NaCl 용액에서 Nb 첨가가 Ti 합금의 부식 거동에 미치는 영향

Effects of temperature, phase, elastic deformation and transformation on inhibition of localized corrosion of hydrogen-charged Ni–Ti superelastic alloy in NaCl solution

Electrochemical turning is an efficient machining method for machining Ti80 pressure-resistant structures owing to its low tool cost and high machining flexibility. However, research has yet to explore the electrochemical turning of the Ti80 alloy, limiting its widespread application in ocean engineering. Accordingly, this study examined the anodic dissolution behavior and electrochemical turning of the Ti80 alloy in NaCl solution. Ti80 specimens underwent electrochemical tests, namely, potentiodynamic polarization and potentiostatic polarization. X-ray photoelectron spectroscopy was employed to characterize the composition of the passive film formed on the Ti80 surface when Ti80 was placed in a 20 wt % NaCl solution; this film's structure was investigated through electrochemical impedance spectroscopy (EIS) and transmission electron microscopy (TEM). The results revealed that the passive film mainly contained TiO2, Al2O3, Nb2O5, ZrO2, and MoO3 and comprised two layers: a compact inner layer and a loose outer layer. The measured thickness of the passive film was about 18 nm from TEM, which was near the predicted value (21.6 nm) calculated by EIS data. The diffraction spots obtained from Fast Fourier Transform (FFT) with interplanar spacings of 0.1238, 0.2399, 0.1039, and 0.1888 nm indicated the (024), (201), (521), and (231) crystal planes of TiO2, respectively, showing a relatively high crystallinity of TiO2 in the passive film. The dissolution morphologies of Ti80 at different current densities and processing times were analyzed; the dissolution mechanism of Ti80 in 20 wt % NaCl solution was identified. Finally, grooves with relatively sharp edges were machined on a Ti80 cylindrical workpiece through electrochemical turning at rotation speeds of 0.011 and 0.005 r/min.

Localized corrosion resistance of Co-Cr alloy in NaCl solution was investigated by using polarization curve measurements. Type 316 stainless steel and Cr were used as comparison materials. According to the polarization curves obtained in this study, the Co-Cr alloy maintained a passive state over a wide potential region. However, the current increment with the localized corrosion was appeared in polarization curves of the type 316 stainless steels. The Co-Cr alloy had high localized corrosion resistance compared to the type 316 stainless steel in NaCl solution. Co-Cr alloy was confirmed to maintain passive state in the potential region, same as that observed for Cr. In addition, the passive current density of the Co-Cr alloy and Cr showed nearly identical values. When used in the environment containing chloride ions, the Co-Cr alloy maintained high localized corrosion resistance with the existence of the chromium oxide film. Because of their excellent corrosion performance, Co-Cr alloys are expected to be safely used as the biomaterials in a long life time.

Laser-based fabrication of superwetting titanium alloy with enhanced corrosion and erosion-corrosion resistance

The electrochemical behavior of cast Mg, AZ91, and cast AZ91 in 0.1 M NaCl solution is investigated by measuring open-circuit potential (OCP), steady-state current-potential, and electrochemical impedance spectra (EIS). The similar electrochemical impedance behavior is found of three corrosion electrodes. There are two capacitances in high-and medium-frequency domains and one inductive loop or component in low-frequency domain. From equivalent circuit simulation, cast AZ91 has the worst corrosion resistance. The EIS results are in good agreement with those obtained by OCP and polarization curves. Based on the Cao theory, a simple corrosion mechanism is put forward, supplying a possible explanation for low-frequency inductive behavior for Mg and its alloy in NaCl solution at OCP.

The corrosion behavior of Al-5Zn-0.03In and Al-5Zn-0.03Ga alloys in 3.5 % NaCl solution has been examined by electrochemical methods, scanning electron microscopy, X-ray microanalysis, electrochemical impedance spectroscopy. The results demonstrate that the alloys differ in the microstructure, corroded morphology and electrochemical properties. For Al-5Zn-0.03In alloy, the precipitates enriched in Al and Zn initiates pitting. For Al-5Zn-0.03Ga alloy, corrosion occurs more uniformly, the corrosion of the alloy occurred via the formation of a surface Ga-Al amalgam alloy. The EIS of Al-5Zn-0.03In alloy contains a capacitive loop and an inductive loop; the inductive loop can be attributed to the presence of the pitting. The EIS of Al-5Zn-0.03Ga alloy contains only a capacitive loop.

Effect of Mo and Mo+N implantation on corrosion resistance of austenitic stainless steel

Titanium alloys have been used in aerospace, aeronautic, automotive, biomedical, structural, and other applications because titanium alloys have less density than materials like steel and support higher stress than Al-alloys. However, components made of titanium alloys are exposed to corrosive environments, the most common being industrial and marine atmospheres. This research shows the corrosion behavior of three titanium alloys, specifically Ti-CP2, Ti-6Al-2Sn-4Zr-2Mo, and Ti-6Al-4V with α, near α, and α + β alloys phases. Alloys were exposed in two electrolytes to a 3.5 wt. % H2SO4 and NaCl solution at room temperature, and their electrochemical behavior was studied by electrochemical noise technique (EN) according to ASTM ASTM-G199 standard. EN signal was filtered by three different methods, and the polynomial method was employed to obtain Rn, kurtosis, skew, and the potential spectral density analysis (PSD). The wavelets method was used, from which energy dispersion plots were obtained. The last method was Hilbert–Huang Transform (HHT), where Hilbert Spectra were analyzed. Results indicated that Rn compared with PSD showed that Ti-6Al-2Sn-4Zr-2Mo presented less dissolution in both electrolytes. Statistical methods showed that the passive layer created on Ti alloys’ surfaces is unstable; this condition is notable for Ti-6Al-2Sn-4Zr-2Mo in NaCl solution.

Effect of Zn addition on the corrosion behaviours of as-cast BCC Mg-11Li based alloys in NaCl solution

Microstructure and electrochemical performance of plasma sprayed Cu11.85Al3.2Mn0.1Ti alloy coating in different corrosive solutions

In order to enhance the performance of 20# steel, this study successfully fabricated AlCoCrFeNi high-entropy alloy coatings with different WC contents (x = 0, 10, 20, 30 wt%) on its surface using plasma cladding technology. The effects of WC content on the microstructure, mechanical properties, and corrosion resistance of the coatings were systematically investigated. The results indicate that without WC addition, the coating consists of a dual-phase structure comprising BCC and FCC phases. With the incorporation of WC, the FCC phase disappears, and the coating evolves into a composite structure based on the BCC matrix, embedded with multiple carbide phases such as W2C, M7C3, MxCγ, and Co6W6C. These carbides are predominantly distributed along grain boundaries. As the WC content increases, significant grain refinement occurs and the volume fraction of carbides rises. The coating exhibits a mixed microstructure of equiaxed and columnar crystals, with excellent metallurgical bonding to the substrate. The microhardness of the coating increases markedly with higher WC content; however, the rate of enhancement slows when WC exceeds 20 wt%. The hardness of 1066.36 HV is achieved at 30 wt% WC. Wear test results show that both the friction coefficient and wear rate first decrease and then increase with increasing WC content. The optimal wear resistance is observed at 20 wt% WC, with a friction coefficient of 0.549 and a wear mass loss of only 0.25 mg, representing an approximately 40% reduction compared to the WC-free coating. Electrochemical tests demonstrate that the coating with 20 wt% WC facilitates the formation of a dense and stable passive film in NaCl solution, effectively inhibiting Cl− ion penetration. This coating exhibits the best corrosion resistance, characterized by the lowest corrosion current density of 1.349 × 10−6 A·cm−2 and the highest passive film resistance of 2764 Ω·cm2.

Study on the deterioration process of a chromium-free conversion coating on AZ91D magnesium alloy in NaCl solution

Recently, high density clear brine has been utilized in the oil and gas exploration field as completion or packer fluid in the annulus between the production casing and tubing. CaCl2 has been widely applied for the clear brine, however, some failure cases of duplex stainless steels or super martensitic stainless steels in high density CaCl2 brine have been reported. The effects of oxygen and/or production gas (CO2/H2S) contamination, or H2S formation as decomposition products of NaSCN-type inhibitor have been discussed. In this study, pH in high concentration brines was evaluated to discuss SCC susceptibility of stainless steels. Especially, the stability of pH in high concentration brines has been closely studied for the fundamental aspect to determine the effect of the variation of local pH on SCC behavior. pH imaging sensor (Scanning Chemical Microscope - SCHEM which can measure the two-dimensional pH distribution) was applied to examine the local pH distribution in high concentration brines. SCC susceptibilities of martensitic stainless steels and duplex stainless steels were evaluated in the combination of various brine concentrations and temperature conditions. The addition of caustic soda to high concentration CaCl2 brine made it stable at higher pH, and also reduced the SCC susceptibility. SCC susceptibility seems to depend on the stability of passive film. Therefore, the depassivation pH is considered to be the important factor affecting SCC in high concentration brines. The effect of the hydrolysis reaction of dissolved metallic ion makes the local pH easily dropped in high concentration brine condition because of its higher activity coefficient of proton and lower buffer power, even if the anodic dissolution is almost negligible like passivation current density. SCC mechanism in high concentration brine is discussed based on the local pH variation and the depassivation pH of stainless steels.

Microstructure, corrosion behavior and cytotoxicity of Zr–Nb alloys for biomedical application

Efficient corrosion inhibition mechanism of barbituric acid and sodium phosphate on AZ91 Mg alloys in NaCl solution