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The scanning strategy is an essential factor that determines the thermal history and combination of melt tracks within parts in the laser powder bed fusion (LPBF) process, which can significantly influence the microstructure evolution, defect formation, and mechanical properties of parts. Herein, the effect of scanning strategies (i.e., Y‐scan, XY‐scan, Rot‐scan, and Island‐scan) on the microstructure and mechanical properties of Inconel 718 (IN718) parts manufactured by LPBF is investigated. The results show that different scanning strategies can lead to different morphologies of melt tracks, and the Rot‐scan is the most beneficial strategy for improving density of parts. Different scanning strategies change the direction of the temperature gradient within parts, resulting in different morphologies of grain growth. The tensile properties of samples built with four types of scanning strategies show superior mechanical properties compared with the cast. The ultimate tensile strength of samples manufactured by Y‐scan, XY‐scan, and Rot‐scan is equivalent to that of the wrought, while the ductility of them is higher than that of wrought. However, tensile properties of samples manufactured by island scanning are lowest due to defects (e.g., pores, spatters) at the overlap of islands. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to explore a structural optimization method to achieve the lightweight design of an aviation control stick part manufactured by laser powder bed fusion (LPBF) additive manufacturing (AM). The utilization of LPBF for the fabrication of the part provides great freedom to its structure optimization, further reduces its weight and improves its portability. Design/methodology/approach: The stress distribution of the model was analyzed by finite element analysis. The material distribution path of the model was optimized through topology optimization. The structure and size of the parts were designed by applying honeycomb structures for weight reduction. The lightweight designed control stick part model was printed by LPBF using AlSi10Mg. Findings: The weight of the control stick model was reduced by 32.64% through the optimization method using honeycomb structures with various geometries. The similar stress concentrations of the control stick model indicate that weight reduction has negligible effect on its mechanical strength. The maximum stress of the lightweight designed model under loading is 230.85 MPa, which is 61.81% larger than that of the original model. The lightweight control stick part manufactured by LPBF has good printability and service performance. Originality/value: A structural optimization method integrating topology, shape and size optimization was proposed for a lightweight AlSi10Mg control stick printed by LPBF. The effectiveness of the optimization method, the printability of the lightweight model and the service performance of LPBF-printed AlSi10Mg control stick was verified, which provided practical references for the lightweight design of AM. [ABSTRACT FROM AUTHOR]

High cracking susceptibility arising from the high thermal gradients is a critical issue of high γ'-fraction Ni-base superalloys fabricated by laser powder bed fusion (LPBF). Here in, laser remelting was used to inhibit cracking and enhance the strength-ductility synergy of additively manufactured CM247LC alloy by LPBF. The effects of laser remelting with different energy densities and scan strategies on microstructure, cracking behavior and mechanical properties of LPBF-processed CM247LC superalloy were systematically investigated. The crack inhibition mechanisms of laser remelting during the LPBF process were revealed. Low energy density of remelting and scan strategy with a rotation of 90° between remelting and prior melting were promising for decreasing the crack density. The crack inhibition caused by laser remelting could be attributed to the partial elimination of defects (e.g. , lack-of-fusion pores), the mitigation of the segregation of elements, the backfilling of the grain boundaries and liquid film, and the reduction of the residual stress and the high-angle grain boundaries (HAGBs). Enhanced mechanical strength and ductility (ultimate tensile strength of 1280 MPa, yield strength of 885 MPa, and elongation of 11.9%) of LPBF-processed CM247LC samples were obtained by optimized-remelting parameters. This work demonstrated the potential of laser remelting in improving the printability of high γ'-fraction Ni-base superalloys fabricated by LPBF. • Laser remelting is successfully used to crack inhibition for additively manufactured CM247LC alloy. • Enhanced mechanical strength and ductility of CM247LC alloy are obtained. • Low energy density of remelting is promising for decreasing the crack density. • Laser remelting can contribute to the mitigation of the segregation of elements. [ABSTRACT FROM AUTHOR]

Laser powder bed fusion (LPBF) additive manufacturing has been advancing in the fabrication of metallic multi-material structures with intricate structures and refined material layouts. Herein, a comprehensive review of the recent achievements of multi-material structures via LPBF is provided in terms of interface characteristics and strengthening methods, critical technical issues and potential applications. It begins with the introduction of multi-material structures and the scope of the review. The interface characteristics (including representative multi-material types printed by LPBF, interfacial microstructure, defects, etc.) and strengthening methods of multi-material structures are then presented. Thereafter, the critical technical issues in LPBF for multi-material structures are discussed with regard to equipment development, data preparation, thermodynamic calculation and process simulation, and powder cross-contamination and recycling. Moreover, the potential applications (particularly in biomedical, electronic, aerospace) are illustrated and discussed. Finally, the outlook is outlined to provide guidance for future research. [ABSTRACT FROM AUTHOR]

Defects (e.g., pores and cracks) and high stress concentration derived from the significant mutation in materials are the critical challenge for multi-material structures fabricated by laser powder bed fusion (LPBF). Introducing a transition zone between dissimilar materials with a composition gradient at the interface may be a promising approach to resolve or minimize these problems. In this work, three distinct CuSn10 copper alloy (CuA)/316 L stainless steel (SS) multi-material gradient structures (i.e. , CS, SC-1, and SC-2) were fabricated by a LPBF system with in-situ powder mixing and feeding capability. A buffer layer material based on the mixture of the two base materials was introduced at the interface between CuA and SS. The effects of the building strategies and interfacial composition gradient transition paths on the interfacial bonding characteristics were investigated. The microstructure evolution and the underlying interfacial bonding mechanisms were discussed. It was found that the interfacial bonding behaviors were critically dependent on the occurrence of liquid metal embrittlement induced by Cu penetration into Fe grains, as well as the width and microstructure gradient of the diffusion zone and high stress concentration at the interface. A non-uniform melting behavior of CuA and SS powders could be induced by the distinct thermal-physical properties between the two materials, which could lead to lack-of-fusion pores at the interface. In the CS sample, printing SS on the CuA with a buffer layer material could inhibit the formation of Cu-penetration cracks and increase the width of the diffusion zone, which may enhance the interfacial metallurgical bonding. This work may enhance the essential comprehension of improving interfacial bonding strength of LPBF-processed multi-material structures. • Copper/steel multi-material gradient structures were fabricated by in-situ powder mixing and LPBF. • Building strategies and composition gradient transition paths affect the interfacial bonding behavior. • A smooth composition transition at the interface could lead to the gradient microstructure. • Building SS on CuA with a buffer layer material could increase the width of the diffusion zone. [ABSTRACT FROM AUTHOR]

High cracking susceptibility is a critical challenge for the application of high γ′-fraction Ni-base superalloys fabricated by laser powder bed fusion (LPBF). This study systematically investigated the effect of process parameters on the cracking susceptibility and microstructure of LPBF-processed CM247LC alloy. The formation mechanisms of liquation cracks and solidification cracks were revealed. The effects of process parameters on solidification behavior, microstructure evolution and local strain level were discussed. The cracking behavior was significantly affected by the high-angle grain boundaries (HAGBs), elemental segregations (e.g., C and O) and stress concentration at cracking regions. An increase in the laser power increased the length of mushy zone and the depth/width ratio of melt pools, resulting in high solidification cracking susceptibility. The overlap between adjacent melt tracks determined by hatch spacing and layer thickness could heal partial cracks through remelting. Nearly crack-free CM247LC samples with enhanced strength-ductility (yield strength of 921 ± 38 MPa, ultimate tensile strength of 1278 ± 3 MPa, and elongation of 16.1 ± 1.3%) were obtained by optimized process parameters. The zigzag grain boundaries, refined grains and reduced grain aspect ratio in the nearly crack-free samples could relieve the stress concentration along the grain boundaries and enhance the bonding of adjacent grains and thus delay the propagation of cracks. This work may provide essential comprehension for improving the LPBF processability of high γ′-fraction Ni-base superalloys. [ABSTRACT FROM AUTHOR]

Recent research has focused on laser in-situ additive manufacturing of metal matrix composites with spatially controllable microstructures (phases). This study, inspired by the process of inserting mesh fibers into reinforced concrete, synthesizes TiN in situ using laser powder bed fusion and N 2 gas. The laser-melted track, embedded with TiN particles, formed a spatially heterostructured Ti composite (SHTC) with a three-dimensional, artificially controlled architecture in a pure Ti matrix. The influences of process parameters on the mechanical properties of the spatially heterostructured Ti composite and the microstructural evolution of TiN/Ti were investigated emphatically. The results showed that the growth direction of the microstructure was changed by laser powder bed fusion additive manufacturing with alternating N 2 –Ar gas under suitable N 2 concentration and melting track spacing. Among all spatially heterostructured Ti composites, the TiN–Ti heterolayer net-like structure achieved a high ultimate tensile strength of ∼1.0 GPa and elongation of 27 %, demonstrating a superior strength-ductility combination than intrinsic pure Ti and uniform TiN composites, as well as traditional layered structure Ti-based composites. During the tensile test, the deformation behavior was monitored in situ using digital image correlation, and the fracture mechanism was investigated. Hetero-deformation induced strengthening and toughening potentially explains the mechanism behind the strength enhancement of spatially heterostructured Ti composites. Furthermore, this work may stimulate research and development in additive manufacturing of spatial heterostructures with configurable structures, targeting synergistic regulation of strength and ductility in the integration of structure-material-function. [Display omitted] • In-situ synthesis of artificial microstructures through switching of printing gases during laser powder bed fusion. • Optimized the in-situ synthesis process through single-track experiments and high-speed photography. • The spatial heterogeneity distribution and mechanical properties of the in-situ synthesized TiN–Ti melt track were determined. • The mechanical properties of Ti composites enhanced by spatial heterostructure and hetero-deformation induced strengthening. [ABSTRACT FROM AUTHOR]

The utilization of components fabricated by directed energy deposition (DED) faces certain limitations that hinder its widespread application. These critical challenges primarily include significant errors in dimension accuracy caused by the unreliable build-up of flowing powder and low surface quality arising from the interlayer cumulative effect and powder adhesion. The present study aims to comprehensively investigate the impact of process parameters and deposition height on the geometrical errors observed in the thin-walled structures fabricated by DED. By establishing a rational relationship between the dimensional error and the sample height, the mechanism underlying the influence of deposition height on printing stability and sustainability is elucidated. Furthermore, an innovative building strategy incorporating a variable speed is proposed to eliminate protrusions at the end of the components. The study also examines the surface roughness of inclined thin walls, revealing a correlation between roughness and both position and angle. The presence of adhering powder on the front side of the parts and the formation of a molten oxide layer on the backside result in a diminished impact of angle on roughness. Ultimately, the findings of this study are validated through the fabrication of a thin-walled axisymmetric curved structure, providing a guide for the printing of large special-shaped parts. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel image processing method and spatters feature extraction algorithm were used to obtain the spatter number, the total spatter area, the spattering angle and the spattering velocity of 8 scenarios. • The droplet spatter features and dynamics exhibited a strong correlation with the gas flow velocity. • The median of the spattering angle under normal melting is around 40° under the SD-A condition and about 60° under the SD-W condition. • With the increase of gas velocity, the spattering angle became smaller, the quantity of micro-spatter increased, and the maximum spattering speed of the spatter became higher — up to 12.8 m/s at 2.5 m/s gas velocity. • The droplet spatter behavior influenced by gas flow parameters are concluded to three ways: gas flow induced, vapor driven, and melt pool extrusion, presented in backside, upper, and frontside relative to the melt pool. The droplet spatters generated by the laser induction directly affect the processing quality of the laser powder bed fusion (LPBF) process, gas parameters are a key factor in this process. In this work, the formation characteristics and dynamic behavior of process-by-products under different gas flow parameters were presented through high-speed imaging. A novel image processing method and spatters feature extraction algorithm were used to obtain the spatter number, the total spatter area, the spattering angle and the spattering velocity of 8 scenarios. With the comparative analysis, scan direction against the gas flow (SD-A) is proved to produce fewer droplet spatters than scan direction with the gas flow (SD-W), and the quantitative relationship between the gas flow parameters and the droplet spatter behavior is established for the first time. The maximum spattering velocity increases to 12.8 m/s as the gas flow velocity rise to 2.5 m/s. Finally, the mechanisms of the droplet spatter behavior influenced by gas flow parameters are discussed. The work provides a theoretically reference for the design and control of gas flow parameters during the large-scale LPBF. [ABSTRACT FROM AUTHOR]