The alloys strengthened by nanoscale γ" phase (a coherent strengthening phase with an ordered D022 structure), renowned for their exceptional mechanical properties, experience an accelerated strength reduction above 650 °C, restricting their high-temperature applications. The conventional explanation attributes this strength reduction solely to insufficient stability of the metastable γ" phase, which also hinders the investigation of its deformation mechanisms above 650 °C. In this study, a high-stability γ" phase is introduced into a NiCoCr-based multi-component alloy system, effectively suppressing its destabilization during high-temperature deformation up to 850 °C. Therefore, this alloy exhibits markedly improved resistance to strength degradation above 750 °C, with only a 4% reduction observed from 750 °C to 850 °C. However, a significant strength reduction (30% reduction) is still observed in this alloy from 650 °C to 750 °C, suggesting that γ" destabilization is not the predominant factor for strength degradation within this intermediate-temperature range. It is observed that the strength reduction from 650 °C to 750 °C originates from a pronounced reduction in dislocation shearing resistance of γ" particles, while the minor strength loss between 750 °C and 850 °C benefits from preserved γ" stability. This work offers novel insights into the temperature-dependent strength reduction mechanism of γ" phase, establishing a theoretical foundation for developing γ"-strengthened alloys.

This work studies the microstructure and mechanical properties of K439B nickel-based superalloy castings with a wall thickness of 1-10 mm. The results show that the melt feeding capacity in thin-walled castings is poor， there are many shrinkage porosity in the 1 mm and 3 mm thin-walled castings， and the 10 mm thick-walled casting has the lowest porosity. Due to the increase of melt solidification rate， all of the secondary dendrite arm spacing， grain size and γ' phase size of the castings increase with the increase of thickness. The tensile tests at room temperature show that the mechanical properties of thin-walled castings are significantly affected by the evolution of microstructure. Due to the synergistic effect of the fine grain strengthening mechanism and precipitate shearing mechanism， the 1 mm thick casting exhibits the highest ultimate tensile strength （1037 MPa） and elongation to fracture （5.6%）.The 3 mm thick casting shows the poorest tensile strength and ductility，with values of 890 MPa and 4.1%， respectively， which can be attributed to its highest porosity level and the resulting severe stress concentration. Although the coarsening of grains and γ' phase reduces the grain boundary strengthening effect of the 10 mm thick casting， the reduced porosity and limited dislocation localization effectively impede the crack propagation，thereby preventing a pronounced deterioration in elongation to fracture.

Liquid metal assisted cracking (LME) are a critical limitation in the performance of Zn-Al-Mg coated High Strength Steel (HSS) during resistance spot welding (RSW). To mitigate this issue, a flash nickel interlayer has been implemented on the steel surface. The mechanism by which the flash nickel interlayer mitigated LME is investigated, focusing on the combined effects of stabilizing grain boundaries and influencing crack plasticity. The findings demonstrate that the flash nickel interlayer induces grain refinement and optimizes grain orientation, enhancing dislocation accumulation near the crack tip to dissipate strain energy. This process increases the proportion of grains with Schmid factors between 0.4 and 0.5, dispersing local stress and altering the crack propagation path. The flash nickel interlayer reduces crack depth by 60.42% and crack quantity by 90.47%. Furthermore, it significantly enhances the strength and ductility of the welded joints, transitioning the fracture morphology from brittle-dominated to a brittle-ductile combination. Ni and Al additions strengthen Fe-Fe bonding and stabilize grain boundaries at the electronic level, whereas Mg addition weakens interfacial cohesion and thus promotes embrittlement. This study elucidates the mechanism of the flash nickel interlayer in mitigating LME across atomic, mesoscopic, and macroscopic scales, offering theoretical and experimental insights for the optimizing HSS during RSW processes and developing anti-embrittlement coatings.

Thin-walled components of advanced Ni-based superalloys pose significant challenges in manufacturing due to limitations in mold filling and microstructural control. This study elucidates the processing-microstructure-property relationships of a novel K439B superalloy fabricated via three distinct processes: Laser Powder Bed Fusion (LPBF) and Investment Casting including Gravity Casting (GC) and Counter Gravity Casting (CGC). The results reveal a stark trade-off between room-temperature (RT) ductility and high-temperature performance driven by intrinsic microstructural differences. CGC samples achieve a 10% increase in strength compared to GC samples, while LPBF samples increase 23% in yield strength and 179% in elongation, exhibiting superior RT strength-ductility synergy. This enhancement is attributed to the cellular structure strengthening and fine grain refinement. However, at high temperature, the LPBF specimens suffer from premature brittle fracture. Micro-structural evidence confirms that this degradation stems from the dissolution of dislocation cellular structures and rapid recrystallization, leading to dislocation annihilation and intergranular failure. In contrast, CGC specimens demonstrate the optimal balance of properties, particularly in creep rupture life, benefiting from reduced casting defects and coherent gamma ' precipitation strengthening. This work provides critical insights into the selection of processes for K439B, highlighting that while LPBF offers exceptional static strength, post-processing is indispensable for high-temperature service stability.

Conventional gravity casting (GC) inevitably causes pores, cracks, elemental segregation, and uneven phase distribution in Ni-based superalloys, which restricts the simultaneous improvement of strength and ductility. In this work, counter-gravity casting (CGC) is employed to prepare IN718 superalloys. The process–structure–performance relationship of the alloy is systematically analyzed via in-situ synchrotron X-ray diffraction and multiscale characterization. CGC, involving pressure-controlled filling and uniform thermal fields, markedly reduces defect clusters, refines and homogenizes γ″/γ′ precipitates, and suppresses grain-boundary δ-phase segregation. It also introduces residual compressive stress and improves the interfacial coherency. These microstructural changes lead to a fracture-mode transition from brittle intergranular fracture in heat-treated GC (HT-GC) alloys to ductile transgranular fracture in as-cast CGC (AC-CGC) alloys. Mechanical tests show that the AC-CGC alloy possesses an ultimate tensile strength of 1064 MPa and a fracture elongation of 16.1%, which are 13.9% and 22.0%, respectively, higher than those of the HT-GC samples. This study verifies that CGC can improve the microstructural uniformity and strength–ductility trade-off. The obtained results act as a valuable reference for developing high-performance metallic materials for the aerospace and energy industries.

Laser powder bed fusion (L-PBF) enables the additive manufacturing of nickel-based superalloys with complex geometries and high design flexibility, while avoiding conventional tooling. However, process instability-particularly spattering during laser-powder interactions-often induces internal defects that compromise mechanical performance. Here, we show that the uniform dispersion of HfO2 nanoparticles within the GH4169 superalloy simultaneously suppresses spattering, refines grains, and enhances mechanical properties. The nanoparticles were homogeneously coated onto the powder surfaces via ball milling and incorporated into the metallic matrix during L-PBF. Their presence markedly stabilized the melt pool by increasing both surface tension and viscosity, and promoted significant grain refinement and localized texture modification. Mechanical characterization revealed a 7.1 % increase in microhardness and a 9.5 % improvement in yield strength. These findings establish a nanoparticle-assisted strategy that couples process stabilization, microstructural optimization, and property enhancement, providing a mechanism-guided pathway toward application-oriented strengthening of metal matrix nanocomposites in additive manufacturing.

Thin-walled aluminum alloys,prized for their high specific strength,are critical to modern aerospace and other advanced industries.Counter-gravity casting(CGC)is a premier method for fabricating such components,where precise control over solidification microstructure is paramount.However,this control is challenged by the complex interplay of forced and natural convection during solidification.This study employs a coupled multiple-relaxation-time lattice Boltzmann(D2Q9)and quantitative phase-field model to simulate dendritic growth in a thin-walled Al-0.576wt.%Cu alloy.Simulations reveal that convection disrupts dendritic symmetry:for equiaxed crystals,solute plumes and asymmetric arm growth are observed,while for columnar dendrites,an optimal applied force exists that refines the microstructure without compromising economic viability.Furthermore,forced convection consistently reduces the inclination angle of primary dendrites.These findings,validated against experimental data,elucidate the micro-mechanisms of dendritic growth under convection,providing critical theoretical guidance for optimizing CGC processes.

This study developed a novel non local dislocation-based crystal plasticity fast Fourier transform (CPFFT) model in DAMASK to quantify the impact of microstructural heterogeneities on the anisotropic evolutions in the microstructure and tensile properties during uniaxial tensile deformation of laser powder bed fused (LPBF-ed) IN718 superalloy in transverse (TD) and building (BD) directions. To quantify the effects of texture and geometrically necessary dislocations (GNDs), four model specifications were compared, including local (LSC) and non local (NSC) single crystal (SC) of specific grains, as well as local (LPC) and non local (NPC) polycrystal (PC) plasticity overall models. In-situ EBSD was conducted during tensile tests in TD and BD to validate the modeling outputs. Modeling results showed that TD loading produced a higher locally accumulated plastic slip and GND density at grain boundaries and slip bands, leading to greater overall dislocation strengthening than BD. GND density had a more significant effect on the deformation behavior in SC than PC models, while contributing more to strengthening in PC than in SC. The anisotropic and heterogeneous deformation in each grain mainly depended on its orientations in different directions, followed by the effects of PC texture and GND density. GND density had the highest hardening effects for <110>//loading direction (LD), followed by <111>//LD and <001>//LD grains. The highest yield strength belonged to <111>//LD grains, followed by <110>//LD and <001>//LD because of their ascending/descending Schmid factor/Taylor factor values. <212>//LD-oriented grains had the highest overall hardening slope, followed by <313>//LD, <111>//LD, <110>//LD, and <001>//LD directions.

The K418B superalloy is fabricated utilizing laser powder bed fusion (LPBF) technology，and an analysis is conducted to examine the impact of process parameters on microdefect，density，microstructure，and hardness by OM，SEM and hardness tester. This is achieved by varying the laser power (ranging from 140 W to 220 W) and scanning speed(between 600 mm/s and 1400 mm/s). The findings reveal that both laser power and scanning speed significantly influence the relative density and defect distribution of the samples. Specifically，low energy density leads to the formation of irregular pores，whereas high energy density is associated with the emergence of spherical pores and solidification cracks. Excessive or insufficient volume energy density (VED) results in decreased density and impaired performance. The optimal processing conditions are identified as a laser power of 180 W and a scanning speed of 1400 mm/s，under which the sample density exceeds 99.95%，with minimal surface defects and only a small quantity of solidification cracks. Microstructure reveals distinct melt pool boundaries and cellular structure，accompanied by a Vickers hardness of 366.8 HV0.2. Notably，the grains at the melt pool boundaries are coarse，with cellular columnar crystals spanning multiple melt pools，indicating rapid solidification. The hardness initially increases and then decreases with VED，aligning with changes in pore content and density. The study attributes cracks primarily to thermal stress and provides a foundational basis for optimizing LPBF processing parameters of K418B alloy，holding potential engineering applications for enhancing the manufacturing quality of critical aero engine components.

Laser powder bed fusion (LPBF) additive manufacturing (AM) enables to three-dimensionally print intricate and customized high-end parts with a great promise for rapid manufacturing applications in aerospace, automobile, and medical industries. However, due to the lack of direct observations of defect formation and phase transformation dynamics, it suffers from keyhole pore residuals and heterogeneous phase structure as a result of repeated heating and cooling, which cause safety concerns and hinder wide industrial adoption. Here, we develop a miniature LPBF (mini-LPBF) setup that is flexible for in situ observations of keyhole and phase transformation dynamics through high-speed x-ray imaging and diffraction when implemented at synchrotron beamlines. The experimental validations of this mini-LPBF setup with an exemplary FeCoNiCrMn high-entropy alloy are carried out at BL16U2 and BL12SW beamlines of the Shanghai Synchrotron Radiation Facility. The subsurface transient dynamics of keyhole and phase transformation are characterized down to melt pool scale: keyhole geometry and its fluctuation induced pore formation are captured in high temporospatial resolution by high-speed imaging; phase transition from face-centered cubic, fully liquid and back to crystalline structures is quantified by time-resolved high-energy diffraction. This mini-LPBF setup provides the powerful infrastructure for keyhole fluctuation induced defect formation and phase transformation dynamics studies and experimental inputs for high-fidelity modeling. The knowledge gained by the aid of mini-LPBF setup through in situ monitoring of laser-metal interaction will improve the process stability and phase engineering for metal AM of novel alloys.

Superalloys have found broad applications in modern industrial aspects, especially in aerospace aspect, due to their superior mechanical properties. Investigations of microstructure evolution in superalloys during solidification, heat treatment and/or even service stages are critical and essential for optimizing processing techniques. Nowadays, PFM has become a powerful tool for studying microstructural evolution in superalloys, enabling the capture of complex phase transformations under realistic processing and service conditions. This paper systematically reviewed the recent advances of PFM applications in superalloys. Originating from thermodynamic formulations and kinetic equations, PFM has evolved into diverse models tailored to dendrite growth, precipitation evolution, creep and rafting behavior, and solute segregation. Recent advances in numerical techniques, including discretization schemes, Fourier spectral solvers, adaptive mesh refinement, and parallel acceleration, have greatly enhanced computational efficiency and accuracy. With these developments, PFM has been increasingly applied to casting, additive manufacturing, and heat treatment, enabling quantitative predictions of interface migration, stability of the γ′ phase, and defect formation. Nevertheless, challenges remain in parameter calibration, multi-physics coupling, and bridging across length and time scales, as well as propagating uncertainties from thermodynamic/kinetic databases, and establishing standardized benchmarks. Looking forward, the integration of AI with phase-field modeling is expected to enable intelligent model construction, adaptive simulation workflows, and multi-fidelity optimization, supporting more efficient microstructure–process–property linkage and accelerating alloy design and process optimization.

Zn’s natural degradability and biocompatibility make it a promising candidate for implants, however, its mechanical properties remain insufficient for bone applications. In this study, the performance of Zn was enhanced by developing Zn-Cu alloys via laser powder bed fusion (LPBF). Optimal LPBF parameters for forming stable tracks were achieved by adjusting laser power and scanning speed. Under optimized conditions of 100 W and 100 mm/s, high-density (99.58

As a cutting-edge paradigm in renewable energy systems, photothermoelectric generation (PTEG) epitomizes next-generation sustainability through the integration of selective absorbers. Inspired by the ultra-black wing nanostructures of Trogonoptera brookiana butterflies, black absorbers were fabricated on laser additive manufactured (LAM) Ti6Al4V alloy substrates (piece-by-piece segmented by wire-electrode cutting) using femtosecond laser subtractive manufacturing (fs-LSM) for PTEG applications. The resultant hierarchical architectures, comprising macropores and laser-induced periodic surface structures (LIPSSs), exhibited remarkable morphological and spectral resemblance to natural black butterfly wings. The PTEG output power and operational stability of the as-prepared functional Ti6Al4V interfaces were regulated by structural layout and post-thermal oxidation annealing. Under one-sun irradiation, the fs-LSM-structured absorber achieved a maximal peak power density of 51.38 μW⋅cm−2, maintained stable output power over 80 min of continuous operation, and sustained performance over 10 PTEG on–off cycles. The developed absorber ranks among the highest-performance fs-laser-processed absorbers reported to date, rivaling and even surpassing many phase-change materials. After 6 months of storage, the PTEG performance remained highly robust, with only slight fluctuations during 12 h of operation. A comparative analysis of PTEG performance for LAM/fs-LSM absorbers subjected to two-round 1 h and 1 h + 3 h thermal-oxidation annealing revealed that the localized surface plasmon resonance (LSPR) effect induced by oxygen-vacancy engineering effectively mitigated the radiative cooling effect (heat loss) of high-surface-area macropores, overcoming the spectral limitations encountered by ultrabroadband absorbers in PTEG applications. The concurrent manifestation of photothermal harvesting capacity and passive radiative cooling effects makes these materials promising candidates for 24 h persistent PTEG, with strong potential for deployment in remote and harsh environments. These findings may also drive innovations in multifunctional fabrication architectures through integrated “freeform additive manufacturing and micro-/nano-hierarchical functional processing.”

A directly cast Co45Ni30Cr10Al7Ti4Nb2Mo2 high-entropy alloy develops a hierarchical L12 precipitate architecture. Coarse primary L12 precipitates with cuboidal morphology and dense secondary nanoscale L12 precipitates provide strong precipitation strengthening while maintaining FCC matrix continuity for plastic deformation. At 77 K, the alloy achieves a yield strength of ∼1010 MPa, an ultimate tensile strength of ∼1726 MPa, and ∼25% elongation. TEM and interrupted synchrotron XRD reveal that cryogenic strain hardening arises from planar slip, partial-dislocation activity, stacking faults, Lomer-Cottrell locks, and progressive lattice-strain accumulation. This demonstrates an effective direct-casting strategy for high-performance cryogenic structural materials.

This research conducts a comparative study on the microstructure and mechanical properties of K4169 superalloy prepared by gravity casting (GC), counter-gravity casting (CGC) and laser powder bed fusion (LPBF). In the LPBF manufacturing process, the high temperature gradient and large cooling rate result in fine grains in the prepared samples (19∼30μm), as well as fine and distributed precipitated phases. This significantly improves their mechanical properties, which are far superior to those of the GC samples and slightly better than those of the CGC samples. The grain size of the CGC samples (650μm) is smaller than that of the GC (380μm) samples, and the size of the precipitated phases is also smaller, so their mechanical properties are better. After the three types of samples undergo SA (solution + aging) heat treatment, the molten pool in the LPBF samples disappears, the average grain size increases (45∼63μm), and a large number of δ phases and carbides precipitate at the grain boundaries, which reduces the plasticity of the LPBF samples. However, their mechanical properties reach the level of forged K4169. The grain size of the CGC samples does not change much, and more spherical carbides precipitate at the grain boundaries, which further improves the strength, making it close to that of the forged K4169 alloy, but the plasticity is further reduced. In the GC samples, there are still coarse and irregular Laves phases, acicular δ precipitated phases, and spherical carbides between the dendrites, and their strength is slightly improved. The analysis shows that the δ phase precipitated in the matrix after heat treatment reduces the plasticity of the K4169 while improving the strength of the material.

Physics-informed grain structure engineering in fusion-based laser additive manufacturing offers great promise for producing high-performance high-entropy alloys, especially for low-cost and compositionally-customized laser directed energy deposition (DED). However, detrimental columnar grains prevalently form in DED due to relatively low solidification rates and extremely high temperature gradients, making them difficult to disrupt and still poorly understood. Here, combining in-situ high-speed synchrotron X-ray imaging and diffraction, thermal imaging, and ex-situ electron microscopy approaches, we reveal a dynamic recrystallization (DRX) mechanism associated with the disruption of epitaxial columnar grains during DED of an exemplary high-entropy Cantor alloy. Multimodal melt pool monitoring enables quantitative analysis of solidification parameters and melt flow characteristics with high temporospatial resolution. Experimental observations combined with thermo-kinetic calculations indicate that both intragranular and intergranular DRX can be activated by localised micro-strains. DRX promotes grain refinement and homogeneity by tailoring energy input with optimally increasing laser power and reducing scan speed, and contributes to a tensile-to-compressive strain reversal during real-time deposition. The results of solidification-dependent grain structure evolution down to melt pool scale provide deeper understanding of in-process grain growth kinetics and enable effective methods for disrupting columnar grain growth during DED processing of novel alloys.

K439B nickel-based alloy is a novel high-temperature material capable of operating at 800 degrees C, which has been widely used in critical components such as combustion chamber housings for aerospace engines. However, the traditional casting process struggles to meet the high qualification rate requirement for high-precision forming of thin-walled complex components. In this study, laser powder bed fusion (LPBF) technology is used to process samples. By adjusting the laser power (140-220 W) and scanning speed (600-1400 mm/s), and using characterization techniques including optical microscopy, scanning electron microscopy, and electron backscatter diffraction, the effects of process parameters of LPBF on the relative density and microstructure are analyzed. The processing window (laser power:160-220 W, scanning speed:1000-1200 mm/s) for manufacturing K439B superalloy via LPBF is summarized, and two process parameters (160 W-1000 mm/s and 220 W-1200 mm/s) within the window are selected to process samples for tensile tests at room-temperature and 800 degrees C. The results show that irregular pores and Ti-C carbides are prone to form under the 160 W-1000 mm/s (volume energy density(VED) = 66.67 J/mm3) parameter. In contrast, the samples processed under 220 W-1200 mm/s (VED = 114.58 J/mm3) have a uniform microstructure without carbide, whose ultimate tensile strength at room temperature is over 1 GPa and elongation is over 25%. However, at 800 degrees C, all LPBF samples exhibit brittleness (with an elongation after fracture of approximately 0.5%), which is mainly attributed to the lack of gamma' phases and dissolution of cellular substructures inside the grains. This study provides process guidance and theoretical support for the engineering application of LPBF fabricated K439B alloy.

The filling and solidification processes in investment casting of typical K4169 nickel-based superalloy complex thin-walled casting are simulated by ProCAST finite element software.The temperature field during the casting process is analysed to predict the formation of defects. The complex thin-walled casting is produced by investment casting with the same process parameters， and its shrinkage level， microstructure， and tensile mechanical properties are studied.The results show that when the pouring temperature is 1530 ℃ and the preheating temperature of the mold shell is 1000 ℃， the filling of the molten metal is stable. The solidification conforms to the principle of sequential solidification. The overall defects of the casting are less； the micro-shrinkage average volume fraction of different parts is counted， and the highest is only 1.01%； the minimum secondary dendrite arm spacing（SDAS） in the thin-walled region is only 18.4 μm， and the maximum secondary dendrite spacing in the thick part is 38.8 μm； the as-cast microstructure of K4169 alloy is dendritic structure. After standard heat treatment， the dendrites grow and coarsen， and the dendritic morphology in the grains is not obvious. The average room temperature tensile strength of the standard heat-treated K4169 alloy is 785.0 MPa， the average yield strength is 659.7 MPa， and the average elongation is 13.9%. The difference in shrinkage porosity level significantly affects the tensile strength and yield strength， but the elongation change is not obvious.

Al-Ce alloys are promising for high-temperature applications due to their thermally stable Al11Ce3 eutectic phase, yet their strength-ductility trade-off remains a critical challenge. This study introduces Zr to Al-5wt.%Ce hypoeutectic alloys to address this limitation. Combining thermodynamic calculations, microstructure characterization, and in-situ synchrotron X-ray imaging and diffraction, we elucidate the mechanisms of Zr-induced grain refinement and strengthening. Increasing Zr content promotes the formation of primary Al3Zr phases, which act as heterogeneous nucleation sites, refining the average grain size from 576 f 182 mu m (Zr-free) to 452 f 148 mu m (0.5 wt% Zr). The Al-5Ce-0.5Zr alloy achieves optimized mechanical properties, with ultimate tensile strength increasing from 126 MPa to 137 MPa and elongation improving from 32 % to 37 %. In-situ experiments reveal that load transfer to the Al11Ce3 phase and enhanced strain hardening in both alpha-Al and Al11Ce3 contribute synergistically to strength and ductility. A quantitative model confirms that stress partitioning to Al11Ce3 rises from 170 MPa to 210 MPa with Zr addition. These findings provide critical insights for designing highperformance Al-Ce alloys via grain refinement and eutectic phase strengthening, advancing their potential in casting and additive manufacturing.