A novel thermo-geometrical model for accurate keyhole porosity prediction in Laser Powder-Bed Fusion

When performing Laser Powder-Bed Fusion, undesired physical phenomena, such as balling, preballing and keyhole, must be avoided in order to achieve high-quality products. To date, keyhole-free process parameters can be identified either using demanding empirical methods or complex numerical simulations, while only a few analytical models can be found in literature for this purpose. In this work, state-of-the-art analytical models for predicting keyhole porosity were summarized and proved to be rather inaccurate because they are only based on thermodynamic principles, whereas they neglect the geometry and both the kinetics and kinematics of the keyhole cavity, which do also influence cavity collapse and porosity formation. Here an innovative physics-based semi-analytical model for predicting the formation of keyhole-related porosities was conceived, in which both thermodynamic and geometrical factors are taken into account. The proposed model was validated by performing single tracks experiments on Ti6Al4V according to a full factorial DoE on laser power and scanning speed. Produced samples were cross-sectioned and analyzed to evaluate keyhole porosity formation. The comparison between experimental data and model predictions confirmed the higher accuracy of the new model with respect to state of the art models. Besides improving the understanding of the keyhole phenomenon, the proposed model may provide a novel, effective and simple tool for fast process parameter optimization in industry

Genotype influence on shelf life behaviour of minimal processed loquat (Eriobotrya japonica (Thunb.) Lindl.) fruit: the role of sugar, acid organics and phenolic compounds

Background: Loquat cultivars cultivated in Southern Italy are very appreciated by consumers for their sensorial characteristics, such as persistent aroma and taste. Apposite maturity indexes for peeling and processing loquat fruit were investigated to increase diffusion of minimally processed loquat. The genotype’s effect on the minimally processed loquat fruit shelf life and quality harvested at commercial maturity (80% yellow color) was investigated on peeled fruit stored at 5 °C for 10 days. The role of sugars, organic acids and phenols composition was observed through in depth qualitative analysis. In addition, several qualitative analyses were carried out to determine the quality of minimal processed fruit. Results: Loquat fruits harvested at commercial ripening stage performed very good palatability and flesh color persistency. Late ripening fruits genotypes shown a low rate of pulp oxidation and quality decay, while early ripening fruits were not suitable for fresh-cut. Genotype had a great influence on weight loss, β-carotene content, fruit respiration, ascorbic acid and total phenols content during the shelf life. Conclusions: This work shows how the amount of the composition of sugars and organic acids as an intrinsic characteristic of genotype influences the quality of loquat fruits minimal processed. The higher values of glucose, sorbitol and ascorbic acid accumulated in the cv ‘Nespolone Trabia’ contributed to a reduction in chilling injury and oxidative stress after cutting. Graphical Abstract: [Figure not available: see fulltext.

Molecular mechanisms of photosensitization induced by drugs XIV: Two different behaviours in the photochemistry and photosensitization of antibacterials containing a fluoroquinolone like chromophore

This paper deals with the photosensitizing activity of FLQs towards two different biosubstrates, membrane and DNA. Thein vitrophototoxic activity of these drugsvs.DNA presents peculiar features with respect to thatvs.membranes, probably due to a specific binding of the drugs to the double helix and to the operativeness of different photosensitization mechanisms with the two types of biosubstrates. A description of the UVA photochemistry and the photosensitizing properties of two significant examples in the FLQ family is reported. The investigated compounds are Enoxacin, 1-ethyl-6-fluoro-1,4-dihydro-4- oxo-7-[1-piperazinyl]-1,8-naphtyridine-3-carboxilic acid and Rufloxacin, 9-fluoro-2,3-dihydro-10-4´-methyl- 1´-piperazinyl-7-oxo-7H-pyrido[1,2,3−de]-1,4-benzothiazine-6-carboxylic acid

Effects of post-printing heat treatment on microstructure, corrosion and wet wear behavior of CoCrW alloy produced by L-PBF process

CoCr alloys are widely used as human implants because of both their superior corrosion resistance and superior mechanical properties (fatigue, wear resistance, etc.) respect to other metal alloys used in biomedical field. In particular, CoCrW alloys are used mainly to produce dental implants. In this study, the effects of thermal treatment on the corrosion resistance and wet wear resistance of CoCrW alloys produced via Laser-Powder Bed Fusion (L-PBF) were investigated, and the corrosion resistance and wet wear resistance of the L-PBF specimens were compared with those of the specimens obtained after forging. The heat treatment involved the solubilization of the alloy at 1150 °C in an Ar-saturated atmosphere, followed by furnace cooling. A detailed microstructural characterization of the L-PBF specimens was carried out using a light microscope and a scanning electron microscope in both the horizontal and vertical growth directions. Scanning Kelvin probe measurements were performed on the heat-treated specimens obtained by three-dimensional printing and forging. The void contents of the specimens were evaluated using the Archimedes’ method and image analysis. Vickers (HV2) hardness measurements were performed to evaluate the mechanical properties of the specimens. The corrosion properties of the specimens were evaluated by carrying out potentiodynamic tests in two different corrosive media (aqueous solution (9 g/L NaCl) at pH = 2 and 7). The corroded areas of the specimens were then examined using scanning electron microscopy (SEM). Finally, tribological tests were performed using the pin (Ti counter material)-on-flat configuration under dry and wet conditions, using the same corrosive environments as those used in the potentiodynamic tests and two different stroke lengths. The worn samples were characterized using SEM to investigate their wear mechanisms, and a stylus profilometer was used to determine the wear rates of the materials. The experimental results showed that the additively manufactured CoCrW L-PBF alloy had higher corrosion resistance than the wrought material. In addition, the additively manufactured material showed better dry and wet wear performances than the wrought material. Nevertheless, the heat treatment did not affect the properties evaluated in this study

Radial bound states in the continuum for polarization-invariant nanophotonics

All-dielectric nanophotonics underpinned by the physics of bound states in the continuum (BICs) have demonstrated breakthrough applications in nanoscale light manipulation, frequency conversion and optical sensing. Leading BIC implementations range from isolated nanoantennas with localized electromagnetic fields to symmetry-protected metasurfaces with controllable resonance quality (Q) factors. However, they either require structured light illumination with complex beam-shaping optics or large, fabrication-intense arrays of polarization-sensitive unit cells, hindering tailored nanophotonic applications and on-chip integration. Here, we introduce radial quasi-bound states in the continuum (radial BICs) as a new class of radially distributed electromagnetic modes controlled by structural asymmetry in a ring of dielectric rod pair resonators. The radial BIC platform provides polarization-invariant and tunable high-Q resonances with strongly enhanced near fields in an ultracompact footprint as low as 2 µm2. We demonstrate radial BIC realizations in the visible for sensitive biomolecular detection and enhanced second-harmonic generation from monolayers of transition metal dichalcogenides, opening new perspectives for compact, spectrally selective, and polarization-invariant metadevices for multi-functional light-matter coupling, multiplexed sensing, and high-density on-chip photonics

Single tracks data obtained by selective laser melting of Ti6Al4V with a small laser spot diameter

Nowadays, advanced metal components with high geometrical complexity can be 3D printed by using the Selective Laser Melting (SLM) technology. Despite SLM resolution and accuracy are generally limited to some tenths of mm, it should be possible to produce finer and more precise details by applying lasers with a small spot diameter. However, to present date the data collected with small laser spot diameters are poor. In this work, experimental data describing the effects of laser power and scan speed on single track formation when applying a small laser spot diameter of 50 \ub5m on Ti6Al4V powder are reported. SEM images and the extracted geometrical data characterizing the obtained single tracks are provided here, as well as their microstructural analysis and microhardness measurements

Photoresponsive multilayer films by assembling cationic amphiphilic cyclodextrins and anionic porphyrins at the air/water interface

Densely packed hybrid monolayers of amphiphilic cyclodextrins incorporating hydrophilic porphyrins are formed at the air/water interface through electrostatic interaction and can be transferred onto quartz substrates by Langmuir–Scha¨fer deposition. The resulting multilayers exhibit a good response to light excitation as proven by fluorescence emission, triplet– triplet absorption and singlet oxygen photogeneration

Intrinsic strong light-matter coupling with self-hybridized bound states in the continuum in van der Waals metasurfaces.

Photonic bound states in the continuum (BICs) provide a standout platform for strong light-matter coupling with transition metal dichalcogenides (TMDCs) but have so far mostly been implemented as traditional all-dielectric metasurfaces with adjacent TMDC layers, incurring limitations related to strain, mode overlap and material integration. Here, we demonstrate intrinsic strong coupling in BIC-driven metasurfaces composed of nanostructured bulk tungsten disulfide (WS2) and exhibiting resonances with sharp, tailored linewidths and selective enhancement of light-matter interactions. Tuning of the BIC resonances across the exciton resonance in bulk WS2 is achieved by varying the metasurface unit cells, enabling strong coupling with an anticrossing pattern and a Rabi splitting of 116 meV. Crucially, the coupling strength itself can be controlled and is shown to be independent of material-intrinsic losses. Our self-hybridized metasurface platform can readily incorporate other TMDCs or excitonic materials to deliver fundamental insights and practical device concepts for polaritonic applications

“Three-bullets” loaded mesoporous silica nanoparticles for combined photo/chemotherapy

This contribution reports the design, preparation, photophysical and photochemical characterization, as well as a preliminary biological evaluation of mesoporous silica nanoparticles (MSNs) covalently integrating a nitric oxide (NO) photodonor (NOPD) and a singlet oxygen (1O2) photosensitizer (PS) and encapsulating the anticancer doxorubicin (DOX) in a noncovalent fashion. These MSNs bind the NOPD mainly in their inner part and the PS in their outer part in order to judiciously exploit the different diffusion radius of the cytotoxic NO and 1O2. Furthermore this silica nanoconstruct has been devised in such a way to permit the selective excitation of the NOPD and the PS with light sources of different energy in the visible window. We demonstrate that the individual photochemical performances of the photoactive components of the MSNs are not mutually affected, and remain unaltered even in the presence of DOX. As a result, the complete nanoconstruct is able to deliver NO and 1O2 under blue and green light, respectively, and to release DOX under physiological conditions. Preliminary biological results performed using A375 cancer cells show a good tolerability of the functionalized MSNs in the dark and a potentiated activity of DOX upon irradiation, due to the effect of the NO photoreleased

Effect of Thermal Treatment on Corrosion Behavior of AISI 316L Stainless Steel Manufactured by Laser Powder Bed Fusion

The effect of post-processing heat treatment on the corrosion behavior of AISI 316L stainless steel manufactured by laser powder bed fusion (L-PBF) is investigated in this work. Produced stainless steel was heat treated in a broad temperature range (from 200 °C to 1100 °C) in order to evaluate the electrochemical behavior and morphology of corrosion. The electrochemical behavior was investigated by potentiodynamic and galvanostatic polarization in a neutral and acidic (pH 1.8) 3.5% NaCl solution. The microstructure modification after heat treatment and the morphology of attack of corroded samples were evaluated by optical and scanning electron microscopy. The fine cellular/columnar microstructure typically observed for additive-manufactured stainless steel evolves into a fine equiaxed austenitic structure after thermal treatment at high temperatures (above 800 °C). The post-processing thermal treatment does not negatively affect the electrochemical behavior of additive-manufactured stainless steel even after prolonged heat treatment at 1100 °C for 8 h and 24 h. This indicates that the excellent barrier properties of the native oxide film are retained after heat treatment