Influence of mechanical agitation on the conformal coating of powders

Agitation is required to produce conformal coatings onto powders when line-of-sight deposition is used. In this work, a piston-crank agitation system has been utilized to deposit W coatings onto Al, yttria stabilized zirconia (YSZ), and Cu powder beds with varying levels of agitation. Based on the agitated powder charge characteristics, agitation was found to fall into one of three visual categories: limited, partial, or full agitation. Limited agitation was found to be insufficient for providing conformal coatings to the entire powder bed and occurred below a maximum acceleration of 17.8 m/s(2) for all the powders tested. Above 17.8 m/s(2), partial agitation was observed and identified by visual features that denote mixing of the powder charge, in particular the formation of spatially varied amplitudes of powder oscillations within the container. Full agitation is then categorized by maximizing the presence of these amplitude features that appear as 'ridges' in the powder charge morphology. This was found to occur at different maximum accelerations based on the material type: Al (22.6 m/s(2)), YSZ (27.9 m/s(2)), and Cu (33.7 m/s(2)). Both partial and full agitation allowed for conformal coverage of the entire powder bed with coating thicknesses ranging from approximately 170 to 220 nm for approximately 3.6 kW center dot h depositions, while limited agitation provided insufficient conformal coatings.

Automated summary

Agitation is necessary for producing conformal coatings onto powders using line-of-sight deposition. This study used a piston-crank agitation system to deposit W coatings onto different powder beds with varying levels of agitation. Based on the visual characteristics of the agitated powder charge, agitation can be categorized as limited, partial, or full. Limited agitation was insufficient for providing conformal coatings, while partial and full agitation allowed for complete coverage. The maximum acceleration required for full agitation varied depending on the material type.