The present study reports on the structure formation in thin epitaxial nickel-aluminum films (Ni1-xAlx; Al atomic fraction up to ) grown on MgO substrates by magnetron sputtering. Experimental and computational data demonstrate that for , the films exhibit the face-centered cubic random solid-solution Ni1-xAlx structure ( phase). Whereas in the range x = 0.11-0.24 the phase coexists with the ordered structure ( phase). The two phases are homogenously intermixed forming a strained coherent nanocomposite, which exhibits a single lattice parameter that expands as the Al content increases. Isothermal annealing of films containing of Al, coupled with structural and nano-mechanical characterization, reveal that the coherent nanocomposite retains its overall integrity for temperatures up to 673 K while the film hardness increases from (as deposited films) to . Further increase of the annealing temperature to 873 K and 1073 K causes the coherent nanocomposite to dissolve into distinct and phase domains and the hardness to decrease down to values of . These findings confirm the metastable nature of the as-deposited thin Ni1-xAlx alloy films and underpin the effectiveness of high supersaturation/undercooling for creating non-equilibrium phases and self-organized nanostructures upon synthesis of multicomponent materials.

Wind turbine blades are critical components, and their structural integrity is essential for uninterrupted operation and minimizing downtime. Although various methods are used to monitor the health of wind turbine blades, several research challenges persist, such as the reliance on manual feature engineering and the limited availability of large amounts of labeled data. In this study, a novel approach is proposed that will overcome the limitations of manual feature extraction and label data challenges. In the proposed work, time series vibration signals from the blade are first converted into spectrograms and passed through a CNN-based autoencoder that is trained solely on healthy data to learn a compact latent representation. Anomalies are then flagged in three complementary ways: (i) by thresholding the autoencoder’s reconstruction error, (ii) by applying an Isolation Forest to the latent features, and (iii) by evaluating the same features with a One-Class SVM. The outputs of these detectors are subsequently benchmarked, providing a systematic comparison of their ability to discriminate between vibration-induced faults, such as cracks and erosion, and normal operation on a controlled test-rig dataset, the autoencoder achieves 97.2 % accuracy, outperforming the Isolation Forest and One-Class SVM by 8%–27%. These results demonstrate that zero-label, deep-feature pipelines can deliver reliable and scalable blade-fault detection, paving the way for more cost-effective predictive maintenance in wind farms.

The nanostructural features of a mechanically alloyed Sb-doped (Ti0.4Zr0.6)0.7Hf0.3NiSn thermoelectric (TE) Half-Heusler (HH) compound were addressed using Transmission Electron Microscopy (TEM) coupled with Energy Dispersive Spectroscopy measurements and Extended X-Ray Absorption Fine Structure (EXAFS) spectroscopy. The EXAFS measurements at the Ni-K, Sn-K, Zr-K, and Hf-L3-edge were implemented in an effort to reveal the influence of Hf and Zr incorporation into the crystal with respect to their previously measured TE properties. The substitution of Ti by Hf and Zr is expected to yield local lattice distortions due to the different atomic sizes of the dopants or/and electronic charge redistribution amongst the cations. However, the material is characterised by a high degree of crystallinity in both the short and long-range order, on average, and the nominal stoichiometry is identified as (Zr0.42Hf0.30Ti0.28)NiSn0.98Sb0.02. The synergistic effect of minimization of extended structural defects or lattice distortions and considerable alloying-induced point defect population contributes to the improved TE properties and leads to the previously reported enhancement of the figure of merit of the mixed HHs.

The present study reports on the structure formation in thin epitaxial nickel-aluminum films (Ni1-xAlx; Al atomic fraction x up to x=0.24) grown on MgO(001) substrates by magnetron sputtering. Experimental and computational data demonstrate that for x<0.11, the films exhibit the face-centered cubic random solid-solution Ni1-xAlx structure (γ). Whereas in the range x=0.11-0.24 the phase coexists with the ordered L12 structure (γ' phase). The two phases are homogenously intermixed forming a coherent and strained nano-solution, which exhibits a single lattice parameter that expands as the Al content increases. Isothermal annealing of films containing x=0.14 of Al, coupled with structural and nano-mechanical characterization, reveal that the nano-solution retains its overall integrity for temperatures up to 673 K, while the film hardness increases from 5.5 GPa (as deposited films) to 6 GPa. Further increase of the annealing temperature to 873 K and 1073 K causes the nano-solution to dissolve into distinct γ and γ' phase domains and the hardness to decrease down to values of 4 GPa. These findings confirm the metastable nature of the as-deposited thin Ni1-xAlx alloy films and underpin the effectiveness of high supersaturation/undercooling for creating non-equilibrium phases and self-organized nanostructures upon synthesis of multicomponent materials.

VO2 based thermochromic thin films can be successfully used for coating usual windows in order to minimize the energy consumption of buildings through a specific temperature driven Metal to Insulator Transition (MIT). A careful analysis on the wide possibilities to optimise such coatings with respect to the desired properties of MIT, followed mainly via the temperature variation of the electron transport properties is reported. Some optimized coatings, investigated by morpho-structural methods as X-Ray Diffraction and Transmission Electron Microscopy and finally by electron transport measurements, have shown stable and reproducible variations of resistivity by about 3 orders of magnitude, over temperatures ranging from 45 ℃ to 65 ℃ and with narrow hysteretic behavior, quite sensitive to processing parameters. The effect of partial pressure of oxygen during the Pulsed Laser Deposition process as well as of the considered substrate are mainly investigated in this work.

The nanostructural features of VO2 thin films, grown on either LSAT (La0.18Sr0.82)(Al0.59Ta0.41)O3, Si or Quartz substrates have been investigated by transmission electron microscopy (TEM/HRTEM) methods. The overall morphology, film thickness, roughness, VO2 phases and relative percentage, as well as residual strains have been elucidated. The electrical and magnetic characterisation complemented the TEM observations, where a smooth transition of metal to insulator (MIT) has been observed, mainly dependent on the relative percentage of the VO2 polymorphs. The effect of the residual strain has been also discussed, in relation to the MIT effectiveness.

Wind turbine blades are critical components of wind energy systems, and their structural health is essential for reliable operation and maintenance. Several studies have used time-domain and frequency-domain features alongside machine learning techniques to predict faults in wind turbine blades, such as erosion and cracks. However, a key gap remains in integrating these methods into a unified framework for fault prediction, which could offer a more comprehensive solution for diagnosing faults. This paper presents an approach to classify faults in wind turbine blades by leveraging well-known signals and analysis with machine learning techniques. The methodology involves a detailed feature engineering process that extracts and analyzes features from the time and frequency domains. Open-source vibration data collected from an experimental setup (where a small wind turbine with an artificially eroded and cracked blade was tested) were utilized. The time- and frequency-domain features were extracted and analyzed using various machine learning algorithms. It was found that erosion and crack faults have unique time- and frequency-domain features. The crack fault introduces an amplitude modulation in the vibration time wave, which produces sidebands around the fundamental frequency in the frequency domain. However, erosion fault introduces asymmetricity and flatness to the vibration time wave, which produces harmonics in the frequency-domain plot. The results also highlighted that utilizing both time- and frequency-fault features enhances the performance of the machine learning algorithms. This study further illustrates that even though some machine learning algorithms provide similar high classification accuracy, they might differ in quantifying error Types I, II, and, III, which is extremely important for maintenance engineers, as it might lead to undetected fault events and false alarm events.

The global goal of achieving 2000 gigawatts of offshore wind power by 2050 has driven the development of the wind energy sector. This ambitious goal is facing a significant challenge in maintaining the efficiency and health of the wind turbines. Wind turbine Blade erosion is among the main critical failure modes that lead to high production losses and maintenance expenses. At present, the industry is utilizing manual or drone-based inspection, however, they are targeting more cost-effective and more informative like to predictive maintenance for erosion and severity by using data science techniques based on SCADA and sensors data. This paper reviews existing erosion blade analysis methods in wind turbines, highlighting their strengths and weaknesses. The method is based on the literature review to determine the state of the art in terms of monitoring, classification, and prediction. Moreover study will evaluate potential predictive maintenance concepts based on key performance matrix extracted from key stakeholders. It can be concluded that a combined concept of vibration, aerodynamic, acoustic, and production loss techniques supported with XGBoost, FFT, and LSTM are the most effective methods.

Gas atomized 316L stainless steel powder was processed with 2 wt.% of nanosized SiO2 in a planetary ball milling (BM) system to produce feedstock material for laser powder bed fusion (L-PBF). X-ray diffraction (XRD) of powders revealed the development of micro-strains over increasing milling durations and the strain-induced ferrite formation. BM was limited in duration to preserve the austenitic phase and morphological characteristics analyzed by electron microscopy. In turn, 316L-2wt.% SiO2 feedstock powder was consolidated by L-PBF with varied process parameters and scanning strategies, that demonstrated a maximum density of 7.84 g/cm3 and relatively stable microhardness values close to 220 HV. A distinct (110) preferred orientation was observed in XRD pole figures of austenite for deeper melt pools over the building direction, whereas in-plane alignment reflected variations in scanning strategy. Furthermore, electron backscatter diffraction revealed columnar grains accompanied by the suspected depletion of SiO2, while electrochemical behavior displayed consistent characteristics.

(Hf,Zr,Ti)Co(Sb,Sn) Solid solutions were prepared by mechanical-alloying followed by hot-press method as an attempt to reduce Hf concentration and therefore the material’s cost without negatively affecting the thermoelectric performance. To this end, two different methods were applied: (a) Hf substitution with its lighter and cheaper homologue Zr; and (b) fine tuning of carrier concentration by the substitution of Sb with Sn. The isoelectronic substitution of Hf with Zr was investigated in Hf0.6-xZrxTi0.4CoSb0.8Sn0.2 solid solutions and resulted in lower power factors and ZTs. However, the low thermal conductivity of Hf0.4Zr0.2Ti0.4CoSb0.8Sn0.2 contributed in achieving a relatively good ZT~0.67 at 970 K. The effect of charge carrier concentration was investigated by preparing Hf0.4Zr0.2Ti0.4CoSb1-ySny (y = 0.15–0.25) compounds. Hf0.4Zr0.2Ti0.4CoSb0.83Sn0.17 composition prepared by six hours milling reached the highest ZT of 0.77 at 960 K.

The structural properties of VO2 thin films, grown on either LSAT or Si substrates by pulsed laser deposition (PLD), are elucidated by means of transmission electron microscopy (TEM) methods. The TEM observations confirmed the successful growth of VO2 by PLD in variable thicknesses, by optimizing the O2 partial pressure and growth temperature. The films adopt a columnar polycrystalline morphology with narrow columns, up to the film thickness height. Four VO2 polymorphs have been detected by electron diffraction and high-resolution TEM (HRTEM) analysis, with M1 being by far the most abundant phase. Post-experimental strain measurements in HRTEM images have revealed that the actual residual strain is minimized due to the columnar morphology of the VO2 grains, as well as intrinsic oxide layers in the VO2/Si epitaxy. The TEM outcomes confirmed the complementary electrical and magnetic measurements in the films, where a transition from a monoclinic M1 to a rutile VO2 R phase has been identified, influenced by the initial percentage of phases in thick VO2 films.

Mg2Si-type compounds are highly promising materials for use in thermoelectric devices for waste heat energy harvesting. These compounds have great potential because they exhibit high thermoelectric performance, but the scalability of their synthesis is a major issue for applications. In this study, Bi-doped Mg2Si0.55-xSn0.4Gex (x = 0 and 0.05) materials were prepared by mechanical alloying combined with hot press sintering in order to increase the mass capabilities of their synthetic route compared with the typical solid state reaction. The optimum thermoelectric properties were achieved for the best Mg2Si0.57Sn0.4Bi0.03 and Mg2Si0.53Sn0.4Ge0.05Bi0.02 compositions by ball milling for 32 h and the maximum figure of merit (ZT) values were 1.07 and 1.2, respectively.

Mechanical alloying has been applied, as an advantageous scalable method, to synthesize Ti1-xZrxNiSn half Heusler materials. This is the first time a synthesis of single phase n-type Ti1-xZrxNiSn half Heusler solid solutions is reported by this technique, along with structural studies and thermoelectric properties. The application of mechanical alloying was successful, as all compositions ranging between x = 0.4-0.8 were in general single phase materials. The lattice thermal conductivity of the series was lower compared to the same compositions prepared by arc melting. Ti0.4Zr0.6NiSn exhibited the minimum lattice thermal conductivity of the series and was selected for doping studies with Sb, with the scope to enhance the thermoelectric performance via the power factor modification. Thermoelectric property measurements resulted in a maximum figure of merit of 0.71 at 762K for Ti0.4Zr0.6NiSn doped with 1.5% Sb.

The electron channeling effect, i.e., the dependence of the characteristic x-ray emission on the crystallographic direction of the incoming beam in an analytical transmission electron microscope was employed to elucidate the crystal site location and distribution of the dopant and host ions in Mg2Si1-xSnx thermoelectric (TE) materials, doped with low amounts of Bi. Experiments performed both in pure Bi-doped Mg2Si and mixed Mg2Si1-xSnx (x = 0.4, 0.6), firmly confirmed that Mg occupies the two tetrahedral T sites, 8c (¼, ¼, ¼) and (¼, ¼, ¾), with some vacancies present, too, whereas Si and Sn the 4a (0, 0, 0) and 4b (½, ½, ½) octahedral C and N sites, respectively. Bi ions follow the trend of Si and Sn, occupying 4a sites, but also there is a partial distribution of them in 4b sites. We moreover observe a certain degree of asymmetry along the {111} directions in Mg2Si1-xSnx, predominately for the variable distribution of Bi and Sn in the lattice, which indicates Bi substitution for Sn in an uneven fashion. The channeling results are in line with TE property measurements, especially in relation to lower thermal conductivity and negative Seebeck coefficient due to Bi incorporation in the lattice. These findings demonstrate once more the effectiveness of the channeling technique to provide direct crystallographic information and refine atom positions in materials, particularly for nanoscale crystal grains.

Mechanical alloying synthesis was applied on the thermoelectric half-Heusler materials in order to explore the potential of such scalable synthesis method in this family of compounds. (Hf,Ti)Co(Sb,Sn) solid solutions were prepared by mechanical alloying followed by hot pressing and their thermoelectric properties were studied in the temperature range of 300-980 K. After successful synthesis, two different methods were applied to enhance the thermoelectric performance of p-type (Hf,Ti)Co(Sb,Sn) materials: (a) adjustment of the Ti/Hf ratio and (b) fine tuning of carrier concentration by the substitution of Sb with Sn. The isoelectronic substitution of Ti with Hf led to an important reduction in the lattice thermal conductivity and a high ZT of 0.84 at 980 K for Hf0.6Ti0.4CoSb0.8Sn0.2. The effect of charge carrier concentration was investigated by preparing Hf0.6Ti0.4CoSb1-ySny (0.15, 0.17, 0.20, 0.23, 0.25) compounds, using different mechanical alloying durations. The Hf0.6Ti0.4CoSb0.83Sn0.17 composition, prepared by 4 h ball-milling, reached an impressive ZT similar to 1.1 at 973 K. (C) 2020 Elsevier B.V. All rights reserved.

The recycling acquisition of silicon waste from photovoltaic industry has gained an increasing attention nowadays, since more than 50% of high purity material ends up as kerf during the wafer cutting process. Currently, different Si-based applications are being exploited in terms of using such Si kerf, in order to lower cost and significantly increase environmental impact. Thermoelectric devices can efficiently contribute towards this recycling approach, via the preparation of highly efficient silicides for power generation. In this work, Bi doped Mg2(Si,Sn,Ge) materials were prepared using Si-kerf originated from photovoltaic (PV) cutting wastes. Different Bi concentrations were studied in terms of thermoelectric properties and performance and a high figure-of-merit of 1.1. was achieved at 800K. In addition, a thorough structural and mechanical property characterization, such as morphology, phase identification, hardness and indentation modulus has been conducted. These results, which were evaluated and compared to materials prepared with pure Si (>99.9%), are presented for the first time for Mg2(Si,Sn,Ge) materials.

The authors study the morphological evolution of magnetron-sputtered thin silver (Ag) films that are deposited on weakly interacting silicon dioxide (SiO2) substrates in an oxygen-containing (O2) gas atmosphere. In situ and real-time monitoring of electrically conductive layers, along with ex situ microstructural analyses, shows that the presence of O2, throughout all film-formation stages, leads to a more pronounced two-dimensional (2D) morphology, smoother film surfaces, and larger continuous-layer electrical resistivities, as compared to Ag films grown in pure argon (Ar) ambient. In addition, the authors’ data demonstrate that 2D morphology can be promoted, without compromising the Ag-layer electrical conductivity, if O2 is deployed with high temporal precision to target film formation stages before the formation of a percolated layer. Detailed real-space imaging of discontinuous films, augmented by in situ growth monitoring data, suggests that O2 favors 2D morphology by affecting the kinetics of initial film-formation stages and most notably by decreasing the rate of island coalescence completion. Furthermore, compositional and bonding analyses show that O2 does not change the chemical nature of the Ag layers and no atomic oxygen is detected in the films, i.e., O2 acts as a surfactant. The overall results of this study are relevant for developing noninvasive surfactant-based strategies for manipulating noble-metal-layer growth on technologically relevant weakly interacting substrates, including graphene and other 2D crystals.

This work reports on the utilization of pulsed laser deposition (PLD) for the preparation of CdS thin films and CdS/Cu(In,Ga)Se-2 heterojunction structures on soda-lime glass (SLG) and Mo-coated SLG substrates, respectively, under various process conditions. Single phase, stoichiometric and high optical quality CdS films are obtained at a fluence of 1.1 J/cm(2) and at deposition temperatures of 200-400 degrees C. The results of this investigation were used to grow CdS on Cu(In,Ga)Se-2/Mo/SLG. Both Cu(In,Ga)Se-2 and CdS layers have been deposited sequentially using PLD without interrupting the deposition process. The influence of CdS deposition temperature on the properties of CdS/Cu(In,Ga)Se-2 heterojunction has been extensively studied and is reported herein for the first time. Low series and high shunt resistances are obtained for the samples where CdS was grown at 200 and 300 degrees C. The CdS/Cu(In,Ga)Se-2 diode grown at CdS deposition temperature of 300 degrees C exhibits the lowest ideality factor and leakage current, indicating the better quality of the diode. The results of this work demonstrate that high-quality CdS/Cu(In,Ga)Se-2 diodes are obtained using pulsed laser deposition in a single-step growth process, eliminating the need for selenization of Cu(In,Ga)Se-2 and the use of other growth techniques such as chemical bath deposition for CdS.

In this work, hot press and hot deformation were applied to p-type Bi2-xSbxTe3 (x = 1.5-1.8) starting powders that have not undergone nanostructuring processing. The effects of hot pressing and hot deformation, as well as Sb-alloying, on the microstructure and the thermoelectric properties of the Bi2-xSbxTe3 alloys were systematically investigated. The results of this study are compared to those of others, which have addressed similar issues in samples prepared with analogous compaction techniques. ZT value of 1.12 at 375 K for hot pressed Bi0.4Sb1.6Te3 and ZT value of 1.24 at 375 K for hot deformed Bi0.4Sb1.6Te3 were achieved. To our knowledge, the latter ZT value is only slightly lower than the highest ever reported (ZT similar to 1.3) for p-type bismuth telluride-based alloys prepared using starting materials without nanostructuring, suggesting that simpler preparation techniques can be applicable in modules fabrication.