Metals and Materials International最新文献

The blister formation mechanism in electrogalvanized steel was studied by analyzing the blister’s internal structure. Electrochemical hydrogen charging was employed to absorb hydrogen into the steel plate and to induce blister formation. Analysis of the blister interior revealed that the initial formation of blisters occurred at the cracks located at the interface between the zinc layer and the steel substrate. These cracks originated from the steel substrate’s intergranular fracture or carbon contaminants’ adsorption on the steel surface. Grain boundary precipitates in hot-rolled plates form the intergranular crack after cold-rolling. A hydrogen anion was found inside the blister formed at the pre-existing intergranular crack. However, methylidyne (CH⁻) and methylene anion (CH₂⁻) dissociated from methane, as well as hydrogen anions were detected inside the blister formed at the carbon-contaminated steel surface. Methane gas is generated by the combination of absorbed hydrogen with carbon inside the crack. This research clarifies the detailed formation mechanism of blisters in electrogalvanized steel.

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The effect of Nb on austenite grain growth kinetics was investigated in 10Cr-3Co-2W martensitic heat-resistant steel under various tempering conditions (temperature and time). The results demonstrate that Nb effectively refines the austenite grain size; this result is attributed to the combined effect of Nb atom solute drag effect and pinning effect of NbC precipitates. Based on the measured values, an empirical model was developed to predict the grain growth behavior of this alloy system. In addition, the key conditions and parameters for application to the microstructure evolution model of MatCalc software were derived. Results will enable the prediction of grain size at different Nb contents and temperature parameters, and provide useful information for designing heat treatment processes and alloys.

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This study aims to investigate the role of oxygen in optimizing the Pore-Free Die Casting (PFDC) process to enhance the quality of aluminum castings by minimizing porosity defects. The effects of oxygen levels on the integrity of high pressure die casting specimens was investigated by injecting oxygen at different durations (1 s, 3 s, and 5 s) through air jet valves installed at the mold cavity. The CT results indicate that increasing the oxygen injection time significantly reduces the porosity volume from 0.9 to 0.18%, with smaller defects in size as well. Notably, after applying the PFDC process, the elongation improved from 2.23 to 4.58%, suggesting that replacing atmosphere in the cavity space with oxygen plays a crucial role in enhancing the mechanical properties of the HPDC specimens. The improvement is believed to be caused by promoting oxidation reactions with the high concentration of oxygen, which leads to a decrease in gas entrapment during the casting process.

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Duplex stainless steels (DSS) had good wear and corrosion resistance, making them potential substitutes instead of martensitic stainless steel as the material for water turbine blades. However, designing a DSS with high wear and corrosion resistance using traditional trial-and-error methods required a significant amount of time and cost. This study proposed a material design method based on machine learning (ML) to accelerate the development of novel DSS. A composition-process-performance database for DSS was established, and four ML model such as K-Nearest Neighbor Regressor (KNR), Ridge Regression (RR), Decision Tree (DT), and Random Forest (RF) were employed to train the database. Predictions of wear and corrosion resistance for DSS were achieved. The predicted and actual values of them demonstrated good consistency. Among the four models, the RF model for microhardness and self-corrosion potential exhibited the best predictive performance with an R² value of 0.90 and 0.87, respectively. Employing the RF model for three rounds of selection obtained three DSS compositions with high wear and corrosion resistance among 69,120 composition-process combinations, then named as 1Cr29Ni11Mo3.5N, 1Cr29Ni8Mo4.5N, and 1Cr29Ni10Mo4.5N. These optimized compositions were further investigated through laser melting deposition (LMD) corresponding samples. Experimental results indicated that the volume ratio of ferrite to austenite in the three samples all reached 3:7. Specifically, 1Cr29Ni11Mo3.5N showed a microhardness of 356 HV_0.2, good wear resistance (1.2579 × 10^–13 m³/Nm of wear rate), and a self-corrosion potential of − 0.12494 V. 1Cr29Ni11Mo3.5N exhibiting high wear and corrosion resistance.

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The effect of substituting equal concentrations of Ni with 0.7 wt% and 1 wt% Cu on the corrosion behavior of Ni-advanced weathering steels (WS) in the simulated tropical marine atmosphere was studied. The results reveal that the effect of substituting Ni with Cu on enhancing the corrosion resistance of Ni-advanced WS is positively correlated with the substitution of Cu, as the concentration of Cu substitution affects the synergistic effect of Cu/Ni in Ni-advanced WS. With the substitution content of 0.7 wt% Cu, the synergy effect of Cu/Ni on enhancing the densification and protection of the rust layer is weakened which promotes the charge transfer process and accelerates the corrosion process of Ni-advanced WS. As the content of Cu substituting Ni increases up to 1 wt%, the synergy effect of Cu/Ni is stronger than that of Ni at the same content. Consequently, modifies the Ni-depleted region in the rust layer, the α-FeOOH content in the rust layer is increased, makes the rust layer dense, and intensifies the charge transfer resistance at the substrate-rust interface, thereby improving the corrosion resistance of the Ni-advanced WS.

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We present a simple, direct, one-step method for obtaining a hydrophobic ZnO nanostructure coating to prevent zinc oxidation (white rust). The corrosion resistance of ZnO nanostructure-coated galvanized steel (GI) was studied using the well-known electrochemical impedance spectroscopy (EIS) technique in a 3.5 wt% aqueous NaCl electrolyte solution. Through the thermal decomposition of zinc acetate dihydrate, a thin film of ZnO nanostructure was grown on top of the GI substrate. All specimens were characterized using FESEM, EDS, and XRD following GI surface modification with ZnO nanostructures. The wettability of the nanostructure-modified GI surface was also investigated using the contact angle method. In a 3.5 wt% aqueous NaCl solution, the ZnO nanostructure coating was more resistant to corrosion than the neat GI substrate. In an aqueous corrosive electrolyte medium, we observed ZnO nanostructures forming a hydrophobic surface on a GI substrate. This hydrophobic thin film coating of ZnO nanostructures is an excellent alternative for protecting the surface of GI substrates; thus, it can eliminate toxic material based coatings on GI substrates.

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In this work, superplastic behavior in tension for the Zn-21Al-2Cu alloy was reviewed as a function of: grain size, temperature and strain rate. The deformation mechanism was studied under conditions where the greatest elongation was reached, characterizing microstructural changes and analyzing the associated mechanical response such as the study of plastic stability. This analysis allowed us to propose a phenomenological model consisting of five steps for the mechanism of superplastic deformation under which dynamic conditions are involved for this alloy. In the first stage, an accommodation of the microstructure was observed, in the second stage sliding by individual grain boundaries (GBS) was activated, which provided the conditions for stationary plastic flow. In the third stage, GBS was hampered by the tendency of grain boundaries remaining from high temperature phase (FβBs) to align at 45°. This fact caused the onset of plastic instability. The fourth stage consisted of a transition in which there was competition between individual and cooperative GBS mechanisms, which increased plastic instability. In the last stage, the FβBs were aligned parallel to tensile direction, which favored the GBS, and an additional diffusion flow mechanism allowed partial recovery of stable plastic flow.

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