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Multi Jet Fusion (MJF) is one of the newly developed additive manufacturing techniques, based on the use of powder bed fusion technology. It provides the opportunity to build up 3D, complex polymer geometries, without the need for support structures. This study evaluates the effect of build location across a 380 × 284 mm2 build plate, on both the dimensional accuracy and surface quality of polyamide 12 (PA12) parts printed using the MJF technique. The cube test samples were printed at each of the four corners and the center of the build plate. Dimensional deviations were determined using optical metrology measurements, while surface deviations were measured using 2D tactile and 3D optical profilometers. The density and the degree of crystallinity of the samples were determined using the Archimedes method and Differential Scanning Calorimetry analysis, respectively. Moreover, the morphology of the internal polymer surfaces was evaluated using Scanning Electron Microscopy. It was concluded that while overall printed part dimensions and crystallinity homogeneity were relatively uniform across the build plate, some variations were observed. Parts printed in particular, closer to the front of the build plate exhibited higher porosity, higher surface roughness along with the highest level of geometry deviation, compared with the CAD drawing. This is likely to be associated with some non- uniformities in heating and cooling of the PA12 polymer parts across the build plate. Science Foundation Ireland I-Form Advanced Manufacturing Research Centre

This study investigated the print homogeneity of Ti-6Al-4 V alloy parts, when printed over a large build area of 250 $$\times$$ × 250 $$\times$$ × 170 mm3, using a production scale laser powder bed additive manufacturing system. The effect of part location across this large build area was investigated based on printed part porosity, microstructure, hardness, and tensile properties. In addition, a Hot Isostatic Pressing (HIP) treatment was carried out on the as-built parts, to evaluate its impact on the material properties. A small increase in part porosity from 0.01 to 0.09%, was observed with increasing distance from the argon gas flow inlet, which was located on one side of the build plate, during printing. This effect, which was found to be independent of height from the build plate, is likely to be associated with enhanced levels of condensate or spatter residue, being deposited at distances, further from the gas flow. Despite small differences in porosity, no significant differences were obtained for microstructural features such as prior β grain, $$\alpha$$ α lath thickness, and phase fraction, over the entire build area. Due to this, mechanical performances such as hardness and tensile strengths were also found to be homogenous across the build area. Additionally, it was also observed based on the lattice constants that partial in-situ decomposition of $${\alpha }^{^{\prime}}\to \alpha +\beta$$ α ′ → α + β phases occurred during printing. Post HIP treatment result showed a decrease of 7 and 6%, in the yield strength (YS) and ultimate tensile strength (UTS), respectively, which was associated with a coarsening of $$\alpha$$ α lath widths. The potential of the laser powder bed system for large area printing was successfully demonstrated based on the homogenous microstructure and mechanical properties of the Ti-6Al-4 V alloy parts.

Additive manufacturing processes, such as Laser Powder Bed Fusion (L-PBF), facilitates the manufacture of porous biomaterials structures, which can be used for example to enhance bone tissue regeneration. In-situ process monitoring techniques such as meltpool emission monitoring are increasingly being applied for the monitoring of the l -PBF processes. This paper investigates the use of statistical anomaly detection to analyse in-situ process monitoring data obtained during l -PBF. In this study a Renishaw 500M was used to produce porous structures, using Ti-6Al-4 V feedstock powder. During the l -PBF process, a co-axial photodiode-based process monitoring system was utilised to generate data relating to both the meltpool and the operational behaviour of the laser. Porous structures were created with intentionally defective layers, whereby the laser power was selectively reduced at specific layers. Control samples were also created where no intentionally defective layers were created. In addition, an un-intentionally defective sample was also analysed. The Generalized Extreme Studentized Deviate (GESD) test was employed to identify any defective layers within the structures. When this approach was applied to data generated during the processing of the structures with reduced input energy layers, the number of defective layers identified corresponded exactly with the known amount. When the test was run on the meltpool data, corresponding to the un-intentional defective structure, 30 layers were identified as defective. When examined, the identified layers corresponded to the physical location of the defect within the sample. The results obtained in this study indicate that the GESD test is an effective and computationally inexpensive method of identifying defective layers created during the l -PBF process.

The present work is concerned with adhesive bonding of thermoplastic composites used in general aerospace applications, including polyphenylene sulfide (PPS), polyetherimide (PEI) and polyetheretherketone (PEEK) carbon fibre composites. Three different surface treatments have been applied to the PEEK, PPS and PEI-based composites in order to enhance the adhesion: atmospheric plasma, ultraviolet radiation (UV) and isopropanol wiping as a control. Water contact angles and free surface energies were measured following the standard experimental procedure based on the employment of three different liquid droplets. Infrared spectroscopy and X-ray photoelectron spectroscopy (XPS) were subsequently performed to characterize the surface chemistry of the samples after treatment. The single lap joints were manufactured and bonded by an Aerospace grade epoxy-based film adhesive originally developed for use on metals but with the ability to bond treated thermoplastics to good strength (supplied by Henkel Ireland). Quasi-static (QS) tests were conducted. The lap shear strength was evaluated, and the failure mechanisms of the different joints were examined for the range of surface treatments considered. It was found that the performances of the PEEK and PPS joints were considerably improved by the plasma and UV treatments resulting in cohesive and delamination failures, while PEI was unaffected by the plasma and UV treatments and performed very well throughout.

This study investigates the use of a statistical anomaly detection method to analyse in-situ process monitoring data obtained during the Laser-Powder Bed Fusion of Ti-6Al-4V parts. The printing study was carried out on a Renishaw 500M Laser-Powder Bed Fusion system. A photodiode-based system called InfiniAM was used to monitor the melt-pool emissions along with the operational behaviour of the laser during the build process. The analysis of the in-process data was carried out using an unsupervised machine learning approach called the Search and TRace AnomalY algorithm. The ability to detect defects during the manufacturing of metal alloy parts was demonstrated.

The nanocomposites of nickel oxide (NiO) and zirconia (ZrO2) (NZNCs) are particularly effective photocathodic materials in p-type dye-sensitized solar cells (p-DSCs) and tandem DSCs (t-DSCs). The t-DSCs obtained from P1-sensitized NZNC as photocathode and nanostructured titania (TiO2) sensitized with squaraine VG10-C8 as photoanode display overall efficiencies of ca. 2% at their best and, more importantly, produced photocurrents that surpassed systematically the values obtained from the parent devices having one photoelectrochemical interface. Such a finding is a consequence of the diminished resistance of the electrolyte the thickness of which is systematically smaller in t-DSCs with respect to parent DSCs with a single photoelectrochemical junction and same interelectrodic separation. The results here reported demonstrate that a careful combination of photoelectroactive electrodes can lead to an increase in current density of more than 15% in the t-DSC with respect to single-junction DSCs employing the same photoelectrodes provided that the whole thickness of the t-DSC is the same as in the single photoelectrode DSC and the photoelectrodes in the t-DSC do not incur in short-circuit phenomena through the electrolyte. For the successful realization of t-DSCs another important aspect is the complementarity of the absorption properties of the chosen colorants with the sensitized electrodes having similar absorbance in their respective ranges of optical absorption. The latter condition in t-DSCs makes possible the achievement of photoactivity spectra with a uniform efficiency of conversion in the whole visible range. For the attainment of efficient t-DSCs the two different photoelectrodes from parent DSCs (i.e. the devices at a single photoeletrochemical interface), should generate anodic and cathodic photocurrent densities with very similar values. Such a matching of photocurrents requires a careful selection of the thickness values for the photoelectrodes especially in case of materials with considerably different characteristics of charge injection. The approach here considered is a promising one for the assembly of quasi-transparent photoelectrochemical tandem devices operating as smart windows that convert light into electrical power. Science Foundation Ireland The Italian Ministry for Education, University and Research (MIUR) Remove first page of file - ROR

A low-cost, modular, robust, and easily customisable continuous liquid-liquid phase separator has been developed that uses a tubular membrane and annular channels to allow high fluidic throughputs while maintaining rapid, surface wetting dominated, phase separation. The system is constructed from standard fluidic tube fittings and allows leak tight connections to be made without the need for adhesives, or O-rings. The units tested in this work have been shown to operate at flow rates of 0.1 – 300 mL/min, with equivalent residence times from 80 to 4 seconds, demonstrating the simplicity of scale-up with these units. Further scale-up to litre per minute scales of operation for single units and tens of litres/minute through limited numbering up should allow these low cost concentric annular tubular membrane separators to be used at continuous production scales for pharmaceutical applications for many solvent systems. In principle this approach may be sufficiently scalable to be utilized in-line, in batch pharmaceutical manufacturing also, through further scale-up and numbering up of units. Several solvent systems with varying interfacial tensions have been investigated, and the critical process parameters affecting successful separation have been identified. An additively manufactured diaphragm based back pressure regulator was also developed and printed in PEEK, allowing highly accurate, adjustable, and chemically compatible pressure control to be accessed at low cost. Enterprise Ireland European Commission - European Regional Development Fund Science Foundation Ireland

Carbon–fibre epoxy composites are widely used for high-performance structural applications, where they are often exposed to harsh environments. The result of moisture ingress has been extensively studied, causing significant deterioration in the mechanical properties of these composites. This study evaluates the performance of five commercial hydrophobic coatings as protective layers, to inhibit moisture ingress into the composite. The coatings evaluated were NeverWet, HydroBead, SHC, Aculon and LiquidGlass. These coatings were characterised and compared in terms of hydrophobicity, surface energy, roughness and chemical composition. This study also evaluated two atmospheric plasma pre-treatments as a means of enhancing the adhesion performance of these coatings. The pre-treatments involved the use of an air plasma for the activation of the epoxy, as well as the plasma deposition of a nanometre thick SiOx interlayer coating. The durability and protective performance of the coatings, with and without the pre-treatments were then compared using an abrasion test as well as a water immersion study. The use of both plasma pre-treatments was found to enhance the adhesion and the abrasion performance of four out of the five coatings. Of the coatings and pre-treatments investigated, the LiquidGlass in conjunction with a SiOx-coating interlayer was found to exhibit the highest abrasion resistance. This was followed by the composite, which was plasma activated prior to the application of the Aculon coating. Only minor differences were observed when comparing the total moisture ingress (M%) of the epoxy, coated with the different hydrophobic layers. The composite coated with the Aculon and SiOx interlayer exhibited the least amount of moisture ingress, at 0.90%, compared to 1.08% of the uncoated specimen. The shear strength of epoxy composite, coated with the LiquidGlass, NeverWet and the activated Aculon combination, were within the range of the uncoated specimens, therefore the moisture ingress was reversible upon heating and no permanent damage to the epoxy–fibre interface was observed. It is concluded that, of the five coatings investigated, both the Aculon coating and LiquidGlass in combination with a SiOx interlayer coating, exhibit the greatest potential as protective layers for carbon fibre epoxy composites.

This study investigates the feasibility of a two-step process for the deposition of wear resistant, nickel-diamond nanocomposite coatings onto steel substrates. The steps involve the spray deposition onto stainless steel substrates, of nickel nanoparticles (40 - 60 nm diameter) and nanodiamonds (approx. 100 nm diameter). This is followed by the sintering of the nanoparticle coating using a microwave plasma. The 0.2 - 2 µm thick nanocomposite coatings exhibited very good adhesion on the steel substrates, based on Rockwell C indentation tests. The morphology and roughness of the coatings was found to be significantly influenced by the sintering temperature, which was investigated in the range 711 to 885 ᵒC. The effect of nanodiamond concentration and spray duration were also investigated. Of the parameters studied, the concentration of nanodiamond in the composite was the dominant factor controlling the wear performance of the coatings, when assessed based on pin-on-disc wear tests. Compared to the nickel coating and the steel substrate, the nickel-diamond nanocomposite coatings exhibited a 126 and 55-fold enhancement respectively, in wear performance. European Commission - Seventh Framework Programme (FP7) European Research Council Science Foundation Ireland

This study reports the development and performance of a pilot-scale barrel atmospheric plasma reactor for the atmospheric plasma activation treatment of polymer particles. The polymer particles treated included acrylonitrile butadiene styrene (ABS) and polypropylene (PP). These particles had diameters in the range of 3–5 mm. The initial studies were carried out using a laboratory-scale barrel reactor designed to treat polymer particle batch sizes of 20 g. A pilot-scale reactor that could treat 500 g particle batch sizes was then developed to facilitate pre-industrial-scale treatments. The effect of operating pulse density modulation (PDM) in the range 10%–100% and plasma treatment time on the level of activation of the treated polymers were then investigated. ABS revealed a larger decrease in water contact angle compared with PP after plasma treatment under the same conditions. The optimal treatment time of ABS (400 g of polymer particles) in the pilot-scale reactor was 15 min. The plasma-activated polymer particles were used to fabricate dog-bone polymer parts through injection molding. Mechanical testing of the resulting dog-bone polymer parts revealed a 10.5% increase in tensile strength compared with those fabricated using non-activated polymer particles. Keywords: Atmospheric pressure plasma, Barrel plasma reactor, Polymer particles, Water contact angle, X-ray photoelectron spectroscopy, Injection moulding

This study evaluates the use of a combination of Raman spectroscopy and optical profilometry as a surface characterisation technique for the examination of oxide layers grown on titanium metal substrates. The titanium oxide layers with thickness of up to 8 µm, were obtained using a low-pressure oxygen microwave plasma treatment of the titanium metal substrate. The effect of the microwave plasma processing conditions (input power, pressure and treatment time) on the Raman bandwidth, intensity and peak position was evaluated. Also, the effect of these processing conditions on the surface roughness parameters (Sa, Sdq, Ssk and Sku) of the oxide layers was investigated. Analysis of the peak positions of Eg and A1g modes indicated that the effects of input power and chamber pressure was to induce a shift towards the lower frequency with increasing input power and pressure (1–2 kPa). The intensity of the Raman bands was found to be dependent on the morphology and surface chemistry of the oxide layer. The intensity of Raman band (A1g), was found to be particularly influenced by the average surface roughness (Sa) and the crystallite size. Exponential and polynomial relations were found to correlate with these properties. A two-latent variable Partial Least Squares Regression model developed on Raman spectral data could predict surface roughness with a coefficient of determination (R2) of approx. 0.87 when applied to the testing of an independent set of titanium oxide test coatings. Keywords: Titanium oxidation, Raman spectroscopy, Surface roughness parameters, Raman intensity, Microwave plasma, Raman mapping

This paper examines a novel additive manufacturing (AM) technique for the fabrication of woven multilaminate composites. The printing studies were carried out using nylon coated carbon fibre Tow in the form of a filament. This pathing technique allows for a woven structure to be integrated with features (such as notches) previously only possible through destructive machining processes. In order to evaluate the performance of these printed composites, bearing response studies were carried out. 6 mm holes were routed into a multilaminate woven composite structure, the resulting part’s mechanical performance was then tested and compared with specimens which had been drilled post printing. Specimen were comprised of 9 woven laminates stacked to form a 3.1 mm thick standardised test coupon for single and double shear testing (ASTM D5961). Current industry standard machining techniques result in fibre discontinuity and damage, this results in suboptimal mechanical performance of composite components. These new ‘Tailor Woven’ specimens achieved single shear bearing strengths of up to 214 MPa and double shear bearing strengths of up to 276 MPa. These values represent an increase of 29% and 63% respectively compared with equivalent composites in which the hole had been drilled. Science Foundation Ireland Irish Manufacturing Research

A novel technique for the fabrication of woven composites using additive manufacturing (AM) is presented and evaluated. To-date fibre reinforced composites deposited by AM exhibit highly anisotropic properties as the individual layers do not interact, this study helps address this by printing of a 0/90 woven structure into one layer to aid in stress distribution. A fibre path generator was created utilising Gcode to emulate the weft-warp components of a woven construction using a continuous carbon fibre filament. This new pathing technique also allows for a woven structure to be integrated with features (such as notches) previously only possible through destructive machining processes. In order to evaluate the performance of the printed composites, open hole tensile studies were carried out in which 6 mm holes were routed into the composite structure and the resulting part’s mechanical performance were compared with specimens which had been die punched as well as an unnotched control group. The latter exhibited strengths equivalent to 49% that of unnotched specimen. In contrast the specimens with woven holes exhibited strengths which were 44% higher, just 7% lower than the strength achieved for the unnotched specimens. Digital image correlation (DIC) analysis also demonstrated significantly reduced strain concentration around the printed hole perimeter, compared with that for the die punched hole.

This work studied the effects of adding short basalt fibers (BFs) and multi-walled carbon nanotubes (MWCNTs), both separately and in combination, on the mechanical properties, fracture toughness, and electrical conductivity of an epoxy polymer. The surfaces of the short BFs were either treated using a silane coupling agent or further functionalized by atmospheric plasma to enhance the adhesion between the BFs and the epoxy. The results of a single fiber fragmentation test demonstrated a significantly improved BF/epoxy adhesion upon applying the plasma treatment to the BFs. This resulted in better mechanical properties and fracture toughness of the composites containing the plasma-activated BFs. The improved BF/epoxy adhesion also affected the hybrid toughening performance of the BFs and MWCNTs. In particular, synergistic toughening effects were observed when the plasma-activated BFs/MWCNTs hybrid modifiers were used, while only additive toughening effects occurred for the silane-sized BFs/MWCNTs hybrid modifiers. This work demonstrated a potential to develop strong, tough, and electrically conductive epoxy composites by adding hybrid BF/MWCNT modifiers.

Additive Manufacturing (AM) is increasingly used for the fabrication of metallic components used in the medical device, aerospace and automotive industries. With the wider adoption of AM in these sectors, there is an increased demand for the in-situ process monitoring of the build process. This study investigates the performance of a photodiode based, co-axial in-situ process monitoring (PM) system, during the Selective laser melting (SLM) of Ti6Al4V alloy parts. The PM system measures the optical and thermal emissions created by the meltpool, as well as the intensity and stability of the laser during the SLM process. The process monitoring software then creates a 2D or 3D representation of the part, based on the signal intensity recorded.The Ti6Al4V alloy parts were manufactured containing internal cavities, with diameters/width’s in the range of 200–600 mm, while varying the input energy between 32.9 and 131.6 J/mm3. A close correlation was established between the laser monitoring photodiode signal intensity and the laser energy input. Along with this, an increase in signal intensity recorded, by the meltpool monitoring photodiode, was observed when the first capping layer above a cavity, was processed by the laser. Further to this, it wasshown that only the first layer was influence by the overhang, with the signal generated by the layersdirectly above this remaining unaffected. In addition to providing data on the laser energy during thebuild process, the PM system also provided valuable information regarding the intensity of the meltpool.A comparison was made between the dimensional measurements obtained using PM software, with those obtained through CT scanning of the parts, post build. It was found that for the 600 mm cavities that the measurements were, at best, within 1.7% of each other. This closeness of such measurements however decreased very significantly as the size of the cavities decreased, with a variation for example, of up to 32%been obtained, for 400 mm cavities. Science Foundation Ireland

The present work investigates the effects of geometry and laser power on the porosity and melt pool formation for 316L stainless steel samples fabricated using the laser powder bed fusion (LPBF) technique. Both cylindrical and conical parts with the same heights were processed at a range of laser powers (60–70 W). An analytical model was used to select a suitable laser power, based on the established processing parameters, but also to predict the resultant melt pool dimensions. Based on the combination of experimental work and mathematical modelling, a novel geometrical factor is proposed, which was demonstrated to successfully improve the implemented model. A decrease in melt pool depths towards the building direction was determined in all the printed samples; this was however not predicted by the mathematical model. Furthermore, the variation in heat extraction exhibited by the conical and cylindrical parts allows the correlation between the melt pool dimensions and the geometrical factor. Finally, the influence of conical and cylindrical shapes on part hardness with increasing distance from the build plate was demonstrated; based on this comparison, it was determined that the cone geometries exhibit both a higher Vickers hardness and density. European Commission - European Regional Development Fund Science Foundation Ireland

Selective Laser Melting allows for the creation of intricate porous structures, that possess favourable biological properties. These structures are known as porous biomaterials. The focus of this paper is to evaluate the use of an in-line photodiode based process monitoring system, for the monitoring of the operational behaviour of the laser, and to correlate this with the resultant parts mechanical performance. In this study the production scale Renishaw 500M was used to produce porous structures, using Ti–6Al–4V feedstock powder. During the process, a co-axial process monitoring system was utilised to generate data relating to both the meltpool and the operational behaviour of the laser. An advanced scanning technique was used to produce the structures, whereby the laser parameters determine the strut dimensions. In this study, the laser input energy was reduced by 33%, 66% and 100%, at specific layers within the structures. Computer Tomography and Scanning Electron Microscopy was utilised to characterise the affected struts within the structures, while quasi-static compression testing was used to determine the structure's mechanical properties. It was demonstrated that as the level of input energy decreased and the number of affected layers increased, a corresponding decrease in the load bearing capacity of the structures occurred. With the structures experiencing a significant loss in strength also exhibiting a change in the failure mode during compression testing. Data generated during the processing of such structures was compared to the data generated during the processing of control structures, with the difference between the two been calculated on a layer-by-layer basis. A clear correlation was demonstrated between the total level of deviation between the two signal sets and a reduction in the load bearing capacity of the structures. This indicates that by comparing build data to a benchmark data set, valuable information relating to the structural integrity of the porous structures can be obtained. European Commission - European Regional Development Fund Science Foundation Ireland Croom Precision Medical Ltd.

Chemically resistant parts for flow chemistry, with integrated mixing elements have been produced using the 3D printing process of fused filament fabrication, from poly(etheretherketone). Poly(etheretherketone) has greater chemical resistance than common fused filament fabrication materials such as acrylonitrile butadiene styrene, polypropylene, or even high-performance plastics like poly(etherimide), in addition to having superior thermal resistance and excellent mechanical strength. Printed reactors were demonstrated to be suitable for liquid–liquid extraction and flow chemistry and to be capable of withstanding pressures of at least 30 bar allowing superheated solvents to be used. Burst tests in simple geometries of 20 minute duration have indicated that increased operating pressures of up to 60 bar could be accommodated in future reactor designs. The ability to use fused filament fabrication for these reactors allows highly customisable, cost effective flow reactors and equipment to be fabricated on relatively inexpensive benchtop scale printers. X-ray microcomputed tomography was utilised to non-invasively image and verify the internal structure of the prints to ensure fidelity in reactor fabrication. This non-invasive method of equipment validation shows potential in helping to demonstrate regulatory compliance for bespoke additively manufactured components, for example in continuous pharmaceutical manufacturing where the methods and printer used in this work should be sufficient to produce, (continuous) manufacturing scale equipment. Enterprise Ireland Science Foundation Ireland Pfizer Inc.

This study investigated the effect of laser power on the properties of Ti-6Al-4V alloy parts produced by additive manufacturing. The printing study was carried out using the laser beam powder bed fusion (PBF-LB) technique (Renishaw RenAM 500M). The laser power was altered in the range of 100–400 W, in order to evaluate the effects of changing the input energy received by the powder particles on the as-built parts. The impact of changing laser power was investigated based on printed part dimensions, porosity, morphology, micro/nanostructure, wear, hardness and tensile properties. It was determined that laser power has a direct influence on part dimensional accuracy, with larger dimensions compared with CAD design under the processing conditions used, obtained at higher powers i.e. 2 % at 250 W, while 4 % at 400 W. The border thickness for rounded edges was found to be ∼0.2 ± 0.06 mm greater than that obtained for straight edges, printed on the same quarter circle samples. A more homogeneous morphology, along with an improved surface finish, was obtained for parts printed using the higher laser powers. The microstructure of the high power alloy, was characterised by wider prior β grains with longer and finer needles, along with superior as-built mechanical properties, when compared to parts produced using lower laser power (100 W). Additionally, shifts in the XRD peak position for parts printed at the lower and higher laser powers, indicate some reduction in the level of residual stress for parts produced at higher powers. Science Foundation Ireland Croom Precision Medical Ltd.

Additive manufacturing is being increasingly used in the fabrication of Ti-6Al-4V parts to combine excellent mechanical properties and biocompatibility with high precision. Unfortunately, due to the build-up of thermal residual stresses and the formation of martensitic structure across a wide range of typical processing conditions, it is generally necessary to use a post-thermal treatment to achieve superior mechanical performance. This investigation aims to obtain a deeper understanding of the microManostructural evolution (alpha' martensite phase decomposition), accounting for the kinetics of phase transformation during the heat treatment of 3D-printed Ti-6Al-4V alloy. As the mechanism of phase transformation and stress relaxation is still ambiguous, in this study the changes in crystal lattice, phase, composition and lattice strain were investigated up to 1000 degrees C using both in situ high temperature X-ray diffraction (XRD) and transmission electron microscopy (TEM). Based on the result a mechanism of phase transformation is proposed, via the accommodation/substitution of Al, V and Ti atoms in the crystal lattice. The proposed mechanism is supported based on elemental concentration changes during heat treatment, in combination with changes in crystal structure observed using the high temperature XRD and TEM measurements. This study provides a deeper understanding on the mechanism of phase transformation through martensitic decomposition, as well as a deeper understanding of the influence of post-thermal treatment conditions on the alloy's crystal structure. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Over the last 20 years microwave power supplies in domestic microwave ovens have increasingly found applications in plasma reactors for processing of functional carbon-based nanostructures for engineering materials, electronics and biomedical applications. However, the packaged magnetrons used in the microwave ovens are known to suffer from moding due to frequency pushing and pulling, both of which may limit the efficiency of the plasma treatment process. This paper explores patent records for high voltage doubler circuits, coupled to the cathode filament heater circuit as the magnetron pushing source and the multimode resonant cavity plasma load as the pulling source. These circuits are compared with microwave oven plasma reactor circuits published in peer reviewed journals. This study highlights that a number of academic research groups have investigated power supply design parameters such as the input transformer voltage, as well as the power level using different capacitors values, as a result the transformer output is poorly described. Identification of moding within the plasma reactors due to magnetron warm-up time and changing cavity load conditions is also poorly reported. This work attempts to address this information gap on microwave oven plasma processes, through the extraction of reports on a packaged magnetron warm-up times and near-field E-probe mode measurement within the Cambridge Fluid Systems MRC 200 plasma reactor using a argon and hydrogen plasma.

This study investigates the material and mechanical properties of both polyamide 12 (PA12) and reinforced glass bead PA12 composites, fabricated using a production scale additive manufacturing (AM) process. The printing studies were carried out using the production scale, Multi Jet Fusion powder bed fusion process. The study demonstrated that the chemical functionality and the thermal properties of the printed PA 12 parts and the glass bead composite, were similar. Almost identical infrared spectra were obtained demonstrating the same chemical functionality. Based on DSC measurements, the melting temperature was 184°C and 186°C and the associated cooling cycle temperature was 150°C and 146°C for the composite and the PA12 respectively. The percentage crystallinity of the glass bead composite was 24 %, compared with the 31% obtained for the PA12 only parts. Based on mechanical tests, the addition of glass beads increased the tensile and flexural modulus by 85% and 36% and lowered the tensile and flexural strength by 39% and 15% respectively. The effect of print orientation during the MJF process was evaluated based on porosity and mechanical performance. Using X-ray micro computed tomography, it was demonstrated that the porosity of the PA12 and composite parts were less than 1%. Polymer and composite parts printed in the ZYX orientation were found to exhibit both the lowest porosity and highest mechanical strengths European Commission - Seventh Framework Programme (FP7) Science Foundation Ireland

The enhancement of photoelectrochemical conversion efficiency of p-type dye-sensitized solar cells (p-DSSCs) is necessary to build up effective tandem devices in which both anode and cathode are photoactive. The efficiency of a p-type device (2.5%) is roughly one order of magnitude lower than the n-type counterparts (13.1%), thus limiting the overall efficiency of the tandem cell, especially in terms of powered current density. This is mainly due to the recombination reaction that occurs especially at the photocathode (or Indium-doped Tin Oxide (ITO))/electrolyte interface. To minimize this phenomenon, a widely employed strategy is to deposit a compact film of NiO (acting as a blocking electrode) beneath the porous electrode. Here, we propose electrodeposition as a cheap, easy scalable and environmental-friendly approach to deposit nanometric films directly on ITO glass. The results are compared to a blocking layer made by means of sol-gel technique. Cells embodying a blocking layer substantially outperformed the reference device. Among them, BL_1.10V shows the best photoconversion efficiency (0.166%) and one of the highest values of fill factor (approaching 46%) ever reported. This is mainly due to an optimized surface roughness of the blocking layer assuring a good deposition of the porous layer. The effectiveness of the implementation of the blocking layer is further proved by means of Electrochemical Impedance Spectroscopy.

Selective Laser Melting (SLM) facilitates the formation of complex, stochastic or non-stochastic, metallic cellular structures. There is a high level of interest in these structures recently, particularly due to their high strength to weight ratios and osteoconductive properties. While the ability to in-situ monitor the SLM process is of key importance for future quality control methods. In this work lattice structures were fabricated, using the single exposure scanning strategy, on a Renishaw 500M SLM machine. The build process was also monitored using a co-axial in-situ process monitoring system. It was found that by increasing the energy input, through increasing the laser power and/or exposure time, the lattice strut diameters, within the 1.5 mm diamond unit cells, increased from 119 to 293 μm, resulting in the major pore diameter decreasing from 1106 to 932 μm. The effect of systematically altering the laser beam spot size on the cellular structures was also evaluated. It was observed that by doubling the laser beam spot size, that there was a 17% reduction in strut diameter and a 22% reduction in mechanical strength of the structures. It was also observed that at constant energy input levels, the lattice structures created using a focused laser exhibited an 81% lower mechanical strength than the structures created using a de-focused laser. Thus, demonstrating that the mode of energy input is critical to achieving the desired strength in these structures. Based on the outputs from the in-situ monitoring system, a broadly linear correlation was obtained between the laser input energy, the associated process monitoring data generated and the mechanical strength of the lattice structures. European Commission - European Regional Development Fund Science Foundation Ireland

Additive manufacturing (AM) is rapidly becoming one of the most popular manufacturing techniques for short run part production and rapid prototyping. AM encompasses a range of technologies, including powder bed fusion (PBF) process. The purpose of this paper is to evaluate and benchmark the mechanical performance of polyamide 12 (PA12) parts, fabricated using a production scale powder bed fusion printing process (HP Multi Jet Fusion printing process). This system has a build volume is 380 × 254 × 350 mm. The printed polymer parts were examined to determine their hydrophobicity, morphology, porosity and roughness. Chemical and thermal properties of the PA12 parts were also evaluated using attenuated total reflection infrared spectroscopy (ATR FT-IR), x-ray photoelectron spectroscopy (XPS) and differential scanning calorimetry (DSC). The study highlights the influence of build orientation on the tensile (ISO 527-1:2012) and flexural (ISO 178:2010) properties. In terms of tensile strength, the parts exhibited isotropic behaviour with a maximum tensile strength of 49 MPa. In terms of flexural testing, the build orientations had a significant effect on the strength of the printed part. The Z orientation exhibited a 40% higher flexural strength, when compared to that of the X orientation. The maximum flexural strength observed was 70 MPa. The results of this rapid, production scale AM study are compared with previous studies that detail the mechanical performance of PA12, fabricated using PBF processes, such as selective laser sintering. European Commission - Seventh Framework Programme (FP7) Science Foundation Ireland

The static water contact angle (CA) quantifies the degree of wetting that occurs when a surface encounters a liquid, e.g. water. This property is a result of factors such as surface chemistry and local roughness and is an important analytical parameter linked to the suitability of a surface for a given bioanalytical process. Monitoring the spatial variation in wettability over surfaces is increasingly critical to analysts and manufacturers for improved quality control. However, CA acquisition is often time-consuming because it involves measurements over multiple spatial locations, independent sampling and the need for a single instrument operator. Furthermore, surfaces exposed to local environments specific to an intended application may affect the surface chemistry thereby modifying the surface properties. In this study, Attenuated Total Reflection-Fourier Transform Infrared (ATR-FTIR) chemical imaging data acquired from wet and dry polymer surfaces were used to develop multivariate predictive models for CA prediction. Partial Least Squares Regression (PLSR) models were built using IR spectra from surfaces presenting differences in the experimentally measured CA in the range 16°-141°. The best performing PLSR models were locally developed and combined to make a global model utilising wet IR spectra which performed well (R2p = 0.98, RMSECV ∼ 5°) when tested on an independent experimental set. This model was subsequently applied to IR spectra acquired from a surface exhibiting spatial differences in surface chemistry and the CA with a reasonable confidence and precision (prediction error within 10°), demonstrating the potential of this method for prediction of the spatially varying CA as a non-destructive in-line process monitoring technique. European Commission - Seventh Framework Programme (FP7)

Process monitoring and sensing is widely used across many industries for quality assurance, and for increasing machine uptime and reliability. Though still in the emergent stages, process monitoring is beginning to see strong adoption in the additive manufacturing community through the use of process sensors recording a wide range of optical, acoustic and thermal signals. The ability to acquire these signals in a holistic manner, coupled with intelligence-based machine control has the potential to make additive manufacturing a robust and competitive alternative to conventional fabrication techniques. This paper presents an overview of the state-of the art of in-situ process monitoring in laser powder bed fusion processes and highlights some current limitations and areas for advancement. Also presented is an overview of real-time process control requirements, which when combined with the emergent process monitoring tools, will eventually allow for in-depth process control of the powder bed fusion process, which is essential for wide-scale industrial credibility and adoption of this technology.

In this study, a functionally graded material (FGM) was fabricated using a powder bed fusion additive manufacturing technique. The FGM evaluated was Ti–6Al–4V, due to its importance in the medical device and aerospace sectors. The microstructure at selected build locations was analysed using both scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) techniques, where a gradient was observed both in terms of grain morphology and texture intensity. In addition, nanoindentation on the FGM sample shows a near quadratic shaped smooth gradient elastic modulus profile, with peak values at the midpoint of the gauge length. A tensile test to failure was conducted on the FGM sample with the aid of digital image correlation for surface strain analysis. Results show a gradient of local maximum principal strain in the highly {0001} textured section, while the reference sample in the control group shows a near-uniform strain distribution throughout the whole gauge length. A crystal plasticity finite element (CPFE) model was developed to explain the effect of texture on the mechanical properties adopting the microscopy-informed texture intensity gradient. Despite exhibiting higher elastic modulus (in the transverse direction, as measured via nanoindentation) the mid-section of the gauge length had a higher concentration of strain when loaded in the axial tensile direction, corresponding to build direction. The microscopy and computational modelling show that this apparent contradiction was explained via a high intensity of {0001} texture in the mid-section, leading to favourable conditions for axial strain accumulation.

Additively Manufactured (AM) titanium (Ti) components are routinely post-thermal heat treated (HT), to reduce internal stresses, as well as to obtain more desirable microstructural features, yielding improved mechanical performance. Currently, there is no consensus on the optimum HT method for AM Ti-6Al-4V, as the mechanism for the main phase transformation ( α ′ (martensite) → α + β (equilibrium)) is still ambiguous. In this study, stress relaxation and phase transformation in the alloy are investigated in detail, via isothermal heat treatments and in situ high temperature X-ray Diffraction (XRD). The latter was carried out at heating rates of 5 and 200 °C/min. The relationship between crystallographic evolution during isothermal treatments and mechanical behaviour was determined. Isothermal holding at 400 °C resulted in an increase in ultimate tensile strength (UTS) and yield strength (YS) by 3.4% and 2.1%, respectively, due to the relief of tensile microstrain. It was found that isothermal treatment conducted between 550 and 700 °C promotes martensitic decomposition, resulting in the formation of a transitional - α t r phase, which has an asymmetrical hexagonal crystal lattice. The formation of this α t r phase was determined to be the main factor contributing to a major decrease in ductility.

Oxides of titanium have found applications in areas such as energy capture, cell attachment to biomedical devices and as catalytic surfaces. This study demonstrates that the use of a microwave plasma can significantly enhance both titanium oxide formation and growth rate, compared with those obtained using conventional furnace treatments. The ability of microwave plasma treatments to control the thickness and morphology of oxides grown on titanium substrates is demonstrated. For a fixed plasma treatment time of 10 min, depending on the input power and treatment pressure, the oxide-layer thickness of between 0.69 and 10.45 μm were obtained. The associated roughness (Ra) values were in the range of 0.11–0.67 μm. This study demonstrated that the morphology of the oxide-layer was particularly influenced by the input power to the plasma, while oxide thickness was depended on the treatment pressure and time. The mechanism of titanium oxidation was also investigated and based on the homogeneous oxidation observed across the titanium metal surface (under the oxide layer), it is also concluded that the mechanism of oxidation is ‘general corrosion’.

This study evaluates the performance of continuous carbon, Kevlar and glass fibre reinforced composites manufactured using the fused deposition modelling (FDM) additive manufacturing technique. The fibre reinforced nylon composites were fabricated using a Markforged Mark One 3D printing system. The mechanical performance of the composites was evaluated both in tension and flexure. The influence of fibre orientation, fibre type and volume fraction on mechanical properties were also investigated. The results were compared with that of both non-reinforced nylon control specimens, and known material property values from literature. It was demonstrated that of the fibres investigated, those fabricated using carbon fibre yielded the largest increase in mechanical strength per fibre volume. Its tensile strength values were up to 6.3 times higher than those obtained with the non-reinforced nylon polymer. As the carbon and glass fibre volume fraction increased so too did the level of air inclusion in the composite matrix, which impacted on mechanical performance. As a result, a maximum efficiency in tensile strength was observed in glass specimen as fibre content approached 22.5%, with higher fibre contents (up to 33%), yielding only minor increases in strength.

WC-Co metal matrix composite is frequently applied in the form of coating to prevent the underlying base materials from serious wear. Cold spray has been successfully used to produce WC-Co coatings in recent years, showing great potential. However, due to the lack of sufficient Co matrix phase for plastic deformation, the fabrication of cold sprayed WC-Co coating naturally requires expensive propulsive gas or very high working parameters, significantly increasing the manufacturing difficulty and cost. This paper aims to use conventional high pressure cold spray to fabricate WC-Co-Ni wear-resistance coatings under moderate working parameters, and to clarify the coating formation mechanism. To achieve this objective, mechanically mixed porous WC-17Co and dense Ni powders were selected as the feedstock with different WC mass fractions, F1 (41.5 wt%), F2 (64.5 wt%) and F3 (74.7 wt%). Working parameters were set at a moderate level (nitrogen, 3.0MPa and 350°C). Experimental results show that the WC reinforcements had no phase transformation and were completely retained in the WC-Co-Ni coatings as compared with in the feedstock. Fracture of the porous WC-Co particles during the deposition process was found to be the reason for such high WC retainability, dominating the coating formation mechanism. Tribological performance test shows that the coating hardness, toughness and wear-resistance performance improved as the WC content increased from the F1 to F3 coating. Wear mechanism analysis demonstrates that the F3 coating exhibited a completely different wear mechanism from the F1 and F2 coatings, thus the F3 coating had the best wear-resistance performance. Keywords: Kinetic spray, Tungsten carbide cobalt, Nickel, Tribology, Sliding wear rate, Tribofilm

In this paper, cold spray in conjunction with powder ball milling was used to fabricate GNP-reinforced copper MMC coatings without crossing materials’ melting points. As a result, non-agglomerated and uniformly-distributed GNPs were included in the cold sprayed MMC powders and coating. No phase change and oxidation occurred during the coating fabrication. The friction coefficient of GNP-reinforced MMC coating reduced by approximately 20% compared to bulk copper. The cold sprayed MMCs also resulted in lower friction coefficient than spark plasma sintered MMCs.

Diamond-reinforced metal matrix composites (DMMC) have great potential for wear-resistance applications due to the superior hardness of the diamond component. Cold spray as an emerging coating technique is able to fabricate coatings or bulk materials without exceeding the material melting point, thereby significantly lowering the risk of oxidation, phase transformation, and excessive thermal residual stress. In this paper, thick DMMC coatings were deposited onto aluminum alloy substrate via cold spray of three feedstock powders: copper-clad diamond and pure copper, and their mixtures. It was found that, due to its low processing temperature, cold spray is able to prevent graphitization of the diamond in the DMMC coatings. Further to that, the original diamond phase was almost completely retained in the DMMC coatings. In case of the coatings fabricated from copper-clad diamond powders only, its mass fraction reached 43 wt.%, i.e. value higher than in any previous studies using conventional pre-mixed powders. Furthermore, it was found that the added copper content powders acted as a buffer, effectively preventing the fracture of the diamond particles in the coating. Finally, the wear test on the coatings showed that the cold sprayed DMMC coatings had excellent wear-resistance properties due to the diamond reinforcement.

Continuous fibre reinforced polymer composites have found a wide range of applications in the automotive and aerospace industry, due to their lightweight properties. Recently the use of additive manufacturing (AM) has been developed for the fabrication of these composites. This study investigates the use of both atmospheric and for the first time, low-pressure (1 Pa) processing conditions, for the AM of continuous carbon, glass and Kevlar fibre reinforced nylon composites. DSC was used to compare the thermal properties of the three types of fibre reinforced filament, prior to printing. It was found that the melting peak was dependent on filament type, which can be related to the polymer processing conditions used during their fabrication. Based on computed tomography measurements, it was found that the use of low-pressure printing conditions yielded a reduction in porosity for the carbon, glass and Kevlar printed composites of 5.7, 1.0 and 1.7 % respectively. The mechanical properties of the composites were compared, using a short beam shear test, which assisted in the measurement of interlaminar properties. An increase in interlaminar shear strength of 33, 22 and 12% was obtained for the carbon, glass and Kevlar fibre reinforced polymer composites respectively, when printed under low-pressure, compared with that obtained at atmospheric pressure. Science Foundation Ireland

This paper evaluates the mechanical properties of woven continuous carbon fibre composites printed by additive manufacturing (AM). Comparison mechanical test studies (tensile, flexural and fatigue) were carried out with two nonwoven AM printed composites (unidirectional and multidirectional fibres), along with those of both a woven composite, as well as a composite reinforced using chopped carbon fibres. Compared with the 17 MPa tensile strength obtained for the chopped fibre composite, the average strength of unidirectional (nonwoven), multidirectional (nonwoven) and woven fibre composites were 39, 13 and 19-fold higher, respectively. The tensile strength of the woven composites was 52% lower than that attained by the unidirectional (nonwoven) fibre composites; and 38% higher than the multidirectional (nonwoven) fibre composites. A comparison was also made between the flexural and fatigue performance of the unidirectional (nonwoven) and woven fibre composites. The flexural strength of the latter was approximately 39% lower than the nonwoven composites, however, the load bearing capacity of woven fibre was superior. This performance difference was supported by the fatigue testing results. At 70% of maximum tensile load capacity after 2 × 105 cycles, the nonwoven composites failed, while the woven composites continued to perform until a level of 85% of maximum load capacity was reached. The superior fatigue strength of the AM fabricated woven carbon fibre composites, demonstrates their potential for use in high cyclic load applications.

This paper investigates the formation of process by-products during the laser processing of titanium alloy powders by Selective Laser Melting (SLM). The study was carried out during the printing of Ti6AL4V parts using a production scale SLM system (Renishaw RenAM500 M). By-product particles were obtained on the surface of powder removed from the area around where the pulsed laser powder treatments had been carried out. The process by-products examined in this study were damaged Ti6AL4V particles along with condensate. The particles were found to exhibit deshelling, fracture, and collision damage. Based on TEM and SEM examination, the condensate particles were found to have sizes in the nanoscale range and exhibited morphologies, similar to those reported in the literature for welding condensates. Energy-dispersive X-ray spectroscopy (EDX) analysis indicated that the condensate formed from processing Ti6AL4V, exhibited a higher level of aluminum than that obtained for the alloy itself, lower levels of titanium with minimal vanadium levels, were also obtained. This may indicate that the alloy partially decomposes, with the emission of the lower melting point alloying element. The use of an in-situ melt pool monitoring system (called Renishaw InfiniAM Spectral), was evaluated for detecting the presence of these by-product particulates, based on photodiode measurements of the melt pool emissions, along with a camera-based imaging of visual per layer conditions. A reduction in the intensity of infrared emissions was detected, in areas where suspected spatter particles had been redeposited. Thus, demonstrating that process monitoring can be used for the in-situ detection of particulate defects formed during printing. Enterprise Ireland European Commission - European Regional Development Fund Science Foundation Ireland

Copper particles embedded into polymer surfaces by cold spray (CS) have been confirmed as a method for antifouling (AF) protection. CS is a low-heat coating process which can be used or employed over large areas. The key parameters that indicate AF potency are particle penetration depth and copper surface coverage. Adaptation of this process towards industrial level requires the process inputs leading to the best outputs to be identified. In this paper, copper particles were deposited onto two polymers used in marine applications with CS, however, without the use of gas-heating hence deposition was free of any additional heat input. Analysis was carried out to determine which process conditions and material properties can lead to most effective AF coating results.