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Laser-powder bed fusion additive manufacturing (LPBF-AM) of metals is rapidly becoming one of the most important materials processing pathways for next-generation metallic parts and components in a number of important applications. However, the large parametric space that characterizes laser-based LPBF-AM makes it challenging to understand what are the variables controlling the microstructural and mechanical property outcomes. Sensitivity studies based on direct LPBF-AM processing are costly and lengthy to conduct, and are subjected to the specifications and variability of each printer. Here we develop a fast-throughput numerical approach that simulates the LPBF-AM process using a cellular automaton model of dynamic solidification and grain growth. This is accompanied by a polycrystal plasticity model that captures grain boundary strengthening due to complex grain geometry and furnishes the stress-strain curves of the resulting microstructures. Our approach connects the processing stage with the mechanical testing stage, thus capturing the effect of processing variables such as the laser power, laser spot size, scan speed, and hatch width on the yield strength and tangent moduli of the processed materials. When applied to pure Cu and stainless 316L steel, we find that laser power and scan speed have the strongest influence on grain size in each material, respectively.

This study used laser additive manufacturing technology to fabricate austenitic–martensitic stainless steel functionally graded materials (ASS-MSS FGM). The microstructure and mechanical properties of ASS-MSS FGM were characterized, and the surface integrity after milling experiments of the ASS-MSS FGM was analyzed. The microstructure of the ASS-MSS FGM exhibited a dense subgrain structure with diverse subgrain types and no fixed growth direction. The microhardness of the ASS-MSS FGM increased from 283 HV to 530 HV due to the increased proportion of the martensitic phase. The ASS-MSS FGM tensile specimens fractured in the austenitic stainless steel region. The tensile strength is 896 MPa, which is increased by 121 MPa compared to ASS. The fracture elongation is 18%, which is increased by 140% compared to MSS. The milling experiments revealed that the degree of work hardening decreased by 8.1% along the building direction of the ASS-MSS FGM. Compared with the austenitic and martensitic layers, the degree and depth of work hardening of the gradient layer were in the transitional zone between them. The microstructure of ASS-MSS FGM after the milling mainly exhibited three deformation phenomena: grain squeezed deformation, grain broken dislodgement, and grain sheared fracture. [ABSTRACT FROM AUTHOR]

In order to fulfill the demands of increasingly complex processes, laser additive manufacturing processes are combined with five-axis linkage technology. The tool axis vector is critical to the accuracy of part shaping. However, due to the machine performance limitation, the previous methods of tool axis planning may cause the laser deposition head to decelerate and wait for the rotary table, leading to an abnormal bulge at the position. Therefore, this paper proposed a tool axis vector optimization method based on automatically smoothing the C-axis rotary angle. First, the adjustment range of the C-axis angle is calculated by forward and negative kinematics, to ensure that the molten pool is still formed at the planned position after adjustment. Then, the positions with large changes in C-axis angle are detected and locally optimized to ensure that the optimized result allows the laser deposition head to maintain a constant speed when linked with other axes. Finally, global optimization is performed using curve smoothing to deal with the corner regions left by the local optimization to make the machine motion smoother. The printing results of S-shaped and elbow parts show a significant improvement in print quality with less wear and tear on the machine, thus demonstrating the effectiveness and feasibility of the method. [ABSTRACT FROM AUTHOR]

The effect of remelting during multi-layer and multi-track laser additive manufacturing is presented. A numerical model is developed for simulating layer-by-layer laser melting along longitudinal and transverse planes. The model incorporates the effect of laser movement, heat and species transport, melting, grain nucleation, growth and remelting. The addition of a new layer is modelled using domain translation with a fixed domain size. Formation of parallel tracks is modelled for the transverse plane simulations by implementing the shifting of a variable heat source based on laser position. Simulations are performed for Al–10%Cu with different layer thickness and hatch spacing to study the effect of remelting. Results show that the model can predict melt pool evolution, species segregation, formation and remelting of columnar and equiaxed grains along both transverse and longitudinal planes. The grain density in the remelted region is found to increase with increasing layer thickness. [ABSTRACT FROM AUTHOR]

The ultrasonic surface rolling process (USRP) is a strengthening process to improve the surface properties and enhance the mechanical performances of metal materials based on severe plastic deformation and high strain rates. In this study, a three-dimensional numerical model was established to investigate the reconstruction mechanism of surface integrity for the laser additive manufactured 316 L stainless steel (LAMed 316 L) subjected to USRP. The accuracy of the USRP model was confirmed by experimental results of residual stress, microhardness, and surface roughness. The results showed that the static pressure played a crucial role in causing the plastic deformation and strain hardening, followed by the decreased surface roughness, improved microhardness, and induced compressive residual stresses. The introduction of ultrasonic high-frequency impact with the smaller force contributed to the high strain rate plastic deformation and the surface tensile stress release, and improved the plastic deformation efficiency greatly. The reconstructed surface integrity of LAMed 316 L was attributed to the plastic strain, strain hardening, and grain refinement. [ABSTRACT FROM AUTHOR]

Gas-induced porosity is almost inevitable in additively manufactured aluminum alloys due to the evaporation of low-melting point elements (e.g., Al, Mg, and Zn) and the encapsulation of gases (e.g., hydrogen) during the multiple-phase reaction in the melt pool. These micropores are highly unstable during post-heat treatment at elevated temperatures and greatly affect mechanical properties and service reliability. In this study, the AlSi10Mg samples prepared by LPBF were subjected to solution heat treatment at 560 °C for 0.5 and 2 h, followed by artificial aging at 160 °C, 180 °C and 200 °C, respectively. The defect tolerance of gas porosity and associated damage mechanisms in the as-built and heat treated AlSi10Mg alloy were elucidated using optical, scanning electron microscopic analysis, X-ray micro computed tomography (XCT) and room temperature tensile testing. The results showed the defect tolerance of AlSi10Mg alloy prepared by LPBF was significantly reduced by the artificial aging treatment due to the precipitation of Mg-Si phases. Fracture analysis showed that the cooperation of fine precipitates and coarsened micropores assists nucleation and propagation of microcracks sites due to stress concentration upon tensile deformation and reduces the tensile elongation at break. [ABSTRACT FROM AUTHOR]

Commercially available 316L (1.4404) stainless steel is commonly used for industrial filtration due to its combination of good material properties, particularly its corrosion resistance, which is a critical factor for filters in corrosive (e.g., saltwater) environments. Recently, laser powder bed fusion (LPBF) has enabled new more complex and efficient filtration pieces to be manufactured from this material. However, it is critical to know how the corrosion resistance is affected by this manufacturing strategy. Here, the corrosion resistance of LPBF manufactured 316L stainless steel is compared with wrought 316L sheet. The corrosion of the samples in saltwater was assessed with asymmetric electrochemical noise, potentiodynamic polarisation curve, and electrochemical impedance spectroscopy. The samples before and after corrosion were examined with scanning electron microscopy and energy-dispersive spectroscopy. The LPBF samples had higher corrosion resistance than the sheet samples and were more noble. The corrosion resistance of the LPBF sample increased with time, while the wrought sample corrosion resistance reduced over time. The corrosion mechanism of both samples was stable with time, formed of a passive film process and a bared material process. This paper presents the first study about the temporal evolution of the LPBF 316L stainless steel corrosion mechanism. [ABSTRACT FROM AUTHOR]

Copyright of Foundry Technology (1000-8365) is the property of Foundry Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In the multilayer thin-walled Inconel 625 alloy structures fabricated by the laser additive manufacturing (LAM) process, the poor plasticity of the interlaminar region often leads to structural fractures. In this paper, an oscillating LAM (O-LAM) technology using a transverse linear beam oscillation (LBO) process was proposed, and the effect of laser scanning speed on the forming accuracy, microstructure, crystallographic texture, and mechanical properties of interlaminar region was studied. The results show that the LBO process refined the grains and increased the number and length of high-angle grain boundaries in the interlaminar region. In addition, the LBO process with high laser scanning speed weakened the preferential orientation along the directions of laser scanning and deposition build-up. In particular, the dominant crystallographic textures of { 1 ¯ 10 } < 1 ¯ 1 ¯ 1 > and { 2 ¯ 21 } < 1 ¯ 1 ¯ 0 > in the interlaminar region were significantly reduced. The analysis of the Schmidt factor and the results of nano-indentation test show that the LBO process with high laser scanning speed reduced the stress concentration, and the elastic modulus and dislocation density in the interlaminar region. Therefore, the LBO process with high laser scanning speed can improve the plasticity and relieve the stress concentration of the interlaminar region, which is conducive to improving the overall mechanical properties of the Inconel 625 alloy multilayer thin-walled structure. [ABSTRACT FROM AUTHOR]

In this study, three types of three-layer functionally graded materials (FGMs) were designed by mainting the average content of the reinforcement constant and changing the span of the composition. The B4C particle-reinforced Al-matrix FGMs and a homogeneous composite (HC) with the same average composition were prepared using the laser additive manufacturing technique. The FGMs had a higher average secondary-phase content and grain size than the HC. Large (black) and reticulated (white) secondary phases corresponding to B4C phase, T phase, and MgZn2 were observed in the as-deposited FGM samples. The content of the secondary phase in the middle layer was generally low. The bottom layer, which was in direct contact with the substrate, exhibited the smallest grain size. The hardness and wear resistance significantly improved owing to the high B4C content in the top layer. The flexural behaviors of each layer of the FGM in different directions were systematically studied. The plasticity of the single-layer material decreased with increase in the B4C content. When the bottom layer had a high B4C content, the flexural ability significantly reduced. Among all the samples, G2 with 8% B4C particle content in the top layer exhibited the best comprehensive mechanical properties. The hardness value, wear rate of the top layer, maximum bending stress, and maximum bending strain of the FGM were 177.5 HV, 0.367 × 10−3mm3/(N·m), 585.6 MPa, and 7.36%, respectively. This study can provide a reference value for the future design and development of wear-resistant gradient materials for aerospace applications.

Phase transition at the initial solidification stage notably affects subsequent phase structure of peritectic alloys, however, detailed dynamics between entangled three-phase region remains ambiguous in the far-from-equilibrium condition during laser additive manufacturing. Here, in-situ peritectic phase transition during single-layer laser printing of an exemplary 304L stainless steel is directly investigated and quantified at high temporospatial resolution by high-speed synchrotron X-ray diffraction and imaging. These quantitative observations clarify the mechanism of coupled peritectic growth and local remelting at three-phase region. The results revealed provide in-depth understanding of phase transformation dynamics and delicate design of phase structure for metal additive manufacturing.

The urgent need for integrated molding and sintering across various industries has inspired the development of additive manufacturing (AM) ceramics. Among the different AM technologies, direct laser additive manufacturing (DLAM) stands out as a group of highly promising technology for flexibly manufacturing ceramics without molds and adhesives in a single step. Over the last decade, significant and encouraging progress has been accomplished in DLAM of high-performance ceramics, including Al2O3, ZrO2, Al2O3/ZrO2, SiC, and others. However, high-performance ceramics fabricated by DLAM face challenges such as formation of pores and cracks and resultant low mechanical properties, hindering their practical application in high-end equipment. Further improvements are necessary before they can be widely adopted. Methods such as field-assisted techniques and post-processing can be employed to address these challenges, but a more systematic review is needed. This work aims to critically review the advancements in direct selective laser sintering/melting (SLS/SLM) and laser directed energy deposition (LDED) for various ceramic material systems. Additionally, it provides an overview of the current challenges, future research opportunities, and potential applications associated with DLAM of high-performance ceramics. [ABSTRACT FROM AUTHOR]

Phase transition at the initial solidification stage notably affects subsequent phase structure of peritectic alloys, however, detailed dynamics between entangled three-phase region remains ambiguous in the far-from-equilibrium condition during laser additive manufacturing. Here, in-situ peritectic phase transition during single-layer laser printing of an exemplary 304L stainless steel is directly investigated and quantified at high temporospatial resolution by high-speed synchrotron X-ray diffraction and imaging. These quantitative observations clarify the mechanism of coupled peritectic growth and local remelting at three-phase region. The results revealed provide in-depth understanding of phase transformation dynamics and delicate design of phase structure for metal additive manufacturing. [ABSTRACT FROM AUTHOR]

Laser additive manufacturing （LAM） enables the integrated direct formation of high-performance metallic components with complex geometry. However， the non-uniform distribution of temperature gradients， in-situ heat treatment effects， non-equilibrium solid phase transformations， and heterogeneous microstructure during the process result in intricate residual stresses that significantly affect the quality and overall performance. A comprehensive review of residual stress in LAM by introducing its fundamental definition and classification is provided in this paper. Furthermore， the particularity， formation mechanisms， characterization methods， and regulation techniques associated with residual stress in LAM is systematically reviewed. The subsequent sections introduce various characterization methods for residual stress in LAM components， along with their respective characteristics. Additionally， the applicability， advantages， and disadvantages of each method are presented. Furthermore， the methods for controlling residual stress can be categorized into post-treatment control and in-situ treatment control. Finally， the joint effect of different types of residual stress should be considered in the study of the cause and evolution mechanism of residual stress in LAM. The characterization method of residual stress should be integrated with various methods to facilitate mutual verification. To mitigate the impact of stress concentration on the printing process and resultant quality， as well as minimize the influence of post-processing stress on part accuracy， it is imperative to investigate in-situ control methods for residual stress and explore real-time online monitoring techniques for LAM.

Refractory high entropy alloys have excellent high temperature mechanical properties， but the high temperature oxidation resistance has always been one of the limiting factors in their application. Four kinds of refractory high entropy alloys AlNbTaTiZr， AlMoNbTiZr， AlMoNbTaTiZr and AlMo0.5NbTa0.5TiZr were designed and prepared by laser additive manufacturing technology. The oxidation mass gain of AlNbTiZr-based refractory high entropy alloys was measured at 900 ℃ and 1000 ℃， and the oxidation layer structure of different samples was studied. The effects of Mo and Ta on the high temperature oxidation resistance of AlNbTiZr-based refractory high entropy alloys were compared and analyzed. The results show that the four kinds of as-deposited high entropy alloys prepared by laser additive manufacturing are BCC＋HCP dual-phase structures. The dendrites are mainly BCC phases with high melting points， and a small amount of HCP phase rich in Al and Zr is distributed among the dendrites. AlNbTaTiZr shows the best oxidation resistance after oxidation at 900 ℃ and 1000 ℃ for a long time， and Ta instead of Mo to some extent improves the oxidation resistance of refractory high entropy alloys.

The utilization of titanium aluminide (TiAl) alloys is widespread in the high-temperature sectors of the aerospace industry, despite their challenging manufacturing process and inherent low toughness. Laser additive manufacturing (LAM), as a solution to these challenges, enhances the capability to form complex components and mechanical properties. The influence of process parameters, heat treatment methods, and reinforcing components on the microstructure of TiAl alloys was studied during the LAM process. The principles of designing TiAl alloys were emphasized from the action mechanism of reinforcing components. A classification standard for the component design was proposed based on the different roles of β-stabilizing elements, α-stabilizing elements, rare earth elements, and composites (a combination of the aforementioned components). Furthermore, the work discussed the evolution mechanism of the microstructure and the strengthening mechanism of mechanical properties in TiAl alloys prepared using LAM. These included solid solution strengthening, precipitation strengthening, grain boundary strengthening, grain refinement, and lattice distortion toughening. Finally, future research directions in LAM TiAl alloys were proposed—the innovative design of TiAl alloys through the structural or interfacial control, the development of multiscale characterization techniques for microstructures, and the advancement of high-performance TiAl alloys using data-driven machine learning approaches.

Copyright of Journal of Materials Engineering / Cailiao Gongcheng is the property of Journal of Materials Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Materials Engineering / Cailiao Gongcheng is the property of Journal of Materials Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Fabricating and introducing new materials with new features is one of the most important goals for many scientific groups. Today, additive manufacturing (AM) is known as one of the new production methods, which can create an excellent opportunity for achieving this goal. As one of the ongoing production processes, the laser AM (LAM) methods have the proper capacity for producing new advanced materials like carbide, nitride, and boride‐based materials. Hence, this work aims to review carbide‐based materials produced by LAM techniques with the composite viewpoint. These materials can act as a matrix, reinforcement, or tertiary component in advanced composites. With this viewpoint, these composite materials were introduced in eight separate sections, which are tungsten carbide, titanium carbide, silicon carbide, niobium carbide, chrome carbide, vanadium carbide, and boron carbide, as well as high entropy alloy composites. [ABSTRACT FROM AUTHOR]

Metallurgical defects in metal laser additive manufacturing (LAM) are inevitable due to complex non-equilibrium thermodynamics. A laser ultrasonic system was designed for detecting surface/near-surface defects in the layer-by-layer LAM process. An approach was proposed for ultrasonic imaging of defects based on variable time window intensity mapping with adaptive 2σ threshold denoising. The Gaussian mixture model hypothesis and expectation-maximization algorithm can automatically differentiate between components dominated by defects and background noises, thereby providing an adaptive threshold that accommodates detection environments and surface roughness levels. Results show that the ultrasonic wave reflection at defect boundaries diminishes far-field ultrasonic intensity upon pulsed laser irradiation on surface defects, enabling defect size and location characterization. This method is applicable to LAM samples with a significant surface roughness of up to 37.5 μm. It can detect superficial and near-surface defects down to 0.5 mm in diameter and depth, making it significant for online defect detection in additive manufacturing.

Oxide eutectic ceramics have excellent high specific strength, high temperature resistance, corrosion resistance, oxidation and creep resistance, and so on, which are considered to be the promising materials to be used in ultra-high temperature oxidation, corrosion and other extreme environments. It shows great application prospects in the new generation of high thrust-to-weight ratio aero-engine for high-temperature hot-end structural components. Laser additive manufacturing technology has become one of the most promising cutting-edge technologies for the preparation of high-performance complex structural components in recent years. Crack defect is easy to occur in the process of laser rapid solidification of ceramics, which seriously affects the quality and performance of the oxide eutectic ceramics components. So, it has become a key factor restricting the engineering application. Two typical laser additive manufacturing technologies for ceramics including laser engineered net shaping and laser power bed fusion were briefly summarized. The crack morphology characteristics of different shaped components formed by the above two technologies were analyzed and compared. The formation mechanism of cracks in laser additive manufacturing of oxide ceramics was explored from the perspectives of microstructure characteristics, stress state. Further, a systematic summary was presented focusing on the improvement of microstructures and the reduction of thermal stress to inhibit crack formation through optimization of process parameters, compositional design, and outfield assistance. Finally, it is pointed out that the future development trends and breakthrough directions of oxide eutectic ceramics by laser additive manufacturing in terms of powder properties, forming primary and secondary factors, and forming technology research.

A new method to prepare large Cu–Cr alloy with both high strength and high conductivity has been developed. Cu–Cr billets are produced efficiently by laser additive manufacturing, and the microstructure of the alloy is changed by severe plastic deformation caused by large cold rolling ratio. The strength of the alloy can be significantly increased to 677 MPa by eliminating pores, introducing texture and refining grain. The deformation twins caused by plastic deformation processing make up for the plasticity loss caused by grain refinement. With the increase of density and the deformation of Cr particles, the electrical conductivity of the alloy is increased to 28.7 MS/m. Our findings not only deepen the understanding of laser additive manufacturing of highly reflective metals, but also provide a new idea for the preparation of high-strength and high-conductivity Cu alloy workpieces.

Laser additive manufacturing (LAM) has attracted significant interest in developing Al alloys due to its potential to fabricate structural components at low cost and high efficiency. Nevertheless, LAM Al alloys still suffer many issues, including heterogeneous microstructure, various defects, and poor mechanical properties, significantly hindering the advancement of LAM Al alloys. This article seeks to provide a comprehensive overview of the current advancements made in the field of LAM Al alloys and attempts to establish an in-depth relationship between microstructural characteristics, defects, and performances. Development status and limitations of LAM technologies are described, microstructural characteristics of Al alloys in LAM are introduced, mechanisms of formed defects and corresponding mitigation measures are discussed, and current quality improvement strategies are summarized. Following the research of previous work, this review will provide an outlook on overcoming the existing challenges and provide a helpful resource and reference for the development of LAM Al alloys.

ABSTRACTThe AlCoCrFeNi2.1 eutectic high-entropy alloys (EHEAs) were prepared using selective laser melting (SLM) to study the tribological properties at high temperatures, focusing on the complex mechanism of the friction process. The density of the SLM EHEAs is 99.70%. The lamellar and cellular structures are unevenly distributed at different locations. In situ XRD demonstrated the transition from BCC to FCC with increasing temperature. A large number of B2 particles are distributed in the BCC matrix. The fluctuation of the friction coefficient is closely related to the shape and size of the wear debris. The hardness of the alloy is ∼105 HV at 1000 °C. The wear rate first increases and then decreases with increasing temperature. The maximum thickness of the oxide film is 13.52 μm at 1000 °C and exhibits delamination. The combination of mechanical, materials and physicochemical effects during friction contributes to the excellent high temperature wear resistance.

Copyright of Journal of Materials Engineering / Cailiao Gongcheng is the property of Journal of Materials Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The solid solution and aging treatment for conventional manufacturing processes might not be suitable for laser additive manufactured titanium alloys due to the different lamellar microstructures. In this study, the influence of aging temperatures (600, 700 and 800 °C) on microstructure and mechanical properties of titanium alloy Ti–6Al–2V–1.5Mo–0.5Zr–0.3Si was investigated. The results indicate that after solid solution treatment at 970 °C followed by water quenching, the alloy mainly consists of coarsening lamellar α phase in martensite α′ matrix. Aging at 600 °C will not change the size of primary lamellar α phase but lead to huge amount of secondary α phases (αs) generating with very fine microstructure. By increasing the aging temperature, the number of αs decreases but with coarsened microstructures. When aged at 800 °C, the width of the αs phase reaches 350 nm, almost 7 times wider than that aged at 600 °C. The changing size of αs obviously influences the property of the alloy. The fine αs leads to high strength and microhardness but low plasticity, and specimen aged at 700 °C with suitable αs size has the best comprehensive properties. [ABSTRACT FROM AUTHOR]

Due to the unparalleled benefits of traditional processing techniques, additive manufacturing technology has experienced rapid development and continues to expand its applications. However, as industrial standards advance, the pressing needs for high precision, high performance, and high efficiency in the manufacturing sector have emerged as critical bottlenecks hindering the technology's progress. Single-laser additive manufacturing methods are insufficient to meet these demands. This review presents a comprehensive exploration of metal hybrid laser additive manufacturing technology, encompassing various aspects, such as multi-process hybrid laser additive manufacturing, additive–subtractive hybrid manufacturing, multi-energy hybrid additive manufacturing, and multi-material hybrid additive manufacturing. Through a thorough examination of the principles of laser additive manufacturing technology and the concept of hybrid manufacturing, this paper investigates in depth the notable advantages of hybrid laser additive manufacturing technology. It provides valuable insights and recommendations to guide the development and research of innovative machining technologies. [ABSTRACT FROM AUTHOR]

This study explores the enhancement of biocompatible titanium‐based implants through surface functionalization for improved bone healing. Specifically, a near‐beta type Ti‐13Nb‐13Zr alloy is 3D printed using laser powder bed fusion and subsequently textured using nanosecond (ns) and picosecond (ps) direct laser interference patterning (DLIP) to create single‐scale and multi‐scale surface textures. On these textures, the cell behavior, morphology, metabolic activity and osteogenic differentiation potential of human bone marrow stromal cells are assessed using fluorescence microscopy and MTS assays. Moreover, tissue non‐specific alkaline phosphatase activity served as an early osteoblast production marker. Compared to untextured specimens, both types of textures exhibited higher metabolic activity and cell proliferation. Single‐scale ns‐DLIP textures encouraged cell extensions anchored in groove regions, while ps‐DLIP textures with hierarchical structures promoted cell extensions attaching to nanostructures on sidewalls. The groove width and nanotopographies in groove areas facilitated cell spreading. Surface topography, roughness, and surface chemistry (surface energy, wettability) influenced cell adhesion, proliferation, and differentiation. A comprehensive evaluation of DLIP‐generated surface textures, including their topography and chemical states, complements the factors affecting in vitro cell behavior. Overall, this research demonstrates the potential of surface‐functionalized 3Dprinted titanium for a novel generation of biocompatible implants. [ABSTRACT FROM AUTHOR]

Laser additive manufacturing is regarded as a new green creation method. It is a technology that is grounded in the principles of laser deposition technology, such as laser cladding and laser cladding welding, and is utilized for achieving the restoration of geometry or comprehensive performance in damaged parts of various components. The current status of additive manufacturing technology both domestically and internationally was specified. Additionally, a detailed introduction was provided regarding the process types of laser additive manufacturing and its applications across various industries. Finally, an outlook on the development trend of laser additive manufacturing technology was presented. [ABSTRACT FROM AUTHOR]

Laser additive manufacturing (LAM) has become a promising technique to directly fabricate high-performance Al 2 O 3 -based eutectic ceramics, but the applicability of laser energy density (LED), a comprehensive index commonly used to regulate the LAM process of metallic parts, in preparing brittle ceramic samples with narrower laser processing windows is not clear yet. In this paper, Al 2 O 3 /GAP/ZrO 2 eutectic ceramics are prepared by LAM to investigate the effects of LED on forming quality and melting dimensions of the as-deposited eutectic samples. The results indicate that the reliability of using LED as a design parameter depends on the way how it is changed. There is a response relationship between the LED and experimental results when individually adjusting laser power P or scanning speed v , but abnormal phenomena are detected when simultaneously changing P and v. It is found that the melting dimensions obtained under higher LED can be unexpectedly smaller. Moreover, there is a significant difference in the melting dimensions despite using the same LED. In addition, 50 layers thin-wall structured Al 2 O 3 /GAP/ZrO 2 eutectic specimens prepared under a constant LED present significant differences in the forming quality. It is revealed that the contribution of P to LED is much greater than that of v , which is not consistent with the same influence degree reflected in the calculation formula. Thus, there are significant limitations to utilizing LED to regulate the LAM process of brittle ceramics in consideration of the sensitivity of their forming quality to changes in laser parameters. [ABSTRACT FROM AUTHOR]

The large scatter in high-cycle fatigue (HCF) life poses significant challenges to safe and reliable in-service assessment of additively manufactured metal components. Previous investigations have indicated that inherent manufacturing defects are a critical factor affecting the fatigue performance of the components, and the HCF life is significantly influenced by the geometric parameters of the critical defects inducing crack nucleation. Therefore, it is highly important to elucidate the correlation of the HCF life with the geometric parameters of critical defects. This study proposes a new fatigue life prediction model for laser additively manufactured AlSi10Mg alloys by including the combined effects of loading stress and defect geometries (size, location and morphology) in terms of domain knowledge-guided symbolic regression (SR). Domain knowledge is extracted from the semi-empirical Murakami, Z-parameter and X-parameter fatigue life models to establish the variable subtrees. The results show that compared with these semi-empirical models, the domain knowledge integration-based SR model has higher prediction accuracy and generalization ability. Moreover, compared with traditional 'black box' machine learning models, SR excels at balancing prediction accuracy and model interpretability, which provides useful insights into the relationship between fatigue life and defect geometries. This article is part of the theme issue 'Physics-informed machine learning and its structural integrity applications (Part 2)'. [ABSTRACT FROM AUTHOR]

There are always microcracks and pores during the laser additive manufacturing of 7xxx aluminum alloy, which significantly limits its performance improvement and application. This work uses additives to suppress defects and improve the alloy's properties. Here three alloys were prepared by the addition of silicon, TiN, or both. Their microstructure and mechanical properties were investigated in detail. The results show that silicon can inhibit the crack generation by reducing the solidification rate. The grain size is large. TiN can refine the grain and it creates pores. The addition of both can restrain the defects, refine the grains and obtain good comprehensive properties. Moreover, the hardness and wear resistance of A3 are slightly lower than A2 due to the brittle phase generated by the addition of Si. The yield strength, tensile strength, elongation, hardness and wear rate of A3 alloy treated by T6 are 214.8 ​MPa, 262.8 ​MPa, 2.59 ​%, 130.9 HV and 2.24 ​× ​10−3 mm3/(N·m). [ABSTRACT FROM AUTHOR]

Laser additive manufacturing (AM) technology is widely applied in manufacturing critical components (e.g., rocket fuel nozzles, satellite antenna mounts and human implants, etc.) in automotive, medical, aerospace and other fields due to the advantages of high manufacturing precision, flexibility and automation. This technology can considerably improve the combination property of printed parts by integrated manufacturing of material structure and performance. Currently, in the focused Gaussian beam, the energy distribution is high in the center and low at the edge is generally employed in laser AM technology. However, it tends to produce a high thermal gradient in the melt pool, resulting in a subsequent generation of porosity and coarse grains. As a new solution to this problem, beam shaping technology can improve printing efficiency and quality by modulating the distribution of laser beam energy. In this paper, the application of beam shaping technology in two mainstream metal laser AM processes (laser powder bed fusion (LPBF) and directed energy deposition (DED)) is systematically reviewed, including the energy distribution, melt pool morphology and part quality of different shaped beams. The effects of different-shaped beams on parts quality mainly depends on their influence on the morphology and internal dynamics of the melt pool. For promoting the application of beam shaping technology in the metal laser AM field, it is necessary to achieve adequate control for the energy input stability of the shaped beam. In addition, how to realize metal laser AM with multi-shaped beams and dynamic beam shaping is also crucial to the future development of metal laser AM technology.

Commercially available 316L (1.4404) stainless steel is commonly used for industrial filtration due to its combination of good material properties, particularly its corrosion resistance, which is a critical factor for filters in corrosive (e.g., saltwater) environments. Recently, laser powder bed fusion (LPBF) has enabled new more complex and efficient filtration pieces to be manufactured from this material. However, it is critical to know how the corrosion resistance is affected by this manufacturing strategy. Here, the corrosion resistance of LPBF manufactured 316L stainless steel is compared with wrought 316L sheet. The corrosion of the samples in saltwater was assessed with asymmetric electrochemical noise, potentiodynamic polarisation curve, and electrochemical impedance spectroscopy. The samples before and after corrosion were examined with scanning electron microscopy and energy-dispersive spectroscopy. The LPBF samples had higher corrosion resistance than the sheet samples and were more noble. The corrosion resistance of the LPBF sample increased with time, while the wrought sample corrosion resistance reduced over time. The corrosion mechanism of both samples was stable with time, formed of a passive film process and a bared material process. This paper presents the first study about the temporal evolution of the LPBF 316L stainless steel corrosion mechanism.

Gas-induced porosity is almost inevitable in additively manufactured aluminum alloys due to the evaporation of low-melting point elements (e.g., Al, Mg, and Zn) and the encapsulation of gases (e.g., hydrogen) during the multiple-phase reaction in the melt pool. These micropores are highly unstable during post-heat treatment at elevated temperatures and greatly affect mechanical properties and service reliability. In this study, the AlSi10Mg samples prepared by LPBF were subjected to solution heat treatment at 560 °C for 0.5 and 2 h, followed by artificial aging at 160 °C, 180 °C and 200 °C, respectively. The defect tolerance of gas porosity and associated damage mechanisms in the as-built and heat treated AlSi10Mg alloy were elucidated using optical, scanning electron microscopic analysis, X-ray micro computed tomography (XCT) and room temperature tensile testing. The results showed the defect tolerance of AlSi10Mg alloy prepared by LPBF was significantly reduced by the artificial aging treatment due to the precipitation of Mg-Si phases. Fracture analysis showed that the cooperation of fine precipitates and coarsened micropores assists nucleation and propagation of microcracks sites due to stress concentration upon tensile deformation and reduces the tensile elongation at break.

In this work, the AlCoCrFeNi2.1 eutectic high-entropy alloys (EHEAs) were fabricated by laser additive manufacturing and subsequently heat-treated at various temperatures between 800 and 1200 °C to achieve excellent strength-plasticity synergy. The high solidification rate of selective laser melting (SLM) leads to instability of the eutectic growth front, resulting in a typical melt pool morphology of equiaxed and columnar crystals for AlCoCrFeNi2.1. The body-centered cubic (BCC) content of ∼82% in the SLM specimens leads to a higher tensile strength of ∼1175 MPa and poorer plasticity of ∼6.42%. After heat treatment, the BCC transforms to face-centered cubic (FCC) and the microstructure changes to a dendrite containing eutectic lamellar structure. As the temperature increases, Ni–Al aggregates, B2 phase particles precipitate and grow in the BCC matrix. Meanwhile, the uniform heating mode eliminates the orientation of the SLM melt pool structure, reduces the internal stress and dislocation density of the SLM alloy. In addition, high-temperature heating promotes the stable growth of lamellar structure. These combined effects allow the strength-plasticity trade-off to be achieved in the heat-treated specimen. The HT-1200 sample has a strength of 1065 MPa and a ductility of 21.97%.

Laser-powder bed fusion additive manufacturing (LPBF-AM) of metals is rapidly becoming one of the most important materials processing pathways for next-generation metallic parts and components in a number of important applications. However, the large parametric space that characterizes laser-based LPBF-AM makes it challenging to understand what are the variables controlling the microstructural and mechanical property outcomes. Sensitivity studies based on direct LPBF-AM processing are costly and lengthy to conduct, and are subjected to the specifications and variability of each printer. Here we develop a fast-throughput numerical approach that simulates the LPBF-AM process using a cellular automaton model of dynamic solidification and grain growth. This is accompanied by a polycrystal plasticity model that captures grain boundary strengthening due to complex grain geometry and furnishes the stress-strain curves of the resulting microstructures. Our approach connects the processing stage with the mechanical testing stage, thus capturing the effect of processing variables such as the laser power, laser spot size, scan speed, and hatch width on the yield strength and tangent moduli of the processed materials. When applied to pure Cu and stainless 316L steel, we find that laser power and scan speed have the strongest influence on grain size in each material, respectively.

With the continuous development of preparation technology, laser additive manufacturing (LAM) has become one of the effective ways to manufacture functionally graded materials due to its unique layer-by-layer stacking technology. However, the repeated and repeated rapid heating and cooling processes in the manufacturing process will generate large residual stress inside the structure, resulting in the destruction of the structure. In this paper, based on a new finite element method called progressive activation element (PAE), a thermo-mechanical coupling model for simulating the process of LAM is established, and the influence of laser power and composition ratio of transition layers on the residual stress of the overall structure is discussed. The results show that there is a positive correlation between the laser power and the residual stress. The PAE method is compared with the traditional "Model Change" method, and it is found that the PAE method has advantages in computational efficiency, especially when calculating the residual stress of functionally graded materials; the efficiency can be improved by about 1650%. When the TC4/Inconel718 functionally graded material is prepared experimentally, the optimal composition ratio of the transition layers is 8:2. This paper provides reference for the understanding and reasonable suppression of residual stress of functionally graded materials in LAM. [ABSTRACT FROM AUTHOR]

This article presents a novel scanning technique for the laser powder bed fusion(LPBF) of Fe-based soft-magnetic alloys, which have low glass forming ability, and microstructural change happens during LPBF process. This techniqueinvolves double scanning where 1) the first scan applied uses high energy density(E =P/vht, where P is the laser power, v is the laser scan speed, h is the hatchspacing, and t is the layer thickness) with different process parameters (P: 30, 40, and 50 W, v: 500, 600, and 700mms-1, h: 20 and 30 µm, and t: 50 µm) to achievehigh density and 2) the second scan employed before the spreading subsequentpowder layer uses low E (=20 Jmm-3, P = 20 W, v = 1000mms-1, h = 20 µm, and t = 50 µm) to refine the microstructure and thus reduce coercivity. Thisincreases the saturation magnetization to a maximum value of 226.81 Am² kg-1and reduces the coercivity to a lowest value recorded (130 Am-1). Likewise, thebulk density (94.59-99.25%) is enhanced significantly with double scanning, especially the samples produced using high P (50 W) resulting from the relievingof the mechanical and thermal stress evolving during the process. [ABSTRACT FROM AUTHOR]

In this article, graphite-reinforced Al2O3 ceramic materials were prepared by directed laser deposition. The effects of graphite addition (3–12 wt.%) on the phase composition, microhardness and fracture toughness of Al2O3 ceramics were studied. The results showed that the process was beneficial for maintaining uniform mixing of graphite and ceramics and thus could avoid the delamination caused by the difference in their densities. When adding 6% and 9% graphite, there were fewer internal defects in the samples, and no obvious new phase was generated after adding more graphite. The microhardness of 6% and 9% graphite-reinforced Al2O3 ceramics reached 18.84 and 18.86 GPa, respectively, and it was close to that of pure Al2O3 ceramics. The microhardness of all graphite-reinforced Al2O3 materials was lower than that of pure Al2O3 ceramics, but the value increased first and then decreased with addition of more graphite. The change in microhardness was similar to the trend of the number of defects, thus, these newly forming defects were an important factor affecting the microhardness. With an increase in graphite addition, the fracture toughness increased gradually. Furthermore, the fracture toughness reached 5.89 MPa m1/2 at 12% graphite addition, which was higher than 4.82 MPa m1/2 of pure Al2O3 ceramics. Adding more graphite was beneficial in enhancing the deflection and pinning of the graphite particles against cracks, resulting in higher fracture toughness. Graphite can improve the fracture toughness of Al2O3 ceramic, prepared by directed laser deposition, and the method can solve the uneven distribution caused by the difference in densities between the two powders. This also provides a new idea for the rapid manufacture of high-toughness ceramic parts at lower cost. [ABSTRACT FROM AUTHOR]

One challenge hampering the structural applications of High-entropy alloys (HEAs) is to overcome the strength-ductility trade-off. Inspired by nature, engineering the HEAs with laminated structure composed of alternating soft and hard layers has the potential to strengthen the HEAs while maintaining the ductility. Here, taking the AlxCrMnFeCoNi HEA as the model material, the laminated HEAs composed by soft and hard layers were successfully prepared by laser additive manufacturing (LAM). The soft and hard laminated layers were achieved through tailoring the Al content. In several combinations of hard and soft, the strength of Al10-Al12 was significantly higher than that of Al12 HEA, indicating that an appropriate soft and hard matching can indeed further strengthen the HEA compared with the homogeneous HEA. [ABSTRACT FROM AUTHOR]

In order to minimize the gaps between the direct laser deposition channels and improve the quality and performance of the formed parts, the process of direct laser deposition is utilized in laser additive manufacturing to create sequential, single- and double-channel deposition layers on 304 stainless steel plates. Under the premise of keeping the layer rate and defocusing amount unchanged, this study investigates the effects of laser power, scanning speed, and powder feeding rate on the morphology and inclusions of single- and double-channel deposited layers. The aim is to determine the optimal process parameter values for direct laser deposition of single-layer, single-channel Inconel 738. The effects of the three process parameters on the response values were investigated using a multi-factor, multi-level experimental design. The evaluation indexes for the analysis included the deposited layer wetting angle and aspect ratio. The analysis involved one-way extreme analysis and ANOVA analysis. The optimal process parameters are a laser power of 550~750 W, a scanning speed of 7~13 mm/s, and the powder feeding rate was 2.1~4.33 g/min. At the same time, the relationship between surface tension and gravity was integrated with the spherical coronal model and Young's equation to develop a mathematical model of the direct laser deposition process at a theoretical level. The mathematical model of the direct laser deposition process was utilized to analyze the correlation between the geometric parameters of the cross-section of the deposited layer. This analysis provides a valuable data reference for future Inconel 738 direct laser deposition. [ABSTRACT FROM AUTHOR]

Two kinds of 25Cr-35NiBr Fe-based superalloy deposits with the distinguishing microsegregation were fabricated through controlling processing parameters of laser additive manufacturing (LAM). The effect of microsegregation on microstructural evolution was investigated thoroughly at high temperature. The results show that the microsegregation of Nb and Ti near cell boundaries plays a dominant role on the microstructural evolution at high temperature. When Nb. and Ti do not segregate significantly near cell boundaries, at elevated temperature the microstructure tends to evolve into a multiscale precipitated phases structure of Cr23C6, Cr7C3 and (Nb, Ti)C to improve the microstructural high-temperature stability. When Nb and Ti are obviously segregated near cell boundaries, at high temperature the microstructure possess a tendency to evolve into a chain (Nb, Ti)C to significantly decline the microstructural high-temperature stability. This research will provide new insights into the performance control and the microstructural evaluation of superalloy fabricated by LAM. [ABSTRACT FROM AUTHOR]