Search Results (152)

The hot deformation behavior of 6A82 aluminum alloy with a copper content of approximately 0.46 wt% was investigated by uniaxial compression tests in a temperature range of 320–530 °C and a strain rate range of 0.01–10 s⁻¹. The effects of deformation heating and friction on flow stress were analyzed and corrected. The results revealed that the reduction in flow stress due to deformation heating is more pronounced at high strain rates (≥1 s⁻¹) and low temperatures (≤390 °C) compared to other deformation conditions. The corrected data illustrated that deformation heating has a more significant influence on flow stress than friction. Hot deformation activation energy (Q) decreased from 322.63 to 236.22 kJ/mol with increasing strain. Based on the corrected flow stress, the evolution of processing maps and microstructural characterization were analyzed to evaluate workability and identify flow instabilities. It was found that strain has a slight effect on the efficiency of power dissipation, whereas the instability parameter varies considerably with increasing strain. The corresponding processing maps showed that the unstable regions undergo more complex variations than the stable regions throughout the hot deformation process. An optimum hot working domain was identified in the temperature range of 440–530 °C and strain rate of 0.01–0.37 s⁻¹. Under these deformation conditions, fine grains and uniformly distributed particles are formed through extensive dynamic recrystallization and coarsening of second phase particles, which facilitate dislocation motion and promote the formation of a sub-grain boundary. Full article

The present study systematically investigated the hot deformation behavior of GH2787 superalloy within the temperature range of 1060–1120 °C and strain rates of 0.1–10 s⁻¹. An Arrhenius-type constitutive equation was developed that accurately predicts the flow behavior, and the calculated thermal deformation activation energy Q is 364,401.19 J/mol. The hot working map was constructed based on the dynamic material model, which identified two preferred processing regions with power dissipation efficiency exceeding 0.3, and no flow instability was observed across the entire parameter range. Microstructural analysis reveals that the extent of dynamic recrystallization significantly increases with rising temperature and strain rate. Discontinuous dynamic recrystallization (via grain boundary bulging nucleation) serves as the dominant recrystallization mechanism in GH2787 superalloy during hot deformation, while continuous dynamic recrystallization (via subgrain rotation and coalescence) acts as a synergistic auxiliary mechanism, jointly driving microstructural evolution. This study provides important theoretical foundations for optimizing the hot working processes of GH2787 superalloy. Full article

During the initial extrusion stage of the as-sintered GNPs/TA15 composite, dislocations accumulated along the GNPs and grain boundaries, leading to the formation of a subgrain structure. As extrusion progressed, these subgrains underwent rotation and transformed into finer grains through dynamic recrystallization. This process resulted in significant grain refinement, with the average grain size decreasing from 3.04 μm to 1.30 μm. Concurrently, the Ti matrix adjacent to the GNPs initially flowed towards the GNPs and subsequently elongated along the extrusion direction (ED). Furthermore, the deformed α grains experienced slip along the {10$\overline{1}$0}⟨11$\overline{2}$0⟩ system, giving rise to the development of [10$\overline{1}$1]//ED and [20$\overline{2}$1]//ED α textures. This study elucidates the influence of GNPs on the microstructural evolution, particularly in terms of grain refinement and the formation of α textures, as a function of increasing extrusion ratios. Full article

This study systematically benchmarks the performance of four single soft magnetic powders—water-atomized Fe–Si–Cr (FeSiCr), silica-coated reduced iron powder (RIP), silica-coated carbonyl iron powder (CIP), and phosphate-coated CIP (CIP-P)—to establish quantitative relationships between powder attributes, deformation substructure, and high-frequency loss for molded power inductors (100 kHz–1 MHz). We prepared toroidal compacts at 200 MPa and characterized them by initial permeability (μ_i), core-loss (P_cv(f)), partitioning (P_cv(f) = K_hf + K_ef², K_h, $K_{\mathrm{e}}$: hysteresis and eddy-current loss coefficients), and EBSD (electron backscatter diffraction)-derived microstrain metrics (Kernel Average Misorientation, KAM; low-/high-angle grain-boundary fractions). Corrosion robustness was assessed using a 5 wt% NaCl, 35 °C, 24 h salt-spray protocol. Our findings reveal that FeSiCr achieves the highest μ_i across the frequency band, despite its lowest compaction density. This is attributed to its coarse particle size (D₅₀ ≈ 18 µm) and the resulting lower intragranular pinning. The loss spectra are dominated by hysteresis over this frequency range, with FeSiCr exhibiting the largest K_h, while the fine, silica-insulated Fe powders (RIP/CIP) most effectively suppress K_e. EBSD analysis shows that the high coercivity and hysteresis loss in CIP (and, to a lesser extent, RIP) are correlated with dense, deformation-induced subgrain networks, as evidenced by higher mean KAM and a lower low-angle grain boundary fraction. In contrast, FeSiCr exhibits the lowest KAM, with strain confined primarily to particle contact regions. Corrosion testing ranked durability as FeSiCr ≳ CIP ≈ RIP ≫ CIP-P, which is consistent with the Cr-rich passivation of FeSiCr and the superior barrier properties of the SiO₂ shells compared to low-dose phosphate. At 15 A, inductance retention ranks CIP (67.9%) > RIP (55.7%) > CIP-P (48.8%) > FeSiCr (33.2%), tracking a rise in effective anisotropy and—for FeSiCr—lower M_s that precipitate earlier roll-off. Collectively, these results provide a microstructure-informed selection map for single-powder formulations. We demonstrate that particle size and shell chemistry are the primary factors governing eddy currents (K_e), while the KAM-indexed substructure dictates hysteresis loss (K_h) and DC-bias superposition characteristics. This framework enables rational trade-offs between magnetic permeability, core loss, and environmental durability. Full article

Turbine blades are the most critical parts of aircraft engines. They are exposed to complex forces at the highest temperature and an aggressive environment. For this reason, the highest demands are placed on their structural quality. In single-crystalline nickel-based superalloy blades, the quality of the dendritic structure, crystal orientation, and local lattice parameter homogeneity is important because such properties affect the strength properties of the casting. For this reason, the structural attributes mentioned above were studied for novel, model-cored blades made of Ni-based superalloy. The blades were studied using scanning electron microscopy, the dedicated original X-ray Ω-scan method, the Laue diffraction, and the X-ray diffraction topography. The differences in the dendrites’ morphology and their array, revealing changes in dendrites’ arm size and arrangement, and changes in dendrites’ symmetry, were observed. Misoriented areas were identified, forming subgrains separated by low-angle boundaries. The location of the subgrains concerning the blade geometry and reasons for their creation were analyzed. The relation between the observed local changes in the lattice parameter and the creation of structural defects was determined. Aspects influencing the formation of structural defects that may reduce the durability of castings in specific areas of the cored blade airfoils have been discussed. Full article

This study investigated the influence of manganese (Mn) on microstructure evolution and property optimization in Al-0.6Mg-0.58Si-0.24Fe-xMn alloys under both as-cast and hot-extruded conditions. The balance mechanisms of Mn in tensile properties and electrical conductivity of Al-Mg-Si alloy were elucidated, achieving synergistic optimization of strength-elongation-conductivity. For non-equilibrium solidified as-cast alloys, JMatPro simulations coupled with Fe-rich phase size statistics reveal an inhibitory effect of Mn on β-Al₅FeSi phase formation. Matthiessen’s rule analysis quantitatively clarifies Mn-induced resistivity variations through solid solution and phase morphology modifications. In hot-extruded alloys, TEM characterization was used to analyze the structure of Al-Fe-Mn-Si quaternary compounds and clarify their combined effects with typical Mg₂Si phases on dislocation and subgrain configurations. The as-cast Al-0.6Mg-0.58Si-0.24Fe-0.18Mn alloy demonstrate comprehensive properties with ultimate tensile strength, elongation and electrical conductivity. The contributions of dislocations, grain boundaries and precipitates to resistivity are relatively minor, so the main source of resistivity in hot-extruded alloys is still Mn. The hot-extruded alloy containing 0.18 wt.% Mn still has better properties, with a tensile strength of 176 MPa, elongation of 24% and conductivity of 48.07 %IACS. Full article

This study systematically investigates the homogenization-induced Laves phase dissolution kinetics and recrystallization mechanisms in laser powder bed fusion (L-PBF) processed IN718 superalloy. The as-built material exhibits a characteristic fine dendritic microstructure with interdendritic Laves phase segregation and high dislocation density, featuring directional sub-grain boundaries aligned with the build direction. Laves phase dissolution demonstrates dual-stage kinetics: initial rapid dissolution (0–15 min) governed by bulk atomic diffusion, followed by interface reaction-controlled deceleration (15–60 min) after 1 h at 1150 °C. Complete dissolution of the Laves phase is achieved after 3.7 h at 1150 °C. Recrystallization initiates preferentially at serrated grain boundaries through boundary bulging mechanisms, driven by localized orientation gradients and stored energy differentials. Grain growth kinetics obey a fourth-power time dependence, confirming Ostwald ripening-controlled boundary migration via grain boundary diffusion. Such a study is expected to be helpful in understanding the microstructural development of L-PBF-built IN718 under heat treatments. Full article

In the Direct Energy Deposition (DED) process, the deposited material experiences intricate thermo-mechanical processes. Subsequent thermal cycling can trigger Dynamic Recrystallization (DRX) under suitable conditions, with specific strain and temperature parameters facilitating grain refinement and homogenization. While prior research has examined the impact of thermal cycling in continuous wave (CW) lasers on DRX in 316 L stainless steel deposits, this study delves into the effects of pulsed wave (PW) laser thermal cycling on DRX. Here, the thermo-mechanical response to PW cyclic thermal loading is empirically assessed, and the evolution of microstructure, grain morphology, geometric dislocation density (GND), and misorientation map during PW DED of 316 L stainless steel is scrutinized. Findings reveal that DRX is activated between the 8th and 44th thermal cycles, with temperatures fluctuating in the range of 680 K–750 K–640 K and grains evolving within a 5.6%–6.2%–5.2% strain range. After 90 thermal cycles, the grain microstructure undergoes significant alteration. Throughout the thermal cycling, dynamic recovery (DRV) occurs, marked by sub-grain formation and low-angle grain boundaries (LAGBs). Continuous dynamic recrystallization (CDRX) accompanies discontinuous dynamic recrystallization (DDRX), with LAGBs progressively converting into high-angle grain boundaries (HAGBs). Elevated temperatures and accumulated strain drive dislocation movement and entanglement, augmenting GND. The study also probes the influence of frequency and duty cycle on grain microstructure, finding that low pulse frequency spurs CDRX, high pulse frequency favors DRV, and the duty cycle has minimal impact on grain microstructure under PW cyclic thermal load. Full article

316LN stainless steel (316LN SS) with a gradient structure was produced by ultrasonic surface rolling processing (USRP). The surface quality of the 316LN SS specimen was improved significantly after the USRP. The experimental results showed that with an increasing number of rolling passes, the thickness of the gradient structure layer increased, and the microhardness decreased in a gradient from the surface to the matrix. The results also indicated that the optimal parameters were as follows: 220 rad/min lathe speed, 0.11 mm rolling space, 0.2 rad/min feed rate, and 5 rolling passes. Under these parameters, the tested surface residual compressive stress (SRCS) value was nearly 32 times higher than that achieved after conventional processing on the surface of 316LN stainless steel. Moreover, the microstructure exhibits an increase in the subgrain boundary density and low-angle grain boundaries (LAGBs, misorientation < 15°) of the steel, providing an easy way to enhance the properties, including the mechanical and corrosion resistance of 316LN stainless steel. Full article

In the framework of the geological mapping of sheet “n. 425—Asinara Island” (NW Sardinia, Italy) of the Italian National Geological Mapping Project (CARG Project), three late- to post-collisional Variscan intrusive units are recognized: (i) Castellaccio Unit; (ii) Punta Sabina Unit; and (iii) sheeted dyke complex. Granitoid rocks from these intrusive units intruded into the medium- to high-grade metamorphic micaschist and paragneiss and the migmatitic complex. A range of deformation microstructures from sub-magmatic to low-temperature subsolidus conditions are recognized. The main observed microstructures are represented by chessboard patterns in quartz and by feldspar sub-grain rotation dynamic recrystallization, indicative of deformation at high-temperature conditions (T > 650 °C). Solid-state high-temperature deformations (T > 450 °C) are provided by feldspar bulging, myrmekites, quartz grain boundary migration and sub-grain rotation dynamic recrystallization. Low-temperature sub-solidus microstructures (T < 450 °C) consist of quartz bulging, mica kinks, and feldspar twinning and bending. These features highlight that the three intrusive units recorded tectonic stresses, which affected the granitoids during cooling without developing a strong penetrative meso/microstructural fabric, as observed in other sectors of the Variscan orogen. The complete sequence of deformation microstructures, recorded in all intrusive units, suggests a weak but still ongoing deformation regime during granitoid emplacement in the Variscan orogen of northwestern Sardinia. These observations are similar to the features highlighted in other sectors of the southern Variscan belt and suggest a complex interplay between transpressional-induced exhumation of the middle/deep crust and magma intrusion. Full article

The present study aims to assess the impact of hot isostatic pressing (HIP) treatment on refractory high-entropy alloy (HEA) WTaMoNbV produced by the laser powder bed fusion (LPBF) process. This was carried out by examining the functional properties of this HEA in terms of mechanical and environmental performance. The microstructure of the tested HEA was evaluated using optical microscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD). Mechanical properties were examined via compression tests, while environmental behavior was evaluated by immersion tests and potentiodynamic polarization. The obtained results demonstrate that HIP treatment improved the alloy’s density from 11.27 to 11.38 g/cm³ and increased its ultimate compression strength by 11.5% (from 1094 to 1220 MPa). This modest favorable effect was attributed to the improvement in bulk properties by eliminating a large part of the sub-grain boundaries and reducing the amount of inherent printing defects, mainly in the form of internal cracking. The advantages offered by HIP were also manifested in surface quality improvement from N11 to N10 grades and enhanced environmental performance, reducing pitting density from 34,155 to 9677 pits/cm². Full article

This study systematically investigated the effects of the addition of the rare earth element yttrium (Y) on the microstructural evolution, mechanical properties, and corrosion behavior of as-extruded Al-5.6Zn-2.5Mg-1.6Cu-0.20Cr (wt.%) alloy through comprehensive characterization techniques, including X-ray diffraction (XRD), tensile testing, corrosion analysis, and electron microscopy. Microstructural characterization demonstrated that the incorporation of yttrium resulted in significant refinement of secondary phase particles within the as-extruded alloy matrix. Moreover, quantitative analysis revealed a substantial increase in low-angle grain boundary (LAGB) density, dislocation density, and the formation of subgrain structures. Notably, the volume fraction of η′ strengthening precipitates showed a marked increase, accompanied by a corresponding reduction in the width of precipitate-free zones (PFZs) along grain boundaries. Following the T74 aging treatment, the alloy with 0.1 wt.% yttrium addition exhibited a remarkable improvement in intergranular corrosion resistance, with the maximum corrosion depth reduced to 107.8 μm. However, it should be noted that the exfoliation corrosion resistance exhibited an inverse correlation with increasing yttrium content, suggesting a concentration-dependent behavior in corrosion performance. Full article

Variations in the microstructural morphology with building direction during selective laser melting (SLM) result in the anisotropic mechanical properties of the specimens, while heat treatment effectively reduces this anisotropy. The degree of anisotropy of the material can be assessed by calculating the variance (σ) of the mechanical properties (strength, hardness) at different building directions at different temperatures. In this work, the effects of heat treatment temperatures (450°, 750 °C, and 1050 °C) and building directions (0°, 45°, 60°, and 90°) on the microstructure, hardness, and tensile properties of selective laser melting (SLM) SS316L were investigated. Unheated SLM SS316L specimens exhibit significant anisotropy (σ_UTS = 16.67, σ_UE = 9.60, and σ_HV = 9.60), while heat treatment effectively reduces this anisotropy. As the heat treatment temperature increases, the melt pool boundaries disappear and grains become uniform at 750 °C, significantly reducing the anisotropy of the mechanical properties (σ_UTS = 14.65, σ_UE = 4.33, σ_HV = 6.72). At 1050 °C, the grain size increases slightly, resulting in a minor rise in anisotropy (σ_UTS = 14.93, σ_UE = 4.97, σ_HV = 8.39) compared to that seen at 750 °C. After heat treatment, the SLM SS316L specimen heated at 450 °C shows the lowest anisotropy. Notably, the specimens built in the 0° direction and heated at 450 °C exhibit finer sub-grains and enhanced mechanical properties, achieving a hardness of 244.43 HV, a tensile strength of 655.85 MPa, and an elongation of 21.25%. Full article

Continuous dynamic recrystallization (CDRX) is widely acknowledged to occur during hot forming and plays a significant role in microstructure development in alloys with moderate to high stacking fault energy. In this work, the flow stress and CDRX behaviors of the TC18 alloy subjected to hot deformation across a wide range of processing conditions are studied. It is observed that deformation leads to the formation of new low-angle grain boundaries (LAGBs). Subgrains rotate by absorbing dislocations, resulting in an increase in LAGB misorientation and the transition of some LAGBs into high-angle grain boundaries (HAGBs). The HAGBs migrate within the material, assimilating the (sub)grain boundaries. Subsequently, an internal state variable (ISV)-based CDRX model is developed, incorporating parameters such as the dislocation density, adiabatic temperature rise, subgrain rotation, LAGB area, HAGB area, and LAGB misorientation angle distribution. The values of the correlation coefficient (R), relative average absolute error (RAAE), and root-mean-square error (RMSE) between the anticipated true stress and measured stress are 0.989, 6.69%, and 4.78 MPa, respectively. The predicted outcomes demonstrate good agreement with experimental findings. The evolving trends of the subgrain boundary area under various conditions are quantitatively analyzed by assessing the changes in dynamic recovery (DRV)-eliminated dislocations and misorientation angles. Moreover, the ISV-based model accurately predicts the decreases in grain and crystallite sizes with higher strain rates and lower temperatures. The projected outcomes also indicate a transition from a stable and coarse-grained microstructure to a continuously recrystallized substructure. Full article

Continuous dynamic recrystallization (CDRX) forms a new recrystallized microstructure through the progressive increase in low-angle boundary misorientations (LAGBs) during the hot forming of metallic materials with high stacking fault energy (SFE), such as aluminum alloys. The present work investigates the effect of deformation parameters on the evolution of the dynamic recrystallization microstructures of an AA1050 aluminum alloy during compression at elevated temperatures. The alloy microstructure is investigated at deformation temperatures and strain rates in the range of 300 °C to 500 °C and 0.001 to 0.8 s⁻¹. A well-defined substructure and subsequent DRX grains provide indication that recrystallization can proceed with continued strain under high-temperature compression. At a strain rate of 0.1 s⁻¹, the DRX fraction is observed to be 0.25 at a temperature of 300 °C. This fraction increases to 0.32 as the temperature rises to 400 °C. The recrystallization mechanism is identified by analyzing the flow stress, the evolution of the subgrain misorientation angle, and the distribution of recrystallized grains. The observations of discontinuous dynamic recrystallization (DDRX) and CDRX under various deformation parameters are discussed. Moreover, the main substructure evolution laws observed from the high-temperature compression of an AA1050 Al alloy are summarized. Full article