The advantages of the Laser Powder Bed Fusion process have led to growing interest from an industrial and academic point of view. However, the diffusion of this process has been slowed by technical ...challenges that have yet to be resolved, including non-optimal surface quality and low repeatability. To fix these issues and recover surface quality, several treatments are available. Our study focuses on one of them: the Directed Energy Deposition (DED) treatment, which in addition can be exploited for the repair of damaged components. In fact, the proposed study has been conducted by using AISI 316 L alloy both for producing parts throughout the L-PBF process and for coating them. Furthermore, a final Laser Scanning (LS) treatment has been carried out with the aim of maximizing the DED coating performances, in terms of surface roughness, microhardness and microstructural properties. To detect the anomalies that can emerge during the previous surface treatments, an optical monitoring system was implemented in the visible range by using a coaxial CCD camera, to monitor the geometry and morphology of the melt pool related to the DED and to the subsequent LS treatment. The results revealed many improvements in terms of surface roughness for the DED coating and even more for the LS treatment. Moreover, the latter was fundamental to improve the microhardness and the microstructural characteristics of the final coating. The data gathered and analyzed by the implemented monitoring system will allow making the treatment more stable and performing for future applications on complex geometries.
•Coatings using DED + LS treatment on a L-PBF substrate were successfully achieved.•Laser scanning significantly improves DED coating performances.•Microstructure after the laser scanning treatment is an equiaxial fine grain.•The produced coating is uniform due to the stability of the melt pool.•Coatings quality was monitored in-process through optical and thermal systems.
The capability of Active Thermography (AT) techniques in detecting shallow defects has been proved by many works in the last years, both on metals and composites. However, there are few works in ...which these techniques have been used adopting simulated defects more representative of the real ones. The aim of this work is to investigate the capability of Pulsed Thermography of detecting shallow spherical defects in metal specimens produced with laser powder bed fusion (L-PBF) process and characterized by a thermal behaviour very far from the flat bottom hole and so near to the real one. In particular, the quantitative characterization of defects has been carried out to obtain the Probability of Detection (PoD) curves. In fact, it is very common in non-destructive controls to define the limits of defect detectability by referring to PoD curves based on the analysis of flat bottom holes with a more generous estimation and therefore not true to real defect conditions. For this purpose, a series of specimens, made by means of Laser-Powder Bed Fusion technology (L-PBF) in AISI 316L, were inspected using Pulsed Thermography (PT), adopting two flash lamps and a cooled infrared sensor. To improve the quality of the raw thermal data, different post-processing algorithms were adopted. The results provide indications about the advantages and limitations of Active Thermography (AT) for the non-destructive offline controls of the structural integrity of metallic components.
Focal pulmonary ground-glass opacities (GGOs) can be associated with bronchioloalveolar carcinoma. The present retrospective study aimed to test the validity of a multistep approach to discriminate ...malignant from benign localised (focal) GGOs, identifies useful diagnostic features on computed tomography (CT), and suggests appropriate management guidelines. A stepwise approach, including oral antibiotics, follow-up high-resolution CT (HRCT) 40-60 days later and CT-guided core biopsy, was used. All cases with localised GGOs detected since 2001 were reviewed. CT features were described according to a structured scheme. In total, 40 patients were evaluated. Of these, 11 patients were diagnosed with benign GGOs, 19 patients had lung cancer and 10 were undetermined. Nonpolygonal shape, apparent radial growth and clear-cut margins were associated with a malignant histology. The specificity of CT findings was low. Diagnostic accuracy increased after oral antibiotics, follow-up HRCT and percutaneous core biopsy. Overall, 18 patients underwent surgery for lung cancer. In conclusion, malignant ground-glass opacities have a fairly typical appearance, but some benign lesions closely mimic their malignant counterparts. The stepwise approach adopted in the present study increased the diagnostic specificity and reduced time to definitive diagnosis. Segmentectomy might be the ideal resection volume for such tumours.
In this paper, we study an unconventional kind of quasi-three-dimensional (3-D) photonic crystal (PhC) with circular lattice pattern: it consists of air holes in a GaAs material (n=3.408) along ...circular concentric lines. This particular PhC geometry has peculiar behavior if compared with the traditional square and triangular lattices, but it is difficult to model by using conventional numerical approaches such as wave expansion method. The resonance and the radiation aspects are analyzed by the 3-D finite-element method (FEM). The model, based on a scattering matrix approach, considers the cavity resonance frequency and evaluates the input-output relationship by enclosing the photonic crystal slab (PhCS) in a black box in order to define the responses at different input-output ports. The scattering matrix method gives important information about the frequency responses of the passive 3-D crystal in the 3-D spatial domain. A high sensitivity of the scattering parameters to the variation of the geometrical imperfection is also observed. The model is completed by the quality factor (Q-factor) estimation. We fabricated the designed circular photonic crystal over a slab membrane waveguide embedding InAs/GaAs quantum dots emitting around 1.28 mum. Good agreement between numerical and experimental results was found, thus validating the 3-D FEM full-wave investigation.
Physical methods of diagnosis are more and more frequently applied in the field of Cultural Heritage either for scientific investigations or for restoration and conservation purposes. X-ray Computed ...Tomography (CT) is one of the most powerful non-destructive testing techniques for the full-volume inspection of an object, as it is able to give morphological and physical information on the inner structure of the investigated sample. The great variety of size and composition that characterizes archaeological findings and art objects requires the development of tomographic systems specifically designed for Cultural Heritage analysis. In the last few years our research group has developed several acquisition systems for Digital Radiography and X-ray CT. We are able to perform high resolution micro-tomography of small objects (voxel size of few microns) as well as CT of large objects (up to 2 m of size). In this paper we will mainly focus the attention on the results of the investigation recently performed on two Japanese wooden statues with our CT system for large works of art. The CT analysis was carried out on site at the Conservation and Restoration Center “La Venaria Reale”, where the statues have been restored before their exposition at the Oriental Art Museum in Turin.
In this paper, we introduce an unconventional photonic crystal (PhC) geometry which defines two resonance frequencies. The presented circular PhC structure behaves as a negative uniaxial crystal and ...admits two preferred propagation directions defined by an extraordinary and an ordinary refractive index representing two field polarizations. The circular grating profile splits the electromagnetic field into a radial (extraordinary field) and a tangential (ordinary field) component, which represent two modes of the periodic structure. The total field in the PhC slab is generated by the superposition effect of the ordinary and extraordinary field produced in the 2-D periodic plane. This field configuration is obtained by the analogy with the dielectric multilayer structure. The presented PhC circular lattice pattern consists of air holes in a GaAs material (n = 3.408) along circular concentric lines which have the same distance defined as the PhC a period. We validate the birefringence theory by the comparison between analytical and numerical results and then between the numerical and experimental ones.
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