The complex geometries of turbine blades require alloys to deliver excellent overall performance across distinct surface orientations; in addition to mechanical anisotropy, oxidation behavior warrants equal attention. By employing a suite of characterization techniques including XPS, FIB-TEM, and SEM, this study systematically investigates the oxidation behavior and elemental diffusion mechanisms of the second-generation La-modified CMSX-4 superalloy across distinct surface orientations. The results indicate that the comprehensive oxidation resistance ranking of CMSX-4 alloy with three surface orientations is (100) > (111) > (110). During the initial stage of oxidation, the higher proportion of gamma' phase on the (100) plane surface leads to the formation of more Al2O3 in the alloy surface layer. Additionally, the shorter gamma'/gamma interface diffusion path on the (100) plane facilitates the diffusion of Al, Ti, and Ta from the matrix to the surface oxide layer, forming a stable oxide layer structure, thereby enhancing the alloy's oxidation resistance. However, in the later stages of oxidation, the higher atomic stacking density of the (111) plane results in superior oxidation resistance compared to the (110) plane. The results can offer a theoretical basis for the manufacturing and service of single-crystal blades with complex shapes.

The high-temperature oxidation resistance of Ni-based single crystal superalloys is paramount to their service reliability. However, conventional ex-situ characterization techniques struggle to capture the transient behavior during the initial stages of oxidation, often obscuring the underlying nanoscale kinetic processes. To this end, we utilized in situ transmission electron microscopy (TEM) to directly observe the oxidation behavior of CMSX-4, a typical second-generation nickel-based single crystal superalloy, during continuous heating. The results indicate that during the gradual temperature increase, the gamma phase preferentially oxidizes, while the gamma' phase, as an intermetallic compound, experiences substantial oxidation only at 600 degrees C. At 800 degrees C, the gamma' phase rapidly oxidizes, driven by the outward diffusion of Ni and Co into the gamma matrix, which results in the extensive formation of NiO and CoO. Furthermore, complementary ex-situ bulk oxidation tests at 1000 degrees C were incorporated to reveal the macroscopic multi-stage kinetics governed by the development of a multilayered scale and the spallation induced by an intermediate refractory-rich oxide band. The selective oxidation of the two phases, along with the observed crystallographic orientation-dependent oxidation behavior and cross-scale correlations, provides valuable insights for designing high-temperature alloys with enhanced oxidation resistance.

Near-α titanium alloy sheets are susceptible to localized failure during complex forming processes, primarily due to their strong initial textures. Elucidating the evolution mechanisms of such strong textures and the competing behaviors of slip systems under varying stress states is crucial for overcoming current bottlenecks in complex forming. In this study, the distinct deformation behaviors of Ti65 alloy sheets subjected to uniaxial tension and three-point bending were systematically investigated by combining experimental characterizations with Abaqus-VPSC multiscale simulations. The results demonstrate that under uniform tensile loading, the mechanical anisotropy is mainly governed by the dependence of the Schmid factor on the initial crystallographic orientation. Deformation is predominantly accommodated by prismatic slip, resulting in texture feature stability. Conversely, the geometric constraints and strain gradients introduced during bending deformation increase the activation tendency of pyramidal slip to accommodate the c-axis deformation of grains. This transition in the dominant slip mode is evident on the extrados of the bent sheet, reducing the stability of the initial texture. Furthermore, the crystal plasticity parameters calibrated using uniaxial tensile data reasonably predicted the heterogeneous deformation characteristics on the intrados and extrados of the bent sheet. This study provides an important theoretical basis for texture control during the forming of complex titanium alloy components.

The sluggish aging response of Inconel 625 alloy has long limited its precipitation strengthening potential, restricting its application in high-demand environments. Conventional γ″ precipitation requires hundreds of hours of thermal exposure, making the process highly time-inefficient. To address this challenge, short-time stress aging was employed to accelerate precipitation kinetics and enhance mechanical performance. Stress-free and stress aging treatments were conducted at 650°C for 50-200 h, and the γ″ precipitation behavior was examined using TEM, EBSD, and first-principles calculations. Stress aging promoted rapid γ″ nucleation, producing a high precipitate number density and fine morphology. Compared with 200 h of stress-free aging, stress aging for only 50 h and 150 h increased the yield strength by 105.8 MPa (16.0%) and 175.9 MPa (26.6%), respectively, while maintaining comparable ductility. The refined γ″ precipitates restricted dislocation slip and promoted the activation of low-Schmid-factor slip systems, stacking faults, and deformation twinning, thereby achieving a superior strength-ductility synergy. These results demonstrate that short-time stress aging is a precise and time-efficient strategy for tailoring γ″ precipitation, providing new insights into microstructure design and performance optimization of Ni-based superalloys.

One of the critical issues in the additive manufacturing of Hastelloy-X (HX) superalloy is solidification cracking, which imposes higher demands on alloy composition design. While rare-earth yttrium (Y) has been recognized for improving the service performance of superalloys, its effect on cracking susceptibility remains controversial. In this study, HX superalloy with and without Y modification was fabricated using directed energy deposition (DED). Advanced characterization techniques were employed to analyze the microstructural difference, specifically the precipitation and segregation behavior at the crack-associated grain boundaries (GB) were quantified using atom probe tomography (APT). The results reveal that the introduced Y predominantly exists as Y2 O3 or segregates at the GB during the DED process. According to the results of density functional theory (DFT) calculations, the segregated Y atoms tend to occupy the sites that would otherwise be preferentially occupied by Mo atoms, leading to a higher concentration of free Mo atoms at the GB. This redistribution modifies the local thermodynamic environment, thereby promoting additional solidification cracking. These findings provide new theoretical insights into the role of Y in HX superalloys and offer a valuable basis for designing crack-resistant, rare-earth-modified superalloys tailored for additive manufacturing applications. (c) 2026 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Near-alpha titanium alloys are known to be susceptible to dwell fatigue debit, which has been linked to microstructure and the microscale slip deformation localization. However, prior research has predominantly focused on primary alpha (alpha p) microstructures, leaving a critical gap in systematic investigations of bimodal microstructures, which are of greater engineering relevance. This study systematically investigates slip activation mechanisms in Ti6321 alloy under pure fatigue and dwell-fatigue loading through integrated slip trace analysis and high-resolution digital image correlation (HR-DIC), focusing on alpha p and secondary alpha (alpha s) colony in transformed beta (beta t) microstructures. Key findings revealed that dwell-fatigue conditions significantly enhance basal and prismatic slip activation compared to pure fatigue, elevating plastic strain localization within slip bands. Hexagonal close-packed (HCP) elastic anisotropy and the superior strain rate sensitivity (SRS) of basal slips drive preferential activation across both hard-and soft-oriented regions, while prismatic slips exhibit sustained strain accumulation due to lower strain hardening. Furthermore, comparing to the alpha p, analysis demonstrates that alpha s colony prevent long-range slip through strain dispersion at interface, reducing dwell sensitivity. These results provide crystallographic insights into the mechanistic linkage between dwell fatigue effects and slip-mediated deformation, offering critical guidance for microstructure-informed alloy design and crystal plasticity model calibration.

In order to overcome the embrittlement of metastable titanium alloys caused by the precipitation of wiso phase during aging, regulation of isothermal w precipitation was investigated in Ti-15Mo alloy. The results show that the sample is brittle when direct aging (A) is applied at 350 degrees C for 1 h after solution treatment (ST). If pre-deformation (D) is performed on the ST sample to induce {332} twins and secondary a '' phase, subsequent aging at 350 degrees C (STDA350) improves the strength to 931 MPa with a good ductility of about 20% maintained. However, when aging is performed at 400 degrees C or 450 degrees C (STDA400/450), the strength can be further improved, but the ductility is dramatically reduced. Atomic-scale characterizations show that the partial collapse of w phase in the STDA350 sample effectively eliminates aging-induced embrittlement, but complete collapse leads to poor ductility in the STDA400/450 sample.

Creep resistance is a key performance metric of high temperature structural components in aeronautics and space manufacturing field, and the strong dependency of creep deformation on alpha phase morphology requires careful consideration in titanium alloy. The dependency of tensile-creep deformation on alpha phase morphology of Ti65 titanium alloy sheet at 650 degrees C has been systematically investigated. The endurance time of creep property could be increased from 7.7 h to 237.5 h by controlling the volume of equiaxed alpha phase. The article focuses on the analysis of the specimens (M1and M2) with two typical microstructure which have creep endurance time of 7.7 h-9.7 hand 225.0 h-237.5 h respectively at 650 degrees C and 240 MPa. Fracture morphology of M1 and M2 specimens was characterized, revealing different fracture modes for M1 and M2. The two samples exhibited different deformed microtexture and the average Kernel Average Misorientation (KAM) value. The micro-cracks in M1 and M2 both initiate at the phase interface with a high misorientation value. Crack propagation diverged fundamentally: M1 cracks propagate along equiaxed alpha grain boundary, but the micro-cracks in M2 propagate along grain boundary and through alpha lamella in a tortuous path. Finally, it is clarified that the significant difference of creep property resulted from distinct deformation mechanisms, with grain boundary sliding coupled dislocation slip governing M1 failure, and dislocation slip within fine alpha lamellae dominating M2. These findings establish alpha-phase morphology optimization as an effective strategy for enhancing creep resistance in high-temperature titanium alloys.

Heat-affected zone (HAZ) softening and corrosion degradation remain major obstacles to achieving property equivalence between welded joints and the base metal (BM) in thin 5052 aluminum alloy sheets. To overcome these limitations, a data-driven optimization strategy for cold metal transfer (CMT) welding was developed by coupling a Random Forest (RF) surrogate model with Bayesian active learning using an Expected Improvement (EI) acquisition function. This ML-guided approach successfully identified a set of optimal low–heat-input parameters. The optimized welded joints achieved tensile strengths exceeding 93% of that of the BM while maintaining comparable ductility and exhibiting nearly identical electrochemical behavior in acidic media. Integrated microstructural and compositional analyses reveal that weld metal grain refinement, spatial confinement of HAZ softening, and reduced compositional gradients collectively enable the simultaneous attainment of mechanical and corrosion property equivalence. This work provides a transferable machine-learning-assisted framework for parameter design and performance enhancement in welded thin aluminum alloy structures.

Ti/Al micro-laminated composite sheet with alternate arrangement of Ti/TiAl3/Al laminate microstructure was fabricated through vacuum hot-pressing method. The uniaxial tensile deformation behavior at high temperature and the bulging formability were investigated by uniaxial tensile experiment and gas bulging experiment, respectively. The results show that the composite sheet hot pressed for 15 min exhibits better plastic deformation behavior because the hard and brittle TiAl(3)layer is thin. When the composite is deformed at elevated temperatures, the cracks of the composite sheet are blunted, which inhibits the propagation of cracks in TiAl(3)layer, so the elongation and limiting bulging rate at 600 degrees C reach 135% and 45%, respectively. At the top region of the bulged spherical shell, the Ti layer and Al layer both undergo severe deformation and are necked, the Ti/Al interface is wavy, the TiAl(3)layer breaks into islands, with Al layer filling their gaps, and no cracks are formed.

Doping with trace levels of rare earth elements is an effective approach to enhancing the oxidation and hot corrosion resistance of superalloys. In this study, the hot corrosion behaviour of ppm lanthanum (La) (0 ppm, 40 ppm, and 200 ppm) modified CMSX-4 superalloy and the action micro-mechanism of La were systematically clarified and summarised by SEM, EDS, EPMA, FIB and TEM. The results indicated that ppm-level La doping significantly decreased the corrosion rate of the alloy by more than half. However, increasing the doping level of La does not affect the hot corrosion kinetics of the modified alloys. Compared to unmodified alloys, La-modified alloys exhibit a denser and more complete surface corrosion product, resulting in longer weight gain "plateaus" on the weight gain curves. Further analysis shows La segregation provides a short-circuit diffusion channel for oxygen and promotes the external diffusion of Al, Ti, and Ta, thereby improving the integrity and densification of the protective oxide film. The hot corrosion reaction of the alloy with lower La content (40 ppm) is generally more stable.

Crack initiation mechanism of dwell fatigue has always been a key problem in rationalizing the dwell effect, and it is not completely understood yet. This study conducted stress-controlled low-cycle fatigue and dwell fatigue tests on Ti-6Al-3Nb-2Zr-1Mo alloy with bimodal microstructure to reveal its microstructural characteristics and crack initiation mechanisms. The study demonstrated that the faceted primary α nodules located near the specimen surface acted as crack initiation sites during both fatigue and dwell fatigue tests. Slip trace analysis revealed that faceted cracking occurred at (0001) basal plane with the maximum Schmid factor value through a special cracking mode referred to as (0001) twist boundary cracking. Innovative criteria of parameters C1 and C2 were proposed based on experimental observation and molecular dynamics simulations, which well identify candidates for (0001) twist boundary crack nucleation. It demonstrated that grain pairs combining a moderately high Schmid factor for basal slip and a well-orientated Burgers vector in the out-of-surface plane was the preferable location for surface (0001) twist-boundary crack initiation, and grain pairs combining a high Schmid factor for basal slip and a high normal stress on basal plane are perfect candidates for subsurface cracking. Based on this, phenomenological models are proposed to explain the surface (0001) twist-boundary cracking mechanism from the perspective of surface extrusion-intrusion-induced micro-notches.

Texture and anisotropy control of rolled strip have always been a technical problem in titanium alloy industry, especially for near-alpha titanium alloys. In order to solve the above problems, we innovatively propose a process method for efficiently preparing weakly anisotropic alloy strips. In this paper, the texture evolution and anisotropy of TA18 titanium alloy strip under various rolling and heat treatment conditions were systematically studied by EBSD and other technical means. The results have showed that the hot-rolled TA18 titanium alloy has a distinct band microstructure along the RD. The obvious tensile properties anisotropy of hot-rolled TA18 titanium alloy is mainly due to the non-uniform microstructure formed and strong T-type micro-texture. The hot-rolled TA18 titanium alloy after 700°C/3h heat treatment occurred complete recrystallization process, which formed the fine and uniform equiaxed grains. Texture components distribution of the titanium alloy changed from typical bimodal texture to the tendency of <0001>//normal direction (ND) base plane texture. The hot-rolled TA18 titanium alloy after heat treatment at 700°C/3h, followed by rolling to 4.8mm at room temperature and annealing at 730°C/1h, could effectively reduce the anisotropy of titanium alloys. Finally, the formation of anisotropy of yield strength was considered as the different slip activation behaviors due to the influence of micro-texture orientation. This study innovatively proposes an efficient method for fabricating alloy strips with reduced anisotropy forTA18 titanium alloy strips.

Laser re-melting has demonstrated significant potential for optimizing the microstructure and enhancing the mechanical properties of magnesium alloys, while also providing solidification conditions analogous to those in laser metal deposition. This enables a scientifically sound evaluation of grain morphology evolution from traditional casting to additive manufacturing of magnesium alloys. However, its practical implementation is often limited by the formation of solidification defects, including porosity and hot cracking. This study systematically investigates the microstructural evolution and mechanisms of defect formation during laser re-melting using ultrafast in-situ X-ray imaging and analytical electron microscopy. The results show that intense melt flow during laser re-melting facilitates the movement of bubbles and unmelted particles, which are entrapped at the solid–liquid interface. These bubbles and particles ultimately evolve into porosities and coarse particles, respectively, within the fusion zone (FZ) and near the fusion line. Additionally, fluid-driven heat transfer promotes extensive static recrystallization and precipitation in the heat-affected zone, resulting in a bimodal grain structure, contrasting with the fine equiaxed grains in the FZ. For high Zn content alloys ( 6 wt pct), the extended solidification range increases susceptibility to liquation cracking. These findings provide critical insights into the microstructural and defect evolution during laser re-melting and offer valuable guidance for advancing the effectiveness and reliability of laser processing techniques for magnesium alloys.

High-precision manufacturing and effective defect control in hot stamping of thin-walled titanium alloy components present significant engineering challenges. Frequent issues like uneven thickness, shape distortion, and cracking necessitate in-depth analysis of their underlying mechanisms. This study employed Global Schmid Factor and Idealized Grain Microstructure Analysis models to investigate the hot stamping behavior of 2 mm-thick novel high-temperature Ti65 alloy sheets with initial transverse texture at 900 degrees C and 1000 degrees C. Results showed that within the 900-1000 degrees C range, Ti65 alloy sheet formability improved with increasing temperature. Fracture locations after stamping at 900 degrees C and 1000 degrees C exhibited temperature dependence. This was attributed to temperature significantly modulating in-plane tensile uniformity and thinning capability by influencing the uniformity and strain distribution of internal plastic deformation, highlighting the crucial role of inherent material anisotropy in hot stamping. Microstructural analysis confirmed that during high-temperature forming, microstructure and texture evolution were governed by phase transformation-deformation interaction, which promoted the activation of alpha-phase prismatic slip systems influenced by the initial texture. This work provided a theoretical basis for optimizing Ti65 hot stamping parameters, suppressing forming defects, and enhancing material performance and production quality.

The facet formation mechanisms under dwell fatigue of Ti150 alloy remain controversial due to multi-factor complexity, especially for the bimodal microstructure consist of primary alpha phase (alpha p) and beta-transformed grains (beta t). Fracture analysis revealed a cluster of aligned faceted region with area ranging from 13,569 mu m2 to 224,995 mu m2 as dwell time increasing. Meanwhile, characterization of facets, subsurface microcracks, and deformation microstructures demonstrates that crack initiation alpha p facets predominantly form on basal slip bands with high Schmid factor values, driven by the combined effects of high shear stresses and normal stresses generated by basal slip-dominated dislocation pile-ups near grain boundaries. In contrast, the characteristic stepped beta t facets formation is collectively governed by two synergistic mechanisms: (1) alternating crack propagation along basal/prismatic slip bands in beta t grains, and (2) phase interface effects where silicides promote crack growth along interfacial voids while impeding crack transmission, causing deflection. This work elucidates the mechanisms of facet formation in various features of the microstructure and highlights the critical role of silicides in dwell fatigue behavior, providing novel insights into enhancing dwell fatigue resistance through microstructure optimization and precipitation control.

Achieving precise control over alpha phase precipitation is crucial for obtaining ultra-high strength in metastable beta-Ti alloys. However, a comprehensive understanding of how deformation products and their reversion counterparts influence alpha phase precipitation behavior in these exceptional alloys remains elusive. This study explores the influence of stress-induced martensite (SIM) and its reversion-induced dislocations on the alpha phase precipitation behavior in a metastable beta-Ti alloy. After loading and reloading, SIM laths formed, and some SIM laths subsequently reversed into the beta phase, introducing band-like regions with dense and parallel arranged <110> dislocations in the beta phase matrix. Such dislocations resulted in a band-like area decorated with short rod-like alpha phase precipitates during isothermal annealing. Meanwhile, the remaining stress-induced martensite decomposed directly into alpha phase, forming a long alpha phase with a morphology similar to the original martensite. Additionally, both sides of the original SIM laths reversed during isothermal annealing, forming {332} <113>(beta) twins at the alpha/beta phase interface. This divided the alpha phase formed in SIM laths from the alpha phase formed directly in the beta matrix. (c) 2025 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

The elucidation of the impact of the initial texture and cooling rate on the variant selection (VS) mechanism of alpha-phase in titanium alloys is essential for optimising their microstructure and mechanical properties. In this study, Ti65 foils featuring three different initial textures underwent annealing in the alpha + beta phase region, followed by cooling at three different rates. Under slow cooling conditions (furnace cooling), the primary mechanism governing texture evolution of alpha-phase is the grain growth of the primary alpha (alpha p) grains. Consequently, the effect of the initial texture on the texture evolution of alpha-phase under slow cooling is ascribed to variations in the alpha p grains in the samples after heat treatments. Additionally, standard disorientation angle theta m distribution maps of the alpha texture under different beta textures are developed to predict the texture of the alpha p grains. In contrast, during rapid cooling (200 degrees C/min cooling and air cooling), texture evolution of alpha-phase is driven by the precipitation of the secondary alpha (alpha s) grains. In this case, a change in the cooling rate has no effect on the VS mechanism of alpha-phase at the alpha p/beta and beta/beta boundaries, but it changes the VS mechanism of alpha-phase at the parent beta grain interior. Therefore, the influence of the initial texture on VS mechanism of alpha-phase under rapid cooling varies with cooling rates, depending on the ratio of alpha s grains precipitated at alpha p/beta and beta/beta boundaries to the alpha s grains precipitated at the parent beta grain interior.