Effect of Annealing with Pressure on Tungsten Film Properties Fabricated by Atmospheric Plasma Spray

In this study, the effects of various annealing conditions on tungsten film fabricated by atmospheric plasma spraying (APS) were studied to analyze the APS tungsten film and an adequate strategy for the improvement of the mechanical properties of the tungsten film In general, the use of the APS method to create tungsten films results in splat boundaries in an oxidized state not unlike semi-cracks. We therefore conducted vacuum annealing of the tungsten film at 800 degrees C and 950 degrees C under less than 0.1 Torr pressure to strengthen the binding force between splats. Additionally, we conducted press annealing in order to achieve a more dramatic improvement. The micro-hardness of the as-sprayed tungsten film, the vacuum-annealed tungsten film, and the press-annealed tungsten film were 1.55, 1.52, and 2.19 GPa respectively. By utilizing analysis methods such as electron back-scatter diffraction, scanning electron microscopy, Raman spectroscopy, and nano-indentation, we found that filling the gap between the splats, while eliminating the oxides, played a critical role in enhancing the mechanical properties of the tungsten film fabricated by means of the APS method.