Deposition Of Subsequent Layers Research Articles

ЧИСЛОВЕ МОДЕЛЮВАННЯ НАПРУЖЕНО-ДЕФОРМОВАНОГО СТАНУ ПРИ АДИТИВНОМУ MIG НАПЛАВЛЕННІ КРЕМНІЄВОЮ БРОНЗОЮ CuSi3Mn1

The article analyzes in detail the stress-strain state during additive manufacturing using silicon bronze CuSi3Mn1 (БрКМц3-1), which is widely used in the machine-building industry for the manufacture of bushings, spring parts, and parts of chemical apparatus. The high cost of non-ferrous copper-based alloys makes it important to use Welding Arc Additive Manufacturing (WAAM) technologies. The processes of layer-by-layer surfacing of silicon bronzes lead to residual stresses at the tensile strength of the material, which can eventually provoke the development of critical defects in the form of cracks. Based on the simultaneous solution of the finite element method for the equations of heat balance and mechanics of a solid deformed body, the peculiarities of temperature distribution and parameters of the stress-strain state for the developed model of a triangular equilateral prism, which is additively generated from CuSi3Mn1 bronze, are determined. Verification of the experimental model with the calculated one was carried out by comparing the thermal cycles of surfacing. Based on the anal-ysis of the results of numerical modeling, it was found that the nature of the temperature change and the magnitude of its decrease in the corresponding layer after the deposition of subsequent layers are the same and do not depend on the deposition trajectory, and the largest residual equivalent plastic deformations are formed in the first layer with a gradual decrease inthe value in each subsequent deposited layer, which is associated with a decrease in the degree of volume of the VAT prism from the 1st to the 10th layer. The lower layers are characterized by a volumetric stress state due to the presence of rigid binders in the form of the substrate and the upper welded layers, which increases the probability of cracking in these layers during the cooling stage due to a decrease in the material's strength below σB< 170 MPa in the temperature range of 475-550 °C

Layer-by-Layer Surface Modification of Alendronate-Loaded Polyester Microparticles-Enabling Protein Immobilization.

The highly inert surface of polyester micro- and nano- drug carriers is a challenging substrate for further modification. The presence of surface moieties suitable for macromolecule coupling is crucial in the development of targeted drug delivery systems. Among available methods of surface activation, those based on adsorption of charged macromolecules may be carried out in mild conditions. In this work, alendronate-loaded microcores of three polyesters: poly-ε-caprolactone (PCL), poly(l-lactide-co-ε-caprolactone) (PLA-co-PCL) and poly(lactic-co-glycolic acid) (PLGA) were coated with three polyelectrolyte shells composed of chitosan/heparin (CHIT/HEP), polyallylamine/heparin (PAH/HEP), and polyethyleneimine/heparin (PEI/HEP) via the layer-by-layer method. Subsequently, the feasibility of model protein immobilization on obtained shells was assessed. Electrokinetic potential measurements confirmed the possibility of deposition of all investigated coating variants, and a positive correlation between initial core ζ potential and intensity of charge alterations after deposition of subsequent layers was identified. PEI/HEP assembly was stable in physiological-like conditions, while PAH/HEP multilayers disassembled in presence of phosphate ions, and CHIT/HEP shell showed limited stability in pH 7.4. Fluorescence assays of fluorescein tagged lysozyme surface coupled via ethylcarbodiimide hydrochloride/N-Hydroxysuccinimide (EDC/NHS) click reaction with all shell variants indicated satisfying reaction efficiency. Poly-ε-caprolactone cores coated with CHIT/HEP tetralayer were selected as suitable for model IgG surface immobilization. Antibodies immobilized on the shell surface exhibited a moderate degree of affinity to fluorescent IgG binding protein.

STRUCTURES OF GRADIENT LAYERS OBTAINED USING THE LASER METAL DEPOSITION (LMD) METHOD

The paper presents the results of structural investigations of a laser-welded layer in the Inconel 625 and Stellite 6 alloy matrix with the addition of WC. The tests involved the use of on plates made of low-alloy steel S355J2C+N. The filler materials used in the tests were nickel-based (Inconel 625) or co-balt-based powders (Stellite 6) having various contents (0-25%) of spherical tung-sten carbide (WC) used as the reinforcing phase. The granularity of the powders was re-stricted within the range of 45 µm to 90 µm. The cladding tests involved making multi-layer overlay welds. Next, non-destructive (VT and PT) and destructive (macro, hardness) tests were carried out. The macroscopic metallographic tests revealed that the three-layer Inconel 625-based overlay welds (with a WC content of up to 15%) had the correct shape and were characterized by full fusion into the base material, ensuring the continuity of the overlay weld.In the case of the Stellite 6-based overlay welds containing 10% of WC, it was possible to observe a through-crack of the overlay welds. The crack was formed in the first layer (as a result of stresses during the solidification of the liquid metal) and developed during the deposition of subsequent layers. The macrostructural tests were supplemented with microstructural observations and microanalysis of the chemical composition (EDS). The above-named tests revealed the good stirring of alloying elements in the overlay weld, indicating the high homogeneity of the overlay weld.The hardness obtained on the surface of the padding weld was 600 HV1.

Wet chemical method for highly flexible and conductive fabrics for smart textile applications

This study reports the preparation of highly flexible and conductive fabrics containing zinc oxide (ZnO), silver nanowires (AgNW) and graphene flakes (GFs) by simple vacuum filtration. The ZnO particles prepared with sol-gel method in large sizes with flower-like shape were used as filler and became the first layer to be coated on the fabric surface. These particles covered the gaps at the junction of the fabric fibers, providing a suitable area for the deposition of subsequent layers of AgNW and GFs. The structural, morphological and conductivity properties of the prepared conductive fabric were investigated by XRD, optical and electron microscopy as well as four-point probe conductivity measurement. The optical images showed that a continuous conductive network was obtained that allowed electron transport across the fabric surface. The fabric was found to have a remarkably low sheet resistance of an average of 1.5 Ω/sq. This result displays that promising candidates suitable for conductive textile applications can be prepared by simple vacuum filtration method.

Improvement of Cooling Effect and Dimensional Accuracy of Wire and Arc Additive Manufactured Magnesium Alloy by Active-Cooling-Based Contacting Copper Blocks

Wire and arc additive manufacturing (WAAM) employing a magnesium (Mg) alloy is superior in terms of safety, energy efficiency, and deposition rate when compared with a process that utilizes lasers and powder materials. However, problems with WAAM employing an Mg alloy include poor dimensional accuracy due to low viscosity of the molten Mg alloy. In addition, since Mg alloys cause a combustion reaction with water, an effective cooling method, such as direct water cooling, cannot be applied. In this study, a solid contact-based active cooling method employing copper blocks with high thermal conductivity was proposed to improve the dimensional accuracy and cooling efficiency of fabricated objects using AZ31. Moreover, the proposed method renders it possible to fabricate a wall structure with high flatness as the molten AZ31 solidifies upon direct contact with the flat surface of copper blocks. In addition, the copper blocks harboring an internal water circulation system achieved a higher cooling efficiency and shortened the interval cooling time between the deposition of subsequent layers. Meanwhile, it was discovered that the arc deflected toward the copper blocks, not onto the substrate or the previous layer when the wire tip approached too close to the blocks.

Simulation of phase evolution in a Zr-based glass forming alloy during multiple laser remelting

Additive manufacturing by laser-based powder bed fusion is a promising technique for bulk metallic glass production. But, reheating by deposition of subsequent layers may cause local crystallisation of the alloy. To investigate the crystalline phase evolution during laser scanning of a Zr-based metallic glass-forming alloy, a simulation strategy based on the finite element method and the classical nucleation theory has been developed and compared with experimental results from multiple laser remelting of a single-track. Multiple laser remelting of a single-track demonstrates the crystallisation behaviour by the influence of thermal history in the reheated material. Scanning electron microscopy and transmission electron microscopy reveals the crystalline phase evolution in the heat affected zone after each laser scan. A trend can be observed where repeated remelting results in an increased crystalline volume fraction with larger crystals in the heat affected zone, both in simulation and experiment. A gradient of cluster number density and mean radius can also be predicted by the model, with good correlation to the experiments. Prediction of crystallisation, as presented in this work, can be a useful tool to aid the development of process parameters during additive manufacturing for bulk metallic glass formation.

Influence of Interlayer Forced Air Cooling on Microstructure and Mechanical Properties of Wire Arc Additively Manufactured 304L Austenitic Stainless Steel

Wire‐and‐arc additive manufacturing (WAAM) is an innovative technology that involves deposition of subsequent layers of molten materials. Due to the high deposition rates, this technology is suitable for the production of large‐scale complex structures. Further enhancement in the productivity can be achieved by an interlayer cooling strategy that reduces idle time between depositions. However, the effect of the interlayer cooling on microstructure and mechanical properties has to be addressed. In this view, the present work compares microstructural features and mechanical properties of WAAM‐produced plates of austenitic AISI 304 L, focusing on the effect of both active interlayer air cooling and possible anisotropy induced by the additive process. Microstructural and mechanical characterization was conducted on samples extracted along the longitudinal, transverse, and diagonal directions to the deposition layers of WAAM plates, processed with and without interlayer active cooling. Results showed no remarkable influence of cooling conditions on the microstructure and mechanical properties of WAAM plates, which are indeed affected by the anisotropy induced by the additive process. The observed anisotropy in the elastic modulus, independent from different cooling conditions, was related to the crystallographic texture consequent to the highly oriented microstructure typically induced by the process.

Mechanical Properties of Hardened 3D Printed Concretes and Mortars-Development of a Consistent Experimental Characterization Strategy.

Today, it is already foreseeable that additive manufacturing of mortar and concrete has groundbreaking potential and will revolutionize or at least fundamentally change the way we build. In recent years, 3D concrete printing (3DCP) with extrusion-based deposition methods has been pushed forward by a growing research community. Albeit being regarded one of the most promising innovations in construction industry, a consistent characterization methodology for assessing the constitutive behavior of 3D printed, hardened cementitious materials is missing, so far, which hinders its widespread use in engineering practice. The major objective of this paper is to fill this gap by developing a new experimental framework that can thoroughly describe the mechanical properties of 3D printed cementitious materials. Based on both a review of state-of-the-art test setups and a comprehensive experimental campaign, the present paper proposes a set of easy-to-use experimental methods that allow us to assess flexural, tensile, shear and compressive strength as well as fracture energy of 3D printed concretes and mortars in a reliable and reproducible manner. The experimental results revealed anisotropic material behavior for flexural, tensile, shear and compressive loading. Furthermore, they confirm that interval time (time gap between deposition of subsequent layers) has a crucial effect on investigated material properties leading to a severe reduction in strength and fracture energy for longer interval times.

Conformal and Smooth TiN Film Growth By Using ALD Method

As the generation of memory devices evolve, the successful fabrication of high aspect ratio (HAR) features becomes more and more challenging. Apart from the traditional patterning, deposition and etch related issues, conformal film deposition onto these HAR structures becomes a critical parameter in determining the overall device yields. It is well established now that compared to conventional deposition techniques such as chemical vapor deposition (CVD) and physical vapor deposition (PVD), atomic layer deposition (ALD) offers a pathway to highest conformality and step-coverage. On the other hand, film conformality, especially roughness property has trade-off relationship to step-coverage property. High-pressure process is appropriate to obtain high step-coverage performance in short ALD cycle time process, but roughness value becomes worse due to higher chance of crystalline film growth at high-pressure process condition. High roughness causes local variations in step-coverage and poses problems for deposition of subsequent layers and device performance.In the present study, we report that it is possible to obtain conformal and smooth TiN film by using low/high pressure two-step growth, initially low-pressure TiN growth, and secondly high-pressure TiN growth on the non-pattern and HAR pattern wafers. Eugenus’s versatile 300mm mini-batch system and HAR structures with approximately 120:1 (Dimension of bottom opening, and total height are approximately 17nm and 2μm, respectively) were used in this research, respectively. TiCl4 and NH3 were used as the precursors for TiN film deposition and grown TiN films were analyzed by using ellipsometry, atomic force microscopy (AFM) and transmission electron microscopy (TEM) to study the film properties and step-coverages. In addition, reactor-scale computational fluid dynamics (CFD) simulations were performed and correlated to on-wafer experimental results and utilized as a predictive tool.It was found that TiN film grown at low-pressure condition was more conformal and smoother than that grown at high-pressure condition, although step coverage value grown at low-pressure condition was worse than that grown at high-pressure condition. By optimizing low/high pressure two-step TiN growth condition, it was achieved that not only better roughness than that of pure high-pressure TiN, but also, better step coverage value than that of pure low-pressure TiN as well as than that of pure high-pressure TiN (Figure 1). Figure 1

Influence of laser power and powder feed rate on the microstructure evolution of laser metal deposited Ti-5553 on forged substrates

In this work, titanium blocks of Ti-5Al-5Mo-5V-3Cr (Ti-5553) have been Laser Metal Deposited (LMD) on forged substrate of the same alloy under varying laser power and powder feed rates. The microstructure has been characterized using optical microscopy, scanning electron microscopy and Electron backscatter diffraction (EBSD) techniques. Microstructure was predominantly large columnar β-grains aligned with the build direction interspersed with fine equiaxed β-grains. Increase in the powder feed rate was found to reduce the average β-grain size and promoted clusters of fine grains to be retained during the deposition of subsequent layers. Increase in the laser power also reduced the average β grain size and promoted greater nano-scaled α precipitates at the substrate interface and initial deposited layers which significantly increased the microhardness in this area. Dendrites exist due to micro-segregation of solutes during rapid solidification which create preferential regions for α nucleation. A difference in texture was observed between specimens manufactured with varying laser powers: a low laser power produced a cube texture and a higher laser power produced a <001> // BD fibre texture.

Fabrication of a nanostructured high strength steel tube by friction-forging tubular additive manufacturing (FFTAM) technology

Abstract A newly developed solid-state 3D-printing route of friction-forging tubular additive manufacturing (FFTAM) is applied to produce a low-carbon steel tube with superior mechanical properties. FFTAM technology is based on high-temperature severe plastic deformation and consolidation of metal chips via the friction stir welding/processing (FSW/FSP) mechanism to achieve a fully-dense tubular shape in a layer-upon-layer manner. This achieve metallurgical bonding between the layers using a rotating mandrel to maintain radial friction followed by press-die forging under hydrostatic pressure. After FFTAM deposition, the initial ferrite-pearlite microstructure of the steel chips is transformed to a triple-phase alloy consisting of ferrite, martensite, and austenite grains. The formation of martensitic phases by rapid cooling during layer-upon-layer deposition led to significant material hardening, and this further modified by the thermo-mechanical history upon deposition of subsequent layers. Transmission electron microscopy (TEM) observations revealed the microstructural refinement of the manufactured steel tube at the nano-scale range (

Characterization of wire arc additive manufactured products: A comparison between as-deposited and inter-layer cold worked specimens

The presence of large dendrites and alloy segregation in as-deposited wire arc additive manufacturing (WAAM) products results in a wide range of mechanical properties that are often inferior to wrought ones. In this study, the effect of inter-layer cold working on the microstructure and mechanical properties of AISI 347 samples manufactured by WAAM has been investigated. The average hardness of single-pass welding, as-deposited, and cold worked WAAM samples were 190 HV, 249 HV, and 323 HV, respectively. Inter-layer cold working has led to an increase in ultimate tensile strength from 576 MPa to 803 MPa and yield strength from 395 MPa to 697 MPa. Also, Inter-layer cold working and thermal energy due to the deposition of subsequent layers have resulted in microstructural evolution and grain refinement through recrystallization. Besides, a semi-quantitative analysis has shown that increasing the amount of cold working by four times resulted in 64 % decrease in average recrystallized grain size.

Directional and oscillating residual stress on the mesoscale in additively manufactured Ti-6Al-4V

In additive manufacturing of metals as compared to conventional processing, the directional track-by-track and layer-by-layer nature of the fabrication process can lead to residual stresses that locally are both directionally and spatially heterogeneous. Much of the existing literature has focused either on the macroscale residual stress inside the entire part, or on the microscale residual stresses that are created around a scan vector, thereby neglecting the intermediate length-scale of the different layers. The objective of this research is to investigate such mesoscale residual stress distributions across several layers in Ti-6Al-4V components produced by laser metal deposition process. The incremental centre hole drilling and incremental slitting methods provide measurements with excellent spatial resolution within and across the layer length scale. In this work, the two methods complemented each other to quantify both mesoscale and directional variations of residual stress that correlate with the deposition pattern. Our findings also provide strong evidence that an oscillatory residual stress variation persists even after thermal cycling that occurs during deposition of subsequent layers.

On the anomaly in the electrical characteristics of thin film transistors with multi-layered sol-gel processed ZnO

A set of bottom-gate Zinc Oxide (ZnO) thin film transistors (TFTs) with active layers containing 1, 4 and 8 layers of spin-coated ZnO were fabricated and their electrical characteristics such as transistor transfer and capacitance-voltage characteristics were analyzed. The transconductance of the single-layered ZnO transistor shows a single peak. On the other hand, multiple peaks and humps were observed in the transconductance and capacitance-voltage characteristics of multi-layered ZnO transistors. The multi-layers were grown by reiteration of the spin-coating process, producing ZnO − ZnO interlayer-interfaces. The surface of the ZnO layer in contact with the ambient contains active sites, resulting in chemisorption of ambient gases such as oxygen prior to the deposition of subsequent layers. The chemisorbed species become negatively-charged and form charge sheets, depleting the surface/interface region. It was proposed that the formation of depletion layers at ZnO − ZnO interlayer-interfaces is the main cause for the observed anomaly.

Finite element modelling for part distortion calculation in selective laser melting

Additive manufacturing (AM) is presently a strong candidate for automotive, medical and aerospace applications. The present work focuses on the influence of laser scanning speed on part distortion, when depositing AISI 304 stainless steel using selective laser melting (SLM). The commercial software ABAQUS was used to develop a 3D finite element model to simulate the deposition process and predict thermal gradients and part distortion. The user subroutine USDFLD was used to model powder to solid phase transformation, and the laser beam effects were modelled using the user subroutine DFLUX. In addition, heat convection within the molten pool was considered by enhancing the thermal conductivity of molten material. Also, the element birth technique was used to simulate material deposition of successive layers. The predicted results were validated by comparing them to the available literature, where a good match was found. It was concluded that higher laser scanning speeds results in lower surface temperatures and higher vertical deflections. In addition, the effect of scanning speed on temperature gradients and part distortion was found to be more evident by the deposition of subsequent layers.

Effect of processing conditions on the microstructure, porosity, and mechanical properties of Ti-6Al-4V repair fabricated by directed energy deposition

In this study, the effect of processing parameters in directed energy deposition (DED) additive manufacturing (AM) on the microstructure and mechanical properties of Ti-6Al-4V was evaluated. A commercial DED system was used to deposit square patches of Ti-6Al-4V onto a substrate with the same nominal composition, with varying conditions to represent those that may be found in actual repair applications. A design of experiments was used to study the effect of substrate thickness, interlayer dwell time (time between deposition of subsequent layers), initial substrate temperature, hatch pattern, and number of deposited layers on the microstructure, porosity, and hardness of the deposition. Varying these processing parameters elucidates how each independently, or all collectively, impact the resulting microstructure and properties of Ti-6Al-4V deposits. As internal pores, or defects, significantly affect the properties of additively manufactured components, this study aimed to identify and quantify those defects in DED. The results from the current study show that with decreasing substrate thickness, the depth of the heat affected zone increased by an average of 400 μm. The density of the part was affected by the number of deposited layers and the initial substrate temperature, increasing with increasing the number of deposited layers, but decreasing with higher initial substrate temperatures. Lastly, the hardness increased with increasing substrate thickness, but was not impacted significantly by the other parameters studied.

Idle time selection for wire-arc additive manufacturing: A finite element-based technique

Wire‐arc additive manufacturing is a metal additive manufacturing process that enables the production of large components at a high deposition rate. This process transfers a large amount of heat to the workpiece, requiring the introduction of idle times between the deposition of subsequent layers so that the workpiece cools down. This procedure prevents the workpiece from collapsing and ensures a suitable interpass temperature. The main challenge is the selection of such an idle time capable of ensuring the required interpass temperature, because the cooling rate of the workpiece changes throughout the process, entailing the need for a different idle time between the deposition of subsequent layers to achieve a constant interpass temperature.This paper proposes an innovative approach to schedule the deposition of interlayer idle times for wire‐arc additive manufacturing process. The technique is based on a finite element analysis of the thermal behavior of the workpiece, by solving the heat transfer equations. The simulation data are processed using the developed algorithm to compute specific idle times for the deposition of each layer, thereby ensuring a constant interpass temperature. The effectiveness of the proposed technique is validated by experiments performed on a test case component. The idle times are calculated using the proposed technique, by simulating the process, and used to manufacture the test case. The temperature data measured during the process are compared with the FE simulation results to verify the accuracy of the model. An analysis of the geometry of the manufactured workpiece confirms that the adoption of the idle times obtained by the proposed technique prevents the occurrence of major structural collapses.

Non-metallic inclusions in 17-4PH stainless steel parts produced by selective laser melting

The character, morphology and distribution of inclusions has been studied in additively manufactured 17-4PH stainless steel parts produced from gas-atomized powder by selective laser melting. A combination of advanced electron microscopy techniques has been used to show that such parts contain oxide inclusions ranging from a few nm to tens of μm across. The coarser inclusions have morphologies that mimic the oxides which accumulate between melt tracks at the build surface, suggesting that these inclusions are incorporated into the build during deposition of subsequent layers. Such features could have deleterious anisotropic effects upon the fatigue and fracture resistance of the built parts. The finer inclusions are equi-axed, reside preferentially at grain boundaries, and could inhibit grain growth during processing via Zener pinning effects. The chemistries of the inclusions include elements such as Al that are not part of the alloy specification. This indicates that the inclusions are exogenous defects that are entrained in the melt during gas atomization due to interactions with the crucible or nozzle materials. Examples of encapsulated oxide material in the powder feedstock support this explanation. These observations highlight the need for careful control of powder pedigree when using additive manufacturing for critical structural components.

Uranium-bearing opals: Products of U-mobilization, diffusion, and transformation processes

Understanding the retention mechanism of U by amorphous silica (i.e., opal) in the environment is of great importance to nuclear-waste disposal because opals can retain U for millions of years. Uraniferous opals from Spor Mountain and the Thomas Range, Utah, U.S.A., are examined in terms of their mineralogical, chemical, and isotopic compositions. Uranium-rich zones composed of most likely vorlanite, CaUO 4 , occur in fibrous opal-CT (termed lussatite) along the interface of the phase with microcrystalline quartz. Red- to black-colored precipitates of vorlanite also occur in the interstices between fibers and grains in lussatite and massy opals, respectively. The high abundance of vorlanite in certain growth zones can be explained by the diffusion of Ca and U along boundaries of layers, grains, and fibers and by the release of Ca and U through the transformation of opal-A into opal-CT and from opal-CT into microcrystalline quartz. Similar O-isotope compositions of opal-CT and associated microcrystalline quartz indicate that crystallization processes and deposition of subsequent layers of opal occurred from fluids of similar origin and T . Differences in the isotope and chemical composition between uraniferous opals/microcrystalline quartz, the SiO 2 polymorph moganite, and pyrolusite indicate the past occurrence of various alteration processes involving fluids of different composition and T . The results of this study indicate that assemblages of opal and microcrystalline quartz can retain U for millions of years as long as confined pore spaces between different generations of opal and quartz or between growth features of opal provide space for the nucleation and adsorption of U-bearing phases and species.

Precipitation and austenite reversion behavior of a maraging steel produced by selective laser melting

Abstract