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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]

Triply Periodic Minimal Surface (TPMS) porous structures are recognized as the most promising bionic artificial structures for tissue engineering. The fatigue properties of additive manufactured porous structures are essential for long-term use in a dynamical bio-skeletal environment. The aim of this study is to study the compression–compression fatigue behaviour and the underlying fatigue mechanism of Gyroid cellular structures (GCS), a typical TPMS porous structure. The high-cycle fatigue results show that both cyclic ratcheting and fatigue damage phenomena contribute to the failure of GCS during fatigue testing. For most fatigue loading stress, the failure samples have nearly 45° fracture bands along the diagonal surface. The fatigue ratio of GCS reaches 0.35 for as-built samples and can be raised to 0.45 after sandblasting treatment. The fatigue ratio values are higher than most of the other bending-dominated lattice structures, suggesting superior fatigue resistance properties of GCSs due to the smooth surface connection between struts. Besides, a systematic investigation of the crack initiation and propagation was conducted by both deformation analysis and finite element method to support experimental phenomena. The results also indicate that the fatigue resistance properties of GCSs are significantly enhanced by sandblasting post-treatment, through removing the adhered powder particles, inducing compressive residual stress on the surface and generating a nanocrystalline zone. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Highlights • A material model based on the SLM-built porous materials was proposed. • The detailed stress and strain distribution were predicted from the FE results. • The fracture can be predicted and was verified by the experimental testing. • The predicted mechanical responses match well with the experimental results. • The Gibson–Ashby formulations were obtained from the FE analysis. Abstract Cellular structures with controllable mechanical properties and porous architecture are the most promising candidates for many applications such as bone implants. Selective laser melting (SLM), one of the additive manufacturing (AM) technologies, enables manufacturing of space filling lattice structures with exceptional load bearing efficiency, customizable stiffness, controllable cell topology, cell size, and porosity. In this work, Schoen Gyroid (SG) unit cell, a triply periodic minimal surface (TPMS) structure, was used to design the cellular structures. As opposed to many other types of unit cells, SG has superior characteristics of self-supporting and high manufacturability for AM technologies. The titanium alloy (Ti–6Al–4V) SG cellular structures were manufactured by SLM. Finite element (FE) method was employed to predict the elastic modulus, compressive yield strength and stress/strain distributions of the SG cellular structures, and the failure occurrence mechanisms were analyzed. The FE results were compared with the experimental data. The results show that through FE method, the mechanical responses of the SG cellular structures can be accurately described and it is possible to customize the mechanical properties of SLM-produced titanium alloy TPMS lattices. Graphical abstract Image, graphical abstract [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]

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: 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]

Nickel-titanium alloys have been widely used in biomedical, aerospace and other fields due to their shape memory effect, superelastic effect, as well as biocompatible and elasto-thermal properties. Additive manufacturing (AM) technology can form complex and fine structures, which greatly expands the application range of Ni-Ti alloy. In this study, the development trend of additive manufactured Ni-Ti alloy was analyzed. Subsequently, the most widely used selective laser melting (SLM) process for forming Ni-Ti alloy was summarized. Especially, the relationship between Ni-Ti alloy materials, SLM processing parameters, microstructure and properties of Ni-Ti alloy formed by SLM was revealed. The research status of Ni-Ti alloy formed by wire arc additive manufacturing (WAAM), electron beam melting (EBM), directional energy dedication (DED), selective laser sintering (SLS) and other AM processes was briefly described, and its mechanical properties were emphatically expounded. Finally, several suggestions concerning Ni-Ti alloy material preparation, structure design, forming technology and forming equipment in the future were put forward in order to accelerate the engineering application process of additive manufactured Ni-Ti alloy. This study provides a useful reference for scientific research and engineering application of additive manufactured Ni-Ti alloys. [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]

[Display omitted] • Sample densification decreases as the volume fraction and unit cell become larger. • TPMS improved the load-carrying capacity of the lattice structure. • The collapse is discussed as leading to structural mechanical properties contrary to some studies. • Varying the geometric characteristics of the lattice structure can change the vibration performance. • TPMS lattice structure has better performance in low frequency vibration isolation. Several research has been done on the conventional strut-based lattice structures, which have the problem of stress concentration in the application. In recent years, a new lattice structure, the triply periodic minimal surface (TPMS) lattice structure is increasingly gaining attention, but its vibrational properties have been less studied. In this study, the IWP-type TPMS lattice structures and ordinary body-centered cubic (BCC) counterparts with similar topology were prepared by selective laser melting (SLM) additive manufacturing (AM) technique. The compression behavior of the structures and the energy absorption capacity were determined by uniaxial compression tests. The frequency response and the damping ratio of the structure were calculated by dynamic vibration transfer rate tests. The results show that the stiffness and inherent frequency of the lattice structure are proportional to the volume fraction and inversely proportional to the cell size. Decreasing the volume fraction and increasing the cell size can be more beneficial to achieve low-frequency vibration isolation. Moreover, the IWP-type triply periodic minimal surface lattice structures have better mechanical properties than BCC structures and have good vibration isolation properties. Insights from this paper provide a reference for improving the load-carrying and vibration isolation performance of lightweight lattice structures. [ABSTRACT FROM AUTHOR]

Abstract Functional graded cellular materials (FGCMs) have attracted increasing attentions for their improved properties when compared to uniform cellular structures. In this work, graded Gyroid cellular structures (GCSs) with varying gradient directions were designed and manufactured via selective laser melting (SLM). As a reference, uniform structures were also manufactured. The surface morphology and mechanical response of these structures under compressive loads were investigated. Results indicate high manufacturability and repeatability of GCSs manufactured by SLM. Optimized density distribution gives these structures novel deformation and mechanical properties. GCSs with density gradient perpendicular to the loading direction exhibit deformation behaviours similar to uniform ones, while GCSs with the gradient parallel to the loading direction exhibit layer-by-layer deformation and collapse behaviour. A novel phenomenon of sub-layer collapses is found in GCSs with gradient parallel to the loading direction. Furthermore, mathematical models were developed to predict and customize the mechanical properties of graded cellular structures by optimizing the relative density of each layer. These significant findings illustrate that graded cellular structures have high application prospect in various industries, particularly given the fact that additive manufacturing has been an enabler of cellular structure fabrication. Graphical abstract Unlabelled Image Highlights • Continuous graded Gyroid cellular structures (GCSs) were fabricated by SLM. • Novel deformation and mechanical properties were gained compared to uniform cellular. • The effect of gradient direction was investigated for GCSs. • Novel sub-layer collapses are founded in GCSs with gradient along building direction. • Mathematical models were developed to calculate Young's modulus and strength of GCSs. [ABSTRACT FROM AUTHOR]

Abstract This work for the first time investigated the effect of laser scan line spacing on the microstructure, phase evolution and nanohardness of Ti-48Al-2Cr-2Nb/RGO (reduced graphene oxide) metal matrix composites (MMCs) fabricated by selective laser melting (SLM). The results show that with increasing the laser scan line spacing from 80 to 140 μm, the average grain size generally decreases from 10.13 to 8.12 μm. The SLM-processed Ti-48Al-2Cr-2Nb/RGO parts are dominated by high-angle (>15°) grain boundaries (HAGBs) and α 2 (Ti 3 Al) phase. With the increase in laser scan line spacing, the contents of HAGBs and α 2 phase both decrease. Due to instantaneous high temperature during the SLM process, some RGO sheets transform to amorphous carbon. The nanohardness of SLM-processed Ti-48Al-2Cr-2Nb/RGO parts increase from 8.13 ± 0.39 GPa to 9.85 ± 0.46 GPa when increasing the laser scan line spacing from 80 to 140 μm, which is much higher than that of the traditional casting TiAl counterparts (4.98 ± 0.10 GPa). Graphical Abstract Unlabelled Image Highlights • The average grain size generally refines with increasing the laser scan line spacing. • The phase transformation mechanism during SLM is determined by HRTEM. • Some RGO sheets transform into amorphous carbon during SLM process. • The nanohardness is much higher than those casting counterparts. [ABSTRACT FROM AUTHOR]

In this study, fully dense Ti-6Al-4V alloy parts were successfully fabricated by an in-situ tooling (skin or shell) via a novel hybrid process of selective laser melting (SLM)/hot isostatic pressing (HIP). In this hybrid process, the in-situ tooling of Ti-6Al-4V parts was prepared via selective laser melting, then filled with Ti-6Al-4V powder, and finally consolidated by hot isostatic pressing to build fully dense complex parts without the need of removal of anything. The interface between tooling and consolidated powder was investigated in detail using scanning electron microscope (SEM) and electron backscattered diffraction (EBSD), and the bond strength was evaluated by tensile and fatigue testing. It was found that there was no obvious element diffusion around the interface, but the pronounced difference in microstructure type and gain size could be seen. Regardless of HIP temperatures, the tensile and fatigue samples preferentially failed on the tooling side due to the coarser Widmanstatten microstructure. Compared with the as-SLMed parts, the samples prepared by this hybrid SLM/HIP process exhibited higher mechanical properties such as superior strength and outstanding ductility, and became more competitive, even than wrought Ti-6Al-4V parts. [ABSTRACT FROM AUTHOR]

TiAl/TiB 2 in-situ metal matrix composites (MMCs) with greatly enhanced nanohardness are prepared via selective laser melting (SLM) for the first time in this study. The effect of TiB 2 reinforcement on the microstructural characteristics, texture evolution and phase transformation of TiAl-based alloy is investigated. The results show that with increasing the TiB 2 content, the average grain size gradually decreases, and the crystallographic orientation transforms from a strong ( 0001 ) direction to ( 10 1 ¯ 1 ) and ( 11 2 ¯ 1 ) directions. Meanwhile, TiB 2 has a great effect on the texture of SLM-processed TiAl/TiB 2 MMCs. With increasing the TiB 2 content, more textured TiAl/TiB 2 MMCs can be produced. The TiAl/TiB 2 MMCs are dominated by α 2 phase and small amounts of γ, B 2 , TiB 2 and TiB phases are also detected. α 2 phase contains the most important texture components of prismatic fiber with { 10 1 ¯ 0 } < 11 2 ¯ 0> orientation, basal fiber with { 0001 } < 11 2 ¯ 0> orientation and pyramidal fiber with { 10 1 ¯ 1 } < 11 2 ¯ 0> and { 11 2 ¯ 2 } < 11 2 ¯ 3 > orientations. The TiB 2 reinforcements are in the forms of the needlelike micro-TiB 2 and irregular nano-TiB 2 particles in the TiAl-based alloy matrix, and the nano-TiB 2 particles are uniformly distributed with the size of 10 nm in length and 3–5 nm in width. The SLM-produced TiAl/TiB 2 MMCs exhibit superior nanohardness of 10.57 ± 0.53 GPa, which is much higher than those of the traditional roll bonding fabricated TiB 2 reinforced TiAl-based alloy. The findings would be a valuable reference for fabricating TiAl/TiB 2 MMCs parts with controlled grain features, crystallographic texture and phase composition, enhanced mechanical properties and complex structures by SLM. [ABSTRACT FROM AUTHOR]

Ti-Nb alloys were in-situ fabricated by selective laser melting (SLM) to study the effect of Nb content on their phase transformation, microstructure evolution, mechanical properties and in vitro apatite-forming capability. Results show that α' martensite and β (Ti, Nb) phase are obtained in SLM-processed Ti-Nb alloys. The increase of Nb content results in the increase of β phase amount but decrease of β grain dimension. The former effect is due to the suppression of martensitic transformation and strengthening of solid solution behavior, while the latter phenomenon can be attributed to the increase of heterogeneous nucleation sites. The Ti-25Nb alloy possesses the lowest modulus of 18.7 ± 1.4 GPa due to the maximum content of β phase. The SLM-processed Ti-45Nb alloy exhibits superior strength of 1030 ± 40 MPa and microhardness of 356 ± 7 HV 0.1 , which is 97.32% and 52.53% higher than cast ones, respectively. The in vitro apatite-forming capability of Ti-25Nb alloy is the most superior compared to other Ti-Nb alloys. It demonstrates that β phase has the ability to induce apatite formation. The research shows that SLM could be used for in-situ fabrication of Ti-Nb bone implants with tailored mechanical and biomedical properties by adjusting Nb addition. [ABSTRACT FROM AUTHOR]

This work presents a comprehensive study on the laser scanning speed on the microstructure development, phase evolution and nanohardness of a TiAl alloy, Ti-45Al-2Cr-5Nb (at.%), processed by selective laser melting (SLM). The experimental results show that when increasing the laser scanning speed from 500 to 800 mm/s, the average grains size decreases from 7.11 μm to 5.43 μm, whereas the crystallographic texture showing a combination of (0001), ( 10 1 ¯ 1 ) and ( 11 2 ¯ 1 ) orientations basically remains unchanged. The SLM-processed TiAl alloy is dominated by high-angle (>15°) grain boundaries (HAGBs) and the contents of HAGBs decrease from 91.6% to 86.1% when the laser scanning speed varies from 500 to 800 mm/s. The α 2 phase decreases while the γ and B 2 phases increase with increasing the laser scanning speed. Moreover, the phase evolution mechanism in the SLM-processed TiAl alloy can be described as follows: (200) β transforms to ( 20 2 ¯ 0 ) α 2 and (110) γ , and then the residual B 2 and the incompletely transformed γ phase randomly distributed in the α 2 phase matrix. The nanohardness of the SLM-process TiAl alloy increases from 7.90 ± 0.32 GPa to 9.49 ± 0.46 GPa with increasing laser scanning speed from 500 to 800 mm/s, which is much higher than those of traditionally manufactured counterparts, such as casting parts (4.98 ± 0.10 GPa) and TiB 2 reinforced TiAl alloy fabricated by roll bonding (6.73 GPa). With the increase of laser scanning speed from 500 to 800 mm/s, compression properties of the SLM-process TiAl alloy increases from 829.41 ± 24.88 MPa to 1216.16 ± 36.48 MPa. [ABSTRACT FROM AUTHOR]

The crystallographic texture, phase composition and evolution, and nanohardness of a Ti–45Al–2Cr–5Nb alloy processed by selective laser melting (SLM) at various substrate preheating temperatures were investigated. The α 2 phase decreases whereas the γ and B 2 phases increase with increasing preheating temperature, and the relationship in orientation between B 2 , α 2 and γ phases is described as follows: 11 2 ̅ 0 α 2 / / 111 γ / / 111 B 2 . The SLM-processed TiAl alloy shows much higher nanohardness than its traditional casting counterpart, which increases with the increase of preheating temperature. The findings would be a valuable reference for fabricating TiAl components with acceptable texture, phase compositions and nanohardness by SLM. [ABSTRACT FROM AUTHOR]

A TiAl-based alloy, Ti–45Al–2Cr–5Nb (at.%), has been processed by selective laser melting (SLM) using different energy density inputs. The experimental results show that when the energy density input increased from 250 J/mm 3 to 350 J/mm 3 , the crystallographic texture varied from a strong (0001) orientation to a combination of (0001), 10 1 ̅ 1 and 11 2 ̅ 1 orientations. The SLM-processed TiAl alloy are dominated by high-angle (> 15°) grain boundaries (HAGBs) and α 2 (Ti 3 Al) phase. The contents of HAGBs and α 2 are 92.8% and 90% respectively at the maximum density input of 350 J/mm 3 . Moreover, a small amount of γ (TiAl) and B 2 phases in a range of several hundred nanometers are uniformly distributed within the α 2 matrix. The phase evolution mechanism in the SLM-processed TiAl alloy can be as follows: (210) β transformed to 20 2 ̅ 0 α 2 and (110) γ, and then the residual B 2 and the incompletely transformed γ phase homogeneously distributed in the α 2 phase matrix. The orientation relationship between B 2 , α 2 and γ phases observed via HRTEM can be expressed as: 111 B 2 / / 1 1 ̅ 0 γ / / 11 2 ̅ 0 α 2 . Those observations and discussions provide a deep insight into the microstructure characteristics and phase evolution in the SLM-processed TiAl alloy, and the findings would be a valuable reference for optimizing the energy density input in SLM to fabricate TiAl components with acceptable grain structure and phase compositions. [ABSTRACT FROM AUTHOR]

[Display omitted] • The additive manufacturability of TPMS structures is investigated. • Defects can be eliminated by the gradient design and higher volume fraction. • Continuously graded TPMS structure show unique layer-by-layer deformation behavior. • The collapse model of TMPS structures affects the energy absorption. • Finite element method can predict the stress distribution and mechanical properties. Owing to their lightweight design, high energy absorption capacity, and excellent thermal and sound insulation properties, lattice structures have many potential applications in the fields of security, aerospace, biomedicine, and heat dissipation. In this study, a gyroid-type triply periodic minimal surface is used to design lattice structures. Gyroid uniform lattice structures and gyroid graded lattice structures are mathematically designed and fabricated using selective laser melting with a SS 316 L stainless steel powder. The mechanical properties of these structures are studied under a compression load, and the deformation differences between the graded and uniform structures are compared. The finite element method is used to simulate the compression process, and the experimental and simulation results are qualitatively compared. Results show that during plastic deformation, the stress change in the graded structure is larger than that in the uniform structure. By controlling the volume fraction, mechanical properties can be specifically tailored, which provides the design guidelines for the application of this structure. [ABSTRACT FROM AUTHOR]

Triply periodic minimal surfaces (TPMSs) have attracted increasing attention for their high manufacturability, biocompatibility, and mechanical properties. In this work, graded Gyroid cellular structures (GCSs) with varying gradient directions were mathematically designed and manufactured via selective laser melting (SLM). The effect of gradients on manufacturing fidelity, i.e. degree of conformity between the manufactured part and engineering design, of these structures was investigated using X-ray computed tomography (CT). The results indicate that relative density and volume fraction of as-built GCSs are higher than those specified in the engineering design due to strut diameters being larger than specification and the presence of bonded powder particles. Manufacturing fidelity is shown to depend on the geometry of the struts in these structures, including inclination angle of struts, relative density, and density gradient direction. Bonded powder particles were particularly present at the upper inner walls of sphere-like pores, where inclination angles are low and as a result there is a lack of support and non-ideal transfer of heat from the melt pool. Decreasing density along the building direction reduces the occurrence of bonded powder particles and increases manufacturing fidelity. The empirical findings in this study provide insight into the effects of part geometry on the quality of its manufacture by SLM. Results are used to establish guidelines for optimal design of cellular structures. [ABSTRACT FROM AUTHOR]

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]