Research on material- and process-related interactions in thermally sprayed multicomponent coating materials using a ternary oxide coating system as an example

• Applicants: Privatdozent Dr. Lutz-Michael Berger; Professor Dr.-Ing. Thomas Lampke
• Subject Area: Coating and Surface Technology
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 512399998

The development of new applications for thermally sprayed coatings is characterized by a variety of challenges. Therefore, much better-defined compositions and controlled microstructures are required than is currently the case in many successful conventional applications. Studying the complex material- and technology-related processes in multicomponent materials during thermal spraying represents the overall objective of the project, in order to avoid changes in the compositions and to be able to produce single-phase coatings with a homogeneous microstructure and defined property profile. This is carried out on the basis of the model system Al₂O₃-Cr₂O₃-TiO₂. In this case, the α-phase (Al,Cr,Ti)₂O₃ (stabilization of corundum) and the E-phase (Al,Cr)₂Ti₂O₇ offer promising opportunities. Numerous previous studies have already shown that differences in the structure of powder materials with the same nominal composition, as well as different spray parameters, cause a strong variance in coating microstructure and properties. Therefore, obtaining knowledge about the location and process of reactions is an essential part of the project. The possible location of the reaction responsible for the change in chemical composition can be limited to the following five areas: (I) During the preparation of the spray powder; (II) Immediately after powder injection in the plasma; (III) In the spray jet; (IV) After "splat formation" on the substrate and subsequent cooling within a splat and between multiple splats; (V) During a post heat treatment of the coating. The coating microstructures are influenced both by the control of the spraying process and by the design of the powder material. By varying the degree of homogeneity of the element distribution in powders of the same nominal composition, the reactivity in the spraying process can be adjusted. For this purpose, simple powder blends of commercially available fused and crushed powders as well as experimentally produced agglomerated and sintered (a&s) powders are used in the project. The localization of the reaction spot is achieved by the investigations of single splats, trapped particles, a detailed process diagnostic and the analysis of the coating microstructures (XRD, EDX, EBSD, ...). An in-depth understanding of the complex interactions between powder material, spray process and coating microstructure allows optimized process parameters to be developed. Using a suitable heat treatment, coatings whose powder materials do not fully react in the spraying process are subsequently homogenized. The coatings are also characterized in terms of their property profile (electrical, corrosive, tribological, mechanical).

• DFG Programme: Research Grants