Stochastic Modelling of Cold Spray Coatings Microstructure

Modern materials manufacturing has evolved toward a better control and optimization at the microscopic scale. Hence, microstructures commonly exhibit complex morphologies mixing various materials including carbon fibers arrangements into polymer matrix. The physical and mechanical features of heterogeneous materials at the macroscopic scale are largely dictated by phenomena appearing at the microscopic level.

In this study, our aim was to simulate the electrical properties of a bi-phased coating obtained by thermal spraying and used to cover the body of recent commercial aircrafts. The role of the coating is to protect the aircraft from lightning impact by ensuring that the surface is conductive enough to evacuate electrical charges.

We developed a 3D stochastic model describing the coating microstructure, derived from experimental images of slices of the material taken with a microscope. The microstructure is constituted of copper particles embedded in a polymer matrix. The particles are separated by thin interstices of polymer. In terms of resistivity, a high contrast prevails between the polymer and the copper particles. Hence, a key issue toward an effective modeling of the microstructure is to accurately reproduce the interstice thicknesses and repartition. To that end, we introduced a new stochastic model derived from the classical Johnson-Mehl tessellation that enabled us to properly reproduce these geometrical characteristics. The method is very general and could potentially be applied to model any microstructure exhibiting similar interstices between aggregates of particles.

Figure1_SimulatedMicrostructure

FIG. Comparison between a slice of a 3D simulation of the coldspray microstructure and a slice of the actual microstructure, as observed on a microscope. The resolution is 0.484 microns per pixel.

Team and funding

This project was funded by the Air Force Office for Scientific Research and involves researchers from the Centre for Mathematical Morphology, MINES ParisTech, and from the Centre for Materials engineering, MINES ParisTech. The team of researchers involved in this project is composed by Vincent Bortolussi, Bruno Figliuzzi, Michel Jeandin and François Willot.

Reference

Morphological Modeling of cold spray coatings, V. Bortolussi, B. Figliuzzi, F. Willot, M. Faessel, M. Jeandin. To appear in Image Analysis and Stereology (2018)

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