Search Results (693)

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

The study investigates the influence of microstructures on fatigue behavior and failure mechanisms of the α-β titanium alloy Ti6246, fabricated via Powder Bed Fusion-Laser Beam (PBF-LB). In particular, the investigation assesses the effect of two post-processing heat treatments, namely α-β annealing at 875 °C (AN875) and solution treatment at 825 °C followed by aging at 500 °C (STA825), on the alloy’s rotating and bending fatigue behavior. The results indicate that the STA825 condition provides superior fatigue resistance (+25%) compared to AN875, due to the presence of a finer bilamellar microstructure, characterized by thinner primary α lamellae (α_p) and a more homogeneous distribution of secondary α lamellae (α_s) within the β matrix. Additionally, an investigation conducted using the Kitagawa–Takahashi (KT) approach and the El-Haddad model, based on the relationship between the fatigue limit and defect sensitivity, revealed improved crack propagation resistance from pre-existing defects (ΔK_th) for the STA825 condition compared to AN875. Notably, the presence of fine α_s after aging for STA825 is effective in delaying crack nucleation and propagation at early stages, while refined α_p contributes to hindering macrocrack growth. The fatigue behavior of the STA825-treated Ti6246 alloy was even superior to that of the PBF-LB-processed Ti64, representing a viable alternative for the production of high-performance components in the automotive and aerospace sectors. Full article

Additive manufacturing (AM), particularly laser powder bed fusion (L-PBF), provides unmatched design flexibility for creating intricate steel structures with minimal post-processing. However, adopting L-PBF for high-performance applications is difficult due to the challenge of predicting microstructure evolution. This is because the process is sensitive to many parameters and has a complex thermal history. Thin-walled geometries present an added challenge because their dimensions often approach the scale of individual grains. Thus, microstructure becomes a critical factor in the overall integrity of the component. This study focuses on applying cellular automata (CA) modeling to establish robust and efficient process–structure relationships in L-PBF of 316L stainless steel. The CA framework simulates solidification-driven grain evolution and texture development across various processing conditions. Model predictions are evaluated against experimental electron backscatter diffraction (EBSD) data, with additional quantitative comparisons based on texture and morphology metrics. The results demonstrate that CA simulations calibrated with relevant process parameters can effectively reproduce key microstructural features, including grain size distributions, aspect ratios, and texture components, observed in thin-walled L-PBF structures. This work highlights the strengths and limitations of CA-based modeling and supports its role in reliably designing and optimizing complex L-PBF components. Full article

This study explores the feasibility of generating a globular microstructure in situ during the thixotropic 3D printing of the EN AW-4043 alloy, starting from a conventional cold-rolled wire. Thermodynamic simulations using Thermo-Calc software were first conducted to identify the semi-solid processing window of the alloy, based on the evolution of liquid and solid fractions as a function of temperature. Guided by these results, thermal treatments were performed on cold-rolled wires to promote the formation of a globular microstructure. A laboratory-scale printing head prototype was then designed and built to test continuous heating and deposition conditions representative of a thixotropic additive manufacturing process. The results showed that a globular microstructure could be achieved in the cold-rolled EN AW-4043 wires by heating them at 590 °C for 5 min in a static muffle furnace. A similar effect was observed when continuously heating the wire while it flowed through the heated printing head. Preliminary deposition tests confirmed the viability of this approach and demonstrated that thixotropic 3D printing of EN AW-4043 alloy is achievable without the need for pre-globular feedstock. Full article

Thermomechanical processing has a significant impact on the porosity and mechanical properties of AISI 316L stainless steel produced by laser powder bed fusion (L-PBF). This work evaluated the effect of three heat treatment conditions: as-built (HT0), annealed at 650 °C for 3 h with air cooling (HT1), and annealed at 1050 °C for 1 h followed by water quenching (HT2), combined with cold and hot rolling at different strain levels. The most pronounced improvement was observed after 20% hot rolling followed by water quenching (HR + WQ), which reduced porosity to 0.05% and yielded the most spherical pores, with a circularity factor ($f_{circle}$) of 0.90 and an aspect ratio (AsR) of 1.57. At elevated temperatures, the matrix becomes more pliable, which promotes pore closure and helps reduce stress concentrations. On the other hand, applying heat treatment without causing deformation resulted in the pores growing and increasing porosity in the build direction. The fractography supported these findings, showing a transition from brittle to more ductile fracture surfaces. Heat treatment combined with plastic deformation effectively reduced internal defects and improved both structural integrity and strength. Full article

Additive manufacturing techniques, such as laser-based powder bed fusion of metals (PBF-LB/M), have now gained high industrial and academic interest. Despite its design flexibility and the ability to fabricate intricate components, LPBF has not yet reached its full potential, partly due to the challenges associated with microstructure control. The precise manipulation of the microstructure in LPBF is a formidable yet highly rewarding endeavor, offering the capability to engineer components at a local level. This work introduces an innovative parallelized Cellular Automaton (CA) framework for modeling the evolution of the microstructure during the LPBF process. LPBF involves remelting and subsequent nucleation followed by crystal growth during solidification, which complicates and burdens microstructure simulations. In this research, a novel approach to nucleation seeding and crystal growth is implemented, focusing exclusively on the final stages of melting and solidification, enhancing the computational efficiency by 30%. This approach streamlines the simulation process, making it more efficient and effective. The developed model was employed to simulate the microstructure of an austenitic advanced high-strength steel (AHSS). The model was validated by comparing the simulation results qualitatively and quantitatively with the experimental data obtained under the same process parameters. The predicted microstructure closely aligned with the experimental findings. Simulations were also conducted at varying resolutions of CA cells, enabling a comprehensive study of their impact on microstructure evolution. Furthermore, the computational efficiency was critically evaluated. Full article

This study systematically explores the synergistic effects of direct aging treatment (480 °C for 6 h) combined with cryogenic treatment (−196 °C for 8 h) on the mechanical properties and microstructural evolution of 18Ni300 maraging steel fabricated via selective laser melting (SLM). Three conditions were investigated: as-built, direct aging (AT6), and direct aging plus cryogenic treatment (AT6C8). Microstructural characterization was performed using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD), while the mechanical properties were evaluated via microhardness and tensile testing. The results show that the AT6C8 sample achieved the highest microhardness (635 HV_0.5) and tensile strength (2180 MPa), significantly exceeding the as-built (311 HV_0.5, 1182 MPa) and AT6 (580 HV_0.5, 2012 MPa) samples. Cryogenic treatment induced a notable phase transformation from retained austenite (γ phase) to martensite (α phase), with the peak relative intensity ratio ranging from 1.42 (AT6) to 1.58 (AT6C8) in the XRD results. TEM observations revealed that cryogenic treatment refined lath martensite from 0.75 μm (AT6) to 0.24 μm (AT6C8) and transformed reversed austenite into thin linear structures at the martensite boundaries. The combination of direct aging and cryogenic treatment effectively enhances the mechanical properties of SLM-fabricated 18Ni300 maraging steel through martensite transformation, microstructural refinement, and increased dislocation density. This approach addresses the challenge of balancing strength improvement and residual stress relaxation. Full article

The rapid growth of the machining market and advancements in additive manufacturing (AM) present new opportunities for innovative tool designs. This preliminary study proposes a design for additive manufacturing (DfAM) approach to redesign a milling cutter head in 17-4 PH stainless steel by integrating topology optimization (TO) and internal coolant channel optimization, enabled by laser powder bed fusion (LPBF). An industrial eight-insert milling cutting tool was reimagined with conformal cooling channels and a lightweight topology-optimized structure. The design process considered LPBF constraints and was iteratively refined using computational fluid dynamics (CFD) and finite element analysis (FEA) to validate fluid flow and structural performance. The optimized milling head achieved approximately 10% weight reduction while improving stiffness (reducing maximum deformation under load from 160 μm to 151 μm) and providing enhanced coolant distribution to the cutting inserts. The results demonstrate that combining TO with internal channel design can yield a high-performance and lightweight milling tool that leverages the freedom of additive manufacturing. As proof of concept, this integrated CFD–FEA validation approach under DfAM guidelines highlights a promising pathway toward superior cutting tool designs for industrial applications. Full article

Titanium alloys, especially Ti6Al4V, are widely used in biomedical implants due to their biocompatibility and mechanical strength. However, their high elastic modulus (>100 GPa), compared to that of human bone (10–30 GPa), often causes stress shielding, reducing implant lifespan. To address this, titanium alloys with lower elastic modulus are under development. In this study, Ti-based multi-element alloy with 16 wt.% Nb samples were fabricated using laser powder bed fusion (L-PBF) from a premixed powder blend of Ti6Al4V and Nb-Hf-Ti. Processing high-melting Nb-based alloys via L-PBF poses challenges, which were mitigated through optimized parameters, including a maximum laser power of 100 W. Eleven parameter sets were employed to evaluate printability, microstructure, and mechanical properties. Microstructural analysis revealed Widmanstätten structures composed of α and β phases, along with isolated spherical pores. Reduced hatch spacing and slower laser speed led to increased hardness. The highest hardness (~43 HRC) was observed at the highest energy density (266 J/mm³), while the lowest (~28 HRC) corresponded to 44 J/mm³. Elastic modulus values ranged from 30 to 35 GPa, closely matching that of bone. These results demonstrate the potential of the developed Ti-based alloy containing 16 wt.% Nb as a promising candidate for load-bearing biomedical implants. Full article

This article studies the effects of a laser remelting treatment on the microstructure and properties of Al-Cu-Mn alloy surfaces, as well as the effects of a heat treatment process on the microstructure and mechanical properties of the matrix zone and remelting zone. The results showed that the remelting zone structure was mainly composed of equiaxed dendrites and fine columnar dendrites. The α(Al) phase and θ(Al₂Cu) phase were greatly refined after laser remelting. The T(Al₁₂CuMn₂) phase was completely dissolved into the α(Al) matrix. The hardness of the remelting zone increased significantly with an increase in the height of the molten pool, and the strengthening mechanism was mainly fine grain strengthening and second phase strengthening. For identical aging treatments, the solution treatment at 530 °C for 4 h yielded the highest hardness. Relative to samples aged without prior solution treatment, hardness increased by 80% in the matrix zone and 59.1% in the remelting zone. When the solid solution process was the same, the time to reach peak hardness was shortened when the aging temperature increased, and the hardness of both the matrix zone and remelting zone reached its peak at 175 °C for 8 h of aging. After aging, the friction coefficient of the alloy decreased due to the increase in the strength of the alloy. Full article

Selective laser melting (SLM) allows the production of complex lattice structures with tunable mechanical properties. This study proposes an integrated approach to enhance the mechanical properties of Inconel 718 (IN718) lightweight structures by applying distinct heat treatment protocols and tailoring key printing parameters. Four lattice geometries—body-centered cube (BCC), diamond, inverse woodpile (IWP), and gyroid—were selected for evaluation. Three heat treatment protocols were applied to assess their effect on mechanical behavior. Additionally, the influence of key SLM parameters such as laser power, scan speed, hatch spacing, and layer thickness on structural performance was investigated. By combining process tailoring and post-processing strategies, this work demonstrates a method to improve the mechanical response of complex IN718 lattices. The results highlight significant improvements in yield strength and energy absorption for high-performance applications in aerospace and automotive engineering. Full article

Laser–MIG hybrid welding–brazing was performed to join TC4 titanium alloy and 5083 aluminum alloy with ER5356, ER4043 and ER2319 filler wires. The effects of the different filler wires on the microstructural features and mechanical properties of Ti/Al welded–brazed butt joints were investigated in detail. The wetting and spreading effect of the ER4043 filler wire was the best, especially on the weld’s rear surface. Serrated-shaped and rod-like IMCs were generated at the top region of the interface of the joint with ER4043 filler wire, but rod-like IMCs did not appear at the joints with the other filler wires. Only serrated-shaped IMCs appeared in the middle and bottom regions for the three filler wires. The phase compositions of all the IMCs were inferred as being made up of TiAl₃. The average thickness of the IMC layer of joints with the ER5356 and ER2319 filler wires was almost the same and thinner than that of the joint with the ER4043 filler wire. The average thickness was largest in the middle region and smallest in the bottom region for all the joints with the three filler wires. The average microhardness in the weld metal of ER5356, ER4043 and ER2319 filler wires could reach up to 77.7 HV, 91.2 HV and 85.4 HV, respectively. The average tensile strength of joints with the ER5356, ER4043 and ER2319 filler wires was 106 MPa, 238 MPa and 192 MPa, respectively. The tensile samples all fractured at the IMC interface and showed a mixed brittle–ductile fracture feature. These research results could help confirm the appropriate filler wire for the laser–MIG hybrid welding–brazing of Ti/Al dissimilar butt joints. Full article

Electron beam melting (EBM) technology has gained prominence owing to its ability to enhance production efficiency and meet green manufacturing standards. However, overhang structures are a significant issue for additive manufacturing due to their need for supporting structures during printing. This increases manufacturing time, requiring more material, extra effort, and a more complex engineering procedure. Therefore, this research aims to develop an intelligent optimization method based on AI-ANFIS/Al-ANN and improved NSGA-III, integrating the AM design, 3D printing, and post-processing phases to enhance the performance of block support structures and the quality of the EBM parts produced. To achieve this, statistical analysis was performed to detail the simultaneous influence of block support type, block support structure design, and EBM parameters on fabricating performance, warping deformation, support removal time, and support volume. After that, intelligent models based on ANFIS/ANN and the advanced NSGA-III method were developed for monitoring and optimizing the performance of specified block support structures. The results reveal that the block support type, block support structure design, and EBM parameters simultaneously significantly affect block support structures’ performance. This study illustrated that the AI models based on ANFIS might provide more accurate and reliable estimation models for monitoring and predicting support volume, support removal time, and warping deformation, exhibiting reduced errors of 0.992%, 1.2%, 1.28%, and 1.06%, respectively, in comparison to empirical measurements, ANN models, and regression models. Finally, the developed intelligent method obtains the optimal block support type, block support design, and EBM parameters to enhance the quality of produced parts, reduce material wastage, and reduce the post-processing time of fabricated EBM Ti6Al4V. Henceforth, smart systems may be employed to create innovative solutions that integrate the AM design, 3D printing, and post-processing stages. This will allow for the monitoring and improvement of AM process performance, as well as the fulfillment of Industry 4.0 requirements. Full article

Conventional WC-Co hard metals have proven to be difficult to manufacture by means of laser powder bed fusion (PBF-LB), resulting in residual pores, crack formation, foreign phase formation, and the inhomogeneous growth of the carbide phase. Alternative compositions such as the W-C-Ti system presented in this study need to be investigated. Through the employment of a high-throughput screening approach, 11 alloy compositions were investigated to determine the influence of the carbon content and tungsten–titanium ratios on microstructure formation and basic mechanical properties. Two screenings were conducted, with one varying the carbon content (10–35 at.%) and the other adjusting the W/Ti ratios (10:90 to 60:40 at.%). Microstructural analyses using scanning electron microscopy (SEM), X-ray diffraction (XRD), and hardness measurements provided insights into phase formation, grain distribution, and mechanical properties. The results showed that increasing the carbon content significantly enhanced the hardness (from 681 HV (10 at.% C) to 1898 HV (35 at.% C)) due to higher δ-(Ti,W)C_1−x carbide phase fractions. Alloys with a higher tungsten content exhibited finer microstructures and an improved crack resistance while maintaining a high hardness (1900–2100 HV). This study identified an alloy with 32.5 at.% W, 32.5 at.% Ti, and 35 at.% C as a promising candidate for further investigation, with properties similar to those of a conventional WC-Co hard metal. Full article

Bending fatigue significantly affects the mechanical stability and lifespan of biomedical implants, such as bone plates and orthopaedic fixation devices, which undergo cyclic loading in the human body. This study examines the microstructure, porosity, and bending fatigue properties of PBF-LB/M SS316L. Samples were analysed across three faces (top, front, and side) using optical microscopy (OM) and scanning electron microscopy (SEM) to observe microstructural features and porosity. Elemental composition was measured by energy-dispersive X-ray spectroscopy (EDX). Phase structures and grain orientations were characterised via X-ray diffraction (XRD) and electron backscatter diffraction (EBSD). Four-point bending fatigue tests, conducted under two loading conditions, below and slightly above the yield point, demonstrated that defects inherent to the PBF-LB/M process, particularly micropores and unmelted powder particles, strongly influence fatigue crack initiation. Real-time monitoring of crack initiation and propagation on the external sample surface was performed using a high-speed digital microscope. These findings indicate the influence of microstructural defects on fatigue performance in PBF-LB/M SS316L, supporting the design and development of more reliable patient-specific biomedical implants. Full article