Metals and Materials International最新文献

In this work, strengthening effects and evolution of precipitates in a pre-deformed Al–Zn–Mg–Cu alloy during ageing were investigated using Vickers hardness measurements, tensile tests, and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). It was found that all cold rolled conditions had higher mechanical strength than the non-deformed condition for all ageing times and that this effect increases at higher deformation ratios. It was also found that the non-deformed condition has a higher age hardening response than that of the cold rolled conditions. A homogeneous precipitate distribution was observed in the non-deformed condition, while the cold rolled conditions contained non-uniformly distributed precipitates due to the introduced dislocations. This led to larger precipitate sizes and a reduction in the precipitate number densities in the pre-deformed conditions. HAADF-STEM analysis revealed differences in the fraction of different precipitate types between the non-deformed and the cold rolled conditions. η', η_2, and disordered η phase were observed in the non-deformed condition, while η', η₂ and the newly identified Y phase were observed in the cold rolled conditions. The disordered η phase contained structural units of the η₁ phase and was associated with reducing the lattice misfit between this phase and the Al matrix. Formation of the Y phase was related to an accelerated nucleation rate in the regions of high dislocation density.

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A group of CoCrFeNiTiNb_x high entropy alloys (HEAs) coatings were produced by laser cladding. The effect of Nb content on the microstructure and wear resistance of the HEAs coatings was investigated. The results indicated that adding Nb promoted the phase transition from BCC to FCC and the formation of Fe₂Nb Laves phase, The diffraction peaks of FCC and BCC phases were firstly shifted to smaller angle as Nb content was increased, and then shifted to larger angle. Adding Nb promoted brittle fracture of more coarse dendrites to formed fine dendrites and equiaxed crystals homogenizing the microstructure in the HEAs coatings, as well as the formation of dense dislocations and dislocation interaction. The microhardness of the HEAs coatings was firstly increased and then decreased as Nb content was increased, and the change of the mass loss and friction coefficient was opposite trend. Compared with CoCrFeNiTiNb_0.0 HEAs coatings, the microhardness of the CoCrFeNiTiNb_1.0 HEAs coatings was improved by 25.00%, the mass loss was reduced by 28.27%, and and friction coefficient was the lowest. The wear mechanism of the HEAs coatings was transformed from the adhesive wear and oxidative wear accompanied by the abrasive wear to the abrasive wear accompanied by the adhesive wear and oxidative wear as Nb content was gradually increased.

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This study investigates the effects of Laser Shock Peening (LSP) on the mechanical properties and microstructure of Wire Arc Additive Manufactured (WAAM) bimetallic components made of Grade 91 Steel and Monel-400. LSP, a surface enhancement technique, was applied to address the residual stress and enhance the mechanical performance of these bimetallic components. Electron Backscatter Diffraction (EBSD) analysis post-LSP showed refined grain structures, contributing to the observed enhancements in mechanical properties. The research revealed that LSP treatment increased the tensile residual stress at the bimetallic interface from 109 ± 2.5 MPa to 185.9 ± 2.5 MPa, indicating a strengthening of the bimetallic interface. The tensile strength of the Grade 91 Steel part increased from 1140 ± 6.5 MPa to 1280 ± 4.5 MPa after LSP, while the Monel-400 section showed a slight decrease in tensile strength from 516 ± 2.5 MPa to 511 ± 6 MPa but an increase in elongation from 31 to 38.5%. Furthermore, microhardness at the interface improved, with a rise from 267 ± 3 HV0.1 to 303 ± 4 HV0.1 post-LSP. The enhanced properties of the bimetallic components are particularly beneficial for applications in the petrochemical and marine industries, where the combined resistance to thermal and corrosive environments is critical. This study provides a new understanding of the application of LSP in improving the mechanical properties of WAAM-produced bimetallic components.

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The ultimate objective of this study is to find a way to replace toxic lead-based solder with a non-toxic replacement that retains all of the desirable characteristics of the conventional solder. In this work, the integral and partial enthalpy of mixing for Sn–Ga–In ternary alloy systems were measured by the help of drop calorimeter along six of the cross sections at different temperatures of 673 K, 723 K and 773 K. Pieces of pure tin were dropped into molten Ga_0.25In_0.75, Ga_0.50In_0.50, Ga_0.75In_0.25 alloys and pieces of pure Indium into Ga_0.25Sn_0.75, Ga_0.50Sn_0.50, Ga_0.75Sn_0.25. In order to calculate the interaction parameter, Redlich–Kister–Muggianu (RKM) model was used which considers the substitutional solution mechanism. Geometric models i.e. Kohler, Muggianu, Chou, Toop, and Hillert have been used to determine the integral mixing enthalpies and compared with experimental data. It has been seen a good agreement between the theoretical models and results of this study.

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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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