Multilayer Deposition Research Articles

Effect of clad height, substrate thickness and scanning pattern on cantilever distortion in direct metal deposition

In metal additive manufacturing, moving heat sources cause spatial and time-dependent variations of temperature and strain that can lead to part distortions. Distortion prediction and optimized deposition parameters can increase the dimensional accuracy of the generated components. In this study, an analytical approach for modeling the effect of clad height and substrate thickness is experimentally validated. Additionally, the influence of the scanning pattern as a function of clad height and substrate thickness is determined experimentally. The analytical model is based on the cool-down phase mechanism and assumes the formation of constant thermal shrinking forces for each deposited layer. The model accurately predicts longitudinal cantilever distortion after experimental calibration when compared with similar experimental conditions. For multi-layer deposition, the scanning pattern has the largest influence on distortion for thin-walled substrates. An optimized deposition strategy with longitudinal scanning vectors leads to a distortion reduction of up to 86%. The results highlight the potential of mechanical modeling and scanning strategy optimizations to increase the shape accuracy for industrial applications in the field of additive manufacturing.

Lattice Boltzmann simulation of phase change and heat transfer characteristics in the multi-layer deposition

The metal droplets deposition method (MDDM) is a rapid prototyping technology, implemented via metallurgy bonding within droplets. The anisotropy of heat transfer and re-melting is caused by an asymmetric deposition process. A lattice Boltzmann method (LBM) model is established to predict the heat transfer and phase change in the multi-layer deposition. The prediction model is verified by the experimental temperature profiles in existing literature. The monitoring points are set to compare the temperature profiles, and decoupling analyze the heat transfer mechanism in different positions. The negative relationships between the re-molten volume of the temperature difference, as well as the influence of the dispositive position and the relative position of the adjacent component are observed and analyzed under the heat conduction. This work is helpful to choose the appropriate temperature conditions and the optimal dispositive method.

Processing window for laser metal deposition of Al 7075 powder with minimized defects

There is a relative lack of data on the processing parameters suitable for laser metal deposition (LMD) of Al alloys, particularly high strength alloys. The objective of this study is to outline a systematic investigation to define the processing window for LMD of Al alloy 7075. Single linear tracks were fabricated by varying the powder mass flow rate, laser power, and scan speed according to a 3 3 factorial experimental design, in order to determine conditions that produce deposits with suitable cross section geometries. Single layer multi-track deposits were fabricated using parameters selected from the linear track experiments, and with varying track overlap values. Low energy input and powder deposition conditions were found to produce single track and multi-track deposits with porosity less than 0.3 and 1 %, respectively. Cuboid samples were produced using parameters selected from the single layer multi-track processing window. However, porosity of at least 4 % was observed in the cross section for all cuboid samples. Liquation cracking was not observed in the samples, despite clear signs of grain boundary liquation. Microcracks with a width of ∼1 μm were observed in the deposited material, and the results indicate that these are solidification cracks due to insufficient eutectic liquid to backfill and ‘heal’ incipient cracks. It is concluded that low energy density and powder mass deposition conditions can produce crack-free single layer deposits of 7075 with low porosity, but the elimination of interlayer porosity and microcracks in multi-layer deposits requires further study.

Multi-physics modeling of direct energy deposition process of thin-walled structures: defect analysis

As a promising additive manufacturing method, direct energy deposition has been widely used to fabricate complex thin-walled parts. However, some defects such as uneven layer surface and excessive build-ups always occur in this process. In this study, a high-fidelity model adopting a novel laser/powder source is developed to simulate the detailed multi-layer deposition process. With layer surfaces being tracked in real-time, laser source model incorporates local incidence angle and defocusing amount to adjust absorbed energy and beam radius on the track surfaces. The powder catchment efficiency varies with the defocusing amount timely. The simulations demonstrate that build-ups are mainly induced by unstable linear powder feed rate and worsen due to laser/powder defocusing and accumulated heat. The layer surface unevenness results from powder positive defocusing, while molten pool dynamics, laser positive defocusing and accumulated heat plays a supplementary role. Eliminating methods are proposed based on the simulations and validated by experiments.

Two‐Tier Nanolaminate Plasmonic Crystals for Broadband Multiresonant Light Concentration with Spatial Mode Overlap

AbstractEffective trapping and nanolocalization of different colored photons simultaneously at the same position remain a challenge in nanophotonics research but can boost applications based on nonlinear multiphoton processes. For achieving broadband nanoscale light concentration, a promising strategy is to employ multiresonant plasmonic devices that support multiple hybridized surface plasmon modes with spatial overlap at several different resonance wavelengths. However, high‐order plasmonic modes from hybridization tend to have a dark multipolar nature and are less useful due to weak interactions with free‐space light. Here, it is reported that nanolaminate plasmonic crystals in a two‐tier configuration can support many (≈10) spatially overlapped and highly‐excitable hybridized plasmonic modes under free‐space light illumination between 400 and 1400 nm. Combination of nanoimprinting lithography and multilayered physical vapor deposition techniques enables wafer‐scale fabrication of nanolaminate plasmonic crystals consisting of nanolaminate nanodome and nanohole arrays as the two closely‐separated subsystems, and measurements demonstrate their multiresonant plasmonic responses in good agreement with numerical calculations. Coupled‐mode theory analysis reveals that the unique broadband multiresonant responses of the two‐tier nanolaminate plasmonic crystals are due to the synergistic effects of the strong near‐field interactions between the modes in the nanodome and nanohole subsystems and the ground‐plane‐like loading effect from the nanohole subsystem.

Evaluation of hierarchical glucose oxidase/Co3Mn-CO3 LDH modified electrodes for glucose detection

A glucose amperometric biosensor has been prepared by a multilayer deposition on a glassy carbon electrode of Co3Mn-CO3 layered double hydroxide, glucose oxidase (GOx) and a biopolymer (carrageenan), respectively. The original transduction step consists in the electrocatalytic oxidation of H2O2, enzymatically formed, in the Co3Mn-CO3 inner-layer at 0.65 V/Ag-AgCl. The sensitivity and the detection limit, obtained with this optimized bioelectrode (Co3Mn-CO3/GOx/carrageenan, 30/20/10 µg), are 12.8 mA M−1 cm−2 and 0.02 mM, respectively. A 3D-porous bioelectrode was also prepared by impregnation of a carbon felt (CF) with a colloidal suspension of Co3Mn-CO3 nanoparticles and then with GOx. The structure and the morphology of the Co3Mn-CO3/CF composite were characterized by X-ray diffraction and electron scanning microscopy and the bioelectrode GOx/Co3Mn-CO3/CF was finally tested in cyclic voltammetry in the presence of glucose.

Microstructural Evolution in the TC17 Titanium Alloy Processed During Laser Stereo Forming

In this paper, the microstructure evolution of TC17 titanium alloy prepared by laser stereo forming (LSF) was investigated. Forged TC17 plate was selected as the base material, and TC17 titanium alloy spherical powder with the size of 50-150 μm was the candidate cladding material. The microstructure in deposited TC17 titanium alloy was consisted of three parts, namely fine grains at the bottom of the deposition area, coarse β columnar crystals at the middle, while coarse β columnar crystals or equiaxed crystals at the top. The microstructure is significantly affected by the thermal cycle history during the LSF process. At different locations of the deposited samples, the composition, morphology, size and volume fraction of the phases in the grains are discrepant, as the metastable β phase and the acicular martensite (α′) structure were obtained at the bottom and in the middle, respectively. Due to thermal cycle during multi-layer deposition, the metastable β phase will gradually evolved into α + β phases. As the subsequent deposition process continued, the temperature in the middle of the deposition area decreased below the transformation point, and α′ is decomposed into α + β. The precipitated α phase gradually grew up under the action of thermal cycle. Meanwhile, the fine secondary α phase precipitated from the metastable β phase, and finally the coarser α lath and inter lath were obtained β structure.

High transparent, low surface resistance ZTO/Ag/ZTO multilayer thin film electrodes on glass and polymer substrates

Zinc tin oxide (ZTO)/Ag/ZTO multilayer thin films were grown by direct current (DC) magnetron sputtering technique at room temperature on soda lime glass (SLG) and different polymer substrates such as polycarbonate (PC) and polyethylene terephthalate (PET) for transparent conductive electrode (TCE) applications. The effect of substrate on the structural, optical and electrical characteristics of ZTO/Ag/ZTO multilayers was investigated. All prepared ZTO/Ag/ZTO films presented amorphous structure as expected from room temperature deposition process and smooth surface quality with very low surface roughness. We found that ZTO/Ag/ZTO multilayer films grown on SLG, PET and PC substrates have very high optical transmission and low surface resistance. Moreover, after ZTO/Ag/ZTO multilayer thin film deposition on polymer substrates, the optical transmission was found to be enhanced because the higher absorption due to Ag layer is compensated by lower reflectance. Our results suggest that ZTO/Ag/ZTO multilayer thin films on any substrate can be a promising alternative to indium tin oxide (ITO) films as a cost-effective, indium-free, flexible and transparent electrode for various applications.

Bioactivity of a Novel Polycaprolactone-Hydroxyapatite Scaffold Used as a Carrier of Low Dose BMP-2: An In Vitro Study.

Scaffolds of polycaprolactone-30% hydroxyapatite (PCL-30% HA) were fabricated using melt stretching and multilayer deposition (MSMD), and the in vitro response of osteoblasts to the scaffolds was assessed. In group A, the scaffolds were immersed in 10 µg/mL bone morphogenetic protein-2 (BMP-2) solution prior to being seeded with osteoblasts, and they were cultured in the medium without BMP-2. In group B, the cell-scaffold constructs without BMP-2 were cultured in medium containing 10 µg/mL BMP-2. The results showed greater cell proliferation in group A. The upregulation of runt-related transcription factor 2 and osteocalcin genes correlated with the release of BMP-2 from the scaffolds. The PCL-30% HA MSMD scaffolds appear to be suitable for use as osteoconductive frameworks and BMP-2 carriers.

Investigation of polyelectrolyte multilayers deposited on corona charged composite polylactic acid / poly(ε-caprolactone) substrates

In the present study chitosan and casein polyelectrolyte multilayers (PEMs) deposited on composite polylactic acid (PDLA) / poly(ε-caprolactone) (PEC) substrates were investigated. The substrate’s morphology was investigated using polarized light microscopy and their degree of crystallization was studied by the application of differential scanning calorimetry. The substrates obtained were charged in a corona discharge system, consisting of a corona electrode (needle), a grounded plate electrode, and a metal grid placed between them. Positive or negative 5 kV voltage was applied to the corona electrode. 1 kV voltage of the same polarity as that of the corona electrode was applied to the grid. The dependences of the normalized surface potentials on the storage times of positively and negatively charged substrates were studied. Layer-by-layer (LbL) technique was used for multilayer deposition on the substrates. PEMs with different number of layers (4 or 8) were obtained. A model drug Benzydamine hydrochloride was loaded in the casein layers in order to evaluate the effect of the kind of substrate on the drug immobilization and release. A study of the drug release kinetics in saline buffer was carried out and the amount of the released drug was calculated spectrophotometrically. It was shown that the experimental results fit to the Peppas model with a very good level of correlation and the model parameters differ depending on the used substrate.

Optically active quadrupole edge modes in arrays of flat metallic nanodisks

Using experimental and simulation methods, we demonstrate that structures consisting of two-dimensional arrays of closely-packed flat metallic nanodisks can support optically active collective resonances associated with the dark edge modes. Our results show that such resonances appear as the refractive index of the superstrate increases, generating a relatively sharp peak with weak sensitivity to the variations of the environment. Using a consecutive multilayer deposition of Si on the top of the arrays we map the development of such a resonance via multi-step red shifting of the Rayleigh anomaly wavelength. The results show that when the Rayleigh wavelength is sufficiently close to the subradiant quadrupole edge modes of the nanodisks, a linearly polarized light can excite such modes, resulting in optically active collective resonance.

Stability, Interfacial Structure, and Gastrointestinal Digestion of β-Carotene-Loaded Pickering Emulsions Co-stabilized by Particles, a Biopolymer, and a Surfactant

Novel Pickering emulsions were stabilized by complex interfaces in the presence of zein colloidal particles (ZCPs), propylene glycol alginate (PGA), and rhamnolipid (Rha) for delivery of β-carotene. The influence of the particle-surfactant, particle-biopolymer, and particle-biopolymer-surfactant mixed interfaces on the physiochemical properties and digestion fate of Pickering emulsions was investigated. It is the first time that three different types of emulsifiers have been used to synergistically stabilize food Pickering emulsions for delivery of lipophilic nutraceuticals. The physicochemical stability, microstructure, rheological properties, and in vitro gastrointestinal digestion of Pickering emulsions were controlled by the addition sequence and mass ratio of multiple stabilizers, which showed the enhanced stability and delayed lipid digestion of the particle-biopolymer-surfactant-stabilized Pickering emulsions. After encapsulation into Pickering emulsions, the retention rate of β-carotene increased 2-fold under UV radiation for 8 h. The coexistence of ZCPs, PGA, and Rha could induce the competitive displacement, multilayer deposition, and interparticle network at the interface. The combination of particles, a biopolymer, and a surfactant delayed the lipolysis during in vitro gastrointestinal tract. By modulating the interfacial composition, the release rate of free fatty acids from Pickering emulsions was reduced from 19.46% to 2.83% through different mechanisms. The novel Pickering emulsion could be incorporated in foods as well as pharmaceuticals for controlled lipid digestion or targeted nutrient delivery purposes.

Synthesis of a planar, multicomponent catalytic surface of Na2CO3/MnO

O2 adsorption on MnO(100) precovered with sodium (Na) multilayers was investigated by X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD). Deposition of Na multilayers leads to a first monolayer of oxidic Na followed by metallic Na island growth. XPS results for the oxidation of the metallic Na islands indicate an incomplete oxidation of Na at 125 K. Oxidation at 350 K completely oxidizes the metallic islands producing a mixture of Na2O and Na2O2. Thermal evolution of the oxidation products was examined. After oxidation at 350 K and flashing to 750 K, Na2O and Na2O2 are the primary oxides on MnO(100). After flashing to 850 K, a solid state reaction of Na2O2/Na2O and the MnO(100) substrate forms a NaMnO2-like surface compound which decomposes above 850 K. Oxygen exchange between CO2 and Na oxides is observed. The strong interaction between CO2 and Na oxide islands forms Na2CO3 on MnO(100). Heating the Na2CO3 covered MnO(100) surface to 600 K for 10 min drives oxidic Na in the first monolayer into the MnO subsurface, and produces a surface exposing islands of Na2CO3 on MnO(100).

Effects of Heat Input on Morphology of Thin‐Wall Components Fabricated by Wire and Arc Additive Manufacturing

In the process of wire and arc additive manufacturing (WAAM), it is crucial to improve the surface quality and maintain a uniform building morphology. Unacceptable morphology of components influences the surface roughness and deposition efficiency, limiting the application of WAAM in the fabrication of complex‐shaped components. Herein, linear energy density is used to estimate the applied heat input. The single‐pass single‐layer bead morphology is analyzed to establish the relationship between linear energy density and the bead width ratio to bead height. In addition, four four‐layer components under different heat inputs are deposited to reveal the process of multilayer deposition. According to the morphology and surface appearance, heat input effects on surface roughness, straightness, and deposition efficiency are investigated. Then, a relationship is established to predict the outcomes of heat input on deposition quality. It is inferred that good deposition performance can be obtained when the linear energy density lies around 600 J mm−1. A simulation based on the Simufact welding software is made on temperature field distribution and thermal cycles to illustrate the relationship, confirmed by 3D scanning results. At last, based on the investigations, a uniform and well‐formed thin‐wall component is fabricated, and its deposition efficiency can reach 80%.

Preparation and characterization of ferulic acid-modified water soluble chitosan and poly (γ-glutamic acid) polyelectrolyte films through layer-by-layer assembly towards protein adsorption

In this study, ferulic acid-modified water soluble chitosan and poly (γ-glutamic acid) polyelectrolyte multilayers films were constructed through the layer-by-layer (LBL) self-assembly technique. Chitosan (CS) or ferulic acid modified chitosan (MCS) and Poly (γ-glutamic acid) (PGA) was alternately deposited on the surface of glass substrate for the enhancement of surface modification. The obtained films were characterized by Fourier transform spectroscopy (FTIR), X-ray diffractometry (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), UV–vis spectroscopy and water contact angle to study its physico-chemical properties including protein absorption. The (PGA/MCS) films showed intense deposition of multilayers built upon the surface roughness and an increase in the exponential growth of multilayer films by UV–vis spectroscopy. Water contact angle indicated that the (PGA/MCS) films performed well with good wettability due to the increase in the number of layers. The LBL multilayer coatings of (PGA/MCS) films surface possessed a reduced amount of protein adsorption. These results indicated that it can resist the protein adsorption and can enhance the biocompatibility towards the biomedical application through the protein interaction. The (PGA/MCS) films has the potential to utilization as a good biomaterial for biomedical purposes to intensify the bio-active surface.

Development of β-carotene loaded oil-in-water emulsions using mixed biopolymer-particle-surfactant interfaces.

In this study, β-carotene loaded oil-in-water emulsions were stabilized by complex interfaces composed of propylene glycol alginate (PGA), rhamnolipids (Rha), and zein colloidal particles (ZCPs). The influence of mixed biopolymer-surfactant, biopolymer-particle, surfactant-particle and biopolymer-surfactant-particle interfaces on the performance of the emulsions was investigated. The stability, microstructure, rheological properties, and in vitro gastrointestinal digestion of the emulsions were controlled by regulating the adding sequence and mass ratio of the multiple stabilizers. The droplet size of the emulsion was in the range of 14-77 μm. After encapsulation into the emulsions stabilized by the complex interfaces, the photothermal stability of β-carotene were increased by 41.53% and 21.52%, respectively. The co-existence of particles, biopolymers, and surfactants could induce competitive displacement, multilayer deposition and an interparticle network at the interface. Compared with a single PGA- or Rha-stabilized emulsion, the complex interface-stabilized emulsion reduced the release of FFA by 28.06% and 26.16%, respectively. The interfacial composition of the emulsion and the delayed lipid digestion further affected the bioaccessibility of β-carotene in the gastrointestinal tract (GIT). The mixed biopolymer-particle-surfactant interface-stabilized emulsion could be incorporated in foods, pharmaceuticals and cosmetics for excellent stability, targeted nutrient delivery and controlled lipolysis.

Evaluation of the Multi-Structural Potential of Ni-Co/SiC Nanocomposite Coatings Electrodeposited in API 5L X80 Steel

The use of nanocomposite coatings on carbon steel has been very promising. In this paper, the formation mechanism of multilayer of Ni-Co/SiC nanocomposite coating electrodeposited in API 5L X80 steel was investigated. The coatings were obtained by galvanostatic deposition technique using a single bath and a single cathodic current density value. The results showed a variation in morphology and chemical composition of the coatings both on the surface and along the cross-section at all time conditions tested, confirming the functional gradient of the coating. The formation of the Ni-Co/SiC nanocomposite coating occurred through the multilayer deposition mechanism, with compositions mostly alternated between Ni and Co. The preferred orientation of the plane (220) and phase structure FCC remained constant on the surface of all the obtained samples. It was observed that the coating became more compact in the region located closer to the substrate, where an increase in micro-hardness was observed.

Impact of geomechanical processes on formation pressure during the long-term operation of gas deposits

Practical experience in the exploitation of hydrocarbon deposits confirms the presence of geomechanical processes and their significant impact on the state of gas-saturated rock massif. The purpose of the paper is to clarify the geological conditions for the formation of technogenic reservoirs and involving additional volumes of gas under the impact of geomechanical factors while operating the gas deposits. A detailed analysis of the known gas and gas condensate fields at the Eastern oil-and-gas-bearing region of Ukraine has been carried out. In particular, changes in formation pressure of in-operation hydrocarbon deposits have been determined, the values of geostatic and effective rock pressures have been calculated, the thickness of the gas column and the volume of gas reserves growth have been compared. All of the abovementioned have granted the possibility to determine the role of geomechanical processes in assisting to produce additional volumes of gas. A formation pressure increase in a number of gas condensate fields at a late stage of development confirms the action of the formation of additional sources of hydrocarbons due to the geomechanical factor. It is shown that at the first stage of the exploitation of hydrocarbon deposits, geological criteria play a decisive role in the formation of the gas-saturated massif condition. Over time, during field exploitation, geomechanical criteria are added to the geological ones, which help to involve additional volumes of gas. At the same time, the resulting increase in reserves at some deposits is up to 50% or more. It has been established that additional volumes of gas are directly proportional to the capacity of the gas-bearingness stage and the total volume of the gas-bearing structure. Multilayer deposits of sandy-aleuritic composition with a large number of productive horizons and without thick persistent reservoir-seal rocks within a single gas-bearingness stage with a hydrodynamic link between productive layers are the most promising from the viewpoint of the researched mechanism (favorable due to the formation of additional reservoirs of technogenic genesis).

UV Flash Sintering of Aerosol Jet Printed Silver Conductors for Microwave Circuit Applications

Recently, there has been significant research focus on the design of high functional density electronic systems, especially for 5G applications. In parallel, to address accurate, high-quality, fine-resolution circuit geometry requirements, increased research into additive manufacturing (AM) printing techniques, such as aerosol jet printing (AJP), has emerged. The issues are complicated by low-loss flexible substrates, such as liquid crystal polymers (LCPs), which are commonly used in the design of high-frequency circuits and systems. These substrates cannot be taken through high sintering temperature processes that are commonly required for silver inks. To avoid permanent damage, it is essential that the sintering temperature remains below the glass transition temperature ( ${\text{T}}_{g}$ ) of the substrates. Recent work on LCP substrates has demonstrated 10%–20% bulk silver (Ag) conductivity by using low-temperature thermal sintering techniques. This article investigates the use of a rapid ultraviolet (UV) flash annealing technique to achieve high conductivity of Ag on LCP for use in high-frequency circuits while maintaining the integrity of the substrate. Results are compared against thermally sintered films. The resulting conductivity was studied as a function of UV exposure time and energy, printed film thickness, surface roughness of the substrate, and multilayer deposition.

Design and fabrication of CuInS2/ZnS-based QLED for automotive lighting systems

This work reports the design, manufacturing and numerical simulation approach of a 6-pixel (4.5 mm2/pixel) electroluminescent quantum dot light emitting device (QLED) based on CuInS2/ZnS quantum dots as an active layer. The QLED device was fabricated using a conventional multi-layer thin film deposition. In addition, the electrical I–V curves were measured for each pixel independently, observing how the fabrication process and layer thickness have an influence in the shape of the plot. This experimental device, enabled us to create a computational model for the QLED based on the Transfer Hamiltonian approach to calculate the current density J (mA cm−2), the band diagram of the system, and the accumulated charge distribution. Besides, it is worth highlighting that the simulator allows the possibility to study the influence of different parameters of the QLED structure like the junction capacitance between the distinct multilayer set. Specifically, we found that the Anode-HIL interface capacitance has a greater influence in the I–V curve. This junction capacitance plays an important role in the current density increase and the QLED turn-on value when a forward voltage is applied to the device. The simulation enabled that influence could be controlled by the selection of the optimal thickness and transport layers during the experimental fabrication process. This work is remarkable since it achieves to fit simulation and experiment results in an accurate way for electroluminescent QLED devices; particularly the simulation of the device current, which is critical when designing the automotive electronics to control these new nanotechnology lighting devices in the future.