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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]

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]

Additive manufacturing (AM) of a nickel-aluminum-bronze (NAB)/15-5 PH multimaterial by laser-powder directed energy deposition (LP-DED) accomplished a combination of excellent mechanical performance and high corrosion resistance. An NAB/15-5 PH interface without cracks and lack of fusion was achieved, which was characterized with an interlayer of Fe x Al dendrites. The formation of the interfacial characteristics was attributed to a synthetic effect of liquid phase separation, Marangoni convection, and atom diffusion. A miscibility gap was generated by a high degree of supercooling in the melt pool, and 15-5 PH solidified prior to NAB to form a dendritic interlayer. Marangoni convection occurred to promote the Al atom diffusion from NAB to 15-5 PH, contributing to the formation of the Fe x Al phase at the interface. The multimaterial sample possessed higher ultimate tensile strength of 754.64 MPa in the transverse direction and 854.57 MPa in the longitudinal direction as compared to that of copper/steel counterparts fabricated by AM. The multimaterial printed by LP-DED exhibited different deformation mechanisms in the transverse and longitudinal directions. In the transverse direction, NAB contributed more deformation than 15-5 PH and determined the improved ductility of the multimaterial; in the longitudinal direction, the brittle Fe x Al dendrites constrained the deformation of NAB and 15-5 PH, which resulted in the early failure of the multimaterial. The multimaterial tended to undergo cracking at the interface of the Fe x Al and Cu phases under stress concentration, which was induced by their crystal incoherence. [Display omitted] • A nickel-aluminum-bronze/15-5 PH multimaterial was achieved by directed energy deposition. • The printed multimaterial obtained high strength and excellent corrosion resistance. • A strong-bonded interface without lack-of-fusion and cracks was achieved. • A Fe x Al dendritic region with low misorientation density was obtained at the interface. • The underlying mechanisms of both interface formation and deformation were discussed. [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]

[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]

To fully exploit the biomechanical properties of titanium (Ti) and biocompatibility of tantalum (Ta), Ti-Ta multi-material structures with different printing sequences were fabricated using laser powder bed fusion (LPBF). The interfacial characteristics, mechanical properties, formation mechanisms, and influence of process parameters on bonding strength at the Ti/Ta (Ta printed on Ti) and Ta/Ti (Ti printed on Ta) interfaces were investigated. At the Ti/Ta interface, a wide diffusion zone led to microstructure evolution along the building direction: coarsened lath α′ grain → refined α′ + β grains → columnar β + cellular β grains. This evolution was attributed to keyhole formation and differences in material density that promoted element diffusion. On the other hand, at the Ta/Ti interface with a narrow diffusion zone, direct microstructure evolution occurred from columnar β + cellular β grains to lath α′ grains due to limited solid-state diffusion and compromised element diffusion caused by gravity and heat dissipation. Optimal bonding strengths of 548.11 MPa and 285.42 MPa were achieved for the Ti/Ta and Ta/Ti interfaces, respectively. During LPBF processing of Ti-Ta multi-materials, reducing scanning speed significantly enhanced bonding strength, indicating its significant impact on interfacial bonding. These findings offer novel insights and references to fabricate Ti-Ta multi-material structures with great potential for biomedical implants through LPBF. • Ti-Ta multi-material structures with different printing sequences were fabricated via LPBF. • Effect of process parameters on interfacial microstructure characteristics and bonding strength was discussed. • Interfacial formation mechanisms under different printing sequences were revealed. [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]

This study presents a methodology for repairing a damaged nickel-based turbine blade via laser powder bed fusion (LPBF) additive manufacturing. Specifically, the CM247LC nickel-based alloy was utilized to repair a damaged SRR99 nickel-based blade with LPBF, followed by hot isostatic pressing (HIP) post-treatment. The LPBF repair process achieved crack-free metallurgical bonding at the CM247LC/SRR99 interface with large epitaxially grown grains. Furthermore, HIP facilitated the formation of γ/γ' phases with comparable dimensions at the interface as well as in the CM247LC and SRR99 regions through recrystallization. Additionally, the columnar grains in the LPBF-printed CM247LC region transformed into coarse equiaxed grains after HIP, accompanied by precipitation of nanoscale Hf-rich carbides. Meanwhile, microcracks in the LPBF-printed CM247LC region and shrinkage pores in the cast SRR99 region were effectively eliminated. The LPBF-printed CM247LC exhibited an 8.62% higher hardness compared to that of SRR99. The repaired samples showed an ultimate tensile strength of 791 MPa, with fracture occurring at the SRR99 side, indicating a reasonable metallurgical bonding strength at the CM247LC/SRR99 interface. The findings offer a novel alternative for the industrial application of repairing damaged nickel-based turbine blades. • A methodology for repairing a damaged nickel-based blade via laser powder bed fusion was proposed. • A crack-free repaired CM247LC/SRR99 interface was achieved. • Few high angle grain boundaries at the interface declined the crack susceptibility. • The interface processed better tensile strength than the SRR99 single crystal. [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]

Magnetic field-assisted laser-based additive manufacturing provides a feasible method for the fabrication and performance improvement of metal parts. In this research, the effects of axial static and alternating magnetic field-assisted laser powder bed fusion on mechanical properties and microstructure of stainless steel 316L are investigated. Under static magnetic field, the epitaxial growth and <001> crystallographic texture along the building direction are inhibited and cellular dendrites are deflected from the solidification direction by thermoelectric magnetic force. With increasing relative density and <110> texture, the ductility of specimens increases significantly and reaches 52.6%. When an alternating magnetic field is applied, the long epitaxial cellular dendrites along the heat dissipation route and cell spacing decrease. The epitaxial growth along the building direction is significantly blocked by the interaction of induced current and magnetic field. The preferred orientation of crystals is also changed, indicating a strong <102> crystallographic texture along the building direction. In addition, the strength and ductility of specimens are improved under an alternating magnetic field. [ABSTRACT FROM AUTHOR]