Coefficient of thermal expansion of nanostructured tungsten based coatings assessed by substrate curvature method

Besozzi, Edoardo; Dellasega, David; Pezzoli, Andrea; Mantegazza, A.; Passoni, M.; Beghi, M.

doi:10.1016/j.matdes.2017.10.001

Cited by 16 publications

(9 citation statements)

References 53 publications

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“…From equations 5 and 6 the CTE of the film, α f , can be derived, if the CTE of the substrate, α s , and the elastic moduli of the film are known. The performances of the setup and more details on the measurements procedure can be found in [25]. Standard thermal annealing treatments are performed in the same apparatus at temperatures between room temperature (RT) and 870 K. All treatments are performed with a dwell annealing time of 1 h, and heating ramps set to ≈ 3 -5 K min −1 .…”

Section: Residual Stresses Cte and Annealing Treatmentsmentioning

confidence: 99%

“…Residual stresses are measured by an optical implementation of the SC method. An ad-hoc developed experimental setup, fully described in [25], exploits a set of parallel laser beams to probe the curvature radius of the coating-substrate system. The scanned area is ≈ 1 cm 2 and the laser beams strike on the uncoated substrate surface before being collected by a high frame rate camera.…”

Section: Residual Stresses Cte and Annealing Treatmentsmentioning

confidence: 99%

“…Young Modulus (E), shear modulus (G), bulk modulus (K) and Poisson's ratio (ν)) at the same time [26,27]. SC, instead, can be exploited to measure the total stresses within the films (σ f ), the residual stresses (σ res ) and the coefficient of thermal expansion (CT E, or α) [25]. The thermal stability of the coatings under high temperatures is assessed by thermal annealing treatments at various temperatures up to 870 K. By performing SC measurements during the annealing treatments, it is possible to derive the evolution of σ f in the film.…”

Section: Introductionmentioning

confidence: 99%

“…The thermomechanical characterization is performed exploiting Brillouin spectroscopy (BS) and the substrate curvature method (SC). The coupling of these two techniques has been shown to be a powerful tool for the characterization of nanostructured films, providing a broad, non destructive characterization of the samples [23,24,25]. In particular, when transparent oxide coatings are investigated, BS can be able to derive, through the detection of surface and bulk acoustic waves, all the elastic moduli of the films (i.e.…”

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Thermomechanical properties of amorphous metallic tungsten-oxygen and tungsten-oxide coatings

et al. 2019

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Metallic amorphous tungsten-oxygen and amorphous tungsten-oxide films, deposited by Pulsed Laser Deposition, are characterized. The correlation is investigated between morphology, composition, and structure, measured by various techniques, and the mechanical properties, characterized by Brillouin Spectroscopy and the substrate curvature method. The stiffness of the films is correlated to the oxygen content and the mass density. The elastic moduli decrease as the mass density decreases and the oxygen-tungsten ratio increases. A plateau region is observed around the transition between the metal-like (conductive and opaque) films and the oxide ones (non conductive and transparent). The compressive residual stresses, moderate stiffness and high local ductility of compact amorphous tungsten-oxide films are interesting for applications involving thermal or mechanical loads. The coefficient of thermal expansion is quite high (8.9 · 10 −6 K −1 ), being strictly correlated to the amorphous structure and stoichiometry of the films. Upon thermal treatments the coatings show a quite low relaxation temperature of 450 K. Starting from 670 K, they crystallize into the γ monoclinic phase of WO 3 , the stiffness increasing by about 70%. The measured thermomechanical properties provide a guidance for the design of devices which include a tungsten based layer, in order to assure their mechanical integrity. mitigating or favoring crack formation. Similarly, in high temperature applications, a significant mismatch between the coefficients of thermal expansion of the coating and of the substrate can induce high interface stresses, with possible coating delamination and device failure. More specifically, in an electrochromic system the W oxide film is part of a complex multilayer system: it is deposited on a transparent conductor, like ITO, and faces the electrolyte, solid or liquid, containing the ions responsible of the electrochromic effect, and can be subject to various and very different stress states [15]. Moreover, in some applications (e.g. solar-cells, thermophotovoltaic) tungsten oxide coatings operate at temperatures above room temperature [16]; this could induce phase transition or recrystallization, with a consequent variation of the as-deposited properties. Although the thermomechanical properties of tungsten based coatings can be crucial for the design of devices which exploit them, relatively fewer studies have investigated the relationship between their nanostructure, composition and mechanical properties [17,18,19]. The goal of this work is to achieve a more comprehensive understanding of the effects of structure, morphology and chemical composition on the thermomechanical properties of different systems of amorphous W-O and WO x coatings, providing useful results for the design of devices. We investigate amorphous films characterized by different oxygen/tungsten ratios and morphologies. To produce them we selected the Pulsed Laser Deposition (PLD) technique, which allows a significant versatility in tailoring the str...

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Section: Residual Stresses Cte and Annealing Treatmentsmentioning

confidence: 99%

Section: Residual Stresses Cte and Annealing Treatmentsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Thermomechanical properties of amorphous metallic tungsten-oxygen and tungsten-oxide coatings

et al. 2019

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“…The elastic properties (i.e. Young's modulus E, Poisson's ratio ν and shear modulus G) and the coefficient of thermal expansion α of the coatings were determined by the combined use of Brillouin spectroscopy and the substrate curvature method in previous works [40,41]. They are summarized in table 1.…”

Section: Sample Pre-and Post-irradiation Characterizationmentioning

confidence: 99%

Nanosecond laser pulses for mimicking thermal effects on nanostructured tungsten-based materials

et al. 2018

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In this work, we exploit nanosecond laser irradiation as a compact solution for investigating the thermomechanical behavior of tungsten materials under extreme thermal loads at the laboratory scale. Heat flux factor thresholds for various thermal effects, such as melting, cracking and recrystallization, are determined under both single and multishot experiments. The use of nanosecond lasers for mimicking thermal effects induced on W by fusionrelevant thermal loads is thus validated by direct comparison of the thresholds obtained in this work and the ones reported in the literature for electron beams and millisecond laser irradiation. Numerical simulations of temperature and thermal stress performed on a 2D thermomechanical code are used to predict the heat flux factor thresholds of the different thermal effects. We also investigate the thermal effect thresholds of various nanostructured W coatings. These coatings are produced by pulsed laser deposition, mimicking W coatings in tokamaks and W redeposited layers. All the coatings show lower damage thresholds with respect to bulk W. In general, thresholds decrease as the porosity degree of the materials increases. We thus propose a model to predict these thresholds for coatings with various morphologies, simply based on their porosity degree, which can be directly estimated by measuring the variation of the coating mass density with respect to that of the bulk.

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Laser Applications in Ceramic and Metal Joining: A Review

Zhao,

Janasekaran,

Fong

et al. 2024

Met. Mater. Int.

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Coefficient of thermal expansion of nanostructured tungsten based coatings assessed by substrate curvature method

Cited by 16 publications

References 53 publications

Thermomechanical properties of amorphous metallic tungsten-oxygen and tungsten-oxide coatings

Thermomechanical properties of amorphous metallic tungsten-oxygen and tungsten-oxide coatings

Nanosecond laser pulses for mimicking thermal effects on nanostructured tungsten-based materials

Laser Applications in Ceramic and Metal Joining: A Review

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