Acta Metallurgica Sinica-English Letters最新文献

In this work, the impact of extrusion and post-extrusion heat treatment (T6) on the microstructure and mechanical properties of the Al-1.2Mg-0.8Si-0.5Mn alloy with different Cu contents (0, 0.6, 1.3 and 2.0 wt%) was studied. Microstructure characterization showed that all extruded alloys exhibited elongated grain structure with an average grain size of ~ 4.8 μm. The dominant texture components were deformation texture (A*, Copper and P texture), while the proportion of random texture initially increased and then decreased with increasing Cu content. After T6 treatment, the grain size of the four alloys increased significantly, but the growth trend decreased with increasing Cu content, and the textures transformed into recrystallized textures (Cube, A and Goss texture). Tensile testing revealed that the designed T6 alloys with 2.0% Cu content exhibited an excellent strength-ductility balance, i.e., a yield strength of 342.9 MPa, an ultimate tensile strength of 424.8 MPa and an elongation of 15.9%. The enhanced strength was mainly attributed to fine grain strengthening, solid solution strengthening and aging strengthening mechanisms. The superior ductility was due to the pinning effect of fine precipitates and high dislocation accommodation capacity caused by heat treatment.

The transpassivation and pitting corrosion behavior of a high-nitrogen stainless steel (HNS), Fe18Cr15Mn3Mo0.92N, were systematically investigated by electrochemical analysis, morphology observation, and X-ray photoelectron spectroscopy surface analysis. It was surprisingly found that no pitting corrosion occurred in the transpassivation region of HNS. This electrochemical corrosion behavior is untypical for stainless steels, i.e., the traditional critical pitting potential method was invalid for HNS. Both N and Cr enrichments in the transpassivation film on HNS were found extremely higher than those in the passivation film. The N existed in the form of [CrN] complex, which could stabilize the above both films. Besides, the corrosion product of N was detected as NH₃ that exhibited an effective corrosion inhibition effect. On this basis, although the transition of Cr from 3-valent to 6-valent was confirmed, the transpassivation film on HNS still maintained it high stability and no pitting was found to occur. Therefore, the real pitting resistance of HNS should be higher than the expected before. And the stable transpassivation film played an important role in its untypical pitting corrosion resistance.

The continued existence of high-energy radiation in nuclear reactors at high temperatures results in the formation of radiation-induced voids, which will further lead to inevitable swellings of polycrystalline structural components and thus premature failures. A deep understanding of the effect of temperature and grain boundary on void evolution in irradiated copper is significant for preventing this kind of failures. Here, the phase-field method was employed to study void evolution in irradiated copper under different temperatures and grain sizes. The results show that, due to the different sensitivities of point defect production rate and vacancy diffusion rate to temperature changes, both the nucleation-growth rate and the coarsening rate during void evolution increase first and then decrease with increasing temperature; moreover, the nucleation mechanism exhibits site-saturated nucleation at low temperatures while continuous nucleation at high temperatures. The presence of grain boundary can accelerate the emergence of void because grain boundaries can absorb more interstitials than vacancies. The finer the grain size, the stronger inhibitory effect of grain boundaries on the growth rate of void, due to the formation of void denuded zone near grain boundaries. At high temperatures, the growth rate of void in fine grains is significantly reduced due to the increase of vacancy diffusion rate and the enhancement of sink effect of grain boundary on vacancy.

Pyrochemical reprocessing utilizing a molten LiCl–KCl eutectic medium is regarded as the most promising approach for recovering uranium and transuranic elements from spent metallic nuclear fuels. However, the harsh corrosiveness of molten chloride poses a significant challenge to the durability of structural materials. Herein, we report the corrosion behavior of 304 SS, 316H SS and Inconel 800H in LiCl–KCl eutectic salt at 550 °C for 100 h under an argon atmosphere. Experimental results indicate that all three materials can form a rather continuous Cr₂O₃-based scale through oxidation reaction at the beginning, but only the scale developed on 800H maintains excellent protection against corrosion throughout the entire exposure period. In contrast, both 304 SS and 316H SS experience considerable active dissolution on the bare substrate under a detached scale. We suggest that the primary reasons for the outstanding resistance of 800H to molten salt corrosion are the high concentration of noble Ni in the system, which lowers the inclination for active dissolution, and the beneficial addition of Al, which accelerates the formation of a less defective Cr₂O₃-based scale. Our work offers an in-depth understanding on the corrosion performance of high-Cr alloys in molten chloride, insights critical for the selection and subsequent development of structural materials for pyrochemical reprocessing applications.

Indirect additive manufacturing (AM) methods have recently attracted attention from researchers thanks to their great potential for cheap, straightforward, and small-scale production of metallic components. Atomic diffusion additive manufacturing (ADAM), a variant of indirect AM methods, is a layer-wise indirect AM process recently developed based on fused deposition modeling and metal injection molding. However, there is still limited knowledge of the process conditions and material properties fabricated through this process, where sintering plays a crucial role in the final consolidation of parts. Therefore, this research, for the first time, systematically investigates the impact of various sintering conditions on the shrinkage, relative density, microstructure, and hardness of the 17-4PH ADAM samples. For this reason, as-washed samples were sintered under different time–temperature combinations. The sample density was evaluated using Archimedes, computed tomography, and image analysis methods. The outcomes revealed that sintering variables significantly impacted the density of brown 17-4PH Stainless Steel samples. The results indicated more than 99% relative densities, higher than the value reported by Markforged Inc. (~ 96%). Based on parallel porosities observed in the computed tomography results, it can be suggested that by modifying the infill pattern during printing, it would be possible to increase the final relative density. The microhardness of the sintered samples in this study was higher than that of the standard sample provided by Markforged Inc. Sintering at 1330 °C for 4 h increased the density of the printed sample without compromising its mechanical properties. According to X-ray diffraction analysis, the standard sample provided by Markforged Inc. and “1330 °C—4 h” one had similar stable phases, although copper-rich intermetallics were more abundant in the microstructure of reference samples. This study is expected to facilitate the adoption of indirect metal AM methods by different sectors, thanks to the high achievable relative densities reported here.

B₄C/Al composites are widely utilized as neutron absorbing materials for the storage and transportation of spent nuclear fuel. In order to improve the high-temperature mechanical properties of B₄C/Al composites, in-situ nano-Al₂O₃ was introduced utilizing oxide on Al powder surface. In this study, the Al₂O₃ content was adjusted by utilizing spheroid Al powder with varying diameters, thereby investigating the impact of Al₂O₃ content on the tensile properties of (B₄C + Al₂O₃)/Al composites. It was found that the pinning effect of Al₂O₃ on the grain boundaries could hinder the recovery of dislocations and lead to dislocation accumulation at high temperature. As the result, with the increase in Al₂O₃ content and the decrease in grain size, the high-temperature strength of the composites increased significantly. The finest Al powder used in this investigation had a diameter of 1.4 μm, whereas the resultant composite exhibited a maximum strength of 251 MPa at room temperature and 133 MPa at 350 °C, surpassing that of traditional B₄C/Al composites.

There is a growing demand for degradable membranes with sufficient mechanical properties to guide tissue regeneration in dental surgery. In the present work, a two-stage rolling process in which the first rolling stage (FRS) adopted a reduction rate of 30% for six passes at various temperatures, while the second rolling stage was rolling at 200 °C for two passes, was employed to prepare a 150 μm-grade Mg–2.0Zn–0.5Y–0.5Nd (ZE21B) Mg alloy sheets for guided tissue regeneration membrane. The microstructure of the thin sheets was gradually refined with increasing rolling passes, and the thin sheets that were rolled at different FRS temperatures exhibit an ellipse texture. The thin sheets rolled at 350 °C for FRS show low elongation due to premature fracture caused by the coarse second phase particles. On account of uniform and fine grains, the thin sheets rolled at 400 °C for the FRS have proper mechanical properties: yield strength of 214.6 ± 8.5 MPa, ultimate tensile strength (UTS) of 246.8 ± 10.3 MPa and elongation to failure of 28.3 ± 1.2%. When rolling at 450 °C for FRS, proper ductility of the thin sheets has been acquired, followed by a decline in UTS since a bimodal structure with fine and coarse grain was developed. Immersion tests demonstrated the FRS temperature had no significant effect on the corrosion behavior and corrosion rate of Mg alloy sheets after 7 days’ immersion in artificial saliva solution. This research has great significance for the production of degradable Mg sheets for guided tissue regeneration membrane.

The knowledge of the phase selection and microstructure evolution of Zr–Fe eutectic alloys is still poorly understood. The presumed eutectic alloy with a nominal composition of Zr_76.0Fe_24.0 was discovered to contain a significant proportion of α-Zr dendrites. Hereby, phase selection and microstructure evolution dependance on composition for Zr–Fe eutectic alloys was experimentally determined by using differential scanning calorimetry (DSC) and meticulous electron microscopes. Eight alloys, spanning the composition range of 73.5–74.7% Zr, were examined to investigate microstructure evolution and non-isothermal crystallization kinetics. Results indicate that in alloys ranging from Zr_73.5Fe_26.5 to Zr_73.9Fe_26.1, the primary FeZr₂ phase demonstrates preferential growth, followed by eutectic microstructure formation during liquid alloy solidification. The volume fraction of FeZr₂ dendrites decreases as the Zr content increases. Conversely, in alloys ranging from Zr_74.0Fe_26.0 to Zr_74.7Fe_25.3, primary β-Zr dendrites preferentially grow, followed by a eutectic reaction in the remaining liquid phase. The content of α-Zr dendrites reduces with decreasing Zr content. As mentioned above, a critical composition range for phase selection is defined as Zr_xFe_100.0−x (73.9 < x < 74.0).

This study investigated the microstructure and mechanical properties of AlNbTiVZr series high-entropy alloys (HEAs) through both experimental studies and density functional theory calculations. Significant improvements in the microstructures and mechanical properties were achieved for the AlNbTiVZr series HEAs by meticulously adjusting the alloy composition and employing homogenization heat treatment. Notably, the specimen designated as Al_0.5NbTiVZr_0.5 demonstrated excellent mechanical properties including a compressive yield strength of 1162 MPa and a compressive strength of 1783 MPa. After homogenization heat treatment at 1000 °C for 24 h, the Al_0.5NbTiVZr_0.5 alloy exhibits brittle-to-ductile transition. Further atomic-scale theoretical simulations reveal that the decrease of Al content intrinsically enhances the ductility of the alloys, thereby indicating that the mechanical properties of the AlNbTiVZr series HEAs were significantly influenced by the chemical composition. Additionally, specific atomic pair formations were observed to adversely affect the microstructure of the AlNbTiVZr series HEAs, particularly in terms of ductility. These findings provide valuable insights for the design and optimization of light weight HEAs, emphasizing the synergistic adjustment of alloy composition and heat treatment processes to achieve a balance between the strength and ductility.