Fine Cellular Structure Research Articles

Effect of scanning strategies on microstructure and wear behavior of Inconel 718 fabricated by selective laser melting

Abstract To study the effect of the rotating angle on microstructure and wear properties of Inconel 718 alloy manufactured by selective laser melting (SLM) technology, parts were fabricated with two different scanning strategies (67°, 90°). The results revealed that the Inconel 718 produced by SLM with a 67° rotating angle exhibits higher surface roughness and a distinct cubic texture {100} < 001 >. Additionally, rotation angle of 90° will enhance grain coarsening and weaken texture strength. The influence of rotation angles on the hardness of SLMed Inconel 718 is negligible at room temperature. The wear resistance of SLMed Inconel 718 is superior at high temperatures compared to room temperature. The wear mechanisms of SLMed Inconel 718 at room temperature and high temperature are primarily governed by abrasive wear and adhesive wear, and oxidation wear, respectively. The favorable wear properties observed at the 67° rotating angle can be attributed mainly to the fine cellular structure and the triboxide layer.

Supercritical N2 induced sandwich type lightweight and strong PP/CF foams with excellent electromagnetic shielding properties

The tremendous advances in communication technology and the explosion of electronic products led to an intensification of electromagnetic pollution, yet the efficient development of lightweight, high-strength fiber composite foams with excellent electromagnetic shielding properties was still a great challenge. Herein, this study, inspired by the sandwich structure, proposes a green foaming method with supercritical N2 to prepare a multilayered structure of carbon fiber reinforced polypropylene (PP/CF) foams, with a dense cellular structure in the core layer and a solid layer in the surface layer. The incorporation of CF improves the crystallization and rheological behavior of PP/CF, which guarantees a fine, dense and uniform cellular structure. This inner fine cellular structure and the solid layer on the surface contribute to the excellent mechanical properties. PP/30 %CF foam with a 1 mm mold opening distance displays an enhancement of 189.9 % in tensile strength and 196.3 % in flexural strength compared to pure PP. This also indicates more lightweight, high-strength and high-rigidity microcellular parts was obtained with less raw materials. Moreover, the formation of CF conductive network and internal foam structure contribute to excellent electromagnetic interference (EMI) shielding performance. The PP/CF composite foams maintain a level of EMI shielding performance greater than 30 dB despite the higher mold opening distance. Specifically, the PP/30 %CF foams at opening distance of 5 mm was enhanced to 58.3 dB·cm3/g with an improvement of 76.7 %. This implies that lightweight microcellular parts with both excellent strength and EMI shielding properties can be prepared, which enables PP/CF foams to possess a wide range of applications in various fields.

Quantitative evaluation of intensity fidelity of super-resolution reconstruction for structured illumination microscopy

Super-resolution structured illumination microscopy (SR-SIM) relies heavily on post-processing reconstruction to obtain high-quality SR images from raw data. Although many SIM reconstruction algorithms have been developed to recover fine cellular structures with high fidelity even from the noisy data, whether the pixel intensities of reconstructed SR images are still proportional to the original fluorescence intensity has been less explored. The linearity between the intensity before and after reconstruction is defined as the intensity fidelity. Here, we proposed a method to evaluate the reconstructed SR image intensity fidelity at different spatial frequencies. With the proposed metric, we systematically investigated the impact of the key factors on the intensity fidelity in the standard Wiener-SIM reconstructions with simulated data, then evaluated the intensity fidelity of the SR images reconstructed by representative open-source packages. Our work provides a reference for SR-SIM image intensity fidelity improvement.

Visualizing the fine structure and dynamics of living cells with temporal polychromatic digital holographic microscopy.

Polychromatic digital holographic microscopy (P-DHM) has demonstrated its capacity to generate highly denoised optical path difference images, thereby enabling the label-free visualization of fine cellular structures, such as the dendritic arborization within neuronal cells in culture. So far, however, the sample must remain more or less stationary since P-DHM is performed manually, i.e., all actions are carried out sequentially over several minutes. In this paper, we propose fully automated, robust, and efficient management of the acquisition and reconstruction of the time series of polychromatic hologram sets, transforming P-DHM into temporal P-DHM. Experimental results have demonstrated the ability of the proposed temporal P-DHM implementation to non-invasively and quantitatively reveal the fine structure and dynamics of living cells.

Effect of Er addition on the microstructure, mechanical properties and corrosion behaviour of Al-Zn-Mg-Cu alloy manufactured by laser powder bed fusion

The purpose of this study is to gain a deeper understanding of the effects of rare-earth element Er on the microstructure and properties of Al-Zn-Mg-Cu alloy manufactured by laser powder bed fusion (LPBF). Compared with the as-printed Al-Zn-Mg-Cu alloy without Er addition, the as-printed Al-Zn-Mg-Cu-Er alloy with a bimodal grain structure had finer cellular structures and denser precipitation phases, which significantly improved the alloy's mechanical and corrosion resistance properties. The tensile strength of the as-printed Al-Zn-Mg-Cu-Er alloy was 383 MPa, which is 137 MPa higher than that of the as-printed Al-Zn-Mg-Cu alloy without Er addition. It was intended to use T6 heat treatment process to further regulate the mechanical properties of the as-printed alloy, but the formation of Si-rich hard and brittle eutectic phases with sizes of 2–5 μm in the matrix resulted in a decrease in the strength of the alloy, which is contrary to the traditional 7xxx aluminum alloys. Besides, the addition of Er element improved the alloy's corrosion resistance by decreasing the corrosion current density and raising the intergranular corrosion (IGC) resistance, and the maximum intergranular corrosion depth decreased from 174 µm to 68 µm after Er addition.

Selective laser melting of Hastelloy-X alloy and cerium oxide reinforced Hastelloy-X composite: Microstructural examination and corrosion behavior

The study investigated the microstructures and corrosion behaviors of Hastelloy X (HX) and HX reinforced by cerium oxide particles (HX-C) produced by selective laser melting (SLM) and compared to the wrought equivalent (HX-W). The aim was to eliminate hot cracking and investigate the HX's corrosion behavior in the presence of cerium oxide particles. The HX samples showed fine cellular and columnar solidification structures with uniform-size sub-cells and severe microcracking. Incorporating cerium oxide particles (1 wt%) resulted in finer and relatively equiaxed grains without microcracking. The HX-W alloy contained a micron-sized carbide (Mo-rich M6C type) within the matrix. The HX-C sample displayed higher porosities compared to the HX sample (1.8 % against 0.3 %). Potentiodynamic polarization and electrochemical impedance spectroscopy tests were conducted in a standard NaCl solution at temperatures of 25, 50, and 70 °C to assess the corrosion behavior of Hastelloy samples. The HX-C matrix showed superior corrosion resistance compared to the HX-W and HX samples due to its finer grain structure and stable passive layer formation. Cerium oxide particles were found to be efficient in decreasing hot cracking and improving corrosion resistance.

Influence of heat treatments on low-power-LPBFed CuCrZr for nuclear fusion applications

In this study, the processability of CuCrZr alloy with additive manufacturing (AM) technology and the performance achievable with Direct Age Hardening treatments for nuclear fusion applications were investigated. This copper alloy is one of the most interesting for the field: it is easier to manufacture through Laser-based additive manufacturing technology and mechanically superior compared to pure copper, and it ensures values of thermal conductivity high enough to be considered a valid substitute for pure copper in many applications.The investigation on CuCrZr alloy was carried out in order to examine the influence of Direct Age Hardening (DAH) treatments on physical and mechanical properties. Laser Powder Bed Fusion technology was used to produce samples with CuCrZr alloy. The additive manufacturing process involved a machine provided with a 370 W IR laser and a preliminary process optimization was carried out to find the printing parameters that assured the highest density (99.15 %), which confirmed the processability of CuCrZr alloy also with low IR laser power. Then, three different DAH treatments were tested and the performance of DAHed material was compared to that of the alloy in as-built conditions. Precipitation phenomena were investigated with DSC analyses, revealing the effectiveness of the treatment already after 1 h. A deep microstructural investigation revealed a fine cellular structure formed during solidification and the presence of nanometric precipitates starting from the as-built condition. The presence of microstructural defects was also investigated. Mechanical performance and thermal conductivity were tested, too: the as-built samples showed limited properties, while very promising results for the use of additively manufactured CuCrZr components have been obtained after the DAHs. The ultimate tensile strength (UTS) and yield strength (YS) doubled the as-built values after 1 h treatment at 550 °C. The thermal conductivity reached three times the initial condition (from 100 W/mK to 300 W/mK).

Crystal plasticity enhanced direct cyclic analysis of cyclic behaviour of LPBF-manufactured AISI 316L

The fatigue performance of Laser Powder Bed Fusion manufactured 316L stainless steel is critical for cyclic loading applications. Additive manufacturing of 316L produces a characteristic microstructure consisting of grains with a fine cellular structure within. This microstructure shows a comparatively high fatigue strength combined with a high defect tolerance. The purpose of this paper is to numerically analyse the local response of this microstructure to cyclic loading and, in particular, the joint action between lack of fusion defects and the surrounding grain structure. The traditional incremental analysis method for polycrystalline alloys is computationally expensive. Therefore, a direct cyclic analysis combined with a phenomenological crystal plasticity model is used in this work to predict the stable cyclic response of the material, resulting in a much lower computational cost. Three statistically equivalent representative volume elements are generated. The considered crystal plasticity parameters are calibrated using experimental tensile stress–strain curves. The comparison with incremental analysis demonstrates the accuracy and efficiency of the proposed method. The shakedown limit, based on the maximum load that allows the convergent cyclic response, significantly depends on the local grain orientation around lack of fusion defects, revealing a reason for the large scatter in the fatigue strength.

Effect of thermal-oxidative and mechanical degradation of recycled LDPE on foaming

In this study, we investigated the effect of recycling process on the molecular structure, viscoelasticity and foaming behavior of low density polyethylene (LDPE). A series of LDPE samples with different recycling process was prepared by multiple extrusion using a twin-screw extruder. The molecular weight distribution (MWD) was characterized by gel permeation chromatography (GPC). Wider MWD indicated the generation of higher molecular weight products. Small-amplitude oscillation rheology showed reduced loss factors, indicating that the chain entanglement was more difficult to relax. Moreover, nonlinear viscoelasticity was investigated using elongational rheology and molecular stress function (MSF) model. The results showed a steeper strain hardening exhibited in recycled LDPE. The correlated parameter β in the MSF model indicated that the recycling did not significantly change the branches regularity in LDPE, while the increasing [Formula: see text], the other correlated parameter, indicated that the chain entanglement was enhanced, which was corresponded to the improvement of high molecular weight component. The foaming results revealed that the recycled LDPE had finer cellular structure and higher nucleation density. Moreover, despite adding PP and active CaCO3 to simulate the impurities, the foamability loss of these mixed samples was well restricted and still valuable. Recycled LDPE is instead better than its corresponding virgin one in foaming performance, exhibiting the application potential for further developments.

Rapid 3D isotropic imaging of whole organ with double-ring light-sheet microscopy and self-learning side-lobe elimination.

Bessel-like plane illumination forms a new type of light-sheet microscopy with ultra-long optical sectioning distance that enables rapid 3D imaging of fine cellular structures across an entire large tissue. However, the side-lobe excitation of conventional Bessel light sheets severely impairs the quality of the reconstructed 3D image. Here, we propose a self-supervised deep learning (DL) approach that can completely eliminate the residual side lobes for a double-ring-modulated non-diffraction light-sheet microscope, thereby substantially improving the axial resolution of the 3D image. This lightweight DL model utilizes the own point spread function (PSF) of the microscope as prior information without the need for external high-resolution microscopy data. After a quick training process based on a small number of datasets, the grown-up model can restore sidelobe-free 3D images with near isotropic resolution for diverse samples. Using an advanced double-ring light-sheet microscope in conjunction with this efficient restoration approach, we demonstrate 5-minute rapid imaging of an entire mouse brain with a size of ∼12 mm × 8 mm × 6 mm and achieve uniform isotropic resolution of ∼4 µm (1.6-µm voxel) capable of discerning the single neurons and vessels across the whole brain.

FEATURES OF MODIFICATIONS IN THE RE-SOLIDIFIED SURFACES OF ADVANCED MATERIALS DUE TO HIGH-POWER PLASMA PULSES

The surface modification of advanced materials was studied through a series of repetitive plasma pulses caused tungsten melting. Features of the affected surface layers in reference materials (IGP W, AM W/WTa, Hastelloy, and EUROFER) for both fusion and fission applications were explored after exposure to plasma in the facilities (QSPA, MPC, and PPA) with different durations of plasma pulses. A detailed surface analysis was carried out with Scanning Electron Microscopy. It was found that the plasma treatment led to the formation of a modified layer as a result of the rapid re-solidification of the exposed surface. The fine cellular structures appeared in the re-solidified layers of the irradiated materials, with typical cell sizes ranging from 150 to 500 nm. An increase in the roughness of the exposed surfaces was attributed to the presence of the cracks and re-solidified layer.

Additive manufacturing of Al18Co30Cr10Fe10Ni32 high entropy alloy by gas atomization and laser powder bed fusion

Dense and crack-free, novel, eutectic Al18Co30Cr10Fe10Ni32 high entropy alloy was additively fabricated by the laser powder bed fusion (LPBF) using gas atomized alloy powders. LPBF parametric optimization was performed as a function of laser power (200–350 W) and scan speed (300–1800 mm/s). Microstructure of the densest sample exhibited a unique trimodal microstructure, along the build direction, consisting of fine cellular, coarse cellular, and conventional lamellar eutectic structures of face centered cubic (FCC) and body centered cubic (BCC) phases. This microstructural variation was significantly different from the starting powder microstructure, and the melt-pool microstructure observed during single laser scanning of arc-melted bulk alloy. The as-built alloy exhibited the outstanding tensile properties of yield strength, σY = 1.06 GPa, tensile strength, σUTS = 1.37 GPa, and elongation at failure, El = 21.3%.

Super toughened blends of poly(lactic acid) and poly(butylene adipate-co-terephthalate) injection-molded foams via enhancing interfacial compatibility and cellular structure

Biodegradable poly(lactic acid) (PLA) foams have drawn increasing attention due to environmental challenges and petroleum crisis. However, it still remains a challenge to prepare PLA foams with fine cellular structures and high impact property, which significantly hinders its widespread application. Herein, phase interface-enhanced PLA/ poly(butylene adipate-co-terephthalate) (PBAT) blend foam, modified by a reactive compatibilizer through a simple reactive extrusion, was produced via a core-back foam injection molding technique. The obtained PLA blend foams displayed an impact strength as high as 49.1 kJ/m2, which was 9.3 and 6.4 times that of the unmodified PLA/PBAT blend and its corresponding foam, respectively. It proved that the interfacial adhesion and cell size both strongly affected the impact strength of injection-molded PLA/PBAT foams, and two major conclusions were proposed. First, enhancing interfacial adhesion could cause a brittle-tough transition of PLA/PBAT foams. Additionally, for foams with high interfacial adhesion, small cell size (<12 μm) was more favorable for the stretching of cells and extension of the whitened region in comparison with big cell size (cell size >60 μm), leading to the drastic toughening of PLA blends. This study provides a feasible, industrially scalable and practical strategy to prepare super toughened and fully biodegradable PLA materials.

Parametric optimization in co-axial laser powder deposition of cobalt-base alloys on DIN 1.2714 die steel

In this work, cobalt-based powders (Stellite 6 and Stellite 12) were deposited on the hot forging die steel (DIN 1.2714) by direct laser deposition using a 2 kW Yb-fiber laser. Single tracks were developed by varying process parameters—powder mass flow rate (25–35 g/min), laser power (800–1100 W), and scan speed (400–800 mm/min). Further, the influence of these process parameters on clad geometry and dilution rate was studied. Optimization of parameters was carried out using grey analysis, and the results were analyzed based on analysis of variance (ANOVA). It was observed that the optimal parameters for Stellite 6 cladding are a powder mass flow rate of 25 g/min, laser power of 1100 W, and a scan speed of 400 mm/min. In contrast, the optimal parameters for Stellite 12 are a powder mass flow rate of 35 g/min, laser power of 1100 W, and a scan speed of 800 mm/min. In addition, a correlation between input and output parameters was established using regression analysis. The micrographs of the single-track cladding developed under optimal parametric conditions consist of fine cellular structure at the clad-surface interface followed by course cellular dendrites and fine equiaxed grains at the surface of the cladding. Stellite 12 cladding exhibits higher hardness (545 ± 10 HV0.3) than Stellite 6 cladding (470 ± 10 HV0.3) due to the formation of more refined grains.

The potato ladybird beetle &lt;I&gt;Henosepilachna vigintioctomaculata&lt;/I&gt; (Motsch.): classification, morphology and harmfulness (review)

The 28-spotted potato ladybird beetle belongs to the subfamily Epilachninae, which is comprised exclusively by phytophagous insects. The potato ladybird beetle is a dangerous pest of potato in the south of the Russian Far East. Besides potato, it causes damage to tomatoes, cucumbers, watermelons, marrows and eggplants. Adult beetles and larvae eat the parenchyma of leaves severely damaging them. As the result, leaves turn yellow and wither. One beetle can eat up to 15 cm2 of leave surface on average per day, and 300-700 cm2 over its lifetime. A larva can eat from 20 to 30 cm2 of leave surface while developing. This significantly reduces the yield. The body of an adult beetle is small (males, 4-6 mm; female, 5-7 mm), dome-shaped, and elliptical. The elytra are yellow or brownish with 28 black round spots. Some spots, especially the ones along the line of junction, can partially merge. The color of the underside of male beetles is lighter than in females. Male beetles have yellow or less frequently darkened prothorax, mesothorax and metathorax, epimera, and the uppermost edge of the sternites of the abdomen. The anal sternite of the abdomen has a curve with two depressions. The underside of a female beetle is black. The uppermost edge of the anal sternite is straight and with a flat depression. The body of a larva is greyish, oval and with numerous setae. There are 4 rows of black chitinous spinules on the back. Depending on an instar, larvae have a different number of projections on the chitinous spinules. Pupae are exarate, light yellow, and have larval skin remnants at the apex of the abdomen. There are two large black spots on the backside of the thoracic segments. The spots on the abdominal segments are smaller. Fairly long protruding setae grow sparsely on the bodies of pupae. Eggs of the potato ladybird beetle are yellow, elongated, with a pointed apex and a flat bottom. The surface of an egg is characterized by a fine cellular structure.

The development of laser powder bed fused nano-TiC/NiTi superelastic composites with hierarchically heterogeneous microstructure and considerable tensile recoverable strain

In this study, we fabricated the TiC nanoparticles decorated NiTi-based superelastic composites via laser powder bed fusion (LPBF) technology. Different from reactionlessness between TiC and NiTi in the conventional processes, high energy density of laser beam triggered strong diffusion behavior of carbon atoms from TiC nanoparticles and resulted in the precipitation of TiCx and attendant Ni-rich even Ti-rich intermetallics. Interestingly, these nanoprecipitates distributed along the intricate network of connected dislocations, architecting a novel submicron-scale cellular reinforcement structure and facilitating the formation of a hierarchically heterogeneous microstructure. The migration and distribution of TiC nanoparticles as well as the forming mechanism of the submicron cellular reinforcement structure were then elaborated. The study indicated laser scanning speed had significant influence on the distribution of TiC nanoparticles, the size of cellular structure and the matrix grain orientation. At the optimized parameter, the LPBF-fabricated nano-TiC/NiTi composites exhibited a weak orientation texture along the building direction, finer cellular structure and a considerable steady recoverable strain of 2.3% at a maximum tensile loading of 300 MPa.

Microstructure and mechanical properties of in-situ oxide-dispersion-strengthened NiCrFeY alloy produced by laser powder bed fusion

Oxide dispersion strengthened (ODS) superalloys are widely used in aerospace and nuclear reactors due to their exceptional creep strength and fatigue crack resistance at elevated temperature. In this work, an ODS NiCrFeY alloy for high temperature applications was fabricated by laser powder bed fusion (L-PBF). The microstructure and mechanical properties at room and elevated temperature of the L-PBF processed ODS NiCrFeY alloy were investigated. It was demonstrated that equiaxed grains with large fraction of low angle grain boundaries and cellular structures with high density of dislocations were obtained in the as-built alloy. Dispersed Y2O3 nanoparticles were in-situ formed in the ODS NiCrFeY alloy. Most of the Y2O3 nanoparticles were located at the cellular walls and pinned with a large number of dislocations. Due to the strengthening effects by dispersed Y2O3 nanoparticles and fine cellular structures, the ODS NiCrFeY alloy showed high ultimate tensile strength of 810, 560 and 250 ​MPa at room temperature, 600 ​°C and 800 ​°C, respectively.

Lightweight and tough PVDF foams via high‐pressure foam injection molding with core‐back operation

AbstractPolyvinylidene fluoride (PVDF) foams prepared by batch foaming have been intensively studied, but it still remains a challenge to fabricate high‐performance PVDF foams for structural applications. Herein, by adding polymethyl methacrylate (PMMA) as the minor component, the blend foams were successfully fabricated using supercritical carbon dioxide (CO2) as a green blowing agent via foam injection molding (FIM) with core‐back operation. The added PMMA could reduce the crystal size of PVDF. Owing to fine cellular structure and small crystal sizes, the injection‐molded blend microcellular foams exhibited superior mechanical properties. Especially, the elongation at break and specific breaking energy of the blend foam with 40% void fraction were separately increased by 184% and 297% compared to that of the PVDF foam. These findings revealed that the lightweight microcellular PVDF foams with improved toughness could be manufactured by the scale‐up and efficient FIM technology, which showed a promising future in automotive and other structural applications.

Composition inhomogeneity reduces cracking susceptibility in additively manufactured AlCoCrFeNi2.1 eutectic high-entropy alloy produced by laser powder bed fusion

Pre-alloyed and blended powders are frequently used feedstock options for additive manufacturing; however, nanoscale compositional inhomogeneities induced by blended powders are often ignored. This composition inhomogeneity is more pronounced in eutectic high-entropy alloys (HEAs) with small solidification ranges and sluggish diffusion effects. In this study, AlCoCrFeNi 2.1 eutectic HEAs were prepared by laser powder bed fusion (LPBF) using both pre-alloyed and blended powders. The alloy built using the pre-alloyed powder (PA) exhibited cellular structures that consisted of ordered body-centered cubic (B2) cells decorated with face-centered cubic (FCC) networks. The composition inhomogeneity in the alloy built using blended powders (BP) led to lamellar structures consisting of alternate FCC and B2 lamellas. The orientation relationships between FCC and B2 in both PA and BP were determined as {110} B2 //{100} FCC , < 001 > B2 //< 011 > FCC . The fine cellular structures in PA resulted in high ultimate strength (1400 MPa) but poor ductility. Solid-state cracking and delay cracking were observed in PA. The straight and extended FCC lamella in BP provided preferential channels and long distances for dislocation slippages, which combined high strength (1200 MPa) and ductility (10%). The improved deformation ability of BP enabled a strain-tolerant microstructure and eliminated the solid-state and delay cracking in as-built LPBF AlCoCrFeNi 2.1 alloys. • AlCoCrFeNi2.1 HEAs were additive manufactured by pre-alloyed and blended powders, respectively. • Cellular structures consisting of B2 cells and FCC networks were associated with cracks. • Lamellar B2/FCC structures resulted in an excellent combination of strength and ductility. • Composition inhomogeneity produced by blended powders eliminated cracks.

Investigation on Weld Characteristic, Welding Position, Microstructure, and Mechanical Properties in Orbital Pulse Current Gas Tungsten Arc Welding of AISI 304L Stainless Steel Pipe

Orbital pipe welding is carried out in this study by Pulse Current Gas Tungsten Arc Welding (PC-GTAW) without metal filler (autogenous) of AISI 304L stainless steel pipe. The dimensions of the specimen are 114 mm outside diameter and the thickness of 3 mm. This study investigates the effect of pulse current parameters, weld position, and pulse width on the characteristics of weld geometry, mechanical properties, and microstructure. The welding method used in this study is the continuous current and pulse current. The mean current of each parameter is the same at 100 ± 0.5 Amperes, but in the pulse current, there are variations in peak current, base current, peak current time, and the base current time. The welding speed used is constant at 1.4 mm/s. The result of weld geometry on the outside of pipe has shown that the flat (0°) position is concave and the overhead (180°) position is convex due to the influence of gravity. The microstructure indicates that the fine cellular dendritic structures appear at PC-GTAW. The PC-GTAW can produce good mechanical properties such as the tensile strength and the micro-hardness. The tensile strength of the specimen is reduced 14.23 % from the base metal at parameter 65-B and the flat position.