Maximum Achievable Thickness Research Articles

Surface Finishing and Coating Parameters Impact on Additively Manufactured Binder-Jetted Steel-Bronze Composites.

In this paper, electroless nickel plating is explored for the protection of binder-jetting-based additively manufactured (AM) composite materials. Electroless nickel plating was attempted on binder-jetted composites composed of stainless steel and bronze, resulting in differences in the physicochemical properties. We investigated the impact of surface finishing, plating solution chemistry, and plating parameters to attain a wide range of surface morphologies and roughness levels. We employed the Keyence microscope to quantitatively evaluate dramatically different surface properties before and after the coating of AM composites. Scanning electron microscopy revealed a wide range of microstructural properties in relation to each combination of surface finishing and coating parameters. We studied chempolishing, plasma cleaning, and organic cleaning as the surface preparation methods prior to coating. We found that surface preparation dictated the surface roughness. Taguchi statistical analysis was performed to investigate the relative strength of experimental factors and interconnectedness among process parameters to attain optimum coating qualities. The quantitative impacts of phosphorous level, temperature, surface preparation, and time factor on the roughness of the nickel-plated surface were 17.95%, 8.2%, 50.02%, and 13.21%, respectively. On the other hand, the quantitative impacts of phosphorous level, temperature, surface preparation, and time factor on the thickness of nickel plating were 35.12%, 41.40%, 3.87%, and 18.24%, respectively. The optimum combination of the factors' level projected the lowest roughness of Ra at 7.76 µm. The optimum combination of the factors' level projected the maximum achievable thickness of ~149 µm. This paper provides insights into coating process for overcoming the sensitivity of AM composites in hazardous application spaces via robust coating.

Fabrication, swift heavy ion irradiation, and damage analysis of lanthanide targets

Abstract One limiting factor in progress in the discovery and study of new superheavy elements (SHE) is the maximum achievable thickness and irradiation stability of current generation actinide targets. The desired thickness of targets, using full excitation function widths, cannot be achieved with current target technology, especially the widely used molecular plating (MP). The aim of this study was to transfer progress in the electrochemistry of lanthanides and actinides to the production of targets. Here, we report on the production of lanthanide targets using anhydrous electrochemical routes. In a first irradiation series, thulium thin films with areal densities up to 1800 μg/cm2 were produced using anhydrous triflate compounds and subjected to irradiation tests, using 6.0 MeV/u 48Ca ions at a fluence of 3.9 × 1014 ions/cm2 and 8.6 MeV/u 197Au ions at fluences in the range of 3.0 × 1011 to 1.0 × 1013 ions/cm2. The thin films were characterised before and after the irradiations using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX).

Method for the fabrication of thick multilayered nickel/iron oxide nanoparticle magnetic nanocomposites

Magnetic nanocomposites consisting of ferrite nanoparticles and magnetic metals have been of interest for use in power electronic components due to their ability to achieve relatively high magnetic permeabilities while also having low losses. Unfortunately, fabrication challenges limit the maximum achievable thickness of these films to ∼ 4 µm, though thicker films are desirable for increased power handling. To overcome these challenges this works seeks to demonstrate a fabrication method whereby thick composite films can be made by constructing sequential composite layers, performing electrophoretic deposition and electro-infiltration steps for each layer. Composite samples of iron oxide nanoparticles electro-infiltrated with nickel that are 1, 3, 5, 7, and 10 layers thick will be fabricated and characterized both structurally and magnetically. Structural measurements accomplished with SEM show that each layer appears to contribute 4 µm to the total thickness, with the one layer sample being 3.99 ± 0.12 µm thick and the ten layer sample being 39.19 ± 3.1 µm thick. Results show that the dc magnetic properties of these composites stay constant as thickness increases, having an average magnetic saturation of 464 kA/m, and coercivity of 2.5 kA/m. The ac magnetic properties similarly showed that the permeability of the composites also stayed consistent at 20. However, the dimensional resonance frequency of the composites decreased as thickness increased, lowering to ∼ 96 MHz for 1 layer (∼4 µm) to ∼ 8 MHz for 10 layers (∼40 µm), revealing a trade-off between thickness of a maximum operating frequency.

Laser Thermochemical High-Contrast Recording on Thin Metal Films.

Laser-induced thermochemical recording of nano- and microsized structures on thin films has attracted intense interest over the last few decades due to essential applications in the photonics industry. Nevertheless, the relationship between the laser parameters and the properties of the formed oxide structures, both geometrical and optical, is still implicit. In this work, direct laser interference patterning of the titanium (Ti) film in the oxidative regime was applied to form submicron periodical structures. Depending on the number of laser pulses, the regime of high contrast structures recording was observed with the maximum achievable thickness of the oxide layer. The investigation revealed high transmittance of the formed oxide layers, i.e., the contrast of recorded structures reached up to 90% in the visible range. To analyze the experimental results obtained, a theoretical model was developed based on calculations of the oxide formation dynamics. The model operates on Wagner oxidation law and the corresponding optical properties of the oxide–metal–glass substrate system changing nonlinearly after each pulse. A good agreement of the experimental results with the modeling estimations allowed us to extend the model application to other metals, specifically to those with optically transparent oxides, such as zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), and tantalum (Ta). The performed analysis highlighted the importance of choosing the correct laser parameters due to the complexity and nonlinearity of optical, thermal, and chemical processes in the metal film during its laser-induced oxidation in the air. The developed model allowed selecting the suitable temporal–energetic regimes and predicting the optical characteristics of the structures formed with an accuracy of 10%. The results are promising in terms of their implementation in the photonics industry for the production of optical converters.

Investigation of Flow-Formability of an AZ31 Magnesium Alloy

Flow-formability of a Ca-added AZ31 magnesium alloy tube is investigated. The flow-forming process is conducted at various temperatures (100–500 °C), thickness reductions (30–85%), and feed rates (0.1–0.56 mm/rev). Inner and outer surfaces of the tubes are heated by means of a thermal element embedded inside the mandrel and a radiation element, respectively. The formed tubes are visually inspected for the occurrence of cracking and fractures. Microstructures and tensile properties of the samples are analyzed by optical microscopy and tensile test, respectively. It is shown that deformation above 200 °C is required for sound processing with the occurrence of dynamic recrystallization (DRX). Up to 200 °C, the twinning-induced shear banding is the dominant phenomenon in microstructural evolution and responsible for the early strain localization and subsequent fracture. By increasing the temperature, the maximum achievable thickness reduction increases. However, at about 300 °C, the maximum thickness reduction reaches a limit value of about 76%. A twist in the deformed part of the tube occurs at greater thickness reductions. A simple analytical model is presented to analyze the occurrence of the twist phenomenon. Accordingly, a flow-formability map is proposed for the alloy. The DRX grain size is shown to follow a power law with the temperature compensated strain rate known as the Zener–Hollomon parameter. While the grain size is not affected by the feed rate, dimensional accuracy is deteriorated at feed rates over 0.2 mm/rev due to the diametral growth of the workpiece. Based on the tensile test results, by increasing the deformation temperature, the tensile strength increases and the ductility decreases, so that the sample processed at 500 °C shows a brittle fracture. The impacts of temperature on the strength and ductility are attributed to the combined effects of microstructural and texture evolutions during the flow-forming process.

INNOVATIONS IN MICRO/NANO PATTERNING USING TOOL-BASED METHODS

In recent years, the trend in miniaturization of products has been pervasive in areas such as information technology, biotechnology, and the environmental and medical industries. Micro/Nano patterning is the key supporting technology that has to be developed to meet the challenges posed by the requirements of product miniaturization and the industrial realization of nanotechnology. Micro/Nano patterning techniques can be carried out by techniquesbased on energy beams or solid cuttingtools (tool-based micro-machining). Tool-based micro/nano patterning is a relatively new area; however, over the lasttwo decades, owing to the predominant trend in miniaturization of products, Micro/Nano patterning using tool-based techniques has become a key supportive technology. The energybeam-based patterning process (electron-beam lithography) hassome limitations due to poor control of 3D structures, low material removal rate and low aspect ratio. Moreover, these processes requirespecial facilities, and the maximum achievable thickness is relatively small. Some of theselimitations can be overcome by a tool-based approach using ultra-precision machine tools and solid tools as cutting elements to produce the micro-features with well-controlled shape and tolerances. These Micro/Nano machining-based patterning techniques have been achieved through a paradigm shift in the ideas and processes of conventional machining. In this paper, an attempt has beenmade to present the recent innovations in tool-based micro/nano patterning processes.

Special Issue on Micro/Nano Machining – Processes, Systems and Control

In recent years, the trend in miniaturization of products is pervasive in areas such as information technology, biotechnology, environmental and medical industries. Micro-machining is the key supporting technology that has to be developed to meet the challenges posed by the requirements of product miniaturization and industrial realization of nanotechnology. Micro-machining techniques can be carried out by techniques based on energy beams (beam-based micro-machining) or solid cutting tools (tool-based micro-machining). Beambased micro-machining have some limitations due to poor control of 3D structures, low material removal rate and low aspect ratio. Moreover, these processes require special facilities and the maximum achievable thickness is relatively small. Some of these limitations can be overcome by tool-based micro-machining techniques using ultra precision machine tools and solid tools used as cutting elements to produce the micro-features with well controlled shape and tolerances. Tool-based micro-machining techniques essentially include precision machining processes as turning, milling, grinding and electrical discharge machining (EDM), whereby material removal is done at the micron level. The advantages of such processes are that almost every material such as metals, plastics and semiconductors can be machined with no limitation in machining shapes. Recently, combinations of conventional material removal processes, such as turning and milling, have been hybridized with non-conventional machining processes like EDM and EDG to fabricate micro-structures with high dimensional accuracy. In order to achieve meaningful implementation of compound micro-machining techniques three important areas are required to be addressed. These are: development of machine tools capable of performing compound micro-machining (i.e. micro turning, micro milling, micro EDM, etc. on the same machine and setup), understanding of process physics to provide relevant background for modeling,measurement, identification of control parameters and application of feedback control in order to control compound and hybrid manufacturing processes and development of compound and hybrid processes. An integrated effort in these areas is needed for successful implementation of tool-based micro-machining. An attempt has been made in this special issue to highlight latest articles on these areas. I would like to express my sincere appreciation to the authors, reviewers and editors for their invaluable contributions for this issue.

Optimizing the Production of Bacterial Cellulose in Surface Culture: Evaluation of Product Movement Influences on the Bioreaction (Part 2)

AbstractThe common way for the production of bacterial cellulose in surface culture is to use culture boxes or beakers with vertical walls, where the maximum achievable thickness is around 4 cm. In order to improve this, it is necessary to study factors limiting the production. In part 1, the mass transfer influences of the substrate have been investigated. Now we look at a “wall effect”. It is noted that the growing cellulose is in contact with the wall of the box or beaker, and moves downwards into the nutrient broth as time proceeds. Experiments have been carried out where this wall contact was eliminated and a constant rate of production over several weeks was found. This indicates the importance of understanding the role of the wall in the usual surface culture.

Determination of limits in deposition of adhering a-C films on silicon produced by pulsed laser deposition

We find a maximum achievable thickness of 600 nm for adhering a-C films deposited upon Si(111) and Si(100) substrates. The pulsed laser deposition method is used to produce hydrogen-free carbon films. Strong compressive stress in the films may lead to partial delamination, the stress-relief morphology depends on film thickness and deposition temperature. Deposition at room temperature shows delamination by buckling, cracking and sinusoidal buckling. Although films grown at 500 °C adhere very well to the silicon substrate, delamination is observed when the film thickness exceeds 600 nm. The failures are only partly located at the interface, mostly in the bulk of the silicon substrate.