In this study, coaxial laser cladding of NiCrAlY powder on a nickel-based superalloy is investigated from an experimental point of view so as to propose an empirical-statistical model for the ...process. The correlations between main processing parameters (i.e. scanning speed, powder feeding rate, and laser power) and geometrical characteristics (i.e. width, height, penetration depth, dilution and wetting angle) of single clad tracks have been predicted and are discussed using regression analysis (RA). The validity of the predictions is confirmed by providing correlation coefficient and analysis of the residuals. The correlations are established as a combined parameter (PαVβFγ) for each studied characteristic of single clad tracks. These correlations finally lead to the design of a processing map that can be practically used to select proper processing parameters for laser cladding of the particular material.
•Coaxial laser cladding of NiCrAlY powder on Inconel 738 superalloy is investigated.•The correlations between processing parameters and geometrical features are predicted.•The correlations are established in terms of a combined parameter (PαVβFγ).•The empirical-statistical model of the process is designed.
Abstract
Radar cross section reduction has been one of the most important research topics in recent years. Plasma-based stealth is a method of reducing the radar cross section, which dampens the ...electromagnetic waves and reduces the amount of return waves. In this paper, a coating of the radioactive nucleus
$$^{241}{\mathrm{Am}}$$
241
Am
on the surface of the cylinder with a radius of 10 cm is considered and the range of the emitted alpha particles and the electron density generated in the air are obtained using the Geant4 code under standard temperature and pressure conditions. By finite element method solution, the radar cross section of the conductive cylindrical object has been simulated and extracted in the presence and absence of plasma created by alpha-particles. The obtained results show a
reduction of 5–8 dB
$$\mathrm{m}^2$$
m
2
in the radar cross section in the frequency range of 2–12 GHz for specific activity source of 1 Ci/
$$\mathrm{cm}^2$$
cm
2
.
•Inconel 718 was laser cladded to a non-weldable A-286 substrate.•Statistical model evaluated the effect of process parameters.•Processing map to avoid solidification cracking was developed.•Dilution ...ratio adjusts the chemical composition and segregation potential.
This paper presents an empirical-statistical approach to predict solidification cracking during laser cladding of Inconel 718 powder on A-286 Fe-based superalloy. This approach is based on a linear regression analysis and empirical-statistical correlations between the key processing parameters (laser power, P; powder feed rate, F; and scanning speed, V) and the geometrical attributes of single laser cladding tracks. These correlations were used for the development of a processing map which assesses the effects of the geometrical characteristics on the solidification cracking and the required conditions to obtain crack-free clads. Scanning electron microscopy was used for microstructural characterization. Thermodynamic calculations using the non-equilibrium Scheil solidification model were also employed. The empirical-statistical analysis showed that the processing parameters directly associated with the height and angle of single laser cladding tracks are P2FV2 and P0.5FV1, respectively. The processing map revealed that the dilution ratio is the governing macrostructural attribute required to avoid solidification cracking. Indeed, a substrate dilution ratio lower than 25% shifts the cladding composition to an alloy regime, which has lower susceptibility to solidification cracking. The role of this macrostructural feature in reducing the susceptibility of the fusion zone to solidification cracking is thoroughly discussed.
We present the personalisation of a 3D electromechanical model of the heart to predict the acute haemodynamic changes associated with CRT. The acute effects of pacing were predicted with the model ...for several pacing con- ditions on two patients, achieving good agreement with invasive haemody- namic measurements. These promising results demonstrate the potential of biophysical models to improve patient selection and plan CRT. Display omitted
► Personalisation of an electromechanical model integrating anatomy, electrophysiology, kinematics and mechanics. ► Quantitative evaluation of the different personalisation steps. ► Prediction of the pressure curves for different pacing conditions. ► Quantitative validation of the predictions from interventional measurements.
Cardiac resynchronisation therapy (CRT) is an effective treatment for patients with congestive heart failure and a wide QRS complex. However, up to 30% of patients are non-responders to therapy in terms of exercise capacity or left ventricular reverse remodelling. A number of controversies still remain surrounding patient selection, targeted lead implantation and optimisation of this important treatment. The development of biophysical models to predict the response to CRT represents a potential strategy to address these issues. In this article, we present how the personalisation of an electromechanical model of the myocardium can predict the acute haemodynamic changes associated with CRT. In order to introduce such an approach as a clinical application, we needed to design models that can be individualised from images and electrophysiological mapping of the left ventricle. In this paper the personalisation of the anatomy, the electrophysiology, the kinematics and the mechanics are described. The acute effects of pacing on pressure development were predicted with the in silico model for several pacing conditions on two patients, achieving good agreement with invasive haemodynamic measurements: the mean error on dP/dtmax is 47.5±35mmHgs−1, less than 5% error. These promising results demonstrate the potential of physiological models personalised from images and electrophysiology signals to improve patient selection and plan CRT.
Hot corrosion behavior of nanostructured scandia (3.6mol%) and yttria (0.4mol%) stabilized zirconia (4ScYSZ) and yttria stabilized zirconia (4YSZ) were investigated. Thus, duplex TBCs (thermal ...barrier coatings), composed of a bond coat (NiCrAlY) and a top coat (4ScYSZ or 4YSZ), were deposited on the IN738LC Ni-based supperalloy by atmospheric plasma spraying (APS). Hot corrosion studies of plasma sprayed TBCs were conducted in 45wt% Na2SO4+55wt% V2O5 molten salt at 910°C for different times. Based on the results, it was revealed that ScYSZ coating has more hot corrosion resistance than YSZ coatings. Moreover, the mechanisms of degradation of both TBCs under corrosion salt were suggested.
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•NiCrAlY coatings were additively manufactured through a laser-aided process.•The additively manufactured coatings had γ/β dendritic structure.•The coatings showed a good oxidation ...resistance at 1200°C.•The oxide scale formed on the coatings consisted of Al2O3 and Al5Y3O12 oxides.
In this study, NiCrAlY coatings were additively manufactured on the surface of IN738 substrate through a laser-aided additive manufacturing approach. The high-temperature oxidation behavior of freestanding coatings at 1200°C was also investigated. The coatings were thick, dense, and well-bonded with dendritic γ/β microstructure. The results proved that the coatings were able to withstand the operating temperature of 1200°C for up to ten cycles. After ten cycles of oxidation, the oxide scales formed on the coatings were mainly composed of α-Al2O3 and Al5Y3O12 phases; however, NiO, Cr2O3 and Ni(Cr,Al)2O4 phases were not detected.
Nanostructured scandia, yttria doped zirconia (5.5SYSZ), 7wt% yttria stabilized zirconia (7YSZ) and 15YSZ thermal barrier coatings (TBCs) were produced by plasma spraying on nickel-based superalloy ...substrates with NiCrAlY as the bond coat. The thermal stability and sintering behavior of the three as-sprayed TBCs at 1480°C were investigated. The results indicated that the thermal stability of SYSZ and TBCs was longer than the 7YSZ TBCs due to higher amount of tetragonal phase. Furthermore, the results demonstrated that the nanostructured 7YSZ coating exhibits higher sintering resistance than 5.5SYSZ TBC.
Solvent-based Poly (amide-imide) (SBPAI)/Cloisite 20A (C20A) nanocomposite containing different amounts of C20A (1–5 wt%) was prepared via solvent method technique and were deposited on sandblasted ...cold-rolled steel (CRS) surface as nanocoating. Different characteristics methods such as SEM, TEM, energy dispersive spectroscopy (EDS-map and -point) and small-angle X-ray diffraction (SAXD), electrochemical impedance spectroscopy and salt spray analysis were utilized for the characterization of nanocomposite samples. Based on the results, SBPAI/C20A nanocomposites with 3 wt% C20A (NC3%) had the higher adhesion strength and corrosion protection compared to the neat SBPAI and other percentages of C20A in nanocomposites. It was due to this fact that the clay-spreading layers in the polymer field prolong the path to reach the underlying layer.
•Effect of Closite 20A (C20A) on the properties of PAI/C20A nanocomposite were investigated.•Coating adhesion measurements showed that nanocomposite with 3wt% C20A has the best adhesion strength.•The sample with 3wt % C20A showed the best corrosion protection.
In this paper, the capacity of OFDM/OQAM with isotropic orthogonal transfer algorithm (IOTA) pulse shaping is evaluated through information theoretic analysis. In the conventional OFDM systems the ...insertion of a cyclic prefix (CP) decreases the system's spectral efficiency. As an alternative to OFDM, filter bank based multicarrier systems adopt proper pulse shaping with good time and frequency localisation properties to avoid interference and maintain orthogonality in real field among sub-carriers without the use of CP. We evaluate the spectral efficiency of OFDM/OQAM systems with IOTA pulse shaping in comparison with conventional OFDM/QAM systems, and our analytical model is further extended in order to gain insights into the effect of utilizing the intrinsic interference on the performance of our system. Furthermore, the spectral efficiency of OFDM/OQAM systems is analyzed when the effect of inter-symbol and inter-carrier interference is considered.
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