Characterisation of shrouded plasma-sprayed Al4C3-Ni alloy composite coatings as novel bond coats for TBCs

Ni/Co-based alloys have been widely employed as bond coats (BCs) in thermal barrier coatings (TBCs) to provide oxidation resistance through the formation of a dense thermally grown oxide (TGO) layer. TGO thickening is a major contributor to TBC failure. Conventional approaches to minimise its growth have included refinement/optimisation of the BC composition, deposition techniques, and post-treatments. However, these approaches have led to only incremental improvements in TBC performance and do not directly address the effect of the thin interfacial oxide layer on the TBC lifetime. In a shift from conventional thinking, the development of an Al4C3-Ni alloy composite bond coat aims to overcome the challenges generated by current TGOs. Post-deposition heat treatment tailors the coating microstructure to form a continuous internal carbide network. At elevated temperatures, the Al4C3 preferentially oxidises to form an interlacing protective Al2O3 “root” that provides better TGO anchoring and reduces TBC thermal mismatch with the substrate. In this paper, the coatings were manufactured through gas-shrouded plasma spraying using various parameters. XRD and carbon analysis were performed on the coatings, and the surface roughness was measured using 3D optical microscopy. The microstructure was observed using SEM. Differences between coatings are discussed in relation to the spraying parameters.