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 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 trend is also
investigated as function of materials stiffness. In this case, as W coatings
become softer, the easier they thermally expand.Comment: The research leading to these results has also received funding from
the European Research Council Consolidator Grant ENSURE (ERC-2014-CoG No.
647554
