Plasma Spray deposition methods of high performing coatings on complex geometries components
An Italian large enterprise, experts in projects in which materials, technology and innovation play a critical role, developed a custom method for the deposition of high performing coatings. This process has been realised for space components with complex geometries in terms of shape and/or size by application of the Plasma Spray technology. The company has also designed and manufactured smart dummy models for deposition trials to plan and test the torch scanning trajectory.
An Italian company developed a deposition method for high performing coatings on components with complex geometries by application of the Plasma Spray technology. More in general, Thermal Spray is a generic term for a group of processes which involve the deposition of coatings from a stream of molten or semi-molten material impinging onto the substrate. Coating technologies allow the design of the surfaces and substrates as a functionally graded system. This is achieved by selecting the best performing bulk material and supplying the required surface properties for the specific targeted applications. High performing thermal spray coatings can provide different functions such as wear and corrosion protection, thermal barrier, clearance control, etc. Plasma Spray, the technology applied by the Italian provider, is the most versatile of all the thermal spray processes and it had been selected as the enabling technology within the Project “ASA - Advanced Structural Assembly” sponsored by the Italian Space Agency (ASI). Within the framework of the Project, manufacturing activities had been carried out to deposit UHTC (Ultra High Temperature Ceramics) on space vehicles components (WLE - Wing Leading Edge) which had been tested in a Plasma Wind Tunnel facility. The utilisation of plasma spray coating technology allows the spraying of almost any metallic or ceramic materials (materials with very high melting point: e.g. oxides, carbides, refractory metals, etc. and specific compositions like graded coatings, ceramic tailored compositions, etc.) on to a large range of substrates with exceptional bond strength, while minimizing distortion of the substrate. In order to ensure the achievement of the required quality of the coatings, as well as the reproducibility of the production process, automated robot assisted manufacturing and control systems are widely used in the field of thermal spray. The trajectory of the torch has a significant influence on the heat and mass transfer during the coating process. The structure and final properties of the coating can be improved by using appropriate trajectories and speed profiles of the torch. Furthermore, a proper design of the torch trajectory could allow avoiding undesirable wastefulness of coating powder. Within ASA project, indeed, the Italian company had the possibility to carry out manufacturing studies to improve the design of the torch scanning trajectory in order to achieve the exacts coating required properties and to optimise the deposition process. To achieve these goals, the Italian company also designed and manufactured smart dummy models for deposition trials to plan and test the torch scanning trajectory. Application of proper dummy models had proved to be a very useful tool to coat the test article in the ASA Project, which was characterized by both large dimension and leading edge shape. Furthermore, the company experience in Thermal Spray processes efficaciously supported the identification of those areas of the component which would be difficult to properly coat and this drove the design of the proper dummy model to plan and test the torch trajectory. On the other side, the large experience in manufacturing processes allowed the production of the proper dummy model, both in terms of geometry and base material in order to test heat and mass transfer.
Innovations & Advantages
The synergy between Plasma Spray process and manufacturing of dummy models supplied a powerful engineering design tool, subject of the present technology offering. The flexibility of the Plasma Spray process, indeed, allows the deposition of almost any material composition, which could be impossible to be used in component manufacturing. More in details, the Plasma technology allows the deposition of many materials but it is most effective for the deposition of materials with very high melting point (eg. oxides, carbides, refractory metals, etc) and specific compositions which are difficult to obtain in a different way like graded coatings, ceramic tailored compositions, ultra high temperature ceramics (UHTC). Moreover, the manufacturing of the dummy models supported the overcoming of the difficulties due to the coating of complex geometries. Thanks to the design and utilisation of dummy models, it was also possible to plan the torch scanning trajectory in order to get a successful coating process in terms of deposit uniformity and to minimize coating powder waste in case of use of high expensive or toxic material. Furthermore, unwanted component overheating occurring during the deposition process could be avoided, without resorting to the common used tool of cooling systems, which can be difficult to be applied or not recommendable. Application of dummy models in coating process trials can also support a proper design of the component in order to limit the difficulties encountered during the deposition process. This involves a particularly high value when the coating process of the component cannot be avoided, as for example in case of space vehicles or orthopaedic prosthesis.
Current and Potential Domains of Application
The experience gathered by the donor within the ASA project could be applied in application different from the thermal coating of highly stressed space components. Optimised and high performance coating of complex geometries in terms of shape and/or size might be needed, for example, in the Energy sector for rotating and non-rotating components of turbines or in the medical sector for the covering of orthopaedic prosthesis.