Real Time Modeling and Control in Plasma Arc Fabrication of Intermetallic Coatings

Successful fabrication of intermetallic coatings on surfaces of manufacturing interest involves regulation of the temperature/ concentration dynamic distributions that develop in the molten layer during the thermal and reaction process. Modeling the spatio-temporal dynamics of this metallurgical process, however, requires partial differential equations that are cumbersome to solve on-line, as part of a real time reference model to the controller. To this end, we present a computationally parallel and meshless model to decipher the dynamics of the thermal coating process and to permit real time monitoring and control of the resulting coating microstructure. The analytical model, which is solved numerically using Matlab, is validated with nickel aluminide coatings processed on a robotic plasma arc laboratory station, through in-process infrared thermal sensing and off-line metallographic analysis. A proportional-integral control scheme, that involves on-line parameter identification and model adaptation, is also developed to facilitate the successful production of binary metal system coatings that exhibit the desired microstructure geometry and characteristics.