Metals and Materials International最新文献

This research aimed to explore the influence of the rare-earth element La on the interface microstructure and mechanical properties of Al/steel bimetallic composites produced through liquid–solid casting. The addition of the rare earth element La refined the morphology of eutectic silicon and ensured its uniform and continuous distribution. The interface structure of the Al/steel bimetallic composite exhibited distinct layering, primarily comprising two layers. The first layer, termed reaction layer I, comprised Al₅Fe₂ and τ₁-Al₂Fe₃Si₃ phases. While the second layer, termed reaction layer II, consisted of Al₁₃Fe₄, τ₅-Al₇Fe₂Si, and τ₆-Al₉Fe₂Si₂ phases. The addition of La did not alter the types of intermetallic compounds present in the Al/steel reaction layer. As the La content increased to 0.3%, there was a notable reduction in the average thickness of both reaction layers I and II, reaching a minimum. The presence of La effectively restrained the growth of intermetallic compounds within the reaction layer. Consequently, the shear strength of the Al/steel bimetallic sample exhibited an initial increase followed by a subsequent decrease with increasing La content. With the addition of 0.3% La, the shear strength of the sample peaked at 30.1 MPa, representing a 66% increase.

Graphical Abstract

Reticular crystal phases and abnormally coarse grains are key problems that restrict the improvement of the mechanical properties and uniformity of Al-Li alloys. The effects of the multidirectional forging (MDF) process on the microstructure at the edge and center and the three-directional mechanical properties of the 2195 Al-Li alloy were investigated. The results show that the strong deformation resistance produced by one heat forging at 400 ℃ with seven upsetting and six stretching (400-7U6S-1) fully broke the reticular crystal phases at the grain boundaries and obtained the dispersed phase structure. The high density of dislocations accumulated by strong deformation promoted the dissolution of the dispersed secondary phases, and the area fraction of the secondary phase particles at the edge and center decreased from 3.88% and 1.97–0.75% and 0.61%, respectively, which prevented the occurrence of intergranular fractures and dramatically improved the ductility. Meanwhile, the dissolution of the second phases enhanced the precipitation force of the T1 phases and inhibited the precipitation of δ’ phases. Furthermore, the higher density of dislocations significantly increased the nucleation rate of dynamic recrystallization and eliminated the abnormally coarse grains, and thus acquired a uniform ultra-fined grain structure and the average grain diameter was reduced from 159 μm to 17 μm. The tensile strength, yield strength and elongation in the width direction increased to 592 MPa, 545 MPa and 8.0%, respectively, and increased by 7.2%, 7.2% and 90.5%, respectively. In particular, the maximum difference in the elongation of the forgings in the width direction decreased from 83.3 to 11.1%.

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In this study, a Ni–Fe–Si–B amorphous composite coating is coated on H13 steel by laser cladding. Coatings are systematically investigated for their microstructure, phase composition, tribological behavior, and mechanical characteristics. X-ray diffraction results demonstrate that the cladding layer can be divided into the interface, transition, and compositionally stable zones, where the coating has both crystalline and amorphous phases, with up to 57% of the coating being amorphous. According to scanning electron microscopy and transmission electron microscopy analyses, the middle and surface regions of the coating mainly consist of (Fe_0.5Ni_0.5)₃Si, Fe₂B, Fe₂NiB, Ni₃₁Si₁₂, and amorphous phases. The in-situ generated Fe₂B phase is uniformly distributed within the coating, leading to a significant enhancement in microhardness. The greatest hardness of the coating is approximately 927.04 HV_0.2. The composite coating exhibits excellent wear resistance, which is approximately 1.71 times greater than that of the substrate. Minor abrasive wear constitutes the primary wear mechanism for the coatings.

Discontinuous plastic flow due to dynamic strain aging (DSA) in a Fe-Ni-based superalloy was investigated by tensile tests in the temperature range from 500 ºC to 800 ºC with different γ′ fraction. Type A serrations were observed in the solutionized and as-aged specimens at 500 ºC, which was a result of diffusion of carbon atoms. The stress amplitude was affected by the dislocation density induced by the presence of γ′ phase. Type C serrations occurred in the solutionized and under-aged samples at 650 ºC and 700 ºC. With the increase of γ′ phase fraction in the initial microstructure, the stress amplitude and duration of type C serrations decreased at 700 ºC. It was demonstrated that the dominant deformation mechanisms of under-aged specimens at 650 ºC and 700 ºC were weakly-coupled dislocation pairs shearing the fine γ′ particles with slip bands, while the deformation mechanism transformed to dislocation climbing at 800 ºC. The model linking serration amplitude, solute concentration at the dislocation line and dislocation density was used to analyze the effect of γ′ dynamic precipitation on the DSA. The dynamic precipitation of γ′ phase during tensile significantly alters the DSA behavior by removing substitutional solutes responsible for γ′ precipitation from the matrix.

Graphical Abstract

Wire arc additive manufacturing (WAAM) is widely used in the rapid prototyping of large parts because of its high deposition rate, high material utilization rate as well as low cost. However, the manufacturing process of magnesium alloy wires is relatively difficult, and the defects and performance of parts are difficult to control. This paper reviews the preparation process of magnesium alloy wires, which aims to achieve surface control and performance optimization of wires. Due to the quality of wires and the high processing temperature, the defects often occur in the deposition process. The common defects of magnesium alloy parts by WAAM are discussed and solutions are given to minimize it. The research advances in microstructure, mechanical properties, damping properties and corrosion properties are summarized. WAAM has performance advantages compared to casting, but the microstructure is inhomogeneous and the properties are anisotropic. Several quality improvement strategies are reported to improve properties and reduce defects. The effectiveness and applicability of these strategies are discussed, and the future prospects of WAAM for magnesium alloys are proposed. The preparation of high-performance wires, the formation mechanism of defects and microstructure are three keys for future improvement of WAAM for magnesium alloy.

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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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