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.

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

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

Comparison between two different modes of non-invasive ventilatory support in preterm newborn infants with respiratory distress syndrome mild to moderate: preliminary data

Despite of improved survival of premature infants, the incidence of long term pulmonary complications, mostly associated with ventilation-induced lung injury, remains high. Non invasive ventilation (NIV) is able to reduce the adverse effects of mechanical ventilation. Although nasal continuous positive airway pressure (NCPAP) is an effective mode of NIV, traumatic nasal complications and intolerance of the nasal interface are common. Recently high flow nasal cannula (HFNC) is emerging as a better tolerated form of NIV, allowing better access to the baby's face, which may improve nursing, feeding and bonding. HFNC may be effective in the treatment of some neonatal respiratory conditions while being more user-friendly for care-givers than conventional NCPAP. Limited evidence is available to support the specific role, efficacy and safety of HFNC in newborns and to demonstrate efficacy compared with NCPAP; some studies suggest a potential role for HFNC in respiratory care of the neonate as a distinct non invasive ventilatory support. We present the preliminary data of a randomized clinical trial; the aim of this study was to assess efficacy and safety of HFNC compared to NCPAP in preterm newborns with mild to moderate respiratory distress syndrome (RDS)

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

Enhanced light-matter interaction in an atomically thin semiconductor coupled with dielectric nano-antennas

Unique structural and optical properties of atomically thin two-dimensional semiconducting transition metal dichalcogenides enable in principle their efficient coupling to photonic cavities having the optical mode volume close to or below the diffraction limit. Recently, it has become possible to make all-dielectric nano-cavities with reduced mode volumes and negligible non-radiative losses. Here, we realise low-loss high-refractive-index dielectric gallium phosphide (GaP) nano-antennas with small mode volumes coupled to atomic mono- and bilayers of WSe2. We observe a photoluminescence enhancement exceeding 10(4) compared with WSe2 placed on planar GaP, and trace its origin to a combination of enhancement of the spontaneous emission rate, favourable modification of the photoluminescence directionality and enhanced optical excitation efficiency. A further effect of the coupling is observed in the photoluminescence polarisation dependence and in the Raman scattering signal enhancement exceeding 10(3). Our findings reveal dielectric nano-antennas as a promising platform for engineering light-matter coupling in two-dimensional semiconductors

Environmental pre-exploitation monitoring of Torre Alfina geothermal system (Central Italy)

An interesting project of geothermal pilot plant, with no-gas emission in atmosphere, has been submitted for approval in the medium-enthalpy geothermal field of Torre Alfina. This prompted us to develop a geochemical and geophysical monitoring of the area with the aim of establishing a background information to reco-gnize anomalous gas emission, induced seismicity and subsidence, possibly related to the field exploitation. The exploration conducted by Enel in the years ‘70 - '80, including the drilling of 9 deep wells, has shown the existence of a medium-enthalpy geothermal field in the Torre Alfina zone, in central Italy. The area has been affected by a very complex geological evolution during the Neogene. It was affected by the Quaternary volcanism of the Tyrrhenian margin which, reached its climax between 0.6 and 0.3 Ma. The present stress field around Quaternary volcanoes of central Italy has a NE to ENE direction of extension, in agreement with the alignment of Quaternary volcanoes and earthquake fault plane solutions, with T axes preferentially oriented between NE and ENE.PublishedPrague, Czech Republic, June 22 to July 2, 20156T. Sismicità indotta e caratterizzazione sismica dei sistemi naturaliope