Modeling the intermetallic coating growth during reactive thermal processing of layered precursors

This paper presents an analytical model for the intermetallic coating growth that occurs during reactive thermal processing of layered elemental precursors when using a moving Gaussian heat source such as a plasma arc. The model, which is solved numerically in real-time, is based on kinetic growth theories, lumped energy and mass balances, and convolution expressions of distributed temperature and concentration Green's fields (accounting for the orientation of their gradient and decomposing heat and mass transfer across the coating from substrate conduction). The numerical results are validated with Ni-Al coatings processed on a robotic plasma arc laboratory station, through in-process infrared thermal sensing and off-line metallographic analysis. It is shown that the predicted coating temperature and thickness of the coating layer compare well with the experimentally obtained results, therefore supporting the use of the model as a real-time basis for design and/or adaptation of a thermal control system for the coating process. Furthermore, the results suggest the applicability of the model to address the growth of intermetallics in melts of uniform and non-uniform initial solute concentration.