In-Situ Processing of Functional Graded Coatings by Means of Atmospheric Plasma Spraying

Functional graded coatings offer outstanding thermo-mechanical performance to meet economic demands. Influencing the microstructure formation of layers of the coated tool determines the distribution and transfer of heat from the impact zone into the forming process and largely effects the tool life cycle and microstructure in the surface area of the parts to be formed. With respect to graded coatings, examinations have already shown the application of vertical graded multilayers with adjustable microstructures. By using different grain-sized powder materials and utilizing other thermal spraying methods it is possible to generate either porous or dense coatings according to their requirement profile. In particular, the utilization of different thermal spray methods leads to high costs due to increased setup times. As opposed to methods encompassing separate thermal spray processes, the process parameters for graded coatings generated by an in-situ process need to become attuned to robot movements and correlated with dynamic behavior.

In this study we investigated the dependencies between the Atmospheric Plasma Spraying process parameters and characteristics as well as the robot movements such as spray distance and spray angle with the microstructure formation. Statistical design of experiments (DoE) is utilized to enable a systematic analysis of influencing factors along with their interactions on the microstructure formation. The investigation is focused on the utilization of Alumina (Al₂O₃) which is widely used as a wear and corrosion resistant coating.