrosive conditions, it is necessary to apply surface treatments to prevent rapid steel degradation. Carburizing treatment is known to independently enhance the corrosion and erosion resistance of MSS. Nonetheless, there is a limited understanding of the impact of carburizing on the synergy between corrosion and erosion in such steels. In this study, we examined two different tribocorrosion conditions, assessing the resistance to slurry erosion and liquid impingement erosion for both carburized and non-carburized AISI420 MSS specimens exposed to a corrosive agent (from an electrochemical test using a 3.5 %-NaCl solution). To provide a basis for comparison, a static corrosion test was also performed to evaluate the environmental impact, with the electrolyte at rest, without flow or particles. Our findings revealed that the carburized layer is responsible for reducing the corrosion current density and increasing corrosion potential of AISI420 MSS. In contrast, slurry and liquid impingement erosion result in an increased corrosion current density and a decreased corrosion potential. The parameters Ω and Ω' (role of carburizing on the relationships between ‘slurry erosion and corrosion’ and ‘liquid impingement erosion and corrosion’ mechanisms interaction, respectively) demonstrated that carburizing application mitigates the impact of slurry and liquid impingement erosion, respectively. Additionally, the carburizing treatment reduces the corrosion rate, total mass loss, and erosion-induced mass loss of the studied samples, minimizing the synergy between erosion and corrosion. Finally, the interactions between the degradation modes reveal that erosion predominantly governs the AISI420 MSS deterioration process.

Vliyanie rotatsionnoy kovki na strukturu, mekhanicheskie i korrozionnye svoystva splava Mg-1,1%Zn-1,7%Dy

In this work, the effect of rotary swaging (RS) with a deformation degree (ε) equal to 1.28 and 2.31 on the microstructure, corrosion resistance and mechanical properties of a potential medical alloy Mg-1.1%Zn-1.7%Dy was studied. It was shown that RS at ε = 1.28 leads to a grain refinement of the studied alloy by 10 times (from ~300–400 µm to ~30–40 µm). An increase in the deformation degree up to ε = 2.31 leads to the formation of an inhomogeneous microstructure with regions containing both grains ~30–40 µm in size and zones with grains ~5–10 µm in size. Grain refinement after Rs leads to an increase in resistance to electrochemical corrosion (corrosion potential increases from -1550 ± 9 mV in the quenched state to -1442 ± 23 and -1454 ± 35 mV after RS at ε = 1.28 and ε = 2.31, respectively), but does not cause a change in the current density. But the degradation rate of the alloy increases with an increase in the deformation degree up to 3.46 ± 1.06 mm/y. The structure refinement after RS at ε = 1.28 leads to a significant increase in the strength of the alloy in comparison with the quenched state (ultimate tensile strength (UTS) increases from 70 ± 13 to 273 ± 7 MPa) with a drop in ductility from 23.1 ± 5.1 to 14.0 ± 2.9%. An increase in the deformation degree up to ε = 2.31 does not lead to an increase in the strength of the alloy (UTS = 267 ± 4 MPa), but causes an increase in ductility (δ = 21.1 ± 1.6%), apparently due to texturechanges, occurring in the alloy.

Corrosion Inhibition in CO2-Saturated Brine by Nd3+ Ions.

This study reports the use of an inorganic corrosion inhibitor to mitigate dissolved CO2-induced corrosion. Using electrochemical techniques (polarization curves, open circuit potential, polarization resistance, and electrochemical impedance), the effect of adding Nd3+ ions on the corrosion resistance of X52 steel immersed in CO2-saturated brine at 20 °C and 60 °C was evaluated. The polarization curves showed that the Icorr values tend to decrease with increasing Nd3+ ion concentration, up to the optimal inhibition concentration, and that the corrosion potential increases at nobler values. Open circuit potential measurements showed a large increase in potential values immediately after the addition of the Nd3+ ions. Similarly, polarization resistance measurements showed similar trends. It was observed that regardless of temperature, Nd3+ ions can reduce the corrosion rate by more than 97% at doses as low as 0.001 M. Electrochemical impedance measurements confirmed the formation of a protective layer on the steel surface, which caused an increase in the magnitude of the impedance module and phase angle, which indicates an increase in the resistance to charge transfer and capacitive properties of the metallic surface. The characterization of the metallic surface showed that the protective layer was formed by Nd carbonates, whose formation was due to a CO2 capture process.

NaF assisted preparation and the improved corrosion resistance of high content ZnO doped plasma electrolytic oxidation coating on AZ31B alloy

In the present research, the NaF assisted plasma electrolytic oxidation (PEO) is designed to fabricate the high-content ZnO nanoparticles doped coating on AZ31B alloy. The microstructure, phase constituents and corrosion behavior of the PEO coatings are investigated systematically. The results reveal that the introduction of NaF promotes the formation of MgF2 nanophases in the passivation layer on Mg alloy, decreasing the breakdown voltage and discharge voltage. As a result, the continuous arcing caused by high discharge voltage is alleviated. With the increasing of NaF content, the Zn content in the PEO coating is enhanced and the pore size in the coating is decreased correspondingly. Due to the high-content ZnO doping, the PEO coating protected AZ31B alloy demonstrates the better corrosion resistance. Compared with the bare AZ31B alloy, the high-content ZnO doped PEO coated sample shows an increased corrosion potential from -1.465 V to -1.008 V, a decreased corrosion current density from 3.043×10-5 A·cm-2 to 3.960×10-8 A·cm-2 and an increased charge transfer resistance from 1.213×102 ohm·cm2 to 2.598×105 ohm·cm2. Besides, the high-content ZnO doped PEO coated sample also has the excellent corrosion resistance in salt solution, exhibiting no obvious corrosion after more than 2000 h neutral salt spraying and 28 days’ immersion testing. The improved corrosion resistance can be ascribed to the relative uniform distribution of ZnO in PEO coating which can transform to Zn(OH)2 and form a continuous protective layer along the corrosion interface.

Study on Corrosion Resistance of LDH/Micro-Arc Oxidation Composite Superhydrophobic Coatings on AZ31 Magnesium Alloy

Because of some defects such as holes and cracks, the corrosion resistance of micro-arc oxidation coating needs to be improved by surface modification. In this paper, LDH/MAO film with a micro-/nano-structure is constructed on the surface of AZ31 magnesium alloy by controlling the composition and concentration of the hydrothermal solution. The superhydrophobic surface is successfully constructed by coating an OTES modifier on the surface of LDH/MAO film by the spin-coating method. The surface morphologies, contact angles, and corrosion resistance of composite coatings are tested. The results show that the OTES-LDH/MAO composite coatings of magnesium alloy can seal the defects in the MAO film well to achieve a superhydrophobic effect and better corrosion resistance. Compared with a MgO ceramic film, the water contact angle of OTES-LDH/MAO composite coatings is increased from 38° to 155°; the corrosion potential increases by 0.7 V, the corrosion current density and polarization resistance decreases and increases by four orders of magnitude, respectively; and the corrosion resistance becomes much higher than that of MAO film.

Synthesis, Characterization, and Properties of Sulfonated CNT‐Doped Poly(aniline‐co‐carbazole)‐PVA Conductive Films

AbstractConductive flexible films are successfully synthesized from polyvinyl alcohol matrix and poly(aniline‐co‐carbazole) charge carrier. To improve the mechanical properties of polyvinyl alcohol and promote charge transition in the conductive copolymer, dual purpose sulfonated multiwall carbon nanotube is added. Conductivity is enhanced via sulfonic acid protonic dopant and mechanical property is increased by its hexagonal nanorods. Nanocomposites are prepared by adding 0.025, 0.050, and 0.075 g of carbon nanotube which is added at 1%, 3%, and 5% loads to the polymer matrix. Films are characterized by infrared, UV–vis, X‐ray diffraction, scanning electron microscopy, and thermogravimetric analysis. Conductivity is measured by the four‐probe technique and mechanical property is assessed through tensile tests and dynamic mechanic thermal analysis. A 5 × 10−6 S cm−1 conductivity and 116 MPa tensile strength are recorded for the conductive film with optimum dopant/nanocomposite loads. The electrochemical property and corrosion resistance are studied by cyclic voltammetry and Tafel curves, respectively. The conductive films show an increase in corrosion potential and a decrease in corrosion current referring to a reliable corrosion protection film. The water uptake and contact angle of the films are measured to be 157% and 80.1° respectively to confirm its required hydrophilic property.

Microstructure and corrosion properties of CoCrCuFeMnNix high‐entropy alloys prepared by powder metallurgy

AbstractCoCrCuFeMnNix (x = 0.5, 1.0, 1.5, 2.0 mol, named Ni0.5, Ni1.0, Ni1.5, and Ni2.0, respectively) high‐entropy alloys (HEAs) were prepared by powder metallurgy. The effects of Ni content on its microstructure and corrosion resistance in a 3.5% NaCl solution were studied. The HEAs with low Ni content consisted of FCC1 primary phase, FCC2 secondary phase, and a few σ phases. While the Ni2.0 alloy was composed of the FCC phase and a small amount of σ phase. The results of polarization corrosion in 3.5% NaCl solution show that the increase of Ni content led to the increase of corrosion potential of the alloy and the decrease of corrosion current density and average corrosion rate. Among them, Ni2.0 alloy had the best corrosion resistance. The electrochemical impedance spectroscopy analysis showed that the increase in Ni content promoted the increase of the polarization resistance of the alloy RCPE and the thickness of the passive film, thus improving the corrosion resistance of the alloys.

Tribo-corrosion behavior of Zn-Ni-Cu and Zn-Ni-Cu-TiB2 coated mild steel

In this investigation , Zn-Ni-Cu and Zn-Ni-Cu-TiB2 were coated on a mild steel specimen using a high velocity oxy fuel thermal spray (HVOF) process. The surface morphology and coated powder distribution of coated specimens were characterized using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and X-ray-Elemental mapping. The pin-on-disc (ASTM G99-17) method was used to examine the wear resistance of the coated and uncoated mild steel specimens. Both coated Zn-Ni-Cu and Zn-Ni-Cu-TiB2 on mild steel saw reduced wear volume loss than uncoated mild steel. The coated samples of Zn-Ni-Cu and Zn-Ni-Cu-TiB2 on Mild Steel were put through a scratch test to determine the adhesion strength of the coating with the substrate. The adhesion strength of coated Zn-Ni-Cu and Zn-Ni-Cu TiB2 mild steel was higher than that of untreated mild steel, indicating a solid link between the coating and substrate and minimal delamination. Using the Vickers hardness test to measure the hardness caused by the coating, it was shown that coated samples of Zn-Ni-Cu and Zn-Ni-Cu-TiB2 coated mild steel had significantly higher hardness than uncoated mild steel. Using ASTM G1-03 and ASTM G-31 standards, a 0.2 M HCl immersion cycle test was conducted for 28 days to test the corrosion resistance of coatings in an acidic media (672Hrs). When compared to Zn-Ni-Cu and Zn-Ni-Cu-TiB2 coated mild steel, the weight loss for the uncoated mild steel was significantly larger. Additionally, XRD examination showed that coated samples had less rust on their surface than uncoated samples. Both Zn-Ni-Cu and Zn-Ni-Cu-TiB2 on Mild Steel were anti-corrosive, as evidenced by increased corrosion potential and reduced corrosion current density when compared to uncoated mild steel, according to electrochemical impedance spectroscopy (EIS)/Tafel study in 0.2 MHCl. The outcomes of each test were very encouraging and demonstrated the durability of these coatings against wear and corrosion.

Corrosion behavior and mechanism of laser powder bed fusion produced CoCrW in an acidic NaCl solution

The corrosion behavior and mechanism of the laser powder bed fusion (L-PBF) produced CoCrW were investigated in 0.9 wt% NaCl solution with a pH of 2. The corrosion resistance of the alloy increases after 28 days of immersion because of the formed oxide film, which results in the increased corrosion potential and the decreased passivation current density on the potentiodynamic polarization test. The corrosion mechanism of the L-PBF-produced CoCrW could be explained by the melt pool formed from the laser melting process, that the melt pools were “shrinking” by the formation and dissolution of the oxide film.

Influence of Milling-Electrochemical Polishing on Corrosion Resistance of NiTi Shape Memory Alloy.

As an important artificial implant material, the corrosion resistance of NiTi shape memory alloy is closely related to the machined surface quality. In this paper, the multiple analysis methods concerning potentiodynamic polarization, impedance spectrum and corrosion morphology are used to analyze the corrosion resistance of the alloy. The potentiodynamic polarization and impedance spectrum test results show that the conductivity and corrosion current density of electrochemical polishing surface decrease, and the polarization resistance and corrosion potential increase compared with milling. After electrochemical polishing, the surface roughness of the milling sample is decreased, and the NiTi alloy of austenite phase is transformed into TiO2, which improves the corrosion resistance of the alloy. In addition, there are pitting corrosion, hole corrosion and crevice corrosion morphology on the milling surface, while the pitting corrosion and hole corrosion exist on the electrochemical polishing surface. The corrosion morphology verified the analysis of potentiodynamic polarization and impedance spectrum. The multiple analysis method proposed in this paper can be used as a more accurate evaluation method for the corrosion resistance of alloy surface, avoiding the error of analysis results caused by the impedance spectrum equivalent circuit and potentiodynamic polarization following Tafel relationship.

Influence of laser remelting on the microstructure and corrosion behavior of HVOF-sprayed Fe-based coatings on magnesium alloy

An HVOF-sprayed Fe-based (Diamalloy 1010) coating deposited on AZ91 magnesium alloy was remelted using 650 W and 1000 W laser power. The microstructure of as-sprayed and laser remelted coatings and their phase composition were analyzed using SEM (Scanning Electron Microscopy) and XRD (X-Ray Diffraction) spectroscopy. The microstructure of the as-sprayed coating included crystalline and amorphous areas, which were shown by TEM (Transmission Electron Microscopy). According to XRD analysis the microstructure consisted of austenite and M7C3 carbides. After laser remelting, the structure of as-sprayed Diamalloy 1010 recrystallized and well-developed dendritic grains were formed. XRD analysis showed that laser remelting did not lead to the formation of new phases. On the other hand, the grain recrystallization and microstructure arrangement in the laser remelted layer led to increased peak intensities of individual phases in the XRD pattern. This combined with a reduction in porosity from 0.7% to 0.0% resulted in an increase in microhardness from 554 ± 8 HV0.1 up to 633 ± 8 HV0.1 after remelting. Potentiodynamic polarization tests and EIS (Electrochemical Impedance Spectroscopy) showed that laser remelting under a power of 650 W can improve the corrosion behavior in 3.5% NaCl. The remelting of the coating using 650 W laser power resulted in an increase in corrosion potential from −425 ± 13 mV to −210 ± 21 mV and a decrease in corrosion current density from 23.57 ± 4.59 μA·cm−2 to 0.44 ± 0.05 μA·cm−2 when compared to the as-sprayed coating.

A Biocompatibility Study of Plasma Nanocoatings onto Cobalt Chromium L605 Alloy for Cardiovascular Stent Applications.

The objective of this study was to evaluate the biocompatibility of trimethylsilane (TMS) plasma nanocoatings modified with NH3/O2 (2:1 molar ratio) plasma post-treatment onto cobalt chromium (CoCr) L605 alloy coupons and stents for cardiovascular stent applications. Biocompatibility of plasma nanocoatings was evaluated by coating adhesion, corrosion behavior, ion releasing, cytotoxicity, and cell proliferation. Surface chemistry and wettability were studied to understand effects of surface properties on biocompatibility. Results show that NH3/O2 post-treated TMS plasma nanocoatings are hydrophilic with water contact angle of 48.5° and have a typical surface composition of O (39.39 at.%), Si (31.92 at.%), C (24.12 at.%), and N (2.77 at.%). The plasma nanocoatings were conformal to substrate surface topography and had excellent adhesion to the alloy substrates, as assessed by tape test (ASTM D3359), and showed no cracking or peeling off L605 stent surfaces after dilation. The plasma nanocoatings also improve the corrosion resistance of CoCr L605 alloy by increasing corrosion potential and decreasing corrosion rates with no pitting corrosion and no mineral adsorption layer. Ion releasing test revealed that Co, Cr, and Ni ion concentrations were reduced by 64–79%, 67–69%, and 57–72%, respectively, in the plasma-nanocoated L605 samples as compared to uncoated L605 control samples. The plasma nanocoatings showed no sign of cytotoxicity from the test results according to ISO 10993-05 and 10993-12. Seven-day cell culture demonstrated that, in comparison with the uncoated L605 control surfaces, the plasma nanocoating surfaces showed 62 ± 7.3% decrease in porcine coronary artery smooth muscle cells (PCASMCs) density and had comparable density of porcine coronary artery endothelial cells (PCAECs). These results suggest that TMS plasma nanocoatings with NH3/O2 plasma post-treatment possess the desired biocompatibility for stent applications and support the hypothesis that nanocoated stents could be very effective for in-stent restenosis prevention.

Influence of strontium and niobium on the physical and biological performance of hydroxyapatite as a bioactive coating on implant materials

The coating of hydroxyapatite (HAP) on the surface of bio-inert metallic implants to augment their bioactivity is in use for the last two decades. Substitution of various materials in HAP further improves the functionality of these coatings. We demonstrate coating of Ti6Al4V alloy sheets with strontium and niobium reinforced HAP using microwave (MW) irradiation technique. Physical characterization revealed, uniform semicrystalline hydroxyapatite coating with enhanced surface roughness and microhardness. The increased surface roughness was accompanied by higher wettability and more protein adsorption. Electrochemical corrosion assessment showed a dramatic increase in corrosion potential and a noticeable decline in corrosion current density suggesting an enhanced anticorrosive behaviour. These implants also exhibited improved hemocompatibility and bacteriostatic properties. Cell viability and confocal microscopy studies of the coated samples showed enhanced cell attachment on the surface. We propose microwave irradiation as a fast and hassle-free alternative for one-pot synthesis and deposition of ionic substituted HAP on metallic implants.

Effect of Al content on the microstructure and properties of CoCrCuFeNiMoAlx high entropy alloy

A new multi-principal Co-Cr-Cu-Fe-Ni-Mo-Al high entropy alloy with good mechanical properties and corrosion resistance was prepared. For the phenomenon of Cu segregation, we report a strategy to tailor the existing form of Cu in HEA from undesired large-scale segregation to uniform distribution in the solid solution phase. The effects of the Al content on the microstructure, mechanical properties and corrosion behavior of CoCrCuFeNiMoAlx (x = 0, 0.32, 0.67, and 1.0) alloys were studied. The results show that when Al content is low, Cu segregation phenomenon is serious, and the microstructure of the alloy is FCC structure and a little BCC structure. With the increase of Al content, the microstructure is gradually transformed into BCC structure, and the Cu segregation phenomenon is improved. In addition, with the increase of Al content, the mechanical properties of the alloy are improved to some extent. According to the experimental results, the hardness increased by 30.4 %and the compressive strength increases by 22.9 %. Moreover, an increasing Al content had a positive influence on the corrosion resistance of the alloy, increased corrosion potential of the alloy and reduced corrosion current.

Hybrid coatings for orthopaedic implants formed by physical vapour deposition and microarc oxidation

This study is focused on the preparation of new hybrid layers intended for surface modification of Ti-6Al-4V alloys for potential orthopaedic and dental applications. Combination of the technology of physical vapour deposition (PVD) and subsequent micro-arc oxidation (MAO) was utilized for the deposition of Ti and ZrTi to form hybrid oxide layers. The oxide layers were prepared using an alkaline electrolyte with glycerol as an additive under micro-arc discharge conditions with different Si content on their surfaces. The hybrid ZrTi coatings with a Zr/Si structure achieved the best tribological properties described by a low friction coefficient of 0.3 and high abrasion resistance. There was also an increase in corrosion potential and polarization resistance of hybrid ZrTi coatings. Although the proliferation of human bone marrow mesenchymal stem cells was slower on these hydrophilic Ti and ZrTi coatings than both on uncoated Ti-6Al-4V and the reference tissue culture polystyrene dishes, both types of hybrid coating promoted greater osteogenic differentiation of these cells, indicated by approx. twice as high activity of alkaline phosphatase. The hybrid oxide layers newly developed in this study – especially the layers with Zr – are therefore promising for coating metallic bone implants.

Microstructural, Mechanical and Corrosion Characteristics of Degradable PM Biomaterials Made from Copper-Coated Iron Powders.

Copper-containing iron-based materials have recently been recognized as potential biomaterials possessing antimicrobial ability. Since then, iron-copper systems have been prepared by different methods and investigated. This article is focused on PM materials made from composite powders. The powders, each particle of which consisted of an iron core and a copper shell, were prepared by electroplating. Test-pieces with copper contents of 0, 3.2, and 8 wt.% were fabricated by pressing and sintering from iron and composite powders. Some microstructural, mechanical, and corrosion characteristics of test-pieces were examined. Microstructures were composed of pores and iron grains with alloyed peripheral regions and copper-free cores. As the copper content in test-pieces was increased, their density and Young’s modulus decreased, and macrohardness, corrosion potential and corrosion current density increased. Likely causes of density and Young’s modulus reduction were higher porosity, low enough copper content, and compliant inclusions in stiff matrix. The increase in macrohardness was attributed to the precipitation hardening which prevailed over softening induced by pores. The increase in corrosion potential and corrosion current density was most likely due to the presence of more noble phase providing surfaces for a faster cathodic reaction.

Carbon fiber surface-modified by polymer derived ceramic incorporated with graphene to strengthen the mechanical and electrochemical properties of ceramic-carbon fiber composite

In this study, the carbon fiber surface is spray coated with polysilazane preceramic precursor and pyrolyzed at different pyrolytic temperatures to form the ceramic-carbon fiber composite (SiCN-CCFC) with dense layer of amorphous SiCN ceramic film. The specific strength and modulus of SiCN-CCFC are enhanced 44.26% and 15.37% with spraying 40 wt.% polysilazane preceramic precursor diluted in acetone and then pyrolyzing at 450 °C compared with those of the pure carbon fiber. The carbon fiber spray coated with 20 wt% polysilazane preceramic precursor with 0.5 wt.% graphene in acetone is pyrolyzed at 450 °C to form the graphene-reinforced ceramic-carbon fiber composite (SiCN-GRCFC) whose specific strength and modulus are enhanced 73.15% and 41.15%, respectively, compared with those of the pure carbon fiber. The results of potentiodynamic polarization reveal the electrochemical properties between the pure carbon fiber and SiCN-CCFC that the corrosion potential increases from −0.0971 V to 0.5862 V, the corrosion current density decreases from 1.72 × 10−2 to 1.32 × 10−7 mA⋅cm−2, and the corrosion rate extremely decreases from 9.98 × 10−2 to 9.54 × 10−7 mm∙year−1. The electrochemical properties between the pure carbon fiber and SiCN-GRCFC show that the corrosion potential increases from −0.0971 V to 0.5873 V, the corrosion current density decreases from 1.72 × 10−2 to 3.61 × 10−6 mA∙cm−2, and the corrosion rate extremely decreases from 9.98×10−2 to 2.88 × 10−5 mm∙year−1. Therefore, it can be concluded that the SiCN coating incorporated with additional graphene content can significantly enhance the mechanical properties and corrosion resistance of the commercial carbon fiber.