Tribological performance and corrosion behavior of CoCrMo alloy

The present work focuses on the Tribological properties and corrosion behavior evaluation of sintered CoCrMo alloy. The CoCrMo alloy was elaborated by Powder metallurgy process at various sintering temperatures (1200°C, 1250°C and 1300°C). The structural properties were characterized by X-ray diffraction and scanning electron microscopy. The tribological characteristics were measured using a dry disc-ball tribometer. The corrosion behavior of the samples was studied using different electrochemical tests in a simulated physiological environment (Hank’s solution). The obtained results show that higher sintering temperatures have a positive impact on the tribological behavior as well as the corrosion resistance of CoCrMo alloys. The sintered samples at 1300°C showed a better resistance to friction wear and a lower corrosion rate.

Corrosion Behaviors of SS310 and IN718 Alloys in Molten Carbonate

Long-lasting metallic materials are key to enabling a robust and reliable molten carbonate electrolyzer. In this paper, the corrosion behaviors of SS310 and IN718 in molten Li2CO3-K2CO3-Na2CO3 under CO2-O2 atmosphere were systematically studied. The results show that IN718 had a lower corrosion rate than that of SS310 because of the higher Ni concentration. In addition, increasing the temperature and decreasing the oxygen concentration can reduce the corrosion rate of both SS310 and IN718. As a result, IN718 is a suitable material to be used in molten salt electrolyzers. Overall, engineering the alloy and molten salt compositions as well as manipulating the gas atmosphere can suppress the corrosion of metallic materials, thereby screening durable metallic materials for high-temperature molten carbonate electrolyzers.

PENGARUH DENSITAS ARUS TERHADAP PERILAKU RETAK BETON BERTULANG YANG MENGALAMI KOROSI TULANGAN

<p align="center"><strong>Abstrak</strong></p><p class="11daftarpustaka"> </p><p>Korosi pada struktur beton betulang dapat mengurangi kinerja struktur dan umur layannya karena volume tulangan yang berkurang. Besarnya jumlah korosi yang dipengaruhi oleh laju korosi dapat digambarkan melalui besarnya densitas arus yang terjadi. Jumlah korosi yang terjadi mempengaruhi perilaku retak pada beton bertulang, oleh karen itu, pada studi ini dilakukan uji eksperimental untuk mengevaluasi pengaruh densitas arus terhadap perilaku retak permukaan beton dari struktur beton bertulang yang mengalami korosi tulangan. Pengujian dilakukan dengan mengaplikasikan variasi densitas arus yaitu 900 µA/cm², 500 µA/cm², 200 µA/cm² and 100 µA/cm² pada pengujian korosi secara elektrik menggunakan larutan NaCl sebagai elektrolit untuk menghasilkan ion Cl^-. Benda uji yang digunakan adalah balok dengan luas penampang 150x150 mm² dan panjang benda uji 300 mm. Tulangan baja diameter 19 mm digunakan pada tengah penampang. Hasil pengujian menunjukkan bahwa perilaku retak dari beton bertulang yang mengalami korosi pada tulangannya memiliki kurva yang bilinear. Selain itu, hasil pengujian menunjukkan bahwa densitas arus yang rendah memiliki kecepatan retak permukaan beton yang lebih tinggi jika dibandingkan dengan benda uji dengan menggunakan densitas arus yang tinggi.</p><p> </p><p>Kata kunci<em>: korosi, beton bertulang, produk korosi, retak, densitas arus</em></p><p align="center"><strong> </strong></p><p align="center"><strong>Abstract</strong></p><p class="Abstract"> </p><p>Corrosion in reinforced concrete structure can reduce structure performance and its service life due to rebar mass loss. Corrosion amount influenced by corrosion rate can be figured out by using current density. Corrosion amount influences the crack behavior of reinforced concrete, therefore, in this study, experimental study was performed to evaluate the effect of current density to surface concrete cracking behavior of corroded reinforced concrete structure. Accelerated corrosion test tests were conducted with various current density. It was 900 µA/cm2, 500 µA/cm2, 200 µA/cm2 and 100 µA/cm2. NaCl solution was used as electrolyte to produce ion Cl^-. The specimens were beam with cross section area 150x150 mm² and 300 mm in length. Rebar with diameter 19 mm was applied in the center of specimen. The results showed that cracking behavior of corroded rebar has bilinear curve that shows the effect of corrosion products movement through cracks. Furthermore, lower corrosion rate has higher cracking speed than higher corrosion rate.</p><p> </p><p>Keywords: <em>corrosion, reinforced concrete, corrosion products, cracking, current density</em></p>

Protection of Aluminum Foils against Environmental Corrosion with Graphene-Based Coatings

Commercial aluminum foils were coated by graphene oxide, and its functionalized derivatives and the corrosion performance of the coated specimens were examined in acidic conditions (lithium perchlorate and sulfuric acid). Electrochemical experiments have shown that all graphene oxide-coated specimens provided up to 96% corrosion inhibition efficiency with a corresponding lower corrosion rate compared to the bare aluminum foil. Our results clearly show that graphene-related materials offer viable alternatives for the protection of aluminum, and this opens up a number of possibilities for its use in a number of commercial applications.

Influence of Co Content and Chemical Nature of the Co Binder on the Corrosion Resistance of Nanostructured WC-Co Hardmetals in Acidic Solution

The electrochemical corrosion resistance of nanostructured hardmetals with grain sizes dWC < 200 nm was researched concerning Co content and the chemical nature of the Co binder. Fully dense nanostructured hardmetals with the addition of grain growth inhibitors GGIs, VC and Cr3C2, and 5 wt.%Co, 10 wt.%Co, and 15 wt.%Co were developed by a one cycle sinter-HIP process. The samples were detailly characterized in terms of microstructural characteristics and researched in the solution of H2SO4 + CO2 by direct and alternative current techniques, including electrochemical impedance spectroscopy. Performed analysis revealed a homogeneous microstructure of equal and uniform grain size for different Co contents. The importance of GGIs content adjustment was established as a key factor of obtaining a homogeneous microstructure with WC grain size retained at the same values as in starting mixtures of different Co binder content. From the conducted research, Co content has shown to be the dominant influential factor governing electrochemical corrosion resistance of nanostructured hardmetals compared to the chemical composition of the Co binder and WC grain size. Negative values of Ecorr measured for 30 min in 96% H2SO4 + CO2 were obtained for all samples indicating material dissolution and instability in acidic solution. Higher values of Rp and lower values of icorr and vcorr were obtained for samples with lower Co content. In contrast, the anodic Tafel slope increases with increasing Co content which could be attributed to more pronounced oxidation of the higher Co content samples. Previously researched samples with the same composition but different chemical composition of the binder were introduced in the analysis. The chemical composition of the Co binder showed an influence; samples with lower relative magnetic saturation related to lower C content added to the starting mixtures and more W dissolved in the Co binder during the sintering process showed better corrosion resistance. WC-5Co sample with significantly lower magnetic saturation value showed approximately 30% lower corrosion rate. WC-10Co sample with slightly lower relative magnetic saturation value and showed approximately 10% lower corrosion rate. Higher content of Cr3C2 dissolved in the binder contributed to a lower corrosion rate. Slight VC increase did not contribute to corrosion resistance. Superior corrosion resistance is attributed to W and C dissolved in the Co binder, lower magnetic saturation, or WC grain size of the sintered sample.

An Investigation of corrosion of friction welded and post-weld heat-treated AA6061/SiC/graphite hybrid composites

The aluminium-based hybrid metal matrix composites have noteworthy applications in sub-sea installations, structures of deep-sea crawlers, submarine parts, engine cylinders, drum brakes etc., as they possess high strength, corrosion resistance, chemical, and dimensional stability. In this investigation, the pitting corrosion behaviour of friction welded and post-weld heat-treated AA6061/SiC/graphite hybrid composites were analysed. The corrosion rates of AW (as welded), ST (Solution treated), STA (Solution treated and Aged), and AA (Artificially Aged) weld joints were experimentally determined. The corrosion behaviour has been discussed in light of microstructure. The experimental results revealed that the STA joints exhibited better corrosion resistance characteristics as compared to AW, AA, and ST joints. The corrosion rate was high for AW joints, followed by AA and ST joints, respectively. Taking into account the corrosion rates of AW and STA joints, the STA joints have a corrosion rate 34.6% lesser than that of AW joints. A comparison of AA and ST with STA joints reveals that the rate of corrosion for STA joints was 31.1% lesser than that of AA joints and 28.8% lesser than that of ST joints. A lower corrosion rate was observed for STA joints as compared to AA, AW, and ST joints.

Corrosion Behaviour of Nitronic Steel in Acidic Environment

Nitronic steel exhibits an austenitic matrix with carbide precipitates along the grain boundaries. The nitronic steel also shows excellent ductility (nearly 2 times of the other stainless steel) which enhances their structural applications. In the view of the performance of nitrogen alloyed steel, the corrosion behaviour of the as-received nitronic steels wasstudied and compared its corrosion behaviour with the conventional stainless steels being used in chemical and hydropower industries. The corrosion study of the nitronic steel and conventional stainless steels was performed in different aqueous solutions (H2SO4 and NaCl). The results obtained from corrosion studies suggest the lower corrosion rate of nitronic steel as compared to the conventional stainless steels. The corroded surfaces were analyzed using an optical microscope and scanning electron microscope for the elemental analysis of corrosion products. Keywords: Nitronic steel; Corrosion; Stainless steel; Acidic solutions

Sensor Development for Corrosion Monitoring of Stainless Steels in H2SO4 Solutions

Equipment made of different stainless steels is often used in the hydrometallurgical processing industry. In this study, an electrical resistance sensor was developed for monitoring corrosion in acidic solutions at high temperature. Two types of stainless steel were used as the electrode materials, namely grade 316L stainless steel (EN 1.4404) and grade 2507 duplex stainless steel (EN 1.4410). The materials and sensors were exposed to a 10% H2SO4 solution containing 5000 mg/L of NaCl at various temperatures. Results from the sensors were verified using electrochemical techniques and postexposure examination. Results showed that the microstructure played an important role in the interpretation of corrosion rates, highlighting the importance of using an appropriate stainless steel for the production of sensors. Electrochemical tests and postexposure examination both showed that the grade 2507 had a significantly lower corrosion rate compared to the grade 316L. Under industrial‑process conditions, the results for the grade 2507 sensor were promising with respect to sensor durability and performance, despite the extremely harsh operating environment.

Corrosion Resistance of Mg Alloy with High Zn Concentration Including Impurity Cu

Mg alloys are very attractive materials for transportation industry due to their toughness and lightness. Recycling Mg alloys is desired for energy saving that otherwise would be required to produce its primary metal. However, secondary produced Mg tends to contain a few impurity elements that deteriorate its corrosion resistance. For example, contamination of Mg alloy by Cu induces second phase of Mg2Cu and it works as strong cathode, resulting in the corrosion rate rapidly increasing. It was previously reported that the corrosion resistance of Mg with impurity Cu was remarkably improved by addition of alloying element Zn. Addition of Zn into Mg formed MgZn2 phase and incorporated Cu into MgZn2 phase instead of Mg2Cu formation. In this way, since Zn serves to improve the corrosion resistance of Mg, Mg alloy with high Zn concentration may form a lot of MgZn2 and may have better corrosion resistance even with high Cu concentration. In this work, the corrosion behavior of Mg-6mass%-1mass%Al (ZA61) with different Cu content up to 1mass% was investigated. As a result, ZA61-1.0Cu had much lower corrosion rate compared to Mg-0.2%Cu and the corrosion rate was almost the same as that of pure Mg.

Influence of Hydrated Lime on the Chloride-Induced Reinforcement Corrosion in Eco-Efficient Concretes Made with High-Volume Fly Ash

The main objective of this study was to analyze the influence that the addition of finely ground hydrated lime has on chloride-induced reinforcement corrosion in eco-efficient concrete made with 50% cement replacement by fly ash. Six tests were carried out: mercury intrusion porosimetry, chloride migration, accelerated chloride penetration, electrical resistivity, and corrosion rate. The results show that the addition of 10–20% of lime to fly ash concrete did not affect its resistance to chloride penetration. However, the cementitious matrix density is increased by the pozzolanic reaction between the fly ash and added lime. As a result, the porosity and the electrical resistivity improved (of the order of 10% and 40%, respectively), giving rise to a lower corrosion rate (iCORR) of the rebars and, therefore, an increase in durability. In fact, after subjecting specimens to wetting–drying cycles in a 0.5 M sodium chloride solution for 630 days, corrosion is considered negligible in fly ash concrete with 10% or 20% lime (iCORR less than 0.2 µA/cm2), while in fly ash concrete without lime, corrosion was low (iCORR of the order of 0.3 µA/cm2) and in the reference concrete made with Portland cement, only the corrosion was high (iCORR between 2 and 3 µA/cm2).