Search Results (312)

Wire arc additive manufacturing (WAAM) is an efficient, low-cost technique for fabricating large-scale metallic components and, in particular, functionally graded materials (FGMs). This review focuses on the fabrication of 316L stainless steel–Inconel 625 FGMs by arc-based WAAM processes, examining Gas Metal Arc Welding (GMAW), Gas Tungsten Arc Welding (GTAW) and Plasma Arc Welding (PAW) in terms of their microstructural outcomes, compositional control strategies, residual stress development and mechanical performance. A critical finding emerging from the reviewed literature is that direct compositional interfaces between 316L and Inconel 625 can yield superior tensile strength and ductility and lower residual stresses compared to smooth gradient strategies, owing to the formation of detrimental secondary phases such as δ-phase, Laves phase and MC carbides at intermediate iron–nickel compositions encountered only during graded builds. The potential of Submerged Arc Additive Manufacturing (SAAM) as a future high-deposition-rate alternative for large-scale FGM fabrication is also discussed. Key challenges, including dilution control, Laves phase formation, residual stress management and the corrosion characterization of the graded region, are identified, together with priority research directions for advancing the industrial adoption of arc-based FGM components. Full article

The segregation of brittle Laves phases remains a critical bottleneck limiting the performance of additive manufacturing (AM) nickel-based superalloys. While its evolution is governed by complex transient physical fields within the melt pool, a quantitative kinetic correlation between processing parameters and microstructural features is currently lacking. In this study, a high-fidelity multiphysics numerical model was developed to establish a cross-scale mapping logic of “Process-Physical Field-Microstructure” by dissecting the global distribution of temperature gradient (G) and solidification rate (R) along the quasi-steady-state melt pool boundary. It is revealed that increasing the scanning speed synergistically enhances R while compressing G. Beyond driving a transition from oriented columnar dendrites to refined mixed-dendritic structures, this shift effectively blocks the continuous enrichment channels of Nb and Mo elements by compressing the “kinetic time window” for solute redistribution. Consequently, the morphology of the Laves phase is forced to evolve from a continuous interconnected chain-like network into dispersed isolated particles. This research clarifies the kinetic essence of microstructural evolution under non-equilibrium solidification, providing critical physical criteria for the precise intervention of deleterious phases and the regulation of microstructural consistency in high-performance AM components. Full article

High-strength stainless steels are essential materials for critical load-bearing aerospace components, and solution treatment serves as a core process governing their strength–toughness balance. However, in novel multi-element alloy systems, the complex dissolution behavior of precipitates and its underlying mechanisms affecting matrix phase transformations require further investigation. This study systematically explores the thermodynamic evolution and microstructural response of a novel Fe-Ni-Cr-Mo-Al-Ti ultra-high-strength stainless steel during solution treatment. The research highlights how solution temperature drives Laves phase dissolution, controls prior austenite grain growth, redistributes local chemical elements, and dictates retained austenite stability. By establishing the relationship between microstructural features and macroscopic properties, this study aims to provide crucial theoretical guidance for optimizing heat treatment protocols to achieve superior comprehensive mechanical properties in advanced high-strength stainless steels. Full article

The feasibility of using brittle δ-Nb₃Al as the reinforcement phase in powder metallurgy nickel-based superalloys depends on both the preparation of near-spherical particles and their phase stability during hot isostatic pressing (HIP). In this study, irregular δ-Nb₃Al particles were converted into near-spherical reinforcement particles by controlled ball milling. The optimized milling condition for obtaining high-sphericity δ-Nb₃Al particles was 200 r/min for 20 h. The morphological evolution during ball milling clarifies a particle-rounding mechanism governed by edge elimination, fine-fragment adhesion, surface consolidation, and re-fragmentation. During subsequent HIP consolidation to introduce the particles into a nickel-based superalloy, extensive interdiffusion occurred between δ-Nb₃Al and the surrounding matrix, resulting in the formation of multilayer interfacial reaction zones and multiple Nb-rich secondary phases, including Laves-(Ni, Cr)₂Nb, Ni₆Nb₇, Nb solid solution, and Ni₃Nb. Quantitative analysis indicates that the retained volume fraction of δ-Nb3Al after HIP is only about 9.85%, much lower than the initial addition level. Combined with thermodynamic analysis based on the effective heat of formation model, the results show that the final phase constitution is governed by the coupled effects of diffusion kinetics and thermodynamic driving force. These findings clarify the intrinsic processing–microstructure–phase transition relationship in δ-Nb₃Al-reinforced powder metallurgy nickel-based superalloys, showing that ball milling controls the powder-state evolution of δ-Nb₃Al, whereas diffusion-driven interfacial reactions during HIP govern its retention and final phase constitution. Full article

Ductile iron suffers from insufficient wear resistance under heavy-load service conditions. Surface engineering technologies offer effective solutions to this problem. However, current research on the application of atmospheric plasma-sprayed (APS) CoCrFeNiNb_x high-entropy alloy (HEA) coatings on ductile iron and the systematic study of compatible heat treatment processes with the substrate are still insufficient. In this study, CoCrFeNiNb_x HEA coatings (x = 0.25, 0.50, 0.75, 1.00) were deposited on QT800-5 ductile iron by APS, and the effects of Nb content and low-temperature annealing (400–600 °C) on coating microstructure and properties were investigated. The x = 0.25 coating exhibited a single face-centered cubic (FCC) solid solution structure, while coatings with x ≥ 0.50 comprised an FCC solid solution and Cr₂Nb-type Laves phase; hardness increased with Nb content, and as-sprayed wear resistance peaked at x = 0.75. Post-deposition annealing at 500 °C yielded a peak hardness of 477.45 HV and reduced the wear rate by 45% relative to the as-sprayed condition, with no measurable degradation of the substrate. These findings offer a practical reference for developing wear-resistant coatings on ductile iron components. Full article

Nickel-based superalloy GH3625 is widely used in extreme environments due to its exceptional high-temperature strength and corrosion resistance; however, optimizing its comprehensive performance through precise microstructural control remains a critical challenge. In this study, the effect of withdrawal rate (10–200 μm/s) on the microstructural evolution, mechanical properties, and corrosion resistance of GH3625 alloy was investigated using a liquid-metal-cooled directional solidification system. The microstructural characteristics, elemental segregation, and phase distributions were systematically analyzed via OM, SEM, and EDS, followed by uniaxial tensile and electrochemical polarization tests. The results show that with increasing withdrawal rate, the solid–liquid interface morphology evolves from cellular to cellular-dendritic and finally to fully dendritic. Correspondingly, the primary dendrite arm spacing decreases from 270.4 μm to 100.2 μm, and the secondary dendrite arm spacing decreases from 66.5 μm to 12.3 μm. The area fraction of the detrimental Laves phase first decreases and then increases, reaching a minimum at 100 μm/s. Correspondingly, the yield strength increases from 282 MPa to 409 MPa, and the corrosion resistance is optimized at 100 μm/s. The microstructure–property relationships are discussed based on second-phase strengthening theory and microstructural refinement. This study provides a theoretical basis and practical process windows for optimizing directional solidification parameters to achieve enhanced mechanical and corrosion performance in GH3625 alloy. Full article

The influence of Ni and Co additions on microstructure and mechanical properties of (CoCrCuTi)_100−xFe_x high-entropy alloys (HEAs) containing 10 or 15 at. % Fe was investigated. The base HEA consisted of dendritic C14 Laves phases with interdendritic Cu-rich FCC regions. When Ni in the range of 2.5 to 10 at. % was added, a reduction in the Cu-rich phase was observed. Conversely, Co additions in the same range initially increased the Cu-rich phase but eventually led to liquid-phase separation (LPS), forming distinct Cu-lean L1 liquid and Cu-rich L2 globular regions. The average Vickers hardness values of (CoCrCuTi)₉₀Fe₁₀ and (CoCrCuTi)₈₅Fe₁₅ HEAs were measured at 790 ± 33 HV and 760 ± 20 HV, respectively. The additions of Ni and Co decreased overall hardness values. However, while Ni additions caused greater microstructural refinement, Co additions eventually led to heterogeneity due to LPS. For instance, the Vickers hardness of (CoCrCuTi)₉₀Fe₁₀ with 2.5 at. % Ni reached a maximum of 706 ± 95 HV, decreasing in hardness and scatter to 646 ± 19 HV when Ni increased to 10 at. %. In contrast, Co additions led to a marked reduction in hardness, from 574 ± 114 HV at 2.5 at. % Co to 442 ± 246 HV at 10 at. % Co. The fracture toughness (KIC), determined using Vickers indentation testing, indicated that Ni additions reduce fracture toughness, while Co additions increase it. Full article

To study the influence of freckle defects on the hot deformation behavior and the inheritance of dynamic recrystallization (DRX) structure in GH4706 alloy, the microstructures of specimens with and without freckles and the evolution laws of hot-processing parameters were compared. Hot compression experiments were conducted on a thermal simulation testing machine at 950–1150 °C, strain rates of 0.001–1 s⁻¹, and 55% deformation. Freckle-containing specimens were tested under DRX critical conditions. The flow stresses of both specimens increase with strain rate or with decreasing temperature. The power dissipation coefficient (η) and instability value (ξ) follow complex laws. Electron back-scattering diffraction (EBSD) was used to analyze DRX microstructures and nucleation mechanisms. The DRX degree of freckle-containing specimens is lower, with a larger average grain size. The DRX mechanism initiates preferentially in freckle-containing specimens, and its volume fraction changes in a complex manner. Grain coarsening occurs in freckle-containing specimens at high temperatures and low strain rates. Freckle defects lead to significant differences in the DRX mechanism of GH4706 alloy. Freckle-containing specimens exhibit both discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX), whereas freckle-free specimens primarily display DDRX and second-phase particle-stimulated nucleation (PSN). The presence of MC carbides and Laves phases within freckle defects provides nucleation sites, further supporting a typical second-phase particle-stimulated nucleation mechanism. Full article

Materials capable of withstanding extreme environments open promising opportunities for nuclear fusion reactors. In this study, equiatomic CrFeTaVW and CrFeTiVW high-entropy alloys are investigated as interlayer materials between W and CuCrZr. Monte Carlo and Molecular Dynamics simulations predicted a bcc-type structure for both systems. Additionally, the Monte Carlo simulation predicts lower potential energy and a more stable structure for both systems than Molecular Dynamics. For CrFeTaVW, the chemical segregation values are lower in MC than in the MD simulation, whereas for CrFeTiVW, the opposite trend is observed, with MC indicating stronger segregation values. After simulation, the high-entropy alloys were prepared by planetary ball milling, consolidated by spark plasma sintering, and analyzed using X-ray diffraction, scanning electron microscopy, and thermal diffusivity. The experimental results for the milled powders confirmed the formation of a bcc structure in both alloys. The consolidated material revealed a bcc-type structure and an Fe₂Ta Laves phase for the CrFeTaVW HEA, while the CrFeTiVW HEA exhibits two different bcc-type structures. The values of CrFeTaVW and CrFeTiVW thermal diffusivity are between 3.5 and 7 mm²/s, which is consistent with the expected values for high-entropy alloys. Overall, the findings indicate that these HEAs have promising properties that can be used in extreme environments. Full article

Wire–Laser Additive Manufacturing (WLAM) is a promising directed energy deposition technique for producing and repairing high-performance components with high material efficiency and strong metallurgical bonding. This study optimizes single-track Inconel 718 claddings deposited by WLAM on AISI 304L stainless steel and S355 structural steel substrates, focusing on the relationships between processing parameters, microstructure, post-deposition heat treatment, and mechanical performance. A systematic parametric assessment evaluated the influence of laser power, laser speed, wire feed rate, and shielding gas pressure on key quality metrics, including dilution, wettability, porosity, and cracking. Distinct optimal processing windows were identified for each substrate, reflecting their different thermal responses: for 304L, 8.5 kW laser power, 0.55 m/min laser speed, 5 m/min wire feed rate, and 2 bar argon; for S355, 9.6 kW laser power, 0.6 m/min laser speed, 4.9 m/min wire feed rate, and 4 bar argon. Post-deposition heat treatment markedly enhanced performance by dissolving Nb-rich interdendritic Laves phase and promoting γ′/γ″ precipitation. As a result, clad hardness increased from ≈225 HV 0.3 (as-built) to ≈412 H V0.3 after heat treatment (+84%). Tensile testing confirmed substantial strengthening, with yield strength increasing from 447 to 853 MPa (horizontal build) and from 488 to 960 MPa (vertical), while ultimate tensile strength rose from 824 to 1057 MPa (horizontal) and from 836 to 1090 MPa (vertical). Mechanical anisotropy remained significant, linked to columnar grain morphology and build orientation. Overall, the results provide practical process window and heat treatment guidelines for reliable industrial implementation of high-quality Inconel 718 claddings on steel substrates for demanding applications. Full article

Refractory high-entropy alloys (RHEAs) have garnered attention for their exceptional high-temperature mechanical properties, making them suitable for aerospace and energy applications. However, balancing strength and ductility remains a challenge due to the presence of Laves phases. In this study, Al_0.5Nb_0.5TiV₂Zr_x (x = 0–2.0) alloys were prepared using vacuum arc melting, and their microstructural evolution and mechanical properties were analyzed. At room temperature, the Al_0.5Nb_0.5TiV₂Zr_0.5 alloy exhibits the highest yield strength (1658.1 MPa), which is primarily attributed to strong lattice distortion induced by Zr and moderate precipitation strengthening from Laves phases. In contrast, at higher Zr contents, excessive Laves phase precipitation promotes stress concentration, leading to a marked reduction in both strength and ductility. High-temperature compression tests revealed that the Al_0.5Nb_0.5TiV₂Zr_0.5 and Al_0.5Nb_0.5TiV₂Zr_1.5 alloys still exhibited over 50% compressive plasticity at 800 °C and 1000 °C. However, when the temperature reached 1000 °C, the instability of the Laves phase led to a reduction in the yield strength to below 160 MPa, indicating that the effect of solid-solution strengthening was no longer significant under high-temperature conditions. These findings clarify the critical role of Zr content and temperature in governing the microstructural and mechanical evolution of the Al–Nb–Ti–V–Zr system and provide a theoretical basis for achieving an optimized strength–ductility balance in RHEAs through compositional control. Full article

HfC possesses high hardness, high melting point, and excellent thermal stability, and is regarded as an important wear-resistant reinforcing phase material. In this study, the laser cladding technique was employed to fabricate CoCrFeNiTi and CoCrFeNiTi/HfC composite coatings on the surface of Q235 substrate. The influence of HfC addition on the phase structure evolution, microstructure, and wear resistance of the coatings was systematically investigated. The results showed that the addition of HfC did not alter the phase structure of the coating, which remained dominated by an FCC solid solution. However, they induced the formation of an in situ TiC strengthening phase and reduced the brittle Laves phase content, thereby optimizing the coating’s toughness. At the same time, the coating transformed from columnar to equiaxed crystals, with significantly finer grains and further improved structural uniformity. Compared with the CoCrFeNiTi coating, the CoCrFeNiTi/HfC composite coating exhibited a more stable friction coefficient, a significantly lower wear rate, and improved wear resistance by approximately 2.4 times. The performance improvement was mainly attributed to the load-bearing strengthening and crack-pinning effect of the in situ TiC, the inhibitory effect of the reduction in the Laves brittle phase on adhesive wear, and the synergistic effect of Hf, which forms a stable oxidation-protective film during friction. Full article

In this study, 3 wt.% Re/Inconel 718 composite was fabricated by laser powder bed fusion (LPBF), and the effects of aging treatments on the microstructure and properties of the Re/Inconel 718 composite were systematically investigated. This study aims to elucidate the synergistic optimization of microstructure and properties in LPBF Inconel 718, achieved through Re alloying and subsequent heat treatment. Results demonstrated that the samples undergo recrystallization and precipitate numerous fine strengthening phases after heat treatment. Concurrently, heat treatment promotes the diffusion of Re within the material, leading to a significant reduction in its concentration in locally enriched regions. The addition of Re improves the mechanical properties and corrosion resistance of the Inconel 718 alloy through synergistic strengthening mechanisms, including dispersion strengthening, solid solution strengthening, and dislocation strengthening. When the two-stage aging is 720 °C × 8 h (FC × 2 h) + 620 °C × 8 h (AC), the optimum mechanical properties are observed. The dissolution of Laves phases, simultaneous precipitation of both γ″ and γ′ phases, and homogenization of microstructure are responsible for the enhancement of the material’s mechanical properties. However, the extensive precipitation of strengthening phases also promotes the formation of numerous microscopic corrosion cells, which accelerates the corrosion rate and leads to a marked reduction in corrosion resistance of the material. This study provides new insights into the laser additive manufacturing of high-performance nickel-based composites. Full article

The microstructure evolution law and the changes in mechanical properties of 442 ferritic stainless steel after annealing treatment at different temperatures are systematically investigated. The results show that, as the annealing temperature increases, the cold-rolled 442 ferritic stainless steel successively undergoes the process of recovery, recrystallization and grain growth, with the microstructure gradually changing from a fibrous to recrystallized structure, and the secondary phases, such as the Nb(C, N) phase, σ phase and Laves phase, precipitate. In terms of mechanical properties, the tensile strength, yield strength and Vickers hardness gradually decrease, while the elongation after fracture gradually increases. When the annealing temperature reaches 800 °C, the material exhibits the optimal comprehensive mechanical properties. The yield strength, tensile strength and elongation reach 371 MPa, 534 MPa and 31%, respectively, and the hardness is 175 HV. The fracture mode of the sample is mainly ductile fracture. EBSD analysis indicates that the strong Brass {110}<112> texture existing in the cold-rolled state gradually weakens with the annealing process, and the {111}<110> texture strengthens, thereby reducing the influence of unfavorable textures. The research results provide theoretical basis and data support for microstructure regulation and performance optimization of 442 ferritic stainless steel. Full article

The formation and evolution of secondary phases, such as sigma (σ), chi (χ), Laves, carbides (M₂₃C₆), and nitrides (Cr₂N), have a fundamental impact on the corrosion resistance of stainless steels. These stages alter the matrix’s local chemistry, compromise the passive film’s quality, and promote micro-galvanic interaction, which enhances localized corrosion issues. The thermodynamic stability, precipitation kinetics, and corrosion consequences of secondary phases in austenitic, ferritic, duplex, and lightweight (Fe–Mn–Al–C) stainless-steel systems are thoroughly reviewed and discussed in this paper. Advances in high-resolution characterization techniques, such as TEM, EBSD, atom-probe tomography, and in situ synchrotron techniques, have made it possible to map corrosion problems caused by secondary phases at the nanoscale. Computational thermodynamics (CALPHAD, DICTRA, TC-PRISMA) and emerging machine-learning models now provide quantitative prediction of phase formation and dissolution. Strategies for mitigation through alloy design, thermal treatment, and surface engineering are summarized, together with additive-manufacturing approaches for microstructural tailoring. Finally, this review highlights the integration of multi-scale modeling and sustainable alloy design to ensure phase-stable, corrosion-resistant stainless steels that enhance asset integrity and infrastructure reliability as per Sustainable Development Goals. Full article