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

•Coefficient of thermal expansion and residual stresses of coatings measured by optimized optical implementation of the substrate curvature method•Different nanostructures obtained by PLD result in different residual stresses and coefficient of thermal expansion.•Nanocrystalline tungsten coatings show a higher compressive residual stress than amorphous like ones.•The coefficient of thermal expansion is strongly correlated to the crystallites dimension.•Amorphous like tungsten coatings have higher coefficient of thermal expansion than nanocrystalline tungsten ones.

The in plane coefficient of thermal expansion (CTE) and the residual stress of nanostructured W based coatings are extensively investigated. The CTE and the residual stresses are derived by means of an optimized ad-hoc developed experimental setup based on the detection of the substrate curvature by a laser system. The nanostructured coatings are deposited by Pulsed Laser Deposition. Thanks to its versatility, nanocrystalline W metallic coatings, ultra-nano-crystalline pure W and W-Tantalum coatings and amorphous-like W coatings are obtained. The correlation between the nanostructure, the residual stress and the CTE of the coatings are thus elucidated. We find that all the samples show a compressive residual state of stress that decreases as the structure goes from columnar nanocrystalline to amorphous-like. The CTE of all the coatings is higher than the one of the corresponding bulk W form. In particular, as the grain size shrinks, the CTE increases from 5.1 10 −6 K −1 for nanocrystalline W to 6.6 10 −6 K −1 in the ultra-nano-crystalline region. When dealing with amorphous W, the further increase of the CTE is attributed to a higher porosity degree of the samples. The CTE of the coatings is also investigated as function of materials stiffness: when stiffness decreases, the CTE increases.

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