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High-power direct laser deposition (HP DLD) was utilized to fast generate AISI 316L stainless steel parts with large size and excellent mechanical properties. In order to efficiently ...manufacture the stainless steel parts with high surface quality and dimensional accuracy, a dry milling finish was applied. During the DLD process, heat retaining powder was employed to prevent buckling deformation. The effect of building direction on the microstructure, mechanical properties and machinability of the stainless steel was investigated. It was found that the microstructure was homogeneous, at the building direction of 0°, while a number of larger dendritic grains were present in the microstructure, at the building direction of 90°. The tensile properties and hardness values at the building direction of 0° were higher than those at the building direction of 90°. For both building directions, the decrement in surface roughness and the increment in cutting force and tool wear, were observed with the increase in cutting speed. The cutting force, tool wear and surface roughness of the additive manufactured stainless steel at the building direction of 0° were relatively higher, which implies that the anisotropy in the machinability could be utilized to increase efficiency and reduce production cost.
In this paper, the UV curable ZrO2-Al2O3 composite ceramic pastes based on SLA-3D printing technology were synthetized firstly, and the corresponding ceramic green bodies were 3D printed, and finally ...the ZrO2-Al2O3 composite ceramic parts were manufactured by a subsequent debinding and sintering process. Our work focuses on the investigation of the microstructure, hardness and fracture toughness of the printed ZrO2-Al2O3 composite ceramics sintered at different maximum sintering temperature and holding time. In case of the sintering temperature of 1500 °C and holding time of 60 min, the actual density, hardness and fracture toughness of the ceramics can reach 3.75 g/cm3, 14.1 GPa and 4.05 MPa⋅m1/2, respectively. If the sintering temperature is higher than 1500 °C, the abnormal grain growth can occur, resulting in some more reductions in the mechanical properties of ceramics; while when the sintering temperature is lower than 1500 °C, the lower driving force makes the grains not fully developed, resulting in a low density of ceramics and worse mechanical properties. With the increase of holding time, the sintering driving force is promoted, making for the grain growth. However, when holding time is more than 60 min, the actual density of ceramics almost remains unchanged, and the mechanical properties of ceramics are not able to be improved further.
Fused deposition modeling (FDM) has unique advantages in the rapid prototyping of thermoplastics which have been developed in diverse fields. However, although great efforts have been made to ...optimize FDM process, the mechanical properties of printed parts are limited by the weak interlamination bonding as well as the poor performance of raw filaments used, such as acrylonitrile butadiene styrene (ABS), polylactic acid (PLA). Adding fibers into thermoplastic matrix and preparing high-performance filaments have been indicated to enhance the properties of fabricated parts. Recently, heat-resistant polyetheretherketone (PEEK) and its fiber reinforced composites were proposed for FDM process due to overcoming the limitation of equipment and process. However, few researches have been reported on the effects of FDM-3D printing parameters on the mechanical properties of fiber reinforced PEEK composites. Therefore, 5wt% carbon fiber (CF) and glass fiber (GF) reinforced PEEK composite filaments were prepared respectively in this study. The effects of various printing parameters including nozzle temperature, platform temperature, printing speed and layer thickness on the mechanical properties (including tensile strength, flexural strength and impact strength) were surveyed. To analyze the microstructure and failure reasons of printed CF/PEEK and GF/PEEK samples, the tensile fractured surfaces were investigated via scanning electron microscope (SEM).
The aim of this work is to develop a high solid loading suspension of Al2O3 dispersed in an UV curable acrylic based resin, suitable for SLA-3D printing micro-components with complex shapes. Silane ...coupling agents KH550, KH560 and the stearic acid (SA) were investigated as the surfactants for Al2O3 particles, and the low viscosity acrylic monomers ACMO, HDDA and NPG2PODA were used as the reactive diluents for Di-TMPTA-based premixed resins. The modified Al2O3 powders exhibit the different wettability with premixed resins to cause the different rheology behaviors among the formulated suspensions. The KH560-modified Al2O3 powders show the better wettability performance with NPG2PODA/Di-TMPTA-based solvents and their corresponding 75 wt% Al2O3 suspensions (44.2 vol% solid loading) with a viscosity ˂ 25,000 mPa·s at 30 s−1 shear rate are successfully prepared. The further analyses approve that hydrophobic structures of KH560 molecules have been introduced on the surfaces of Al2O3 powders. This consequence results in the lowest sediment rate and contact angle between the KH560-modified Al2O3 powders and NPG2PODA/Di-TMPTA-based resins, which contributes to their better wettability performance. The optimum parameter of NPG2PODA concentration of prepared suspension is range from 50% to 70% in the premixed resin. Finally, Al2O3 ceramic micro-component with 99.5% density was fabricated via an SLA process and subsequent sintering. Both the Al2O3 suspensions and sintered micro-components exhibit good homogeneous microstructures, indicating an optimistic dispersal uniformity of KH560-modified Al2O3 particles in the premixed resins.
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•Ceramic micro-component is fabricated by a SLA process and sintering.•UV-curable Al2O3 suspension is prepared for SLA 3D-printing process.•Hydrophobic structures are introduced on the surface of Al2O3 powders.•Modified Al2O3 show a better wettability with the UV-curable resins.•Acrylic monomers NPG2PODA reduce the viscosity of Al2O3 suspensions.
Compacted graphite iron (CGI) plays an important role in contemporary manufacturing of automobile engine, and coated tool is the best choice for milling of CGI. But studies about the estimation of ...the wear of coated tool are still rare and incomplete. As tool wear is the main factor that affects the quality of machined surface, in this study, we proposed an intelligent model-adaptive neuro fuzzy inference system (ANFIS) to estimate the tool wear, and ANFIS was learned by the improved particle swarm optimization (PSO) algorithm. As the PSO algorithm is easy to fall into the local minimum, the vibration and communication particle swarm optimization (VCPSO) algorithm was proposed by introducing the self-random vibration and inter-particle communication mechanisms. Besides that, to obtain the optimal combination of milling parameters, the multi-objective optimization based on minimum cutting power, surface roughness and maximum material removal rate (MRR) was studied using VCPSO algorithm. The experimental results showed that the ANFIS learned by VCPSO algorithm (ANFIS-VCPSO) has better performance for the estimation of tool wear compared with other intelligent models. The VCPSO algorithm was tested using Benchmark functions, and the results showed VCPSO algorithm has the global optimization ability. Meantime, the best combinations of milling parameters under different tool wear status were obtained through VCPSO algorithm. The proposed ANFIS-VCPSO model as a new intelligent model can be applied for real-time tool wear monitoring, which can improve the machining efficiency and prolong tool life. In order to meet the requirements of green and intelligent manufacturing, the best combination of milling parameters was also obtained in this work.
For multi-ceramic materials based on the stereolithography (SL) principle, a 3D printing strategy was developed, and then an Al2O3-Si3N4 functionally graded material (FGM) ceramic part was fabricated ...using this strategy. Six groups of mixtures, with a Si3N4 content gradient of 20 vol% and a certain bimodal particle size distribution, were prepared using UV-curable pastes. A modified formula was proposed to evaluate the relationship between the actual minimum voidage of mixtures and the viscosities of their corresponding pastes. The viscosity of each paste was controlled using the prediction formula and optimization of dispersants. To design theprinting layer thickness, a mathematical relationship was established between Si3N4 content and curing depth of paste. The Al2O3-Si3N4 green body without deformation was printed using optimized parameters such as a layer thickness of 40 μm and a paste viscosity of ∼13,000 mPa·s. Finally, using debinding and sintering, denseparts having a complicated shape were obtained.
Nanopores that exhibit ionic current rectification (ICR) behave like diodes such that they transport ions more efficiently in one direction than in the other. Conical nanopores have been shown to ...rectify ionic current, but only those with at least 500 nm in length exhibit significant ICR. Here, through the finite element method, we show how ICR of conical nanopores with lengths below 200 nm can be tuned by controlling individual charged surfaces, that is, the inner pore surface (surfaceinner) and exterior pore surfaces on the tip and base side (surfacetip and surfacebase). The charged surfaceinner and surfacetip can induce obvious ICR individually, while the effects of the charged surfacebase on ICR can be ignored. The fully charged surfaceinner alone could render the nanopore counterion-selective and induces significant ion concentration polarization in the tip region, which causes reverse ICR compared to nanopores with all surfaces charged. In addition, the direction and degree of rectification can be further tuned by the depth of the charged surfaceinner. When considering the exterior membrane surface only, the charged surfacetip causes intrapore ionic enrichment and depletion under opposite biases, which results in significant ICR. Its effective region is within ∼40 nm beyond the tip orifice. We also found that individual charged parts of the pore system contributed to ICR in an additive way because of the additive effect on the ion concentration regulation along the pore axis. With various combinations of fully/partially charged surfaceinner and surfacetip, diverse ICR ratios from ∼2 to ∼170 can be achieved. Our findings shed light on the mechanism of ICR in ultrashort conical nanopores and provide a useful guide to the design and modification of ultrashort conical nanopores in ionic circuits and nanofluidic sensors.
Anti-fatigue performance is vital for components used in aerospace industry, and cutting processes were widely considered to modify the workpiece anti-fatigue performance. However, most of the ...existing researches only associated the anti-fatigue performance to the cutting condition and surface integrity, without revealing the effect of material microstructure. In this work, the Incoloy A286 and titanium alloy TC17, two kinds of commonly used material in aerospace industry, were adopted as samples to reveal the influence mechanism of material microstructure on the high-speed cutting modified anti-fatigue performance. It was found that, due to the different microstructure, especially the grain structure and size, the effects of cutting process on the machined surface integrity and anti-fatigue performance of these two materials were different. For Incoloy A286, the large size and cubic structure increased the difficulty in deformation and breaking of grains, making the cutting parameters have limited effect on grain refinement. Hence, the fracture toughness of machined surfaces decreased on the whole with an increased feed rate and depth of cut, which reduced the fatigue life. For titanium alloy TC17, the small lath-shaped grains were easy to deform and break, resulting in the notably grain refinement of machined surfaces, which contributed to the prolonged fatigue life when the feed rate and depth of cut increased. All in all, the material microstructure may change the effect rule of cutting process on the machined workpiece anti-fatigue performance, and thus the cutting condition should be designed by considering the material microstructure.
High-performance osmotic energy conversion (OEC) requires both high ionic selectivity and permeability in nanopores. Here, through systematical explorations of influences from individual charged ...nanopore surfaces on the performance of OEC, we find that the charged exterior surface on the low-concentration side (surfaceL) is essential to achieve high-performance osmotic power generation, which can significantly improve the ionic selectivity and permeability simultaneously. Detailed investigation of ionic transport indicates that electric double layers near charged surfaces provide high-speed passages for counterions. The charged surfaceL enhances cation diffusion through enlarging the effective diffusive area, and inhibits anion transport by electrostatic repulsion. Different areas of charged exterior surfaces have been considered to mimic membranes with different porosities in practical applications. Through adjusting the width of the charged ring region on the surfaceL, electric power in single nanopores increases from 0.3 to 3.4 pW with a plateau at the width of ~200 nm. The power density increases from 4200 to 4900 W/m2 and then decreases monotonously that reaches the commercial benchmark at the charged width of ~480 nm. While, energy conversion efficiency can be promoted from 4% to 26%. Our results provide useful guide in the design of nanoporous membranes for high-performance osmotic energy harvesting.
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•Effects of individual charged surfaces on osmotic energy conversion are studied.•Charged surfaceL is essential to achieve high-performance osmotic power generation.•EDLs near charged surfaces provide high-speed passages for counterions diffusion.
Constitutive model is very important in finite element simulation of Inconel 718 cutting process. However, there are few constitutive models for Inconel 718 which are suitable for the cutting ...process. In this research, firstly, dynamic behavior of Inconel 718 at high strain rate and elevated temperature of the same order as the practical cutting process was obtained using SHPB(Split Hopkinson Pressure Bar) test. In the tests, the strain rate was 5000–11000s−1, and the temperature was 500–800°C. Secondly, thermal and strain rate effect were discussed. Strain rate softening effect was found at high strain rate and discussed, and it was temperature dependent. Finally, a modified Johnson–Cook model was established.
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