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
Selective laser melting (SLM) is one kind of additive manufacturing process to fabricate metal parts through laser melting. A maraging steel 300 was manufactured by SLM. And the influence of process ...parameters (laser powder, scanning speed and scanning space) on the relative density of maraging steel 300 was investigated first. Then a series of block and plate specimens were manufactured. Some specimens were taken as control groups, and others underwent heat treatment by solution treatment (ST) and solution treatment +aging treatment (ST+AT) respectively. The investigation involved microstructure, microhardness, tensile strength and impact toughness. It is shown that: low or high laser power, scanning speed or scanning space all reduced the relative density, and the optimized process parameters could be obtained by orthogonal experiment. After ST, the cellular structure and microscopic segregation disappeared, and the new smaller particles precipitated out after AT. The Ni, Mo and Ti dissolved in the matrix during ST separated out again forming tiny Ni3Mo, Fe2Mo and Ni3Ti particles during AT. The microhardness and tensile strength dropped a little with elongation increasing after ST. While they increased significantly with elongation decreasing after AT. The impact toughness increased little after ST, but decreased sharply after AT.
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IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UM, UPCLJ, UPUK, ZRSKP
This work investigates the solution phenomenon, aging behavior and room-temperature mechanical properties of maraging steel manufactured by selective laser melting (SLM). Different heat treatment ...experiments, including solution treatment (ST), direct aging treatment (DAT) and solution + aging treatment (SAT) are designed. Microstructure analysis indicates that ST and SAT will eliminate the cellular and lath structures, but DAT has little effect on these. The content of austenite increases with the addition of DAT temperature and holding time. While austenite is almost undetectable in ST and SAT samples. Meanwhile, both the elongation and toughness of the samples with DAT gain a slight improvement with the temperature increasing. Importantly, DAT yields similar microhardness, tensile strength and impact toughness to SAT, although the resultant microstructures are completely different. The results demonstrate that DAT can achieve the similar mechanical properties to SAT samples. Samples with high mechanical properties (microhardness of 653.93 HV and ultimate strength of 2126.30 MPa) have been obtained by DAT at 520 °C for 6 h as well as solution treatment at 900 °C for 1 h and aging treatment at 520 °C for 6 h. This investigation reveals the evolution regularity of microstructure, microhardness, tensile performance and impact toughness of maraging steel manufactured by SLM after different heat treatments.
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IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UM, UPCLJ, UPUK, ZAGLJ, 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
Highlights
We first report on H
11
Al
2
V
6
O
23.2
with large layer spacing as cathode for aqueous zinc-ion battery, which accelerates the diffusion of Zn
2+
.
The graphene-wrapped H
11
Al
2
V
6
O
...23.2
nanobelts can improve electronic conductivity, and potentially inhibit the dissolution of elements in the aqueous electrolyte.
H
11
Al
2
V
6
O
23.2
@graphene exhibits high capacity and stable cycling stability even at an ultra-high mass loading of ~ 15.7 mg cm
−2
.
Rechargeable aqueous zinc-ion batteries (AZIBs) have their unique advantages of cost efficiency, high safety, and environmental friendliness. However, challenges facing the cathode materials include whether they can remain chemically stable in aqueous electrolyte and provide a robust structure for the storage of Zn
2+
. Here, we report on H
11
Al
2
V
6
O
23.2
@graphene (HAVO@G) with exceptionally large layer spacing of (001) plane (13.36 Å). The graphene-wrapped structure can keep the structure stable during discharge/charge process, thereby promoting the inhibition of the dissolution of elements in the aqueous electrolyte. While used as cathode for AZIBs, HAVO@G electrode delivers ideal rate performance (reversible capacity of 305.4, 276.6, 230.0, 201.7, 180.6 mAh g
−1
at current densities between 1 and 10 A g
−1
). Remarkably, the electrode exhibits excellent and stable cycling stability even at a high loading mass of ~ 15.7 mg cm
−2
, with an ideal reversible capacity of 131.7 mAh g
−1
after 400 cycles at 2 A g
−1
.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
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
Overhanging surface is inherent geometric restraint during selective laser melting (SLM), which is suitable for various complex parts fabrication. In order to improve the fabricating quality of ...overhanging surface, a series of experiments were designed to investigate the effects of inclined angle, scanning speed, laser power, accumulated residual stress, and scanning vector length on overhanging surface fabrication. Analysis found that overhanging surface would warp easier when the inclined angle and the scanning speed became smaller and the warping trend will be larger as the laser power became larger. The relationships of laser power, scanning speed, and the critical inclined angle were mutual restraint, that is, larger inclined angle will be designed when the laser power becomes larger and scanning speed gets smaller, or vice versa: the selection of the fabricating parameters will be determined by established inclined angle of the overhanging surface. More serious warp would happen as the processing layers increased as a result of residual stress accumulation, and it was found that longer scanning vector were more helpful to stress accumulation, leading to more serious warp than shorter vector. At last, two effective methods were adopted to optimize overhanging surface fabrication, including adjusting part orientation to improve the inclined angle at the key position, and controlling regional parameters to reduce energy input. Above two ways were adopted to manufacture complex parts with typical overhanging surface, the results proved that adjusting part orientation and controlling regional parameters were effective ways to improve the fabricating quality of overhanging surface. In this study, the basis for building overhanging surface by SLM was provided from the view of process and design, and the preliminary solutions were proposed to manufacture complex metal parts with lower risk.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The study reported one concept for fabrication of glutamic acid functionalized graphene quantum dot-gold hybrid. The hybrid exhibits nanostar-like structure, excellent redox behaviors and was ...successfully applied in fabrication of electrochemical aptasensor for detection of acetamiprid with ultrahigh sensitivity and selectivity.
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•We report synthesis of functional graphene quantum dot-gold and use as redox probe with catalyst.•Hybrid of graphene quantum dot and gold nanostars offers an obviously enhanced catalytic activity.•The proposed aptasensor exhibits ultra high sensitivity and selectivity of acetamiprid detection.•The acetamiprid sensing nanoplatform can be easily extended to detect a variety of insecticides.
Glutamic acid-functionalized graphene quantum dots (Glu-GQD) was prepared by pyrolysis of citric acid and glutamic acid and used as reducing agent and stabilizer to produce Glu-GQD/Au in the presence of tannic acid. The resulting Glu-GQD/Au was covalently connected with aptamer (Apt) of acetamiprid to obtain one redox probe with catalyst. The study shows that Glu-GQD/Au offers nanostar-like structure with average particle size of 102.5 nm, composing of several nanometer-sized gold nanocrystals with the rich of sharp edges and corners. The unique structure makes gold nanostars good electrocatalytic activity, which was further improved by combination with Glu-GQD. In the redox probe, Glu-GQD can carry out reversible redox reaction on the electrode surface due to its high electroactivity. Gold nanostars in-situ catalyzes redox reactions of Glu-GQD and leads to an improved electrochemical behavior. Aptamer can specifically bind with acetamiprid and produce sensitive and selective electrochemical response. The electrochemical aptasensor based on Glu-GQD/Au-Apt/graphene aerogel exhibits ultrahigh sensitivity and selectivity for detection of acetamiprid. The differential pulse voltammetric signal linearly decreases with increasing acetamiprid concentration in the range from 1.0 fM to 1 × 105 fM with detection limit of 0.37 fM (S/N = 3). The aptasensor has been successfully applied in electrochemical detection of acetamiprid in vegetables.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Cobalt nanocrystal has been widely used as nano-enzyme for sensing and catalysis due to its high stability and low cost, but poor catalytic activity limits its applications in bioanalysis. The study ...reports one strategy for synthesis of cobalt-graphene nanohybrid. Histidine-functionalized graphene quantum dot (His-GQD) was bound to graphene sheet via π-π stacking and then combined with cobalt ions in the presence of cetyltrimethylammonium chloride to form stable complex and finally reduced under nitrogen to obtain Co-His-GQD-G. The as-synthesized nanohybrid offers well-defined three-dimensional structure and quasi-superparamagnetism. The cobalt nanoparticles were well dispersed on graphene sheets. The unique structure improves oxidase-like activity of Co-His-GQD-G. Further, Co-His-GQD-G was used as the nanozyme for colorimetric detection of chlorpyrifos. Co-His-GQD-G catalyzes oxidization of 3,3′,5,5′-tetramethylbenzidine into blue product. Thiocholine produced by hydrolysis of acetylthiocholine under catalysis of acetylcholinesterase inhibits catalytic activity of Co-His-GQD-G and leads to a reduced oxidization rate. Chlorpyrifos inhibits activity of acetylcholinesterase and brings an enhanced absorbance of blue product. The absorbance at 652 nm linearly increases with increasing chlorpyrifos concentration in the range of 2–20 ng mL−1 with detection limit of 0.57 ng mL−1 (S/N = 3). The method was successfully applied in determination of chlorpyrifos in peach by preparing Co-His-GQD-G magnetic gel sheet.
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•one concept of synthesizing Co-graphene hybrid using CTAC as soft template was firstly reported.•The hybrid has three-dimensional structure, superparamagnetism and excellent oxidase-like activity.•The method offers the advantage of sensitivity, rapidity and stability for detection of chlorpyrifos.•The reusability of Co-His-GQD-G were achieved by preparing Co-His-GQD-G magnetic gel sheet.•The work can be widely used for synthesis of graphene-metal nanozymes with good catalytic activity.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The Selective Laser Melting (SLM) process fabricates components from powders by adding material and its processing principle is based on track overlapping regime, which has been studied in this ...paper. The inter-layer stagger scanning strategy was employed to avoid nonuniform distribution of energy input. By theoretical deduction and experimental observation, three types of overlapping regime were revealed: intra-layer overlapping regime, inter-layer overlapping regime and mixed overlapping regime with coexistence of the first two types. The overlapping patterns and the corresponding microstructures were then discussed. Experimental result showed that specimens fabricated by inter-layer overlapping regime had high relative density when track space was not larger than 0.2mm. A cooling insert with relative density of about 93% was also obtained at track space of 0.12mm.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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