Search Results (64)

Accurate prediction of the stacking fault energy (SFE) is critical for controlling deformation mechanisms, specifically transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP), in high-manganese (high-Mn) austenitic steels, which are of growing importance in automotive and structural applications that demand exceptional strength–ductility combinations. This study presents a systematic comparative evaluation of six supervised machine learning (ML) models—Multiple Linear Regression (MLR), Random Forest (RF), Extra Trees (ETs), Gradient Boosting (GB), Support Vector Regression (SVR), and a stacking ensemble—trained on a curated, outlier-cleaned experimental database of Fe-Mn-C-Si-Al-Cr-Ni-N spanning SFE values from 5.0 to 63.0 mJ/m² (mean 23.7 ± 11.2 mJ/m²). After Z-score outlier removal (|Z| > 3) and 80/20 train–test splitting with nested 5-fold cross-validation hyperparameter optimization using GridSearchCV, ET and GB achieved training R² values of 0.988 and 0.990, respectively, confirming that SFE is highly predictable from alloy composition alone. The stacking ensemble delivered the best generalization on the independent held-out test set (test R² = 0.603, RMSE = 5.60 mJ/m², MAE = 4.86 mJ/m²), outperforming all the individual learners. Random Forest feature importance analysis identified Al (22.3%), Fe (20.5%), and Mn (17.7%) as the three most influential compositional variables, collectively explaining 60.6% of the predicted variance. Pearson correlation analysis confirmed that Al was the strongest individual linear predictor (r = +0.421, p < 0.001), whereas Fe showed a significant negative correlation (r = −0.327, p < 0.001). Mn, C, and the remaining elements showed no statistically significant linear correlations with SFE, underscoring the dominance of nonlinear compositional interactions. Composition–SFE design maps derived from the GB model delineate the TRIP/TWIP regime boundaries in the Mn–C and Mn–Al composition spaces, providing a validated computational tool for targeted high-Mn steel alloy design. Full article

This study systematically investigates the effect of trace Ti addition on the impact toughness and underlying deformation mechanisms of high-Mn austenitic steel from 298 K to 4.2 K through instrumented Charpy impact testing, dynamic J-R curve analysis, and multi-scale microstructural characterization (SEM, TEM). The results show that Ti addition leads to the formation of Ti(C,N) precipitations, which act as microcrack initiation sites and significantly reduce the impact-absorbed energy at room temperature (298 K) from 249 J to 189 J. However, as the temperature decreases to liquid nitrogen (77 K) and liquid helium (4.2 K) temperatures, the impact toughness of the Ti-added steel does not deteriorate further and remains comparable to that of the Base steel. This temperature-dependent behavior originates from a transition in the dominant deformation mode. At room and moderately low temperatures, deformation is primarily governed by dislocation slip, whose strong interaction with coarse precipitates leads to premature cracking. At cryogenic temperatures, the significantly reduced stacking fault energy (SFE) shifts the deformation mechanism to the predominant formation of high-density nano-twins. These dense deformation twins enhance the matrix via the dynamic Hall–Petch effect and mitigate the detrimental effect of precipitates by alleviating interactions between dislocations and precipitates. Full article

By optimizing the carburizing heat treatment process, the grain size of the carburized layer of M50NiL steel was successfully refined to the sub-micron level. The mechanism for the generation of a large number of sub-micron crystal regions (SMCR) is that dislocations are entangled and linked due to the pinning effect of nanometer-sized carbides. In this study, a stacking fault energy (SFE) model for austenite in M50NiL steel was established. First-principles calculations were employed to investigate the effects of alloying elements, as well as the position and quantity of carbon (C) atoms, on the generalized stacking fault energy (GSFE). The variations in SFE were further analyzed in combination with differential charge density calculations. The simulation results revealed that the addition of alloying elements excluding nickel led to a reduction in the unstable stacking fault energy. Differential charge density analysis indicated that this decrease was associated with the weakening of Fe–Fe bonds in the L0 layer, where stacking faults occurred. When C atoms are interstitially dissolved near the L0 layer, the Fe–Fe bonds near the L0 layer are enhanced, and the unstable stacking fault energy is correspondingly increased. Compared with the pure iron system, the combined effect of alloying elements and C atoms in M50NiL steel maintained a relatively low level of both the unstable stacking fault energy and the stacking fault formation barrier, provided that C atoms were not dissolved in the L1 layer. This condition was favorable for dislocation slip. Meanwhile, the stable stacking fault energy significantly increased, enhancing the stability of austenite. Based on these simulation results, the relationship between the GSFE of austenite in M50NiL steel and the formation of subgrains and twins within the submicron crystalline regions of the carburized layer was discussed. Full article

Super duplex stainless steels (SDSSs) can be effectively fabricated via Laser Powder Bed Fusion (LPBF), yet achieving the necessary phase balance remains a critical metallurgical challenge. The rapid solidification rates inherent to the LPBF process typically result in a predominantly ferritic microstructure. Since CSL boundaries—specifically high-symmetry ∑3 twins—form preferentially in the austenite phase, achieving a high fraction of these boundaries in the ferritic as-built LPBF state remains a significant challenge. To address this limitation, we implemented a feedstock modification strategy by mechanically blending 2507 SDSS powder with 3 and 6 wt.% elemental nickel prior to LPBF processing. The microstructural evolution, phase distribution, and boundary character were comprehensively evaluated using Electron Backscatter Diffraction (EBSD). Analysis revealed that the addition of nickel did not compromise densification, with all samples achieving relative densities exceeding 99.2%. While the base alloy remained 98.5% ferritic, the addition of 6 wt.% Ni successfully promoted the formation of approximately 31.1 wt.% austenite, characterized by intragranular laths formed via a massive-like transformation mechanism⁶. Crucially, despite the theoretical increase in Stacking Fault Energy (SFE) associated with high nickel content, the restored austenite phase exhibited a significant fraction of high-symmetry CSL ∑3 twin boundaries (rising to 7.05%). These findings demonstrate that compositional modification can overcome the kinetic limitations of the LPBF process, facilitating the development of a favorable Grain Boundary Character Distribution (GBCD). Full article

This study investigates the microstructure and mechanical properties of copper (Cu) and graphene/Cu (Gr/Cu) composites produced via high-pressure torsion (HPT) under 5 GPa at room temperature. Microstructural analysis revealed significant grain refinement, with average grain sizes of 0.39 μm for pure Cu and 0.35 μm for Gr/Cu composite. The Gr/Cu composite exhibited slightly higher microstrains and effective stacking fault energy (SFE). Tensile tests showed ultimate tensile strengths of 689 MPa (pure Cu) and 674 MPa (Gr/Cu), with the latter demonstrating improved ductility (~10% elongation). Ab initio calculations confirmed a 27% increase in SFE for Gr/Cu, aligning with experimental results. These findings highlight the potential of Gr/Cu composites for applications requiring high strength and efficient heat dissipation. Full article

This study employs first-principles calculations combined with the Special Quasirandom Structure (SQS) technique to investigate the impact of three interstitial elements C, N, and O, on the mechanical properties and stacking fault energy (SFE) of NiCoCr medium-entropy alloys. The results indicate that non-metallic O, C, and N tend to occupy octahedral interstitial sites, which can effectively release stress concentration and enhance the strength and deformability of the material. Differential charge density analysis shows that the dissolution of C, N, and O significantly alters the surrounding electronic environment, strengthening the interaction between solute atoms and metal atoms, thereby hindering dislocation glide and increasing the strength and hardness of the material. Elastic property analysis indicates that NiCoCr alloys doped with C, N, and O exhibit good ductility and anisotropic characteristics. Furthermore, the study of stacking fault energy reveals that the doping with C, N, and O can significantly increase the stacking fault energy of NiCoCr alloys, thereby optimizing their mechanical properties. These findings provide theoretical evidence for the design of advanced high-entropy alloys that combine high strength with good ductility. Full article

As a promising candidate for next-generation aviation structural materials, lightweight refractory high entropy alloys (HEAs) exhibit high strength, low density, and excellent high-temperature performance. In this study, we investigated the influence of local chemical ordering on the properties of Ti–V–Zr–Nb–Al HEAs using Monte Carlo (MC) simulations based on density functional theory (DFT) calculations. We established that the chemical short-range ordering (SRO) in Ti–V–Zr–Nb–Al HEAs increases with the Al content, resulting in a gradual increase in stacking fault energy (SFE). This theoretical investigation suggests that SRO can be utilized to tailor the performance of HEAs, thereby providing guidance for the scientific design of macroscopic mechanical properties. Full article

Stacking fault energy (SFE) can significantly affect the plastic deformation mechanism of metal materials and then affect their mechanical properties. Changing the stacking fault energy by microalloying rare earth elements is an effective means to control the plastic deformation mechanism and optimize the mechanical properties of the metal materials. Based on first principles, the HRTEM technique and GPA method, the effects of Nd content on the SFE and microstructure of Cu alloys were studied. The results show that the Nd element can significantly reduce the SFE of pure copper. But the change in the Nd element content has little influence on the SFE of the alloy. In addition, with the increase in Nd content, the grain size and twin size are refined. The GPA results show that strong tensile strain is formed inside the twin, and alternating tensile strain and compressive strain structures are formed on the (-11-1) plane at the tip of the twin. Full article

Stacking fault energy (SFE) is a critical property governing deformation mechanisms and influencing the mechanical behavior of materials. This work presents a unified framework for understanding and predicting SFE based solely on an electronic structure representation. By integrating density of states (DOS) spectral data, dimensionality reduction techniques, and machine learning models, it was found that the SFE behavior is indeed represented within the electronic structure and that this information can be used to accelerate the prediction of SFE. In the first part of this study, we established quantitative relationships between electronic structure and microstructural features, linking chemistry to mechanical properties. Using principal component analysis (PCA) and uniform manifold approximation and projection (UMAP), we identified key features from high-resolution vector representation of DOS data and explored their correlation with SFE. The second part of this work focuses on the predictive modeling of SFE, where a machine learning model trained on UMAP-reduced features achieved high accuracy (R² = 0.86, MAE = 15.46 mJ/m²). To bridge length scales, we extended this methodology to predict SFE in alloy systems, leveraging single-element data to inform multi-element alloy design. We illustrate this approach with Cu-Zn alloys, where the framework enabled rapid screening of compositional space while capturing complex electronic structure interactions. The proposed framework accelerates alloy design by reducing reliance on costly experiments and ab initio calculations. Full article

This study examines the mechanical behavior and deformation mechanisms of hot-forged 304L stainless steel for cryogenic applications such as LNG storage and low-temperature structural systems. Tensile testing revealed a significant strength increase from 618 MPa at room temperature to 1432 MPa at cryogenic temperatures, with elongation decreasing from 83.7% to 23.3%. Charpy impact testing showed a 28% reduction in absorbed energy at cryogenic temperatures due to enhanced strain-induced martensitic transformation (SIMT). The observed mechanical responses are attributed to reduced stacking fault energy (SFE) at lower temperatures, which promotes SIMT, deformation twinning, and dislocation interactions, affecting material strength and toughness. SEM and EBSD analysis confirmed extensive martensitic transformation, increased deformation twinning, and reduced remaining austenite, indicating a γ → ε → α’ transformation pathway that governs strain hardening. The high strain rate during Charpy impact testing induced localized adiabatic heating, partially suppressing SIMT and modifying fracture behavior by enhancing localized plasticity. These findings emphasize the interplay between SFE, strain rate, and phase transformation in governing the cryogenic mechanical performance of 304L stainless steel. Full article

The drawability and microstructural homogeneity of twinning-induced plasticity (TWIP) steel were improved during the wire drawing process by utilizing a temperature gradient along the wire’s radial direction. The surface temperature of the wire increased by applying heat to the die during the drawing process, thereby creating a temperature gradient across the wire during wire drawing. The drawability of the wire subjected to the temperature gradient with warm die (WD) increased by approximately 33% compared to that of conventional wire drawing with cold die (CD). The higher temperature of about 300 °C at the surface region of the wire with the WD suppressed the twinning rate at the surface region owing to the increase in the stacking fault energy (SFE) from 34 to 55 mJ/m², leading to a uniform twinning rate along the wire’s radial direction compared with the CD wire, finally resulting in the improvement of the homogeneity in the microstructure and mechanical properties of TWIP steel. As a result, the drawability of the TWIP steel improved. Therefore, the general conclusion was derived that controlling the SFE within the area of the workpiece by tailoring the temperature can improve the formability in TWIP steels during the plastic forming process. Full article

Miniaturized components for enhanced integrated functionality or thin sheets for lightweight applications often consist of face-centered cubic metals. They exhibit good strength, corrosion resistance, formability and recyclability. Microfabrication technologies, however, may introduce cold work or detrimental heat-induced lattice defects into the material, with consequences for the mechanical properties. Austenitic stainless steels (1.4310, 1.4301) and aluminum alloys (EN AW-5005-H24, EN AW-6082-T6) were selected for this study. The influence of pulsed fiber laser cutting, microwaterjet cutting, and annealing on the strain–stress behavior was investigated. The micro-tensile test setup comprised a flex-structure force sensor, a laser extensometer, and a dedicated sample holder. Fiber laser cut 1.4310 samples exhibited early failure at low fracture strain in narrow shear band zones. The shear band zones were detectable on the sample surface, in the laser extensometer images, in the horizontal sections of the stress–strain curves, and in the microstructure. Inside the shear band zones, grains were strongly elongated and exhibited numerous parallel planar defects. Heat-induced chromium carbides, in combination with low stacking fault energy (SFE) and elevated carbon content, favored shear band zone formation in 1.4310. In contrast, microwaterjet cut high SFE materials EN AW-5005-H24 and EN AW-6082-T6, as well as low-carbon austenitic stainless steel 1.4301, exhibited uniform plastic deformation. Full article

Grains of commercially pure titanium (CP-Ti) can be refined via rotary-die equal-channel angular pressing (RD-ECAP) to meet higher application requirements. However, the grain refinement mechanism of CP-Ti during RD-ECAP has not been fully studied. Herein, CP-Ti was processed up to four passes by RD-ECAP to obtain an ultrafine-grained structure. The microstructure evolution, refinement mechanism, and dynamic recrystallization (DRX) behavior was investigated by TEM and EBSD analysis. The results revealed that after two passes, banded structures with numerous LAGBs inside were detected, while after four passes, most grains were equiaxed with HAGBs and the average grain size was about 0.5 μm. The fraction of HAGBs reached 78.6% for the four-pass sample, which was higher than that of two-pass sample. The fraction of deformed grains declined and the proportion of recrystallized grains increased as the pass number increased from two to four. The misorientation gradient analysis showed that subgrains with LAGBs evolved into new grains with HAGBs gradually to generate ultrafine grains. The refinement mechanism of CP-Ti during RD-ECAP can be concluded as continuous DRX (CDRX). In addition, the relationship between DRX type and the processing conditions as well as stacking fault energies (SFEs) of metals was innovatively explored, providing a new approach for predicting microstructure. Full article

For materials with high stacking fault energy (SFE), such as aluminum alloys, dynamic recovery (DRV) and dynamic recrystallization (DRX) are essential softening mechanisms during plastic deformation, which lead to the continuous generation and refinement of newborn subgrains (2° ˂ misorientation angle ˂ 15°). The present work investigates the influence of compression parameters on the evolution of the substructures for a 1050 aluminum alloy at elevated temperatures. The alloy microstructure was investigated under deformation temperatures ranging from 300 °C to 500 °C and strain rates from 0.01 to 0.1 s⁻¹, respectively. A well-defined substructure and subsequent subgrain refinement provided indication of the evolution laws of the substructure under high-temperature compression. Corresponding experimental data on the average subgrain size under various compression conditions were obtained. Two different independent average subgrain size evolution models (empirical and substructure-based) were used and applied with several internal state variables. The substructure model employed physical variables to simulate subgrain refinement and thermal coarsening during deformation, incorporating a corresponding dislocation density evolution model. The correlation coefficient (R) and root mean square error (RMSE) of the substructure-based model were calculated to be 0.98 and 5.7%, respectively. These models can provide good estimates of the average subgrain size, with both predictions and experiments reproducing the expected subgrain size evolution using physically meaningful variables during continuous deformation. Full article

High-manganese steel (high-Mn) is valuable for its excellent mechanical properties in cryogenic environments, making it essential to understand its deformation behavior at extremely low temperatures. The deformation behavior of high-Mn steels at extremely low temperatures depends on the stacking fault energy (SFE) that can lead to the formation of deformation twins or transform to ε-martensite or α′-martensite as the temperature decreases. In this study, submerged arc welding (SAW) was applied to fabricate thick pipes for cryogenic industry applications, but it may cause problems such as an uneven distribution of manganese (Mn) and a large weldment. To address these issues, post-weld heat treatment (PWHT) is performed to achieve a homogeneous microstructure, enhance mechanical properties, and reduce residual stress. It was found that the difference in Mn content between the dendrite and interdendritic regions was reduced after PWHT, and the SFE was calculated. At cryogenic temperatures, the SFE decreased below 20 mJ/m², indicating the martensitic transformation region. Furthermore, an examination of the deformation behavior of welded high-Mn steels was conducted. This study revealed that the tensile deformed, as-welded specimens exhibited ε and α′-martensite transformations at cryogenic temperatures. However, the heat-treated specimens did not undergo α′-martensite transformations. Moreover, regardless of whether the specimens were subjected to Charpy impact deformation before or after heat treatment, ε and α′-martensite transformations did not occur. Full article