Search Results (18)

The microstructures of the as-cast and annealed Zr₅₆Cu₁₉Ni₁₁Al₉Nb₅ were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM), their microhardness values were tested, and their corrosion behaviours in Hank solution were studied. XRD results and SEM analysis showed that the as-cast sample was amorphous, and crystallisation occurred in the samples annealed at 923 K for 5–30 min with crystals of Zr₂Cu and Zr₂Ni. Microhardness gradually increased and then levelled off, due to higher crystallisation degree with longer annealing time. Passivation occurred for all the samples in Hank solution. Prolonged annealing time leads to the initial rise and then a drop in corrosion resistance. Annealing for 5 min resulted in the highest corrosion resistance, with high corrosion potential E_corr at −0.007 V_SCE, versus saturated calomel electrode (SCE), i.e., 0.234 V_SHE, versus standard hydrogen electrode (SHE), the smallest corrosion current density i_corr at 2.20 × 10⁻⁷ A·cm⁻², the highest pitting potential E_pit at 0.415 V_SCE (i.e., 0.656 V_SHE), the largest passivation region E_pit–E_corr at 0.421 V_SHE, the largest arc radius, and the largest sum of charge transfer resistance and film resistance R_ct + R_f at 15489 Ω·cm². Annealing for 30 min led to the lowest corrosion resistance, with low E_corr at −0.069 V_SCE (i.e., 0.172 V_SHE), large i_corr at 1.32 × 10⁻⁶ A·cm⁻², low E_pit at −0.001 V_SCE (i.e., 0.240 V_SHE), small E_pit − E_corr at 0.068 V_SHE, the smallest arc radius, and the smallest R_ct + R_f at 4070 Ω·cm². When the annealing time was appropriate, the homogeneous microstructure of nanocrystals in an amorphous matrix resulted in improved passivation film, leading to the rise of corrosion resistance. However, if the annealing time was prolonged, the inhomogeneous microstructure of larger crystals in an amorphous matrix resulted in a drop in corrosion resistance. Localised corrosion was observed, with corrosion products of ZrO₂, Cu₂O, CuO, Ni(OH)₂, Al₂O₃, and Nb₂O₅. Full article

A novel prediction model for crack development of reinforced concrete (RC) piles with localized chloride corrosion in the marine environment is proposed. A discrete method is used to solve the corrosion pit radius model and a crack extension model is developed to investigate the initiation and extension of cracks. The maximum corrosion degree of the reinforced concrete pile is predicted according to the limit crack criterion, and finally, a sensitivity analysis is carried out on the important parameters of crack extension. The results show that the radius of the corrosion pit, the depth corrosion pit, and the cross-sectional area loss of reinforcement gradually increase as the corrosion level increases. The loss of the local reinforcement section at crack initiation increases with the increase in the ratio of concrete cover to initial diameter and increases with the increase in the pitting factor. The required pit depth for reinforcement cracking increases with the increase in the ratio of concrete cover thickness to diameter. The loss of the cross-sectional area of reinforcement and the radius of the corrosion pit increase with the increase in the initial diameter of reinforcement. Increasing the pitting factor can reduce the pit depth and make the crack width develop faster before reaching the limit crack width. Increasing the concrete cover thickness can provide an improvement in the propagation of cracks. A comparative analysis shows that the localized corrosion pattern is more in conformity with marine engineering practice. Full article

To investigate the effect of laser shock peening parameters on the corrosion resistance of an E690 high-strength steel cladding layer, NVE690 high-strength steel powder was selected for testing at various power densities of pulse lasers. The surface roughness and residual stress of the treated samples were measured, and the microstructure morphology of the sample surface was observed. The electrochemical corrosion tests were conducted with an electrochemical workstation to measure the electrometer polarization, obtain the impedance curve, and observe the electrochemical corrosion. As the laser power density increased, the surface grains of the E690 high-strength steel cladding layer continued to refine until nanocrystals formed, and the residual compressive stress on the surface increased. The residual compressive stress on the surface rendered the passivation film stable and dense; furthermore, the refinement of surface grains inhibited the initiation and propagation of microcracks. The positive shift of the corrosion potential increased from −1.004 to −0.771 V, the corrosion current density decreased from 114.5 to 5.41 μA/cm², the radius of the impedance spectrum curve increased, and the peeling pits, as well as corrosion micropores on the surface, gradually became no longer evident after electrochemical corrosion. After laser shock treatment, the corrosion resistance of the cladding layer sample was substantially improved. Full article

In this study, Al_0.8CrFeCoNiCu_0.5B_0.1 high-entropy alloy coating was prepared on the surface of 5083 aluminum alloy using laser cladding technology. The corrosion behavior of the coating and substrate in 3.5% NaCl solution was analyzed using experimental methods, including polarization curves and electrochemical impedance spectroscopy. The corrosion current density of Al_0.8CrFeCoNiCu_0.5B_0.1 coating is 2.04 × 10⁻⁷ A/cm ². The passivation range width reaches 2.771 V, and these polarization test results are superior to the substrate. The Al_0.8CrFeCoNiCu_0.5B_0.1 coating exhibited selective corrosion behavior, with the Cu-rich FCC1 phase and Cr-poor phase being susceptible to corrosion, leading to localized pitting and intergranular corrosion traces, but the corrosion did not spread extensively. The intergranular distribution of Cu is the main reason for the intergranular corrosion trace features. In contrast, the substrate exhibited overall corrosion. The Nyquist plot of the Al_0.8CrFeCoNiCu_0.5B_0.1 coating consisted of a single capacitive semicircle arc in the high-frequency region with a larger radius than the substrate. In conclusion, using the Al_0.8CrFeCoNiCu_0.5B_0.1 high-entropy alloy as a coating can significantly improve the corrosion resistance of the 5083 aluminum alloy substrate. Full article

The electrochemical properties of as-cast Zr₅₆Cu₁₉Ni₁₁Al₉Nb₅ metallic glass and samples annealed at different temperatures were investigated using potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS) in phosphate buffer saline (PBS) solution. It was shown that passivation occurred for the as-cast sample and the samples annealed at 623–823 K, indicating good corrosion resistance. At higher annealing temperature, the corrosion resistance first increased, and then decreased. The sample annealed at 823 K exhibited the best corrosion resistance, with high spontaneous corrosion potential E_corr at −0.045 V_SCE, small corrosion current density i_corr at 1.549 × 10⁻⁵ A·cm⁻², high pitting potential E_pit at 0.165 V_SCE, the largest arc radius, and the largest sum of R_f and R_ct at 5909 Ω·cm². For the sample annealed at 923 K, passivation did not occur, with low E_corr at −0.075 V_SCE, large i_corr at 1.879 × 10⁻⁵ A·cm⁻², the smallest arc radius, and the smallest sum of R_f and R_ct at 2173 Ω·cm², which suggested the worst corrosion resistance. Proper annealing temperature led to improved corrosion resistance due to structural relaxation and better stability of the passivation film, however, if the annealing temperature was too high, the corrosion resistance deteriorated due to the chemical inhomogeneity between the crystals and the amorphous matrix. Optical microscopy and scanning electron microscopy (SEM) examinations indicated that localized corrosion occurred. Results of energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) illustrated that the main corrosion products were ZrO₂, CuO, Cu₂O, Ni(OH)₂, Al₂O₃, and Nb₂O₅. Full article

The effect of shot peen forming on the corrosion-resistant of 2024 aluminum alloy in a salt spray environment was studied with an electrochemical workstation. The surface morphology and cross sectional morphology of the original and shot peen-formed sample were studied by a scanning electron microscope. After shot peen forming, the salt spray corrosion resistance of 2024 aluminum alloy was worsened (the corrosion rates of the original alloy and the shot peen-formed alloy were 0.10467 mg/(cm²·h) and 0.27333 mg/(cm²·h), respectively, when the salt spray corrosion time was 5 h). The radius of capacitive reactance arc of the sample subjected to shot peen forming was smaller than that of the original sample. When the salt spray corrosion time was 5 h, the doping density (N_A) of the original alloy was 2.5128 × 10⁻¹³/cm³. After shot peen forming, the N_A of the alloy increased to 15 × 10⁻¹³/cm³. For the shot peen-formed sample, pitting corrosion first occurred in the crater lap zone and became severe with salt spray time. The cross sectional morphology of both original and the shot peen-formed samples shows that severe intergranular corrosion occurred in the salt spray environment. However, for the original sample, the intergranular corrosion distribution was lamellar. For shot peen-formed sample, the intergranular corrosion distribution was network. Full article

Cavitation in a propeller causes erosion, accelerating corrosion, and tearing off blades in severe cases. Despite the maintenance requirements caused by cavitation, few studies have investigated the cavitation resistance of small ship propellers. Therefore, in this study, these characteristics were investigated through a demonstration test in the coastal waters of South Korea. Cavitation erosion characteristics were analyzed according to the low- and high-rotational speed of the propeller, and the weight was measured every 10 h for 100 h of sailing. The erosion pits were qualitatively compared through liquid penetrant testing (PT) and quantitatively compared by image processing with color edge detection. The results showed that propeller weight loss at high speed was double that at low speed. The cavitation erosion exhibited one cycle each of incubation, acceleration, deceleration, and steady state at low speed, while the acceleration and deceleration periods repeated at high speed. According to PT and color edge detection, the concentration of pits in the low- and high-speed conditions increased towards the trailing and leading edges, respectively. Further, in the radial direction, the trend was similar in both conditions, and the largest number of pits were detected in the region of 0.7–0.9R, where R is the propeller radius. Full article

The objective of this work was to study the corrosion behavior of 2xxx aluminum alloys in the marine environment and the degradation of mechanical properties caused by corrosion as well as to provide support for the lightweight design of marine equipment. The corrosion characteristics of 2297-T8 and 2195-T8 were observed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) at 3, 6, 9, and 12 months of exposure, and the mechanical properties were obtained via uniaxial tensile testing. The results of the study showed the following: (1) With an increase in the exposure time, the corrosion products on the surface of 2297-T8 gradually increase, and the corrosion products on the surface of 2195-T8 accumulate rapidly. (2) The results of EDS show that the corrosion products of 2297 are mainly Al oxides and that those of 2195 are composed of Al, Fe, Mn, Si, etc. (3) Through the corrosion pit diameter, corrosion pit depth, and corrosion mass reduction rate surface, the trend of an increasing average radius of the corrosion pits and the corrosion mass reduction rate surface varies linearly, and the average depth of the corrosion pits increases dramatically after 9 months of exposure time. (4) According to the mechanical properties of the study surface, in a marine atmosphere, the degradation of 2297-T8 ductility is higher than that of 2195-T8, while the degradation of the yield stress is lower than that of 2195-T8. Full article

This paper presents the results of the multi-aspect surface characterization of X39Cr13 steel samples subjected to technological processes specific to medical instrumentation, such as heat and thermochemical treatment, as well as sterilization, which are implemented in corrosion resistance measurements. The application of numerical methods of fractal analysis to averaged profiles obtained from SEM images resulted in double-log plots of structure function, from which the determination of the fractal parameters of interest was possible. The discussion was focused on the fractal dimension D, which governs relative height variations upon scaling in length, and corner frequency f_c, which separates the scaling behavior of different-order structures (particles and their aggregates). The obtained results show that the heat treatment leaves behind a granular structure of steel (D₂ = 2.43; f_c2 = 1.97 nm), whereas corrosion tests reveal the appearance of pits (D₁ = 2.17; f_c1 = 0.303 nm; D₂ = 2.59; f_c2 = 4.76 nm). In turn, the ion nitriding improves the resistance of steel X39Cr13 to local corrosion. The fractal analysis also shows that the structure of the nitrided layer differs insignificantly from that of the untreated material, seen only as a shortening of the radius of the self-similarity area by a factor of two (f_c2 = 1 nm). Full article

Aluminum alloy is widely used in aerospace structures. However, it often suffers from a harsh corrosion environment, resulting in different damage such as pitting corrosion, which leads to a reduction in the service life of aerospace structures. In the present study, the pitting corrosion with a radius of 1 mm and a depth of 0.6 mm was manufactured using hydrofluoric (HF) acid on a 2024-T3 aluminum alloy plate (400 mm × 400 mm × 2 mm) to simulate the corrosion state of equipment. A signal acquisition system with a square sensor network of 12 piezoelectric transducers (PZTs) was established. The sensor path weighting reconstruction algorithm for the probabilistic inspection of defects (SPW-RAPID) is proposed based on corrosion damage characteristic parameters including signal correlation coefficient (SDC), root mean squared error (RMSE), and signal energy damage index (E1) to explore the monitoring efficacy of pitting corrosion. The sensor path weight w, which is the product of value coefficient a and impact factor l, is established to modify the corrosion damage characteristic parameters. The results indicate that the SPW-RAPID algorithm can improve the accuracy and clarity of image reconstruction results based on SDC, RMSE and E1, which can locate the pitting corrosion with a radius of 1 mm and a depth of 0.6 mm, and the positioning error is controlled within 0.1 mm. The research work may provide an available way to monitor tiny corrosion damage on an aluminum alloy structure. Full article

This paper analyzed the corrosion behavior and corrosion performance of ER8 wheel steel through a full immersion test. The average corrosion rate of the ER8 wheel specimen in 2.0% NaCl solution shows a gradual increase over the whole corrosion cycle. Although the corrosion rate showed fluctuations at 3.5% and 5.0% concentration before 576 h, the corrosion rate also showed a steady increase after 576 h. The corrosion rates of specimens at different concentrations after 2160 h were over 0.12 mm/year. With increasing immersion times or concentrations of NaCl solution, the coverage area of the corrosion products dominated by iron oxides gradually increased, and the corrosion products on the surface became denser. The corrosion products were primarily γ-FeOOH, α-FeOOH and Fe₃O₄. As the density of the surface corrosion products increased, cracks and holes appeared on the surface of the rust layers, which made the rust layer unable to protect the substrate from further corrosion. After removing the corrosion products, pitting corrosion appeared on the surface of the substrate. The radius of the capacitive reactance arc gradually decreased with the increasing immersion time. The impedance modulus in the low-frequency region decreases and then increases with increasing NaCl solution concentration, which is the highest in 3.5% NaCl solution. I_corr increased with an increasing Cl⁻ concentration, which was similar to the mechanism of catalytic electrolysis due to Cl⁻. The specimens with rust layers have worse corrosion resistance when the immersion time is extended. The corrosion product did not protect the substrate but accelerated the corrosion process. Full article

Research on improving the corrosion resistance of carbon steel has become a hot topic in the iron and steel field in recent years. Copper plating on the surface of carbon steel is considered an effective means to improve its corrosion resistance, but the copper-plated carbon steel material prepared by this method has the problems of poor abrasion resistance, easy delamination of copper layer and similar issues, which affect the service performance of the copper-plated carbon steel material. To solve this problem, a new type of material whose surface is copper and the copper element is gradually diffused into carbon steel was developed by a plating-diffusion method, which is defined as a copper-carbon steel gradient material. Carbon steel with a copper plated surface and the Cu-Fe/carbon steel gradient material with 80% Cu content on the surface were prepared by the same method. The cross-sectional microstructure and composition of different samples were analysed, and the corrosion behaviors of samples in 3.5% NaCl solution were studied by the linear polarization curve method and electrochemical impedance spectroscopy. The cross-sectional microstructure result shows that the diffusion of copper in carbon is mainly carried out along its grain boundary, and the diffusion of copper will inhibit the growth of grains during heat treatment. As shown in the results of corrosion behaviors, there is no pitting corrosion in the corrosion process of all samples, as well as the stable passive film. All samples showed active dissolution. Compared with carbon steel, the corrosion potential of the Cu/carbon steel gradient material becomes more positive from −600 mV to −362 mV, the corrosion current density decreases from 53.0 μA/cm² to 30.6 μA/cm² and the radius of electrochemical impedance spectroscopy enlarges while the corrosion resistance is improved, and the corrosion resistance is mainly obtained by its surface copper layer. The corrosion resistance of Cu-Fe/carbon steel gradient material is lower than that of Cu/carbon steel gradient material, while it is still better than carbon steel, and it shows a clear passivation trend during corrosion. Therefore, the copper/carbon steel gradient material can significantly improve the corrosion resistance of carbon steel. Even after the surface copper layer is destroyed, the gradient material can protect the matrix and improve the service life of the material. Full article

In this paper, electrochemical corrosion tests and full immersion corrosion experiments were conducted in seawater at room temperature to investigate the electrochemical corrosion behavior and the corrosion mechanism of high-strength EH47. The polarization curve, EIS (electrochemical impedance spectroscopy), SEM (scanning electron microscope), and EDS analyses were employed to analyze the results of the electrochemical corrosion process. The electrochemical corrosion experiments showed that the open circuit potential of EH47 decreases and then increases with an increase in total immersion time, with the minimum value obtained at 28 days. With an increase in immersion time, the corrosion current density (I_corr) of EH47 steel first decreases and then increases, with the minimum at about 28 days. This 28-day sample also showed the maximum capacitance arc radius, the maximum impedance and the minimum corrosion rate. In the seawater immersion test in the laboratory, the corrosion mechanism of EH47 steel in the initial stage of corrosion is mainly pitting corrosion, accompanied by a small amount of crevice corrosion with increased corrosion time. The corrosion products of EH47 steel after immersion in seawater for 30 days are mainly composed of FeOOH, Fe₃O₄ and Fe₂O₃. Full article

Compared with other materials, high-volume fraction aluminum-based silicon carbide composites (hereinafter referred to as SiCp/Al) have many advantages, including high strength, small change in the expansion coefficient due to temperature, high wear resistance, high corrosion resistance, high fatigue resistance, low density, good dimensional stability, and thermal conductivity. SiCp/Al composites have been widely used in aerospace, ordnance, transportation service, precision instruments, and in many other fields. In this study, the ABAQUS/explicit large-scale finite element analysis platform was used to simulate the milling process of SiCp/Al composites. By changing the parameters of the tool angle, milling depth, and milling speed, the influence of these parameters on the cutting force, cutting temperature, cutting stress, and cutting chips was studied. Optimization of the parameters was based on the above change rules to obtain the best processing combination of parameters. Then, the causes of surface machining defects, such as deep pits, shallow pits, and bulges, were simulated and discussed. Finally, the best cutting parameters obtained through simulation analysis was the tool rake angle γ₀ = 5°, tool clearance angle α₀ = 5°, corner radius r = 0.4 mm, milling depth a_p = 50 mm, and milling speed v_c = 300 m/min. The optimal combination of milling parameters provides a theoretical basis for subsequent cutting. Full article

In order to theoretically research the tooth surface maximum contact stress of a Cylindrical Gear with Variable Hyperbolic Circular-Arc-Tooth-Trace (VH-CATT), the computing formula of maximum contact stress of VH-CATT cylindrical gear is investigated according to Hertz formula in this paper. Insufficient contact fatigue strength will lead to pitting corrosion, plastic deformation of tooth surface and other damages. Therefore, the maximum contact stress of tooth surface must be carried out. The contact stress calculation formula is particularly considering the effect of normal force, total carrying length, synthetical curvature radius, and position angle. The present work establishes analytical solutions to research the effect of different parameters for the contact stress of VH-CATT cylindrical gear incorporating elastic deformation on the tooth surface, and which have shown that the different module, transmission ratio, pressure angle, tooth width, and the cutter head radius have a crucial effect on the contact stress and contact ellipse of VH-CATT cylindrical gear along the tooth width direction. Moreover, a finite element analysis is carried out to verify the correctness of the theoretical computing formula of contact stress of VH-CATT cylindrical gear. By contrast with the theoretical calculated value and the stress value of finite element analysis, its error is very small. It is indicated that the derived formula of contact fatigue strength of VH-CATT cylindrical gear has high accuracy and can accurately reflect the real contact stress value of tooth surface, which is beneficial for research on tooth break reduction, pitting, wear resistance and fatigue life improvement of the VH-CATT cylindrical gear. The study results also have a certain reference value for the design and check calculation of the VH-CATT cylindrical gear. Full article