A fundamental investigation of the development of grain structure of 316L stainless steel fabricated by selective laser melting (SLM) was conducted. Finite element analysis (FEA) was carried out in ...order to reveal the growth mechanism of grains under rapid solidification conditions. From this analysis, the crystal growth patterns were determined as a function of the temperature gradient along grain development orientation. A detailed discussion of preferred crystal orientation of dendrites was performed by geometrical analysis in conjunction with experimental findings. In addition, the dendrite spacings were measured, and the variation in spacings as a function of scan speed was studied. It was found that, the rapid solidification induced by high-speed laser scanning brought about sub-micron grains within the final solidified microstructure and a high volume energy density ω could cause the increase of primary dendrite spacing. Furthermore, the result also indicated that both grain size and densification level dependent on ω could affect the mechanical properties significantly. As the ω was settled at the optimal value of 125.00J/mm3, a high Vicker hardness of 281.6HV0.1, a large tensile strength of 590MPa and an attendant elongation rate of 21.1% were obtained.
(a) Schematic diagram analyzing the growth direction of solidification front and preferred growth orientation of the gains; (b) velocity vector plots in the melt pool with the action of Marangoni effect in cross-section view. (ω=125.00J/mm3); (c) “layer-layer” melt pool boundary; (d) “track-track” melt pool boundary Display omitted
•Crystal growth patterns were determined as a function of the temperature gradient along grain development orientation.•Rapid solidification brought about sub-micron grains and high energy density cause the increase of primary dendrite spacing`•Both grain size and densification level dependent on energy density could affect the mechanical properties significantly
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
This paper presents a comprehensive review and analysis of ship hull cleaning technologies. Various cleaning methods and devices applied to dry-dock cleaning and underwater cleaning are introduced in ...detail, including rotary brushes, high-pressure and cavitation water jet technology, ultrasonic technology, and laser cleaning technology. The application of underwater robot technology in ship cleaning not only frees divers from engaging in heavy work but also creates safe and efficient industrial products. Damage to the underlying coating of the ship caused by the underwater cleaning operation can be minimized by optimizing the working process of the underwater cleaning robot. With regard to the adhesion technology mainly used in underwater robots, an overview of recent developments in permanent magnet and electromagnetic adhesion, negative pressure force adhesion, thrust force adhesion, and biologically inspired adhesion is provided. Through the analysis and comparison of current underwater robot products, this paper predicts that major changes in the application of artificial intelligence and multirobot cooperation, as well as optimization and combination of various technologies in underwater cleaning robots, could be expected to further lead to breakthroughs in developing next-generation robots for underwater cleaning.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Selective laser melting (SLM) technology can manufacture complex lattice structures, which effectively reduces the manufacturing constraint and significantly increases the design freedom for lattice ...structure. In this study, additive manufacturing and topology optimization are combined for designing Face Centre Cube (FCC), Vertex Cube (VC), and Edge Centre Cube (ECC) structures, which are manufactured via SLM technology. Mechanical performance is evaluated, and a Gibson-Ashby model is developed to predict the performance of the three structures including different levels of porosity. The results show that FCC and VC lattice structures have better mechanical behaviour compared with that of the ECC lattice structure; however, their energy absorption efficiency is inferior to that of the ECC lattice structure. Comparisons between various SLM built lattice structures made from 316L stainless steel prove that the performance of topology-optimized lattice structures is superior to the majority of lattice structures. This result verifies the feasibility of lattice structure unit selection via topology optimization technology. Various work conditions are simulated for topology optimization to obtain a lightweight lattice structure with optimal performance under specific conditions.
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•Proposed a lightweight design method for a topology-optimized lattice structure unit based on actual working conditions.•Designed and tested three types of topology-optimized lattice structures.•Created a Gibson-Ashby model for the three topology-optimized lattice unit structures.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Selective Laser Melting (SLM) is a powder bed based technology to fabricate metal parts through laser melting, it provides excellent mechanical properties and freedom. The authors study the influence ...of laser energy on spattering, the investigation analyzed the formation principle, appearance and compositions of spattering. Results indicate that as the laser energy input increases from 0.32×105W/cm3 to 1.30×105W/cm3, the intensity and the quantity of spattering increases, the metal liquid jetted out even reach to the height of 11cm. Major sources of spattering included three types, which were mainly caused by recoil pressure, Marangoni effect and heat effect in molten pool, these three different sources of spattering leading to three types of spattering morphology correspondingly. The solidified spattering particles have an average size of approximately 162μm, much larger than the original powder size of 32μm, and these spatter particles present various appearances. The compositions of spattering powers are almost the same as the original powders, but the contents of O, Si and C increase dramatically. The spattering particles are embedded into the surface and interior of the SLM-fabricated parts. These results are helpful in controlling the intensity of spattering, improving stability and repeatability of the SLM fabrication process.
Formation mechanisms of different types of spatter: (a) morphology of spherical splashing (type-I splashing); (c) morphology of coarse spherical morphology (type-II splashing); (d) morphology of irregular splashing (type-III splashing). Display omitted
•As the laser energy input increases from 0.32×105W/cm3 to 1.30×105W/cm3, the intensity and the quantity of spattering increases, the metal liquid jetted out and reached to the height of 11cm.•Spattering included three types mainly caused by recoil pressure, Marangoni effect and heat effect in molten pool, these three different sources of spattering leading to three types of spattering morphology correspondingly. The compositions of spattering powers are almost the same as the original powders, but the contents of O, Si and C increase dramatically.•Spattering particles have an average size of approximately 162µm compared with the original powder size of 32µm. The spattering particles are embedded into the surface and interior of the SLM-fabricated parts to deteriorate the finial fabricated parts.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Bimetallic structures can combine the performance of dissimilar metal materials to meet the multifunctional requirement in industrial solutions. In this paper, steel-bronze bimetallic structures were ...fabricated via self-developed multi-material selective laser melting (SLM) equipment. In order to investigate the influence of laser power, scanning speed, and hatching space on the interfacial characterization, three factors and five levels of orthogonal experiments were performed on twenty layers of CuSn10 tin bronze after forming the 316 L stainless steel. Optical microscope (OM), large depth field microscope, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), tensile properties, electron backscattering diffraction (EBSD) and nanoindentation were used to characterize these bimetallic structures to validate the impact from process parameters. The large depth field microscope revealed protrusions at the steel/bronze interface, and its height increased and then decreased with increasing volumetric energy input. Besides, the generation of interfacial defects is related to the interfacial process parameters, and it is found that the types of defects are mainly classified as holes and cracks. Insufficient energy will cause cracks in the horizontal direction and then lead to bonding failure. Conversely, higher energy input will generate microcracks in the vertical direction. The defects near the interfacial region are the main factors affecting the ultimate strength of the bonding strength. As a result, the steel-bronze bimetallic structure displays optimal joint ultimate strength of 459.54 ± 3.08 MPa with elongation of 5.23 ± 0.65%, and minimum joint ultimate strength of 199.02 ± 0.56 MPa with elongation of 1.70 ± 0.22%. Their fracture morphology also exhibited gully-like and fan-shaped features, respectively. Additionally, the EBSD results show that there are fine grain regions appeared in the interfacial region, which helps increase the average nano-hardness of the interfacial region. This study provides a reference for the influence of process parameters on the interfacial characterization and mechanical properties of steel-bronze bimetallic parts prepared by selective laser melting.
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IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This article presents a method for manufacturing CuSn/18Ni300 bimetallic porous structure, and it mainly aims to discover microstructure and mechanical properties of CuSn/18Ni300 bimetallic porous ...structure. The microstructure, bonding strength and fracture morphology of CuSn/18Ni300 bimetallic parts manufactured by selective laser melting were examined by X-ray diffraction, tensile test and scanning electron microscopy, respectively. Compression behavior and energy absorption behavior were investigated by compression tests. Analyses of microstructure show that CuSn/18Ni300 specimen consists of α-Fe phase, α-Fe/α-Cu mixed area and α-Cu phase. Microhardness at the interface of CuSn/18Ni300 bimetallic porous structure decreases from 18Ni300 part to CuSn part. The bonding strength of CuSn/18Ni300 specimen is 144.1 ± 41.59 MPa, which is much lower than the tensile strength of CuSn specimen. Additionally, we demonstrate that the compression behavior of CuSn/18Ni300 bimetallic porous structure can be subdivided into five stages, including the first linear elasticity, the first collapse plateau, the second linear elasticity, the second collapse plateau and the end densification. The energy absorption of CuSn/18Ni300 porous structure is higher than that of CuSn porous structure, and energy absorption increases as the porosity decreases. These findings provide a solution for optimizing the compression behavior and energy absorption of porous structure.
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•Designed and manufactured body-center-cubic CuSn/18Ni300 bimetallic porous structures.•Studied on the microstructure and bonding strength of CuSn/18Ni300 bimetallic specimens.•Compression behaviors of CuSn/18Ni300 bimetallic porous structures can be subdivided into five stages.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Due to the rapid melting and solidification mechanisms involved in selective laser melting (SLM), CoCrMo alloys fabricated by SLM differ from the cast form of the same alloy. In this study, the ...surface morphologies, enhancement of mechanical properties and change to microstructure by heat treatment were discussed. Results showed that the microstructure of sample fabricated by SLM consisted mainly of face-centered-cubic (FCC) cobalt-rich solid solutions and carbide scattered cobalt-rich solid solutions, where Cr and Mo were dissolved in the Co-base phase and M23C6. The carbide scattered Co-base phase existed in the form of even margins. The tensile fracture of SLM-fabricated parts was mostly quasi-cleavage brittle fracture. Heat treatment transformed the SLM-fabricated parts such that failure occurred through ductile rather than brittle fracture, causing an increase in the tensile strength and elongation of the SLM-fabricated parts in addition to reduced yield strength and hardness. Some annealing twins were formed after heat treatment, which were demonstrated by TEM. These results will contribute to the development of biomedical CoCrMo alloys fabricated by SLM.
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IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UM, UPCLJ, UPUK, ZRSKP
In general, mechanical properties of most materials under dynamic loading are completely different from those under static/quasi-static loading. In this paper, a comparative study between the ...selective laser melted Ti-6Al-4V alloy and its heat-treated counterpart was carried out. After heat treatment, the microstructure transformed from full fine acicular α' into basket-weave morphology with coarsened α + β lamella, grain boundaries α tended to globularization, and the volume fractions of β phase and LAGBs increased due to the α′→α + β transformation and increasing of dislocation density respectively. During high strain rate tension, strain was dispersive in the elastic deformation region, then it began to concentrate at the centre of samples and increased until fractured as loading time increased. As expected, evident reduction in the UTS and σy and increase in the ε were caused by heat treatment, however both of them increased as the strain rate increased due to the twinning deformation occurred in the α/β interface phase, thus contributed to improving the strength and plasticity of SLMed TC4 alloy under high strain rate loading simultaneously. This work provided a relationship between microstructure and dynamic responses of SLMed TC4 alloy, which contributes to exploiting the performance potential of SLMed alloy.
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IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•The alumina-based, namely, octagon and rhombus structures were designed and fabricated by digital light processing.•The Young’s modulus of the designed structures valued between 0.5 ...and 4 GPa which were comparable to natural bone.•The simulated permeability and wall shear stress of the designed structures were between 4.10 × 10−9 to 23.2 × 10−9 m2 and between 4.9 × 10−4 to 84.4 mPa.•The in vitro cell experiments showed that the proliferation of the cell in the scaffolds depended on the pore structure and the pore size.
Porous scaffolds can be used for treating bone defects. To manufacture porous scaffolds similar to bone, two types of ceramic scaffolds with different porosity, namely, octagon and rhombus scaffolds were designed and fabricated by Digital Lighting Process technology. Compression test, finite element analysis, computational fluid dynamics (CFD), and in vitro cell experiment were conducted for systematic investigation of the properties of the scaffolds. The results showed that the elastic modulus of alumina octagon and rhombus lattice structure was within 0.5–4 GPa. Through the CFD simulation, the permeability of the scaffold was found to be in the range of 4.10 × 10−9 to 2.32 × 10−8 m2 and the wall shear stress of different structures ranged from 4.9 × 10−4 to 84.4 mPa. Live/dead staining and Cell Counting Kit-8 assay showed that all groups were biocompatible and beneficial to cell proliferation except for octagon structure with 1.049 mm pore and rhombus structure with 0.6 mm pore. Analysis of the results of the mechanical properties, CFD simulations, and in vitro cell studies indicated that the porous scaffolds suitable for bone engineering were 0.566 mm-pore-size octagon unit and 1.0 mm-pore-size rhombus unit with elastic modulus of 3834.9 and 599.8 MPa, respectively.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Residual powder is a defect in powder bed fusion-based additive manufacturing (3D printing), and it is difficult to completely remove it from as-printed materials. In addition, it is not necessary to ...apply 3D printed implants with residual powder in the clinic. The immunological response triggered by the residual powder is an important area of study in medical research. To further understand the possible immunological reactions and hidden dangers caused by residual powders in vivo, this study compared the immunological reactions and osteolysis caused by typical powders for four implant materials: 316 L stainless steel, CoCrMo, CP-Ti, and Ti-6Al-4V (particle size range of 15–45 μm), in a mouse skull model. Furthermore, the possible immunological responses and bone regeneration induced by the four 3D printed implants with residual powder in a rat femur model were compared. In the mouse skull model, it was found that the 316L-S, CoCrMo-S, and especially the 316L-M powders, upregulated the expression of pro-inflammatory factors, increased the ratio of RANKL/OPG, and activated more functional osteoclasts, resulting in more severe bone resorption compared with those in other groups. In the rat femur model, which is more suitable for clinical practice, there is no bone resorption in implants with residual powders, but they show good bone regeneration and integration ability because of their original roughness. The results indicate that the expressions of inflammatory cytokines in all experimental groups were the same as those in the control group, showing good biological safety. The results answered some critical questions related to additively manufactured medical materials in vivo and indicated that as-printed implants may have great potential in future clinical applications.
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