Deposition Geometry Research Articles

Quality assurance in additive manufacturing of thermoplastic parts: predicting consolidation degree based on thermal profile

Additive manufacturing is one of the most prominent and promising technologies in the field of manufacturing. However, its current dissemination is largely limited to the prototyping role due to inadequate quality assurance. The detailed process-geometry-property relationships are still to be unveiled, despite AM being a highly repetitive process. In this work, we aim to address this gap of insight by leveraging a numerical approach in predicting the thermal behaviour of the deposition to quantify the properties of the printed part. In particular, we present a prediction of the consolidation strength in fused filament fabrication. The proposed protocol is universal and can be applied to any deposition condition and geometry. This contribution has important implication for prefabrication quality assurance in AM as it allows to link process parameters with part properties for any geometry hence opening new avenues for process optimisation.

Quality assurance in additive manufacturing of thermoplastic parts: predicting consolidation degree based on thermal profile

Additive manufacturing is one of the most prominent and promising technologies in the field of manufacturing. However, its current dissemination is largely limited to the prototyping role due to inadequate quality assurance. The detailed process-geometry-property relationships are still to be unveiled, despite AM being a highly repetitive process. In this work, we aim to address this gap of insight by leveraging a numerical approach in predicting the thermal behaviour of the deposition to quantify the properties of the printed part. In particular, we present a prediction of the consolidation strength in fused filament fabrication. The proposed protocol is universal and can be applied to any deposition condition and geometry. This contribution has important implication for prefabrication quality assurance in AM as it allows to link process parameters with part properties for any geometry hence opening new avenues for process optimisation.

Finite element analysis of in-situ distortion and bulging for an arbitrarily curved additive manufacturing directed energy deposition geometry

With the recent rise in the demand for additive manufacturing (AM), the need for reliable simulation tools to support experimental efforts grows steadily. Computational welding mechanics approaches can simulate the AM processes but are generally not validated for AM-specific effects originating from multiple heating and cooling cycles. To increase confidence in the outcomes and to use numerical simulation reliably, the result quality needs to be validated against experiments for in-situ and post-process cases. In this article, a validation is demonstrated for a structural thermomechanical simulation model on an arbitrarily curved Directed Energy Deposition (DED) part: at first, the validity of the heat input is ensured and subsequently, the model’s predictive quality for in-situ deformation and the bulging behaviour is investigated. For the in-situ deformations, 3D-Digital Image Correlation measurements are conducted that quantify periodic expansion and shrinkage as they occur. The results show a strong dependency of the local stiffness of the surrounding geometry. The numerical simulation model is set up in accordance with the experiment and can reproduce the measured 3-dimensional in-situ displacements. Furthermore, the deformations due to removal from the substrate are quantified via 3D-scanning, exhibiting considerable distortions due to stress relaxation. Finally, the prediction of the deformed shape is discussed in regards to bulging simulation: to improve the accuracy of the calculated final shape, a novel extension of the model relying on the modified stiffness of inactive upper layers is proposed and the experimentally observed bulging could be reproduced in the finite element model.

Simulation and experimental studies on microstructure evolution of resolidified dendritic TiCx in laser direct deposited Ti-TiC composite

This paper describes the formation process of resolidified dendritic TiCx in laser direct deposited (LDD) Ti-40 vol%TiC composite via a combination of a thermodynamic consistent phase field (PF) model and an LDD model. The LDD model simulated the LDD process of this composite and provided the temporal and spatial temperature fields in the molten pool for the PF model, which predicted the solidification process of TiCx dendrites at different zones in the molten pool. The improved PF model introduced a grain index to link different crystallographic orientations for polycrystalline growth, which improved the computational efficiency by solving one PF equation instead of multiple phase variables. A two-sublattice model was utilized to establish the thermodynamic database of TiCx. The predicted temperature history, deposition geometry as well as the morphology of polycrystalline TiCx dendrites matched the experimental observation. As the temperature decreases, microsegregation occurred to the distribution of carbon over the dendrite where dendrite tips had a higher carbon concentration. Due to the increased undercooling, TiCx dendrites grew at an increased speed from top to bottom of the molten pool. Within 0.007 s, the dendrites were fully developed and inhibited further growth of each other.

Electrical Conductivity and Optical Properties of Pulsed Laser Deposited LaNi₅ Nanoscale Films.

This work presents pulsed laser deposition as a method to obtain unoxidized LaNi5 nanoscale films and describes their temperature and thickness dependent electrical conductivity and the spectral dispersions of some optical properties. AB5-type rare earth element (REE)-nickel compounds are currently studied from both theoretical and practical points of view. Special challenges are posed during the preparation of these nanomaterials, which can be overcome using finely tuned parameters in a preparation process that always involves the use of high energies. Film deposition was made by laser—induced vaporization, with short and modulated impulses and electro–optical tuning of the quality factor, mainly on glass and one SiO2 substrate. Deposition geometry dependent linear thickness increase, between 1.5–2.5 nm per laser burst, was achieved. Film structures and phase compositions were determined using XRD and discussed in comparison with films obtained by similar deposition procedures. Temperature and scale dependent properties were determined by studying electrical conductivity and optical properties. Electrical conductivity was measured using the four-probe method. The observed semiconductor-like conductivity for film thicknesses up to 110 nm can be explained by thermal activation of electrons followed by inter-insular hopping or quantum tunneling, which, on the other hand, modulates the material’s native metallic conductance. Films with thicknesses above this value can be considered essentially metallic and bulk-like. The spectral behaviors of the refractive index and absorption coefficient were deduced from differential reflectance spectroscopy data acquired on a broad ultraviolet, visible, near- and mid-infrared (UV-VIS-NIR-MIR) domain, processed using the Kramers-Krönig formalism. Their study led to the identification of the allowed interband transitions. Electronic behavior in the energy bands near the Fermi level and in the surface and interface-states was described, discussing the differences between experimental data and the classical free-electron theoretical model applied for the bulk intermetallic alloy, in correlation with theoretical optical properties or experimental X-ray photoelectron spectroscopy (XPS) results from references. However, the dielectric-like shape of the reflectance of the thinnest film was in accordance with the Lorentz–Drude model.

Crystalline Ti-nanostructures prepared by oblique angle deposition at room temperature

Nanostructured Ti thin films are fabricated by oblique angle deposition (OAD) in combination with electron beam evaporation in an ultrahigh vacuum chamber at room temperature on thermally and natively oxidized Si(100) substrates. The incidence angle θOAD of the incoming particle flux with respect to the substrate normal is varied between 70° ≤ θOAD ≤ 84°. This highly oblique deposition geometry leads to the formation of highly porous, thin, crystalline films consisting of separated Ti columns that are oriented toward the incoming particle flux. The influence of the incidence angle on the texture, morphology, and columnar tilt angles of these Ti thin films is investigated. It is found that the texture depends on the angle θOAD of the incoming particle flux. High-resolution transmission electron microscopy reveals that highly oblique deposited Ti columns tend to grow with single crystalline morphology. The orientation of the lattice planes in the Ti columns with respect to the substrate normal changes remarkably as the incidence angle is varied. Moreover, the orientation of the lattice planes differs from the growth direction of the columns. The samples are analyzed using x-ray diffraction measurements such as in-plane pole figure measurements and θ-2θ x-ray diffraction patterns, as well as by using transmission electron microscopy and scanning electron microscopy.

The effects of forced interpass cooling on the material properties of wire arc additively manufactured Ti6Al4V alloy

To achieve improved microstructure and mechanical properties, an innovative wire arc additive manufacturing (WAAM) process with forced interpass cooling using compressed CO2 was employed in this study to fabricate Ti6Al4V thin-walled structures. The effects of various interpass temperatures and rapid forced cooling on deposition geometry, surface oxidation, microstructural evolution, and mechanical properties of the fabricated part were investigated by laser profilometry, optical microscopy (OM), scanning electron microscopy (SEM), hardness testing and mechanical tensile testing. Results show that the microstructural evolution and mechanical properties of the deposited metal are not greatly affected by an increasing interpass temperature, however, the deposited wall tends to be widened, flattened and exhibit increased surface oxidation through visible coloration. When rapid forced cooling using CO2 is used between deposited layers, slightly higher hardness values and increased strength can be obtained. This is mainly attributed to the combined effects of less surface oxide and high density dislocation caused by the generation of large amounts of fine-grained acicular α within the microstructure. Furthermore, forced interpass cooling not only improves deposition properties, but also promotes geometrical repeatability and also improved manufacturing efficiency through the reduction of dwell time between deposited layers.

Comparative study of sculptured metallic thin films deposited by oblique angle deposition at different temperatures.

Metals with a wide range of melting points are deposited by electron beam evaporation under oblique deposition geometry on thermally oxidized Si substrates. During deposition the sample holder is cooled down to 77 K. It is observed that all obliquely deposited metals grow as tilted, high aspect ratio columns and hence with a similar morphology. A comparison of such columns with those deposited at room temperature (300 K) reveals that shadowing dominates the growth process for columns deposited at 77 K, while the impact of surface diffusion is significantly increased at elevated substrate temperatures. Furthermore, it is discussed how the incidence angle of the incoming particle flux and the substrate temperature affect the columnar tilt angles and the porosity of the sculptured thin films. Exemplarily for tilted Al columns deposited at 77 K and at 300 K, in-plane pole figure measurements are carried out. A tendency to form a biaxial texture as well as a change in the crystalline structure depending on the substrate temperature is found for those films.

Transient three-dimensional geometrical/thermal modelling of thermal spray: Normal-impinging jet and single straight deposits

A new time-dependent approach to the geometrical and thermal modelling of the deposit footprint in thermal spray processes is proposed. Based upon a three-dimensional finite-difference numerical technique, the model is composed of two integrated sections: a geometrical analysis, accounting for deposit geometry analytical prediction, and a thermal analysis that computes the system temperature history. Primary process factors for the simulation, i.e. plume distribution parameters, jet heat transfer properties and temperature-dependent deposition efficiency are determined in a preliminary stage of model application. Through computation of the simulated impact surface temperature at each instant during the simulation, the deposition efficiency-mediated growth of the deposit is accurately predicted at arbitrary values of torch feed speed. The model is flexible as it only relies on an initial calibration stage performed at a specific set of process parameters to be able to predict deposition geometries at arbitrary conditions, thus avoiding the need of complex simulations and/or knowledge of single splats impact properties. Moreover, this modelling approach has the potential to be extended to several thermal spray processes at arbitrary values of process parameters (e.g. torch design, materials, etc.), opening the way for spray automation in difficult-to-spray geometries and/or repair applications. The proposed modelling framework has been validated on Combustion Flame Spray (CFS) deposition of CoNiCrAlY alloy on stainless steel substrates, yielding low errors (<5% on average) in predicting the deposit footprint at various torch feed speeds.

Model-based analysis of thermal and geometrical effects in a microscale methanol fuel cell

This paper reports the development of a mathematical model to predict the performance of a microscale methanol fuel cell with a single fuel/electrolyte channel. Performance of the cell is investigated as a function of fuel stream inlet temperature and catalyst deposition geometry. The model is fit to experimental data by maximizing the coefficient of determination, R2. Results show that peak power density with regard to total exposed catalyst surface area is inversely proportional to catalyst deposition width and proportional to fuel stream temperature. For both parameters, the mathematical model was found to compare well with experimental results in the operating regime preceding and including maximum power density. The model presented here can be used to optimize these parameters during the design phase.

Localized segregation of gold in ultrathin Fe films on Au(001)

The growth of up to 10 monolayer-thick Fe films on a Au(001) surface was investigated during deposition at room temperature and during annealing using low-energy electron diffraction and x-ray photoemission spectroscopy as well as locally with low-energy electron microscopy and photoemission electron microscopy. The growth proceeds with a submonolayer of Au segregating to the surface of Fe, which is in agreement with previous studies. Annealing was found to be critical for the presence of Au on the Fe surface. Our findings show that Au segregation proceeds by the formation of cracks in the Fe film, starting at the annealing temperature of 190 {\deg}C, through which Au diffuses towards the surface. We explain the localized Au segregation with a shadowing effect due to the oblique deposition geometry. As a result, an Fe film with significantly improved roughness, but covered with a Au overlayer, is obtained. This study shows the necessity to employ spatially-resolved techniques to fully understand the growth modes of the layered epitaxial systems.

Effect of spherical blockage configurations on film cooling

With increasing inlet temperature of gas turbines, turbine blades need to be effectively protected by using cooling technologies. However, the deposition from the fuel impurities and dust particles in the air is often found inside film holes, which results in partial hole blockage. In this paper, the deposition geometry is simplified as a rectangular channel, and the effect of three blockage ratios is investigated by using the computational fluid dynamics. In addition, water droplets are also released from the coolant inlet to provide a comparison of the results with and without mist injection. It is found that the lateral film cooling effectiveness is reduced with increasing blockage ratio. For all the cases with the blowing ratio 0.6, 1% mist injection provides an improvement of the cooling performance by approximately 10%.

3D-finite element simulation and image processing based prediction of width and height of single-layer deposition by micro-plasma-transferred arc process

This paper reports on prediction of width and height of single-layer deposition by micro-plasma-transferred arc (μ-PTA) deposition process. It involved (i) 3D finite element simulation (3D-FES) of the melt pool using specific power of the micro-plasma, travel rate of worktable, deposition material feed rate, and temperature-dependent properties of the substrate material; (ii) calculation of its dimensions using image processing technique; and (iii) prediction of deposition width and height. The proposed approach was validated by comparing the predicted values with the corresponding experimental values for single-layer deposition of AISI P20 tool steel using different combinations of the μ-PTA deposition process parameters. Values of average errors as 6.11 and 7.15% for width and height of the single-layer deposition validates the simulation-predicted results. Study of influence of μ-PTA process parameters on deposition geometry revealed that micro-plasma power and travel rate of worktable significantly affect the width and height of the deposition layer. The proposed approach will be of great help in selecting the optimum values of deposition process parameters for any combination of substrate and deposition material thus improving accuracy and productivity of the additive layer manufactured parts.

Au nanostructure fabrication by pulsed laser deposition in open air: Influence of the deposition geometry.

We present a fast and flexible method for the fabrication of Au nanocolumns. Au nanostructures were produced by pulsed laser deposition in air at atmospheric pressure. No impurities or Au compounds were detected in the resulting samples. The nanoparticles and nanoaggregates produced in the ablated plasma at atmospheric pressure led to the formation of chain-like nanostructures on the substrate. The dependence of the surface morphology of the samples on the deposition geometry used in the experimental set up was studied. Nanocolumns of different size and density were produced by varying the angle between the plasma plume and the substrate. The electrical, optical, and hydrophobic properties of the samples were studied and discussed in relation to their morphology. All of the nanostructures were conductive, with conductivity increasing with the accumulation of ablated material on the substrate. The modification of the electrical properties of the nanostructures was demonstrated by irradiation by infrared light. The Au nanostructures fabricated by the proposed technology are difficult to prepare by other methods, which makes the simple implementation and realization in ambient conditions presented in this work more ideal for industrial applications.

Quantitative analysis and predictive engineering of self-rolling of nanomembranes under anisotropic mismatch strain

The present work presents a quantitative modeling framework for investigating the self-rolling of nanomembranes under different lattice mismatch strain anisotropy. The effect of transverse mismatch strain on the roll-up direction and curvature has been systematically studied employing both analytical modeling and numerical simulations. The bidirectional nature of the self-rolling of nanomembranes and the critical role of transverse strain in affecting the rolling behaviors have been demonstrated. Two fabrication strategies, i.e., third-layer deposition and corner geometry engineering, have been proposed to predictively manipulate the bidirectional rolling competition of strained nanomembranes, so as to achieve controlled, unidirectional roll-up. In particular for the strategy of corner engineering, microfabrication experiments have been performed to showcase its practical application and effectiveness. Our study offers new mechanistic knowledge towards understanding and predictive engineering of self-rolling of nanomembranes with improved roll-up yield.

Analytical modeling and experimental investigation of laser clad geometry

Based on rapid prototyping and laser cladding, laser material deposition (LMD) can be used to produce a near-net shape component in which the deposition quality and geometry characteristics of the previous layer, especially the first layer, determines the deposition quality and process stability of LDM-ed parts. A theoretical model for the first deposition layer in the LMD process has been developed to estimate the clad geometry (width, depth, and height) depending on the process parameters (laser power, powder feed rate, and scanning speed). This model contains two constants that are calculated based on the experimental results. The theoretical results are discussed and compared with the experimental data from the perspective of mass energy and line mass. The theoretical results are in accordance with the experimental results with reasonable accuracy that indicates the capability of predicting the clad geometry.

Phase-space dependent critical gradient behavior of fast-ion transport due to Alfvén eigenmodes

Experiments in the DIII-D tokamak show that many overlapping small-amplitude Alfvén eigenmodes (AEs) cause fast-ion transport to sharply increase above a critical threshold in beam power, leading to fast-ion density profile resilience and reduced fusion performance. The threshold is above the AE linear stability limit and varies between diagnostics that are sensitive to different parts of fast-ion phase-space. Comparison with theoretical analysis using the nova and orbit codes shows that, for the neutral particle diagnostic, the threshold corresponds to the onset of stochastic particle orbits due to wave-particle resonances with AEs in the measured region of phase space. The bulk fast-ion distribution and instability behavior was manipulated through variations in beam deposition geometry, and no significant differences in the onset threshold outside of measurement uncertainties were found, in agreement with the theoretical stochastic threshold analysis. Simulations using the ‘kick model’ produce beam ion density gradients consistent with the empirically measured radial critical gradient and highlight the importance of including the energy and pitch dependence of the fast-ion distribution function in critical gradient models. The addition of electron cyclotron heating changes the types of AEs present in the experiment, comparatively increasing the measured fast-ion density and radial gradient. These studies provide the basis for understanding how to avoid AE transport that can undesirably redistribute current and cause fast-ion losses, and the measurements are being used to validate AE-induced transport models that use the critical gradient paradigm, giving greater confidence when applied to ITER.

Flash-evaporation printing methodology for perovskite thin films

Printing solutions have attracted wide attention from various research fields, but thin films made by printing technologies still cannot match the quality of the films made by conventional thin-film deposition methods. In this study, a flash-evaporation printing (FEP) technology, which employed a freestanding carbon nanotube (CNT) flash evaporator, was developed to address this issue and to achieve a compact physical vapor deposition geometry. The target material precoated on the CNT flash evaporator was printed onto a substrate by gas-phase transportation. The FEP methodology presented a printable solution for hybrid perovskite thin films. The as-fabricated photovoltaic devices showed power conversion efficiencies of ∼10.3%, and the thin films were also utilized as potential photodetectors. In addition, this technology can also be used to print patterns and a wide variety of materials on large panels. The environmentally friendly and cost-effective FEP technology will be of significant benefit to printed electronics, organic electronics and future flexible electronics.

Combinatorial synthesis and high-throughput characterization of structural and photoelectrochemical properties of Fe:WO3 nanostructured libraries

Porous and photoelectrochemically active Fe-doped WO3 nanostructures were obtained by a combinatorial dealloying method. Two types of precursor materials libraries, exhibiting dense and nano-columnar morphology were fabricated by using two distinct magnetron sputter deposition geometries. Both libraries were subjected to combinatorial dealloying enabling preparation and screening of a large quantity of compositions having different nanostructures. This approach allows identifying materials with interesting photoelectrochemical characteristics. The dealloying process selectively dissolved Fe from the composition gradient precursor W–Fe materials library, resulting in formation of monoclinic single crystalline nanoblade-like structures over the entire surface. Photoelectrochemical properties of nanostructured Fe:WO3 films were found to be composition-dependent. The measurement region doped with ∼1.7 at % Fe and a film thickness of ∼ 900–1100 nm displayed highly porous WO3 nanostructures and exhibited the highest photocurrent density of ∼ 72 μA cm−2. This enhanced photocurrent density is attributed to the decreased bandgap values, suppressed recombination of electron–hole pairs, improved light absorption as well as efficient charge transport in the highly porous Fe-doped film with single crystalline WO3 nanoblades.

Glancing angle deposition of SiO2 thin films using a novel collimated magnetron sputtering technique

A novel deposition flux collimation technique has been explored in combination with glancing angle deposition geometry in radio frequency magnetron sputtering deposition technique with a motive to tailor the refractive index of silicon di-oxide thin film. In this technique, a collimating plate has been placed in parallel to the substrate at variable substrate to collimator distances (DSC=4mm, 6mm and 9mm) and the effect of DSC on various properties of the deposited film at different spatial locations on the substrate has been investigated. The use of such collimator was found to be highly effective in reducing the refractive index of the deposited film. A lowest refractive index of ~1.31 @ 550nm of SiO2 was achieved by using this novel collimation technique in combination with glancing angle deposition geometry which is not possible by glancing angle deposition geometry alone in the framework of non-directional deposition flux in magnetron sputtering technique. Variable angle spectroscopic ellipsometry (VASE) has been employed to accurately determine thickness and refractive index of the deposited films at various spatial locations of the sample. Ellipsometry data fitting model at different spatial locations has been verified by simulating the transmission spectrum based on the layer structure model obtained from ellipsometry modeling and then comparing it with that of the experimentally measured transmission spectra. For a given DSC an optimum location on the substrate surface was obtained to exhibit lowest refractive index. FTIR measurement showed no significant difference in bonding behavior of SiO among different representative spots of the deposited SiO2 samples. AFM measurement on various spatial locations indicates a possible strong correlation between variation of refractive index and the grain size which is again affected by the degree of collimation and ad atom kinetic energy at various spatial locations.