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A challenge remains in achieving adequate surface roughness of SLM fabricated interior channels, which is crucial for fuel delivery in the space industry. This study investigated the surface roughness of interior fine flow channels (1 mm diameter) embedded in SLM fabricated TC4 alloy space components. A machine learning approach identified layer thickness as a significant factor affecting interior channel surface roughness, with an importance score of 1.184, followed by scan speed and laser power with scores of 0.758 and 0.512, respectively. The roughness resulted from thin layer thickness of 20 µm, predominantly formed through powder adherence, while from thicker layer of 50 µm, the roughness was mainly due to the stair step effect. Slow scan speeds increased melt pools solidification time at roof overhangs, causing molten metal to sag under gravity. Higher laser power increased melt pools temperature and led to dross formation at roof overhangs. Smaller hatch spaces increased roughness due to overlapping of melt tracks, while larger hatch spaces reduced surface roughness but led to decreased part density. The surface roughness was recorded at 34 µm for roof areas and 26.15 µm for floor areas. These findings contribute to potential adoption of TC4 alloy components in the space industry. [ABSTRACT FROM AUTHOR]

The poor wettability and weak interfacial bonding of diamond/copper composites are due to the incompatibility between diamond and copper which are inorganic nonmetallic and metallic material, respectively, which limit their further application in next-generation heat management materials. Coating copper and titanium on the diamond particle surface could effectively modify and improve the wettability of the diamond/copper interface via electroless plating and evaporation methods, respectively. Here, these dense and complex composites were successfully three-dimensionally printed via selective laser melting. A high thermal conductivity (TC, 336 W/mK) was produced by 3D printing 1 vol.% copper-coated diamond/copper mixed powders at an energy density of 300 J/mm3 (laser power = 180 W and scanning rate = 200 mm/s). 1 and 3 vol.% copper-coated diamond/copper composites had lower coefficients of thermal expansions and higher TCs. They also had stronger bending strengths than the corresponding titanium-coated diamond/copper composites. The interface between copper matrix and diamond reinforcement was well bonded, and there was no cracking in the 1 vol.% copper-coated diamond/copper composite sample. The optimization of the printing parameters and strategy herein is beneficial to develop new approaches for the further construction of a wider range of micro-sized diamond particles reinforced metal matrix composites. [ABSTRACT FROM AUTHOR]

High electrical and thermal conductive metals (HETCM) play a key role in smart electronics, green energy, modern communications and healthcare, however, typical HETCM (e.g., Ag, Au, Cu) usually have relatively low mechanical strength, hindering further applications. Selective laser melting (SLM) is a potentially transformative manufacturing technology that is expected to address the issue. Ag is the metal with the highest thermal conductivity, which induces microscale grain refinement, but also leads to high internal stresses by SLM. Here, we select Ag7.5Cu alloy as an example to demonstrate that multi-scale (micro/meso/macro) synergies can take advantage of high thermal conductivity and internal stresses to effectively strengthen Ag alloy. The mimicry of metal-hardened structures (e.g., large-angle boundary) is extended to the mesoscale by controlling the laser energy density and laser scanning strategy to manipulate the macroscale internal stress intensity and mesoscale internal stress direction, respectively, to form mesoscale large-angle "grains", resulting in multiple mutual perpendicular shear bands during fracture. The presented approach achieved a significant enhancement of yield strength (+ 145%) and ductility (+ 28%) without post-treatment. The results not only break the strength-ductility trade-off of conventional SLM alloys, but also demonstrate a multi-scale synergistic enhancement strategy that exploits high thermal conductivity and internal stresses. [ABSTRACT FROM AUTHOR]

A significant requirement for a bone implant is to replicate the functional gradient across the bone to mimic the localization change in stiffness. In this work, continuous functionally graded porous scaffolds (FGPSs) based on the Schwartz diamond unit cell with a wide range of graded volume fraction were manufactured by selective laser melting (SLM). The micro-topology, strut dimension characterization and effect of graded volume fraction on the mechanical properties of SLM-processed FGPSs were systematically investigated. The micro-topology observations indicate that diamond FGPSs with a wide range of graded volume fraction from 7.97% to 19.99% were fabricated without any defects, showing a good geometric reproduction of the original designs. The dimensional characterization demonstrates the capability of SLM in manufacturing titanium diamond FGPSs with the strut size of 483–905 µm. The elastic modulus and yield strength of the titanium diamond FGPSs can be tailored in the range of 0.28–0.59 GPa and 3.79–17.75 MPa respectively by adjusting the graded volume fraction, which are comparable to those of the cancellous bone. The mathematical relationship between the graded porosity and compression properties of a FGPS was revealed. Furthermore, two equations based on the Gibson and Ashby model have been established to predict the modulus and yield strength of SLM-processed diamond FGPSs. Compared to homogeneous diamond porous scaffolds, FGPSs provide a wide range of mutative pore size and porosity, which are potential to be tailored to optimize the pore space for bone tissue growth. The findings provide a basis of new methodologies to design and manufacture superior graded scaffolds for bone implant applications. [ABSTRACT FROM AUTHOR]

Ti-6Al-4V Gyroid triply periodic minimal surface (TPMS) lattices were manufactured by selective laser melting (SLM). The as-built Ti-6Al-4V lattices exhibit an out-of-equilibrium microstructure with very fine α′ martensitic laths. When subjected to the heat treatment of 1050 °C for 4 h followed by furnace cooling, the lattices show a homogenous and equilibrium lamellar α + β microstructure with less dislocation and crystallographic defects compared with the as-built α′ martensite. The as-built lattices present very rough strut surfaces bonded with plenty of partially melted metal particles. The sand blasting nearly removed all the bonded metal particles, but created many tiny cracks. The HCl etching eliminated these tiny cracks, and subsequent NaOH etching resulted in many small and shallow micro-pits and develops a sodium titanate hydrogel layer on the surfaces of the lattices. When soaked in simulated body fluid (SBF), the Ti-6Al-4V TPMS lattices were covered with a compact and homogeneous biomimetic hydroxyapatite (HA) layer. This work proposes a new method for making Ti-6Al-4V TPMS lattices with a homogenous and equilibrium microstructure and biomimetic HA coating, which show both tough and bioactive characteristics and can be promising materials usable as bone substitutes. [ABSTRACT FROM AUTHOR]

Selective Laser Melting (SLM) process is a metallic additive manufacturing technique that directly manufactures strong, lightweight and complex three dimensional parts in a layer-by-layer to scan and melt the metal powder for aerospace applications. However, there are still certain evaluation criteria such as fracture toughness and tensility of cellular structure made by SLM which were not reported before. This study presents new and novel methods in additive manufacturing and evaluates the local failure mechanism of 316L cellular lattice structures made by SLM under uniaxial tension and three point pending load. The effect of different build directions of the 316L lattice structure on the fracture toughness properties are compared to the Ashby and Gibson models. Also, the effect of different build directions on tensile properties of 316L cellular structures has been investigated. Microcomputer tomography (CT) reveals that the cellular structure parts with different build directions were manufactured free of defect by the SLM. The density of the lattice structure samples was found at 1.35 g/ cm 3 for both vertical and horizontal building directions while the relative density of solid struts is 96.25%. The tensile and fracture toughness properties in vertical building direction samples are higher than those samples that were built in horizontal building direction. There was no big difference between the Ashby and Gibson micromechanical model to predict fracture toughness and Single Edge Notch Bend (SENB) test results from 0.2 to 0.5 MPa m 0 . 5 . [ABSTRACT FROM AUTHOR]

Triply periodic minimal surface (TPMS) structures have already been shown to be a versatile source of biomorphic scaffold designs. Therefore, in this work, Ti–6Al–4V Gyroid and Diamond TPMS lattices having an interconnected high porosity of 80–95% and pore sizes in the range of 560–1600 μm and 480–1450 μm respectively were manufactured by selective laser melting (SLM) for bone implants. The manufacturability, microstructure and mechanical properties of the Ti–6Al–4V TPMS lattices were evaluated. Comparison between 3D micro-CT reconstructed models and original CAD models of the Ti–6Al–4V TPMS lattices shows excellent reproduction of the designs. The as-built Ti–6Al–4V struts exhibit the microstructure of columnar grains filled with very fine and orthogonally oriented α′ martensitic laths with the width of 100–300 nm and have the microhardness of 4.01±0.34 GPa. After heat treatment at 680 °C for 4 h, the α′ martensite was converted to a mixture of α and β, in which the α phase being the dominant fraction is present as fine laths with the width of 500–800 nm and separated by a small amount of narrow, interphase regions of dark β phase. Also, the microhardness is decreased to 3.71±0.35 GPa due to the coarsening of the microstructure. The 80–95% porosity TPMS lattices exhibit a comparable porosity with trabecular bone, and the modulus is in the range of 0.12–1.25 GPa and thus can be adjusted to the modulus of trabecular bone. At the same range of porosity of 5–10%, the moduli of cortical bone and of the Ti–6Al–4V TPMS lattices are in a similar range. Therefore, the modulus and porosity of Ti–6Al–4V TPMS lattices can be tailored to the levels of human bones and thus reduce or avoid “stress shielding” and increase longevity of implants. Due to the biomorphic designs, and high interconnected porosity and stiffness comparable to human bones, SLM-made Ti–6Al–4V TPMS lattices can be a promising material for load bearing bone implants. [ABSTRACT FROM AUTHOR]

Highlights: [•] A unique cell type called gyroid is designed to construct lattice structures. [•] Curved cell surface as a self-supported feature avoids support structures. [•] Lattice structures with a wide volume fraction range were made. [•] Lattice structures were made at different orientations. [•] Strength and modulus increase with the increase in the volume fraction. [ABSTRACT FROM AUTHOR]

Abstract: Metal additive manufacturing (MAM) of complex parts with overhangs typically requires the use of sacrificial support structures to hold the part during the process. This structures which are built simultaneously with the part, anchors the overhang geometry to the base plate and prevent distortion/curling resulting from thermal stresses. They are necessary, but add constraints to the geometries that the processes can make. The design and selection of support structure can influence the manufacturability of complex metal parts, material and energy utilization, manufacturing time and cost. This study takes a new step on the design and manufacturing a more efficient support through the novel application of lattice structures with very low volume fraction. Experiments were conducted in direct metal laser sintering (DMLS) machine using titanium alloy Ti6Al4V powder. Experimental results revealed that the type of structure, volume fraction and cell size are the main factors influencing the manufacturability, amount of support, and built time of lattice support structures. Lattice supports with very low volume fraction up to 8% were built, saving significant amount of materials used in the support while reducing built time of making MAM parts. [Copyright &y& Elsevier]

Abstract: Metallic additive manufacturing techniques, in particular the selective laser melting (SLM) process, are capable of fabricating strong, lightweight and complex metallic lattice structures. However, they still face certain process limitations such as geometrical constraints and in some cases the need for support structures. This study evaluates the manufacturability and performance of SLM produced periodic cellular lattice structures, which are designed by repeating a unit cell type called gyroid consisting of circular struts and a spherical core. The effect of unit cell size on the manufacturability, density and compression properties of the manufactured cellular lattice structures were investigated. Micro-computer tomography (CT) scan results reveal that the gyroid cellular lattice structures with various unit cell sizes ranging from 2 to 8mm can be manufactured free of defects by the SLM process without the need of additional support structures. The Scanning Electron Microscope (SEM) micrographs show that the lattice structures made by SLM have a good geometric agreement with the original computer-aided design (CAD) models, but many partially melted metal particles are bonded to strut surfaces. The struts within the gyroid cellular lattice structures with smaller unit cell sizes have higher densities due to their shorter scan vector lengths in the SLM process. The yield strength and Young''s modulus of the Gyroid cellular lattice structures increase with the decrease in the unit cell size due to the denser struts of the lattice structures with smaller unit cell sizes. [Copyright &y& Elsevier]

Abstract Silver, as a precious metal, is widely used in the consumer goods industry and high-tech fields. Selective Laser Melting (SLM), as an Additive Manufacturing (AM) technique, has the potential to make complex structural components of Ag alloy but is often limited by the high reflectivity and thermal conductivity of Ag. This study seeks to determine the optimum solution to this limitation by identifying the most suitable laser device, material and parameters for manufacturing Ag alloy through SLM. The effects of laser power, scanning speed and scanning strategy on the morphology, microstructure, density and mechanical properties of Ag alloy are described. It reveals that the density and Vickers hardness of Ag alloy are largely determined by the molten pool size, grain size, residual stress and cooling rate. Results of experiments and theoretical calculations further reveal that the heterogeneity and anisotropy formation of microstructure and defects are related to variations in the cooling rate and thermal gradient caused by the laser scanning strategy. The high scanning speed of the laser and high thermal conductivity of the Ag lead to higher cooling rates, thereby enabling SLM processed Ag alloy to have a density as high as 96.7% and hardness of up to 148.9HV. Graphic abstract Unlabelled Image Highlights • Selective laser melting can increase hardness by up to 200% by improving grain refinement and increasing residual stress. • High reflectivity and thermal conductivity can be addressed by optimized laser devices with high power and short wavelengths. • Homogeneous components can be obtained by placing laser scanning tracks of uniform length parallel to the XY axles. [ABSTRACT FROM AUTHOR]

After a brief introduction on selective laser melting (SLM) and "ex situ" manufacture of metal matrix composites (MMCs), this paper reviews the capacities and benefits of SLM to activate and control various "in situ" reactions during fabrication of 3D parts. It introduces several systems (such as Al/Fe2O3, AlSi10Mg/SiC, Al/ZnO, Ti/C, Ti/SiC, Ti/Si3N4, Ti/Mo2C, Fe/SiC, etc.) used to manufacture Al‐based, Ti‐based, and steel‐based "in situ" MMCs. Then, it illustrates the novel microstructural characteristics of these SLM‐made "in situ" MMCs for different cases, as they may appear from nano‐particles to nano‐whiskers and dendritic reinforcements homogeneously distributed in a metal matrix. It also focuses on SLM associated "in situ" mechanisms, explaining how an "in situ" reaction propagates based on "decomposition, diffusion, and reformation" and how the growth mechanisms turn into different morphologies such as rounded particles, whiskers, or polygonal block shapes. The influence of various SLM parameters (such as energy density, laser power/speed, powder layer thickness, and the size of initial powder particles) and the SLM "in situ" challenges are also discussed. This paper describes the advancements to manufacture metal matrix composites (MMCs) using selective laser melting (SLM) from reactive powders. Based on various metal‐based powder systems, it discusses how different novel microstructures and properties can appear in the "in situ" made MMCs. As an example, the shown figure illustrates the propagation of "in situ" products throughout an Al/Fe2O3 powder mixture. [ABSTRACT FROM AUTHOR]

Abstract Here, heat treatment-dependent microstructural evolution and tensile properties obtained by uniaxial tensile test and small punch test (SPT) of the selective laser melting (SLM)-fabricated GH4099 alloy are investigated. The columnar grains characterized by predominant Cube texture exponent in the as-SLM condition transform into random-oriented recrystallized grains with profuse twins after solution treatment. Upon aging, dispersed nano-sized coherent γ' precipitates generate. Uuniaxial tensile test results indicate a balance of ultimate tensile strength (UTS) and uniform elongation in the aged sample, i.e., ∼1206 MPa and ∼ 21% vs. ∼948 MPa and ∼ 27% in the as-SLM sample. The present study highlights the predominant role of dispersed coherent γ' precipitates on the appreciable work hardening ability and hence better tensile property. The analysis of work hardening rate curves indicates the dislocation accumulation rate is comparable between the aged sample and the solution-treated sample, both of which are higher than that in the as-SLM counterpart. Appreciably, lower dynamic recovery rate exists in the aged alloy due to strong γ' particle-dislocation interactions, which favors higher work hardening rate among the three conditions. Nevertheless, the strong S, Rotated-Copper and Rotated-Goss components originating from preferential grain growth allow for uniform elongation decreased in the aged sample. Meanwhile, unified correlation equations between SPT and uniaxial tensile test are established for the present GH4099 alloy, which aims at providing an empirical relationship to evaluate tensile properties of the SLM-fabricated GH4099 alloy undergone various post-heat treatment. • A decent combination of UTS of ∼1206 MPa and uniform elongation of ∼21% is obtained in SLM-processed GH4099 after aging. • Dislocation accumulation rate and dynamic recovery rate change with heat treatments during tensile deformation. • Appreciable work hardening ability contributes to the good tensile property in aged GH4099. • Unified correlation equations between small punch test and uniaxial tensile test are established for the present alloy. [ABSTRACT FROM AUTHOR]

[Display omitted] • Bio-inspired lattice structures were manufactured by selective laser melting. • The effect of unit cell types on manufacturing precision was investigated. • Heterogeneous lattice structures results cell-by-cell and layer-by-layer fracture. • Three strategies for unit cell design and optimization were introduced. Bio-inspiration offers researchers innovative perspectives and methodologies, stimulating the advancement of high-performance, high-durability, and added-value materials, structures, and products. Inspired by the lightweight, high-strength, and highly stable glass sponges (GSs), five types of glass sponge lattice structures (GSLSs) were successfully designed and manufactured by selective laser melting (SLM) with Ti6Al4V. By conducting a comparative analysis of unit cell design and manufacturing deviations, we assess their impact on the compressive properties of GSLSs. Notably, the original GSLS with circle-/grid-like heterogeneous geometries exhibits outstanding overall compression performance, including stability, stress dispersion and unique cell-by-cell and layer-by-layer fracture mechanisms among GSLSs, which are attributable to their reinforced diagonal struts and heterogeneous unit cells. Hence, three strategies for unit cell design and optimization were proposed. These discoveries guide the future design and optimization of lattice structures (LSs) and offer potential applications for GSLSs in aerospace, biomedicine, automobiles, architecture, and wearable products. [ABSTRACT FROM AUTHOR]

The leverage of selective laser melting (SLM) successfully fabricate metal matrix composites (MMCs) metamaterials with freeform intricate triply periodic minimal surface (TPMS) structures that are not possibly fabricated by conventional methods and exhibit exceptional mechanical properties. SLM fabricated high precision MMCs metamaterial TPMS structures are of great potential in energy conversion, heat management and lightweight applications. Due to the self-supporting geometric characteristics of TPMS, the metamaterial structures could effectively overcome the manufacturing constraints of SLM. Besides, their freeform capability offers great opportunities to be bi-functional or multi-functional through the selection of materials as well as the design optimization of structure. Diamond can offer unique advantages in the field of heat management due to its outstanding thermal and mechanical properties. The addition of micro-sized diamond particles into copper can tailor its coefficient of thermal expansion (CTE) while enhancing its thermal conductivity (TC). SLM fabricated diamond reinforced copper MMCs metamaterials with TPMS structure could bring outstanding thermal-mechanical bi-functional properties for prospective lightweight thermal management applications. In our previous work, the interfacial bonding issue between diamond particles and Cu matrix was resolved by a coating of copper on micro-sized diamond particle reinforcement. In this present work, 1 vol% Cu-plated diamond/Cu metamaterials with three various TPMS (Gyroid-G, Schwarz Primitive-P, Diamond-D) structures were successfully fabricated via SLM for the first time. Their bi-functional heat transfer and compression behaviors were evaluated by measurement and numerical simulation for three TPMS (G, P, D) structures and TPMS (D) structures with various lattice thicknesses. From the lightweight perspective of three TPMS structures with 0.2 mm wall thickness, the order of these structure is TPMS P structure, TPMS G structure, TPMS D structure (0.2 mm wall thickness, 0.2 P > 0.2 G > 0.2D). If heat transfer performance is an important consideration, The 0.2D structure can be selected from the three TPMS structures. This research also investigated the continuous design of TPMS D structure with various wall thickness and creatively proposed a flexible TPMS design paradigm toward advanced thermal-mechanical bi-functional Cu-plated Diamond/Cu metamaterials via SLM for prospective lightweight thermal management applications. • 1 vol% Cu-plated diamond/Cu metamaterials TPMS structures were firstly and successfully fabricated by SLM. • The thermal-mechanical property of 1 vol% Cu-plated diamond/Cu metamaterials SLM scaffolds was altered by tuning wall thickness of TPMS structures. • TPMS D structure (0.8 mm wall thickness) possessed excellent heat transfer efficiency, ultimate compressive strength (492.77 MPa), and specific energy absorption (19.87 J/g). [ABSTRACT FROM AUTHOR]

This paper presents a study on the layer-by-layer synthesis of stainless-steel (SS) and nano-hydroxyapatite (nHA) composite using selective laser melting (SLM). The microstructural and elemental examinations, tensile and nanoindentation tests were conducted. The effects of material ratios and laser scanning speeds on cracks and pores were identified by the cross-section morphology of samples fabricated by SLM. High content of nHA resulted in the particle aggregation at the melt pool boundaries and the cracks on these areas. Increasing in laser scanning speed shortened the solidification time of melt pools, thus withstood aggregation of nHA and decreased the degree of cracks. Optimum material ratio and laser scanning speed were determined for SLM of SS/nHA composite in order to fabricate load-bearing bone implants. A uniform distribution of Ca and P elements was detected on the top surfaces of as-SLM fabricated composite, which could facilitate good bone osseointegration. The highest tensile strength, elastic modulus and hardness of SS/nHA samples produced at optimum processing condition were found to be higher than that of the human bone, which provides the possibility to fabricate SS/nHA porous scaffolds with tailored mechanical properties for load-bearing bone applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • A unique bio-inspired circle-/grid-like heterogeneous Ti6Al4V glass sponge lattice structure can be successfully fabricated by selective laser melting. • Glass sponge lattice structure exhibits the highest compressive properties compared with other commonly used lattice structures. • Unique cell-after-cell and layer-by-layer fracture mechanisms of glass sponge lattice structure provide its interior and entire integrity during compression. High precision lattice structure (LS) shows great potential applications in aerospace, acoustic, biomedical, and wearable products due to its multifunctional characteristics and excellent mechanical properties. Inspired by lightweight, high-strength, and high-stability glass sponges (GSs), a unique circle-/grid-like heterogeneous glass sponge lattice structure (GSLS) was successfully designed and manufactured by selective laser melting (SLM) with Ti6Al4V alloy. Compared with the commonly used body-centred cubic (BCC), face-centred cubic (FCC), honeycomb and diamond LSs, GSLS displays the strongest compressive properties (E = 1560 MPa, σ max = 40 MPa, σ y0.2 = 34 MPa, W = 5.95 J). The normalised elastic modulus and normalised compressive strength of GSLS are almost 1.4 and 1.3 times, 2.6 and 2.4 times, 2.7 and 3.5 times, 18 and 8.3 than that of FCC, BCC, honeycomb, and diamond LSs, respectively. Most importantly, unlike the 45° diagonal shear failure of homogeneous BCC and FCC, the FEA simulation reveals that the heterogeneous unit cell in GSLS can enhance the strut connectivity, disperse the stress, and exhibits a unique fracture mechanism of cell-after-cell and layer-by-layer. The fracture mechanism of GSLS can improve the load-bearing capability, maintain strength, and protect its interior and entire integrity during compression. [ABSTRACT FROM AUTHOR]

• A functionally graded diamond network with high quality was fabricated. • 3D printed Cu with coarse surface was utilized for in-situ growth of diamond. • Thermal conductivity and compressive strength were improved significantly. A novel functionally graded structure of diamond was developed with significantly enhanced thermal conductivity and compressive strength, based on synergistic effects combining chemical vapor deposition (CVD) and selective laser melting (SLM). In-situ diamond growth was achieved without conventionally complex pretreatment steps thanks to the high surface roughness of as-printed graded copper scaffold. The continuous diamond film coated on graded copper scaffold forms a monolith with interconnected network, acting as an effective layer for heat conduction with an exceptional increase (459%) in thermal conductivity compared with copper counterpart. The functionally graded structure also demonstrates a progressive mechanical response to loading compared with the uniform structure. This work opens a new avenue for realizing three-dimensional diamond structure and proves its multifunctionalities, especially for high-power electronics applications. [ABSTRACT FROM AUTHOR]