Development of novel metallic feedstock materials for heating elements produced by thermal spraying

• Applicant: Professorin Dr.-Ing. Kirsten Bobzin
• Subject Area: Coating and Surface Technology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 538498638

In the course of the project, new high-entropy alloys (HEA) have been developed and characterized by melt metallurgy for future application as thermally sprayed heating elements. Heating elements produced by thermal spray (TS) offer the advantage that they add only a few hundred micrometers to the surfaces to be heated and allow dynamic temperature control due to their low thermal mass. Conventional metallic heating alloys have a relatively low resistivity, so long, thin conductive tracks must be applied to achieve the necessary heating resistance. In contrast, ceramic semiconductors based on TiO2 can be applied over large areas due to their high resistivity. Since these ceramic semiconductors consist of suboxides, their application temperature is limited due to the re-oxidation that occurs. HEA tend to offer higher resistivities than conventional alloys and mostly exhibit consistently good properties at elevated temperature. In previous work, the addition of Si and Zr, which have relatively small and large atomic radii, respectively, to the Al0.5CoCrFeNi HEA resulted in enhanced lattice distortion, which significantly increased the resistivity. In addition, thermal expansion, fracture toughness, phase stability under argon, and oxidation in air were investigated. Using the alloys Al0.5CoCrFeNiZr0.2Si0.2 and Al0.5CoCrFeNiZr0.5Si0.2, the positive results of melt-metallurgical alloy development are tob e transferred to TS coatings. The processing of the alloys with TS leads to a modified microstructure, which is expected to further increase the resistivity and thus positively influence their suitability as heating elements. To this end, TS-specific fine powders are to be procured at the beginning of the project as a custom-made product. In order to achieve the lowest possible oxidation and homogeneous coatings with the fine powder, high velocity air fuel (HVAF) spraying will be selected as a process variant. The coatings will be investigated for their resistivity, thermal expansion and fracture toughness and compared with the material data of the fused samples. For the final qualification of the developed coating system, cyclic heating tests are carried out to check the heating behavior as well as the thermal shock resistance.

• DFG Programme: Research Grants
• International Connection: Canada
• Cooperation Partner: Professor Andre McDonald, Ph.D.