Reduction of shadowing effect during laser cladding of fused silica glass using sub-micron powders

Fused silica glass is a commonly used high-performance material in scientific and industrial applications, due to the exceptional optical, mechanical and thermal properties. However, its production can be challenging and expensive due to the high processing temperatures required, in both manufacturing and geometrical structuring. In this work we have studied additive manufacturing of transparent fused silica glass using the laser cladding process. Here a CO2-laser is used to locally melt the glass, while injecting a stream of glass powder into the hot-zone. A challenge specifically addressed in this work is the shadowing effect, i.e., when the injected powder interacts with the laser beam resulting in non-stable heating dynamics, and partial sintering of powder prior to reaching the substrate surface. To reduce these effects, we have studied the use of sub-micron sized glass powders in order to minimize the laser beam interactions, both absorption and scattering. Using fumed silica powder injected via a single, off-axis nozzle, combined with additional powder cone shaping gas, transparent silica glass has been fabricated with an achieved deposition efficiency of up to 30 %. Typical, single deposition tracks have a width of approximately 850 μm with single layer heights of up to 150 μm.