Effect of Particle Velocity on Porosity and Residual Stress in Aerosol Deposited Refractory Films

Aerosol deposition (AD) is an impact consolidation process utilizing high velocity micron-sized powder at room temperature in vacuum. The unique properties of AD allow it to be used to produce refractory coatings (ex. tantalum and alumina) on temperature sensitive substrates. Due to particle deformation during deposition, AD films exhibit large residual stress which can result in delamination or cracking. Beam curvature measurements during Ta deposition were obtained using an in-situ laser displacement diagnostic and verified ex-situ using Almen strip displacement measurements to determine coating stress. In-flight Ta particle velocity was varied by modifying nozzle geometry. This work finds that higher particle velocity results in increased residual stress. This study also determined that higher particle velocity resulted in higher Ta coating density. Using image analysis, the density was determined to span ~66-86% dense over a range of ~320-840 m/s particle velocities. Therefore, the desired coating properties dictate the necessary particle velocity.