Search Results (267)

The effects of (Zn + Mg) total content (9.6–11.7 wt.%) combined with multi-directional forging (MDF) on the microstructure and properties of high-strength Al–Zn–Mg–Cu alloys were systematically investigated. Our results demonstrate that the alloy obtains significant grain refinement, which is attributed to the dynamic recrystallization in the MDF process. Specifically, Al-8.6Zn-1.55Mg-1.9Cu-0.11Zr (Zn + Mg = 10.15 wt.%) obtains the maximum recrystallization ratio (51.8%) and the weakest texture strength, and also forms the mortise and tenon nested grain structure. Increasing the total (Zn + Mg) content can achieve significant performance enhancement, which is attributed to the refinement of the η′ phase; however, a higher total (Zn + Mg) content will lead to the continuous distribution of coarse η-MgZn₂ phases formed along the grain boundary, accompanied by the broadening of precipitate-free precipitation zones (PFZs). Compared with other alloys, Al-8.6Zn-1.55Mg-1.9Cu-0.11Zr (Zn + Mg = 10.15 wt.%) maintains high strength while ensuring desirable plasticity due to its mortise and tenon nested grain structure. In addition, its desirable grain boundary precipitation behavior makes it exhibit the best corrosion resistance. These findings indicate that maintaining the total (Zn + Mg) content around 10 wt.% achieves a balance between strength and corrosion resistance, offering a theoretical foundation for the design of high-strength and corrosion-resistant Al–Zn–Mg–Cu alloys. Full article

While existing studies on Guatemalan jadeite have predominantly focused on green varieties, the coloration mechanisms and origin of its blue counterparts remain poorly understood. Therefore, the present study provides the first comprehensive investigation of the Guatemalan blue jadeite using an integrated analytical approach, which combines Raman spectroscopy, micro X-ray fluorescence (µ-XRF), electron microprobe analysis (EMPA), X-ray diffraction (XRD), UV-Vis spectroscopy, and Cathodoluminescence (CL) imaging on seven representative samples. The results demonstrate that these jadeites consist of two distinct phases: a primary jadeite phase (NaAlSi₂O₆) and a secondary omphacite that form by metasomatic alteration by Mg-Ca-Fe-rich fluids. Spectroscopic analysis reveals that the blue coloration is primarily controlled by Fe³⁺ electronic transitions (with characteristic absorption at 381 nm and 437 nm) coupled with Fe²⁺-Ti⁴⁺ intervalence charge transfer, supported by μ-XRF mapping showing strong Fe-Ti spatial correlation with color intensity. CL imaging documents a multi-stage formation history involving initial high-pressure crystallization (Jd-I) followed by fluid-assisted recrystallization forming Jd-II and omphacite. The detection of CH₄, CO and H₂O in the fluid inclusions by Raman spectroscopy indicates formation in a serpentinization-related reducing environment, while distinct CL zoning patterns confirm a fluid-directed crystallization (P-type) origin. These findings not only clarify the chromogenic processes and petrogenesis of Guatemalan blue jadeite but also establish key diagnostic criteria for its identification, advancing our understanding of fluid-derived jadeite formation in subduction zone environments. Full article

This study investigates the microstructure evolution and mechanical properties of DSS2209 duplex stainless steel fabricated via cold metal transfer wire arc additive manufacturing (CMT-WAAM). The as-deposited thin-wall components exhibit significant microstructural heterogeneity along the build height due to thermal history variations. Optical microscopy, SEM-EDS, and EBSD analyses reveal distinct phase distributions: the bottom region features elongated blocky austenite with Widmanstätten austenite (WA) due to rapid substrate-induced cooling; the middle region shows equiaxed blocky austenite with reduced grain boundary austenite (GBA) and WA, attributed to interlayer thermal cycling promoting recrystallization and grain refinement (average austenite grain size: 4.16 μm); and the top region displays coarse blocky austenite from slower cooling. Secondary austenite (γ₂) forms in interlayer remelted zones with Cr depletion, impacting pitting resistance. Mechanical testing demonstrates anisotropy; horizontal specimens exhibit higher strength (UTS: 610 MPa, YS: 408 MPa) due to layer-uniform microstructures, while vertical specimens show greater ductility (elongation) facilitated by columnar grains aligned with the build direction. Hardness ranges uniformly between 225–239 HV. The study correlates process-induced thermal gradients (e.g., cooling rates, interlayer cycling) with microstructural features (recrystallization fraction, grain size, phase morphology) and performance, providing insights for optimizing WAAM of large-scale duplex stainless steel components like marine propellers. 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

In this study, we investigated the formation mechanism of organo-metal halide perovskite nanostructures through a two-step process categorized as dissolution–recrystallization. It is proposed that the initial formation of nanostructures is governed by the generation of seed grains, whereas the Ostwald ripening model explains only the subsequent growth stage of these structures. We suggest that newly generated grains—formed adjacent to pre-positioned grains—experience compressive stress arising from volume expansion during the phase transition from PbI₂ to the MAPbI₃ perovskite phase. Owing to their unstable state, these grains may serve as effective seeds for the nucleation and growth of nanostructures. Depending on the dipping time, diverse morphologies such as nanorods, plates, and cuboids were observed. The morphology, including the aspect ratio and growth direction of these nanostructures, appears to be strongly influenced by the residual compressive stress within the seed grains. These findings suggest that the shape and aspect ratio of perovskite nanostructures can be tailored by carefully regulating nucleation, dissolution, and growth dynamics during the two-step process. Full article

Ti₂AlNb-based alloys are widely used in aerospace applications due to their excellent high-temperature mechanical properties. This study aims to investigate the texture, microstructural evolution, and phase transformation behavior of Ti₂AlNb-based alloy sheets during heat treatment and their effects on tensile properties. During heat treatment, B2 → O phase transformation occurs at 550 °C and 650 °C, while Ostwald ripening takes place at 700 °C and 850 °C. The α₂ phase undergoes spheroidization around 1000 °C due to grain boundary separation and recrystallization. Additionally, the B2, O, and α₂ phases all exhibit strong textures. The B2-phase texture follows a cubic orientation ({100}<001>), rotated ~30° around the normal direction (ND). The O-phase texture consists of a strong {100}<010> rolling texture and a weaker texture component <001>//RD, influenced by the B2-phase texture, rolling deformation, and variant selection during O-phase precipitation. Each B2 grain generates four variants, forming distinct O-phase textures within the same grain. The α₂-phase texture exhibits typical rolling textures, [0001]//TD, <$\overline{1}$2$\overline{1}$0>//ND, and {11$\overline{2}$0}<01$\overline{1}$0>, remaining stable after heat treatment. Tensile tests show that the rolled sheet has better ductility along the rolling direction (RD), while the transverse direction (TD) demonstrates higher yield strength (up to 1136 MPa). The anisotropy in tensile properties is mainly attributed to the O-phase texture, with minor contributions from the α₂-phase and B2-phase textures. These findings provide a theoretical basis for optimizing the mechanical properties of Ti₂AlNb-based alloys. Full article

Cu-Fe in situ composites often face challenges in achieving high strength during cold rolling due to the inefficient transformation of partial Fe phases into fibrous structures. To uncover the underlying mechanisms, this study systematically investigates the co-deformation behavior of Cu and Fe phases in a Cu-10Fe alloy subjected to cold rolling at various strains. Through microstructure characterization, texture analysis, and mechanical property evaluation, we reveal that the Cu matrix initially accommodates most applied strain (ε_vm < 1.0), forming shear bands, while Fe phases (dendrites and spherical particles) exhibit negligible deformation. At intermediate strains (1.0 < ε_vm < 4.0), Fe phases begin to deform: dendrites elongate along the rolling direction, and spherical particles evolve into tadpole-like morphologies under localized shear. Concurrently, dynamic recrystallization occurs near Fe phases in the Cu matrix, generating ultrafine grains. Under high strains (ε_vm > 4.0), Fe dendrites progressively transform into filaments, whereas spherical Fe particles develop long-tailed tadpole-like structures. Texture evolution indicates that Cu develops a typical copper-type rolling texture, while Fe forms α/γ-fiber textures, albeit with sluggish texture development in Fe. The low efficiency of Fe fiber formation is attributed to the insufficient strength of the Cu matrix and the elongation resistance of spherical Fe particles. To optimize rolled Cu-Fe in situ composites, we propose strengthening the Cu matrix (via alloying/precipitation) and suppressing spherical Fe phases through solidification control. This work provides critical insights into enhancing Fe fiber formation in rolled Cu-Fe systems for high-performance applications. Full article

This study proposes a novel unified constitutive model that systematically integrates the microstructure evolution and macroscopic stress–strain response during the hot deformation of a Ni-based superalloy. The proposed model incorporates a suite of microstructural variables, including damage fraction, recrystallization fraction, δ phase content, average grain size, and dislocation density. Furthermore, the model explicitly considers critical macroscopic stress state parameters, specifically the magnitude and orientation of maximum principal stress, hydrostatic stress component, and Mises equivalent stress. A comparative analysis of rheological curves derived from uniaxial tension and compression experiments reveals that the prediction errors of the proposed model are less than 3%. The model is subsequently implemented to investigate the evolution characteristics of the damage accumulation fraction and δ phase content under varying stress directions and initial δ phase contents. An advanced computational framework integrating the finite element method with the proposed constitutive model is established through customized subroutines. The framework exhibits exceptional predictive accuracy across critical regions of disk forging, as evidenced by a close agreement between computational and experimental results. Specifically, the relative errors for predicting recrystallization fraction and average grain size remain consistently below 8% under varying stress–strain conditions. Testing results from four representative regions demonstrate a good alignment of high-temperature tensile properties with the macroscopic stress–strain distributions and microstructure characteristics, thereby confirming the model’s reliability in simulating and optimizing the forging process. Full article

Pseudotachylytes and cataclasites record transient seismic slips within the brittle–ductile transition zone and ductile flow layers. Investigating the mechanisms of pseudotachylytes can provide the most direct geological evidence for revealing seismic fault slip and coseismic processes. We investigate the deformation and chemical composition of pseudotachylytes, cataclasites, and mylonites collected from the Anning River fault zone in this study. Three kinds of pseudotachylyte veins were found in granite gneiss and cataclasite. Microstructural analyses show that pseudotachylytes and cataclasites developed within granitic gneiss and mylonites, and EBSD analysis indicates granitic gneiss deformed at temperatures of 250–350 °C. All of the pseudotachylytes are enriched in Fe and Ca, with SiO₂ content closely resembling that of the wall rock of granitic gneiss. The geochemical results indicate that pseudotachylytes originated from the in situ melting of granitic gneiss, which was produced during coseismic frictional heating. Based on the deformation and geochemical data of mylonites, cataclasites, and pseudotachylytes, a simple model of the seismogenic layer is established for rock deformation during coseismic, post-seismic relaxation, and interseismic periods. Mylonite represents the rheological flow of the brittle–ductile transition zone during interseismic periods, cataclasites display brittle fracturing during coseismic rupture, and pseudotachylytes stand for localized melting induced by coseismic frictional heating. During the post-seismic relaxation, crack healing and static recrystallization of quartz occur. Full article

Modern aero-engines need alloys that sustain both strength and ductility at high temperatures. However, conventional titanium alloys face inherent trade-offs between strength and ductility. In situ TiB-reinforced titanium matrix composites could fill this gap, but their texture evolution and hot-working mechanics are still poorly understood. In this study, TiB-reinforced IMI834 titanium matrix composites were synthesized using in situ technology in a remelting furnace. Meanwhile, the evolution of microstructure and texture in the hot-rolled titanium matrix composites was examined through both Abaqus simulations and experimental observations. Results indicate that dynamic recrystallization occurred in the microstructure of the composites at a deformation level of 95%. Due to the specific orientation relationship between the TiB whiskers and Ti matrix, the hot-rolled composites developed a pronounced [11-20]_Ti // rolling direction fiber texture. TiB whiskers rotated toward the rolling direction, enhancing the intensity of the [11-20]_Ti // rolling direction fiber texture, consistent with the predictions from numerical simulations. Tensile tests revealed that the combined effects of grain refinement and the rotation of TiB whiskers along the rolling direction increased the yield strength of the hot-rolled composite to 1153 MPa, while simultaneously raising the elongation to 10%. Full article

Grain boundary engineering (GBE) has been widely used to modify grain boundary (GB) networks to improve GB-related properties in polycrystalline materials. With the development of miniaturized and lightweight terminal connectors comes a greater demand for phosphorus bronze. A fine grain size and excellent GB characteristics are the keys to synergistically enhancing mechanical strength and bending workability. In this study, the effects of the annealing temperature on the grain boundary character distribution (GBCD) optimization and the bending properties of phosphorus bronze were studied by means of electron backscatter diffraction and a 90° bending test. The results show that the deformed microstructure of the as-received material recrystallizes upon annealing at 400 °C for 1 h. The average grain size is 1.6 μm, and a large number of special boundaries (SBs) are present, accounting for 71.5% of all GBs. Further, the incoherent Σ3, Σ9, and Σ27 boundaries are the most abundant, effectively disrupting the network connectivity of random high-angle grain boundaries. The grain size gradually increases with the annealing temperature increase. The fractions of the Σ9 and Σ27 boundaries gradually decrease. Although the proportion of SBs further increases at higher temperatures, most SBs at these temperatures are coherent Σ3 boundaries that do not contribute to the direct optimization of GBCD. Moreover, in the absence of a significant difference in tensile strength, the GBCD-optimized fine-grained sample demonstrates smooth surfaces without orange peel effects when bent at 90° with R/t = 0 in the bad way. This improvement is attributed to the uniform deformation of fine grains and special boundaries, which enhances the bending workability of the GBCD-optimized fine-grained strips. Full article

High Nb-TiAl alloy components fabricated by laser-directed energy deposition (LDED) exhibit promising applications in aerospace and other high-temperature (HT) fields. It is essential to elucidate the microstructure evolution under HT and high-pressure conditions. In this study, we systematically investigated the room temperature (RT) and HT compression properties of the alloy under various processing parameters, revealing the microstructure evolution during compression. A reduction in laser power (P) decreases the proportion of columnar dendrites while increasing the proportion of epitaxial dendrites, thereby facilitating the transformation of columnar dendrites into equiaxed dendrites. Additionally, lowering the P reduces the size of the α₂ + γ lamellar colony (LC) and refines the microstructure of the alloy. The ultimate compressive strength (UCS) of the alloy at RT increased from 1065.5 ± 255.5 MPa at 750 W to 1240.1 ± 104.7 MPa at 450 W. The RT compression fracture is primarily characterized by cleavage surfaces and cleavage steps. The strain rate exhibits a negative correlation with the HT UCS of the alloy. Under conditions of 40% engineering strain, the UCS of the alloy at 900 °C rises from 890.7 ± 98.1 MPa at a strain rate of 0.5 mm/min to 1260.8 ± 91.0 MPa at 5 mm/min. Dislocation and stacking faults can easily occur during the compression process at RT, while dislocations and dynamic recrystallization are more prevalent during compression at 900 °C. Samples subjected to higher strain rates exhibit a lower number of dynamically recrystallized grains, resulting in a higher UCS. Full article

Laser shock peening (LSP) is an effective method to improve the fatigue property of metallic materials, and a thorough understanding of its strengthening mechanism is crucial for technology application. In this study, the LSP and fatigue tests of TC4 titanium alloy have been carried out. Combined with the structural characterization and the crystal plasticity finite element (CPFE) simulation, the relationship of stress distribution, microstructure evolution and fatigue performance caused by LSP is revealed. The results indicate that the material’s fatigue life initially increases and subsequently declines with the rising pulse energy. At the optimal pulse energy condition, the laser-shocked specimen demonstrates a 126% increase in fatigue life relative to the untreated specimen, which is accompanied by the higher residual compressive stress along the depth. Meanwhile, the grains become more refined with a uniform size change gradient, and the β phase content drops from 4.1% to 2.2%. Notably, regions with <$\stackrel{-}{1}$2$\stackrel{\mathrm{-}}{1}$0> crystal orientation can be selectively achieved. With the favorable <$\stackrel{\mathrm{-}}{1}$2$\stackrel{\mathrm{-}}{1}$0> slip direction orthogonal to the applied fatigue loading axis, the generation and propagation of dislocations are effectively constrained, thereby significantly enhancing the material’s fatigue performance. The stress distribution and fatigue life in models with different grain sizes and phase contents are further analyzed by the CPFE method, showing good consistency with the experimental results. Theoretically, the excessively high pulse energy causes the transient temperature (1769 °C) to surpass the melting point (1660 °C), which can affect the recrystallization structure and stress distribution. Full article

The Mg-8Li-3Al-0.3Si dual-phase alloy (LA83-0.3Si) was subjected to six multi-directional forging (MDF) passes in the present work, then its microstructure, mechanical properties, and work hardening and work softening effects were examined and analyzed. The results indicate that the continuous dynamic recrystallization (CDRX) mechanism of the LA83-0.3Si dual-phase alloy gradually transitioned to a discontinuous dynamic recrystallization (DDRX) mechanism as the temperature increased after MDF. This temperature change induced a transition in the basal texture from bimodal to multimodal, significantly reducing the texture intensity and weakening the alloy’s anisotropy. At 310 °C, the AlLi phase nucleated into coated particles to stabilize the structure. Additionally, the increase in the forging temperature weakened the synergistic deformation capability of the α/β phases, while the hardening behavior of the β-Li phase provided a nucleation pathway for dynamic recrystallization (DRX). MDF significantly enhanced the strength and ductility of the LA83-0.3Si alloy. The alloy’s strength continued to rise, while elongation decreased as the forging temperature increased. The ultimate tensile strength (UTS) and elongation (EL) reached 267.8 MPa and 11.9%, respectively. The work hardening effect increased with the forging temperature, whereas the work softening effect continuously diminished, attributed to the enhanced hardening behavior of the β phase and the reduced ability to transfer dislocations. Full article