Effect of stand-off distance for cold gas spraying of fine ceramic particles (< 5 μm) under low vacuum and room temperature using nano-particle deposition system (NPDS)

The nano-particle deposition system (NPDS) is a novel fabrication method for metallic and ceramic coatings at room temperature that sprays dry nano-sized powder or micro-sized powder without binders or additives. NPDS has been used to coat metal, ceramic, and polymer substrates with various metal and ceramic powders such as TiO2, Al2O3, Ni, and Sn. Deposition results have been reported, but the process parameters have not been evaluated in detail. The effect of the stand-off distance (SoD), which is an important process parameter and is easily controlled during fabrication, was evaluated in this study to better understand the process. Numerical analysis of the impact velocity of particles using the commercially available ANSYS CFX software package and experiments examining Al2O3 deposition on sapphire wafers (Al2O3) using NPDS was carried out. In NPDS, the impact velocity of particles is one of the most important deposition parameters because the sole energy source for bonding is the kinetic energy of the particles. The SoD range was set from 1 to 7 mm in 2-mm increments. Numerical analysis showed that the impact velocity of particles increased with increasing SoD. The impact velocity of particles correlated with the mechanical properties of the deposited layers. High impact velocity resulted in high mechanical properties for the deposited layer within the range of SoD tested. SoDs longer than 7 mm were not evaluated because the width and thickness of deposited layer were not suitable for patterning. Additionally, numerical analysis also helped explain the deposition geometry, especially the width of the deposited pattern under the 1-mm SoD condition. The numerical analysis used in this study can be applied to research on the effects of other process parameters.