Modeling the Melting and Dissolution Stages During Thermal Processing of Intermetallic Coatings from Layered Precursors

Abstract

This paper presents a simple analytical model of the temperature and concentration dynamic distributions during thermal processing of intermetallic and metal-matrix composite coatings, such as nickel aluminide coatings on steel substrates, by melting, e.g., preplated aluminum/nickel layers using a moving heat source such as a plasma arc. Such a source of Gaussian power distribution scans the surface of the coating, giving rise to the temperature evolution and component dissolution during the thermal melting and reaction process. The model is based on a system of 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), and is solved numerically in real-time. The simulation results are validated on Ni–Al coatings processed using a robotic plasma arc laboratory station, through in-process infrared thermal sensing and off-line metallographic analysis. It is shown that the predicted temperature and dissolution penetration values compare well with the experimentally obtained results, therefore supporting the model as a real-time basis for design and/or adaptation of a thermal control system for the coating process.