Metals and Materials International最新文献

This study explored the application of a high-density pulsed electric current (HDPEC) to mitigate strain hardening in a cold-rolled A6061 aluminum alloy while examining the simultaneous application of HDPEC with furnace heating to reveal the contributions of thermal and athermal effects. The results showed that significant strain-hardening relief was achieved through the HDPEC treatment, particularly at 300 A/mm² for 260 ms, resulting in a 23% reduction in strength and an 86% increase in ductility. Microstructural analysis revealed a shift to fine and equiaxed grains with reduced dislocation density, which was primarily attributed to thermal effects. HDPEC annealing exhibits superior efficiency compared to the conventional annealing treatment, offering cost and time advantages. In addition, this study validated the synergistic impact of HDPEC and furnace heating, with furnace heating supplementing energy requirements, facilitating practical HDPEC implementation. These findings suggest that the HDPEC method and the combined method with conventional heating are promising alternatives for strain-hardening alleviation in A6061 aluminum alloy manufacturing, supporting the development of an eco-friendly and efficient process.

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The trapping behavior of hydrogen atoms at the interfaces between different precipitated carbides (TiC, VC and NbC) and ferrite matrix under alloying elements (Mn, Cr, Mo, Cu, Ni and Si) are studied by first-principles method. The trapping ability of different interface traps are quantitatively compared by analyzing the segregation energies of hydrogen atoms. The trapping ability of mismatched dislocation cores and their intersections is stronger than that of coherent interfaces. The orders of H trapping ability of the carbides in different interface traps are discussed. It is found that the addition of alloy elements leads to an increasement in the segregation energy relative to their corresponding sites in the clean interface, except for Cu addition in VC/Fe and TiC/Fe and Ni in VC/Fe Fe-on-C configurations.

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Rejuvenation has been considered to be an effective method for enhancing the mechanical properties of metallic glass. Herein, the effect of two rejuvenation methods, by enthalpy relaxation and through cryogenic thermal cycling (CTC) treatment, on the mechanical properties and energy state of a relaxed Cu₄₉Hf₄₂Al₉ bulk metallic glass (BMG) is investigated. It is revealed that the method of rejuvenation by enthalpy relaxation is applicable to the present relaxed metallic glass system, where the energy state is lifted to a higher one from the relaxed state and the compressive plasticity surpasses that of the as-cast MG after rejuvenation. The CTC treatment can also recover the compressive plasticity of the relaxed MG even though only with a slight increase in the energy state. The combination of the above two methods, however, shows an unexpectedly stronger rejuvenation effect in the relaxed Cu₄₉Hf₄₂Al₉ BMG, where the energy state of the optimally rejuvenated sample is comparable to that of the as-cast sample and the compressive plasticity of the optimally rejuvenated sample is more than twice and six times that of the as-cast sample and the relaxed sample, respectively. Our results show that a significant rejuvenation effect can be achieved by combining two or more rejuvenation methods, which opens a new route to tailor the properties of MGs.

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High entropy alloys have emerged recently as promising candidates for high-temperature applications. This study explores the detailed oxidation behavior of CoCrFeMnNi alloy by using a combination of in-situ, short-duration and long-duration high-temperature exposure up to 1000 ^⁰C. The study reveals Cr and Mn played a significant role in the oxidation/passivation of the alloy. It was found that Cr enhanced the oxidation resistance, especially by limiting oxygen diffusion and was quite effective up to 600 ^⁰C. However, at higher temperatures, Mn continuously diffuses towards the surface and forms a poorly adherering oxide scale. Study on CoCrFeNi and CoFeMnNi alloys to investigate the roles of Cr and Mn individually revealed that under similar conditions, CoCrFeNi had a relatively continuous and less spalled oxide layer with better adherence to the alloy compared to cantor alloy. However, compared to Cr-containing alloys, the CoFeMnNi alloy did not have a continuous, well-adhering, non-protective oxide layer making the alloy prone to severe and faster oxidation. Same was apparent from significant internal oxidation, the appearance of massive cracks, and voids. Before and after the oxidation, CoCrFeMnNi and CoCrFeNi were single-phase fcc structures while CoFeMnNi decomposed into a two-phase alloy due to significant uptake of oxygen. Prolonged oxidation and molten-state studies revealed that the oxidation behaviour of HEAs is a thermodynamic-driven process, and CoCrFeMnNi is expected to gradually lose Mn to surface oxide followed by migration of Co, Ni and Fe, which otherwise hardly migrated or participated in the oxidation process. High-temperature heat treatment in vacuum confirmed that the migration to the surface was driven by its oxidation at the surface.

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Optimization of properties in certain metallic materials relies on the ability to leverage precipitation strengthening effects via application of appropriate processing techniques, including heat treatment, to control precipitate morphologies. Traditional methods to monitor precipitate growth during heat treatment employ post-quench microscopy and hardness measurement, but these have limited ability to monitor small-scale or incremental changes in precipitate morphology that are relevant to material property profiles. Laboratory-scale small-angle X-ray scattering (SAXS) techniques in combination with heated-stage capability represent a novel approach for improved understanding of microstructural evolution and design of heat treatment schedules, by enabling analysis with high spatial resolution and time-dependent information. In the current study, heated-stage SAXS experiments were used to recreate four heat treatments on AA7050-T7451 alloys and successfully monitor precipitate growth over a temperature range of 160–220 ℃, with hold times of 0–120 min. SAXS measurements indicated precipitate diameters ranging from 7.1 to 9.8 nm, with increased precipitate growth corresponding to higher temperatures and longer hold times. Precipitate volume fraction and calculated hardness values ranged from 1.3 to 2.9% and 78–94 HRB. Results from this work indicate that laboratory-based SAXS is a highly accurate method for measurements at the nanometer length scale, as well as high temporal resolution, and this approach lends itself to both room temperature and high-temperature precipitate quantification, potentially eliminating the need for time- and resource-intensive synchrotron-based SAXS for precipitate analysis. Additionally, laboratory-based SAXS can facilitate a more accessible and economical investigation that is particularly beneficial for process design and analysis where higher-volume testing is required.

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In this study, the pulse-reverse electrodeposition method was utilized to fabricate Ni reinforced with various carbon allotropes (Carbon Nanotube (CNT), Graphite (Gt), and Graphene (Gr)) coatings. The impact of carbon addition and type on the microstructural features and electrochemical behavior of the Ni coating was studied. Microstructural characterization was conducted using Field-Emission Scanning Electron Microscopy, Atomic Force Microscopy, X-ray diffraction pattern, and Raman spectroscopy. The findings revealed a transition from a porous pyramid-like structure to a denser and uniform microstructure with addition of reinforcing particles. Additionally, Atomic Force Microscopy investigations demonstrated reduced surface roughness for CNT, Gt, and Gr inclusions, with Ni-Gr displaying the lowest roughness. Evaluation of the electrochemical properties through Electrochemical Impedance Spectroscopy and polarization measurements showed a 30%, 54%, and a remarkable 60% enhancement in corrosion protection for Ni reinforced with CNT, Gt, and Gr coatings, respectively. Polarization tests confirmed a substantial reduction in corrosion current density, from 6.2 µA/cm² for Ni coating to 1.9, 0.4, and 0.1 µA/cm² for Ni-C coatings with CNT, Gt, and Gr carbon allotropes, respectively, indicating the exceptional corrosion resistance of Ni-Gr composite coating prepared by the used method.

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The present study, with its practical implications, evaluates the relationship between microstructure and specific wear rate/friction coefficient in A356 alloy and A356/Al₂O₃ and A356/WC composites after casting and hot-extrusion. The characterization of crystalline phases was carried out using X-ray diffraction, and the microstructure was characterized by scanning electron microscopy. The comprehensive use of rotating (Pin-on-Disk) and linear reciprocating wear testers ensures a thorough understanding of the materials’ specific wear rate and friction coefficient behaviors. The results show a direct relationship between specific wear rate, friction coefficient, microstructure evolution, and hardness in the systems studied after casting and hot extrusion. In addition, the specific wear rate and friction coefficient decrease as the load increases during tests; however, the friction coefficient is more sensitive to hardness values at low loads; at as-cast conditions, this value decreases concerning the reference sample a 13% and 10% for the A356/Al₂O₃ and A356/WC composites, but at the extruded conditions, increases by 30% and 111%, which is in a direct relationship to values of hardness obtained.

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Although the mechanical properties of shot-peened metallic alloys need to be explored carefully by changing shot-peening parameters, the mechanical properties of shot-peened AISI 4340 steel were not investigated well. In this study, the changes in the mechanical properties of shot-peened AISI 4340 steels with the shot-peening time are investigated. In the early stage, shear strain dissolves the Mo-rich carbides in the matrix, which reduces the mechanical properties of the shot-peened sample. In the later stage, sufficient shear strain induces grain refinement at the surface region, and the strength-ductility enhancement occurs owing to back-stress hardening evolution. The results show the shear straining during shot peening does not always enhance the strength of metallic alloys due to the dissolution of precipitates. Thus, the mechanical properties of shot-peened AISI4340 steel depends on the shot-peening time and an optimal processing time is required for obtaining a high strength–ductility combination.

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Wire Arc Additive Manufacturing (WAAM) produces metal components with crucial properties dependent on process parameters. Understanding the effects of these parameters on microstructure and mechanical properties is vital for optimizing WAAM. This study investigated the impact of varying travel speeds (TS) on the microstructure and mechanical properties of low carbon steel ER70S-6 alloy produced by WAAM process. The hypothesis centred on the impact of different TS values on heat input (HI) and cooling rates, and the subsequent effects on the resulting microstructure and mechanical properties of the deposited material. ER70S-6 alloy was deposited at three different TS: 120, 150, and 180 mm/min. Microstructure and mechanical properties (microhardness, tensile strength, elongation) were evaluated for each TS condition. Distinct microstructures were observed in the deposited samples, influenced by cooling rates at different TS. Distinct microstructures emerged in different regions of the deposits due to varying cooling rates at different TS. Higher TS (180 mm/min) significantly reduced pores and cracks while enhancing yield strength (YS) and ultimate tensile strength (UTS) up to 25.2 ± 0.77% elongation and 502.3 ± 3.17 MPa UTS, respectively. However, UTS remained slightly lower (93%) than the catalogued value for ER70S-6 (540 MPa), indicating a mild softening effect. TS significantly influenced the microstructure and mechanical properties of WAAM-produced ER70S-6 alloy. This study provides key insights into optimizing WAAM parameters for low carbon steel, paving the way for improved component production for diverse industrial applications.

The application of acoustic emission (AE) has applied to detect the yield and fracture of materials. In this study, the deformation characteristics of the magnesium alloy (AZ31B-H24) were characterized during tensile testing using AE signals. First, the AE signals of AZ31B-H24 sheets with thicknesses of 1 and 3 mm were investigated during tensile deformation. Numerous AE signals were generated during yielding and fracture, and their signal characteristics were analyzed. The signals for yield deformation and fracture deformation were observed to differ. The duration of the yield signal was longer than that of the fracture signal, and the energy of the yield signal was lower than that of the fracture signal. Based on these characteristics, the AE signals were categorized using the clustering method, an unsupervised learning algorithm, into four categories: Cluster 1 comprises the AE data obtained at the yield point of the magnesium alloy plate. Clusters 2 and 3 comprise those obtained in the stages from work hardening to failure. Finally, Cluster 4 comprises those obtained during the fracture point. The average value of each AE parameter was obtained. In the frequency domain, the peak frequency of the yield signal was higher than that of the fracture signal. The energy and amplitude of the signal were the highest in the fracture.

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