Acta Metallurgica Sinica-English Letters最新文献

The complex compositions of high-entropy alloys (HEAs) enable a variety of phase structures like FCC single phase, BCC single phase, or duplex FCC + BCC phase. Accurate and efficient prediction of phase structure is crucial for accelerating the discovery of new components and designing HEAs with desired phase structure. In this work, five machine learning strategies were utilized to predict the phase structures of HEAs with a dataset of 296. Specifically, a two-step feature selection strategy was proposed, enabling pronounced improvement in the computational efficiency from 2047 to 12 iterations for each model while ensuring fewer input features and higher prediction accuracy. Compared with traditional valence electron concentration criterion, the prediction accuracy of collected dataset was highly improved from 0.79 to 0.98 for random forest. Furthermore, HEAs with compositions of Al_xCoCu₆Ni₆Fe₆ (x = 1, 3, 6) were developed to validate the prediction results of machine learning models, and the mechanical properties as well as corrosion resistance were investigated. It is found that the higher Al content enhances the yield strength but deteriorates corrosion resistance. The present two-step feature selection strategy provides an alternative method that is feasible for predicting the phase structure of HEAs with high efficiency and accuracy.

Improving the high-temperature performance of Inconel 718 (IN718) alloys manufactured via laser powder bed fusion (LPBF) has been the most concerned issue in the industry. In this study, the effects of Ti₂AlC inoculants on microstructures and high-temperature mechanical properties of the as-built IN718 composites were investigated. According to statistical results of relative density and unmelted particle area in as-built alloys, the optimal energy of 112 J/mm³ was determined. It was observed that the precipitation of the MC carbide was significantly enhanced with the addition of Ti₂AlC, restricting the precipitation of the Laves phase. The MC particles were uniformly distributed along the subgrain boundaries, which contributed to the dispersion strengthening. Meanwhile, the MC particles served as nucleation sites for heterogeneous nucleation during the solidification process, facilitating the refinement of columnar and cellular grains. The simulated Scheil–Gulliver curves showed that the precipitation sequence of phases did not change with Ti₂AlC inoculants. The as-built 1%Ti₂AlC/IN718 sample demonstrated an ultimate tensile strength of 998.78 MPa and an elongation of 18.04% at 650 °C, revealing a markedly improved mechanical performance compared with the LPBF-manufactured IN718 alloys. The high-temperature tensile strength of 1%Ti₂AlC/IN718 sample increased to 1197.99 MPa by heat treatment. It was suggested that dislocation strengthening and ordered strengthening were two most important reinforcement mechanisms.

For a long time, the conventional superplastic forming temperature for Ti alloys is generally too high (~ 900–920 °C), which leads to too long production cycles, heavy surface oxidation, and property reduction. In this study, an ultrafine bimodal microstructure, consisting of ultrafine equiaxed microstructure (0.66 μm) and 43.3% lamellar microstructure, was achieved in the Ti–6Al–4V alloy by friction stir processing (FSP). The low-temperature superplastic behavior and deformation mechanism of the FSP Ti–6Al–4V alloy were investigated at temperatures of 550–675 °C and strain rates ranging from 1 × 10⁻⁴ to 3 × 10⁻³ s⁻¹. The FSP alloy exhibited superplastic elongations of > 200% at the temperature range from 550 to 650 °C, and an optimal superplastic elongation of 611% was achieved at 625 °C and 1 × 10⁻⁴ s⁻¹. This is the first time to report the low-temperature superplasticity of the bimodal microstructure in Ti alloys. Grain boundary sliding was identified as the dominant deformation mechanism, which was effectively accommodated by the comprehensive effect of dislocation-induced β phase precipitation and dynamic spheroidization of the lamellar structure. This study provides a novel insight into the low-temperature superplastic deformation behavior of the bimodal microstructure.

The present work investigates the microstructural evolution and mechanical properties in a novel medium-Si 12%Cr reduced activation ferritic/martensitic steel cladding tube (Fe–11.8Cr–0.2C–1.4W–0.17Ta–0.2V–0.55Si–0.5Mn, wt%) during multi-pass cold rolling and annealing. The initial hot-extruded tube exhibited a full martensitic matrix with the prior austenite grain size of ~ 32 μm. After annealing, Cr₂₃C₆ and TaC particles were precipitated, which are basically unchanged (152–183 nm and 84–113 nm, respectively) during the manufacturing process. Meanwhile, with the cold-rolling strain (ε) increasing and subsequent annealing, the martensitic lath gradually diminishes, and the recrystallization volume fraction (f_r) is increased. Based on the static recrystallization kinetics model, a clear relationship between f_r and ε is established, in which the newly proposed kinetic equation demonstrates a strong correlation with the experimental results. Furthermore, the yield strength (σ_YS = 362 MPa) of the final annealed state was much lower than that (σ_YS = 482 MPa) of the initial annealed state, which can be attributed to the recrystallization from the martensitic matrix to ferritic matrix. Various strengthening mechanisms are further discussed, and the calculated strengths are in good agreement with the experimental results. This work provides a guidance for the optimization of cold-rolling and annealing treatments in the manufacture of cladding tube.

Magnesium (Mg) alloys are usually subjected to torsion deformation during processing or manufacturing. However, the torsional behavior remains underexplored at the atomic level compared to uniaxial deformation. In this work, atomistic simulations are employed to understand the deformation mechanism during torsion around (langle 10overline{1 }0rangle) and (langle 11overline{2 }0rangle) axes of Mg. We reveal that the onset of plasticity occurs near the surface due to stress-gradient effect and the deformation mechanisms are highly dependent on torsion axis. Specifically, the prismatic and basal slip dominate torsion around (left[ {11overline{2}0} right]) axis. During torsion around (left[10overline{1 }0right]) axis, (left{ {11overline{2}1} right}) twinning can be activated, whereas (left{ {10overline{1}1} right}) twinning is formed due to local stress but detwinned eventually. Moreover, extensive cross slip and interactions between basal and prismatic dislocations are observed and the associated mechanisms are discussed. These novel atomic-scale insights provide deeper understanding of the plastic deformation mechanisms of Mg under torsional loading.

This work investigated the effects of grain size (GS) on individual slip mode activities and the corresponding Hall–Petch coefficients in a rolled basal-textured pure Mg sheet under uniaxial tension using statistical slip trace analysis and electron backscatter diffraction. The studied regions covered a total of 1150 grains, in which 136 sets of slip traces were identified and analyzed in detail. The basal < a > slip always dominated the deformation, whose frequencies decreased (from 81.0% to 62.5%) with increasing GS (from 10 to 85 μm). The prismatic < a > slip activity increased from 10.8% (10 μm) to 27.5% (85 μm), while that for pyramidal II < c + a > slip was almost constant. Critical resolved shear stress (CRSS) ratios were estimated based on the identified slip activity statistics, and then the Hall–Petch coefficients (k) of individual slip modes were calculated. The k value for prismatic < a > slip (194 MPa·μm^1/2) was lower than that for pyramidal II < c + a > slip (309 MPa·μm^1/2), which implies that pyramidal II < c + a > slip was more GS sensitive. Twinning activity exhibited a positive correlation with GS, though it remained limited partly due to the unfavorable loading direction. The macroscopic Hall–Petch relationship was divided into two regions, i.e., the k value (753 MPa·μm^1/2) for the coarse-grain region (30–85 μm) was significantly larger than that (118 MPa·μm^1/2) of the fine-grain region (10–30 μm), which could be attributed to the transition of predominant deformation mechanisms from slip to slip combined twinning with increasing GS. This work provides detailed and quantitative experimental data of the GS effects on individual slip activities of Mg and provides new insights into the Hall–Petch relationship for individual slip modes.

In dry storage, spent fuel is typically stored in casks constructed from neutron absorbing materials (NAMs). The (B₄C+Al₂O₃)/Al composite, which incorporates in-situ amorphous Al₂O₃ (am-Al₂O₃) formed on fine aluminum powder as a reinforcing phase, can serve as an integrated structural and functional NAM for dry storage applications. Welding is crucial in the fabrication of these casks. In this study, friction stir welding was performed on (B₄C+Al₂O₃)/Al composite sheets at a welding speed of 50 mm/min and rotation rates ranging from 500 to 1000 r/min. The microstructure of the weld joints was analyzed, and the intrinsic relationship between fracture behavior and microstructure was elucidated. Results showed that defect-free joints were achieved at rotation rates of 500 and 750 r/min, while tunnel defects were observed at 1000 r/min. The ultimate tensile strength of the joint welded at 500 r/min was 205.7 MPa, with a strength efficiency of 82%. Microstructural analysis revealed that the grains within the nugget zones (NZs) coarsened and the Al₂O₃ network was disrupted due to the welding thermo-mechanical effect, resulting in softening within the NZs. Fracture locations for all three joints were consistently observed at the NZ boundary on the advancing side (AS). Finite element simulations confirmed that cracks propagated along the NZ boundary on the AS, where stress concentration occurred during tensile testing.

Although Ti scaffolds offer great potential in orthopedic applications, their porous nature raises new questions, such as low relative density and high surface area. This work investigated the gradual decrease in the strength of Ti scaffolds during long-term immersion in Hank’s solution. After 180-day immersion, the samples have a 23.3% and 26.6% reduction in yield strength and a 9.0% and 11.2% reduction in compressive strength in dynamic and static solutions, indicating potential failure during the long-term service. A large exposure area to the solution leads to a high corrosion rate, which results in the consumption of the scaffolds and, consequently, decreased strength. Although the covered deposits on the scaffolds reduce the ion release to some extent, the scaffolds still have a slowly ongoing decrease in strength. Based on the durability considerations, some methods, such as decreasing porosity and surface treatments, are proposed to alleviate this phenomenon of Ti scaffolds.

In this study, cryogenic cycling treatment was used to process the hot-rolled Mg-4.5Al-2.5Zn alloy sheets to research the influence on mechanical properties and microstructure. Optical microscopy, electron back-scatter diffraction and transmission electron microscopy were applied to characterize the microstructures and analyze the mechanisms. The consequences indicate that the cryogenic cycling treatment has significantly influence on improving the mechanical properties. With the cycle of cryogenic cycling treatment increasing to 5 cycles, the sample processed by 3 cycles presents the highest ductility (~ 18.6%), while the 4-cycle one shows the highest strength (~ 311.8 MPa). The improvement can be attributed to fine grains, introduced high-density dislocation, 9.8%-fraction low-angle grain boundaries (LAGBs), the precipitation of Mg₁₇Al₁₂ phase and the texture with the intensity of 17.5. Although the average grain sizes of the samples processed by cryogenic cycling treatment have no obvious difference, internal stress variations induced by cryogenic cycling treatment significantly influence LAGBs, the basal texture evolution, and the prismatic < a > slip, pyramidal < c > slip and pyramidal < c + a > slip activation.

To develop a melting-based larger-scale fabrication process for oxide dispersion strengthened (ODS) steel, this study proposed a method of zone melting with built-in precursor powder (ZMPP), followed by hot forging and aging treatments. A 50 kg ingot was successfully prepared, highlighting the scalability of this innovative process. Microstructural analysis revealed a predominantly lath martensite matrix with a small amount of ferrite in the hot-forged ODS steel, without oxide particle aggregation. Aging at 750 °C resulted in the formation of sub-micron-sized Cr₂₃C₆ particles at grain boundaries and martensitic lath interfaces, accompanied by a high-density (7.64 × 10²³ m⁻³) nano-scale (~ 6 nm) Y–Si–O complex oxides after 25 h. Additionally, the hot-forged sample exhibited a high yield strength (871 MPa) but limited ductility (5.0%). Aging treatments led to an increase in ductility but a decrease in yield strength. Notably, prolonged aging maintained the strength level of steels while enhancing ductility, with a 23.3% total elongation observed after 25 h. The novel ZMPP method, preparing high-quality ODS steels with uniform microstructure and good mechanical properties, provided a new avenue for large-scale production of ODS steels.