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

TL;DR

This study explores how the morphology, composition, and mechanical properties of amorphous tungsten-oxygen and tungsten-oxide coatings are interconnected, revealing how oxygen content influences stiffness, residual stresses, and thermal behavior for potential load-bearing applications.

Contribution

It provides new insights into the correlation between composition, structure, and mechanical properties of amorphous tungsten-oxide films using combined spectroscopic and curvature methods.

Findings

Stiffness decreases with increasing oxygen content and decreasing density.

Amorphous tungsten-oxide films exhibit moderate stiffness, high ductility, and high thermal expansion.

Crystallization at 670 K increases material stiffness by about 70%.

Abstract

In this work, we investigate the correlation between morphology, composition, and the mechanical properties of metallic amorphous tungsten-oxygen and amorphous tungsten-oxide films deposited by Pulsed Laser Deposition. This correlation is investigated by the combined use of Brillouin Spectroscopy and the substrate curvature method. The stiffness of the films is strongly affected by both the oxygen content and the mass density. The elastic moduli show a decreasing trend as the mass density decreases and the oxygen-tungsten ratio increases. A plateaux region is detected in correspondence of the transition between metallic and oxide films. The compressive residual stresses, moderate stiffness and high local ductility that characterize compact amorphous tungsten-oxide films make them promising for applications involving thermal or mechanical loads. The coefficient of thermal expansion is quite high (i.e. 8.9 $\cdot$ 10$^{-6}$ K$^{-1}$), being strictly correlated to the amorphous structure and stoichiometry of the films. Under thermal treatments they show a quite low relaxation temperature (i.e. 450 K). They crystallize into the $\gamma$ monoclinic phase of WO$_3$ starting from 670 K, inducing an increase by about 70\% of material stiffness.