Residual stress and adhesion of thermal spray coatings: microscopic view by solidification and crystallisation analysis in the epitaxial CoNiCrAlY single splat

Fanicchia, F.; Maeder, X.; Ast, J.; Taylor, A.A.; Guo, Y.; Polyakov, M.N.; Michler, J.; Axinte, D.A.

Abstract

A new approach is proposed to achieve an in-depth understanding of crystallisation, residual stress and adhesion in epitaxial splats obtained by Combustion Flame Spray. Modelling of the fundamental process mechanisms is achieved with the help of experimental observations providing details with a sub-micrometre spatial resolution. At this scope, High Angular Resolution Electron Backscatter Diffraction and Transmission Electron Microscopy analysis are employed to provide insights into crystallisation and residual stress levels, while FIB-milled microcantilever beam bending is used for fracture strength measurements in the case of single splats. A comparison to fully-developed coatings is achieved by employing the X-ray Diffraction technique and pull-off methods for residual stress and fracture strength, respectively. The methodology is applied to metallic CoNiCrAlY material sprayed onto a Ni-based superalloy substrate. The establishment of different crystallisation regions: epitaxial and polycrystalline, is the result of variations in the heat flux direction at the solidification front. Significant dislocation density is also reported, indicating the relevance of impact dynamics and plastic deformation mechanisms. The comparison with fully-developed coatings suggests a reduction in inter-splat bonding at splat overlapping.

Citation

Fanicchia, F., Maeder, X., Ast, J., Taylor, A., Guo, Y., Polyakov, M., …Axinte, D. (2018). Residual stress and adhesion of thermal spray coatings: microscopic view by solidification and crystallisation analysis in the epitaxial CoNiCrAlY single splat. Materials and Design, 153, https://doi.org/10.1016/j.matdes.2018.04.040

• Journal Article Type: Article
• Acceptance Date: Apr 13, 2018
• Online Publication Date: Apr 24, 2018
• Publication Date: Sep 5, 2018
• Deposit Date: May 31, 2018
• Publicly Available Date: Apr 25, 2019
• Journal: Materials & Design
• Print ISSN: 0261-3069
• Electronic ISSN: 0264-1275
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 153
• DOI: https://doi.org/10.1016/j.matdes.2018.04.040
• Keywords: Thermal spray, Splat, Crystallisation, Epitaxial growth, Residual stress, Solidification microstructure,; Fracture mechanism, Plastic deformation
• Public URL: https://nottingham-repository.worktribe.com/output/949851
• Publisher URL: https://www.sciencedirect.com/science/article/pii/S0264127518303101