Recently, several models have been developed to simulate the plasma spraying process. The present paper extends our previous model (Wan et al., 1999a) to the plasma spray system of two-component materials with two different feed nozzles. It accounts for plasma-particle interaction, particle heating/melting/evaporation and solidification on the substrate. A special visualization algorithm has been developed to demonstrate the effects of various parameters on particle conditions while in flight, growth of functionally graded materials and distribution of the two components in the coating. Visualization of thermal processes is a challenging task if it has to be used for materials design and system development. It requires special schemes for data management in a multivariate system that includes at least velocity, temperature and species in four co-ordinates (space and time). Our effort is focused on developing a visualization scheme which goes far beyond the process animation and can be ultimately used for virtual prototyping of the processes, an area that needs special research efforts. Simulation and visualization have been performed for spraying of zirconia and NiCrAlY powders, with many combinations of powder injection features, e.g., number of nozzles, nozzle location and injection velocity. The fluctuation of the voltage is also simulated and animated to show its effect on both plasma gas and particle behavior. The optimized operating parameters are deduced from the distribution of these two materials in the coating layer. Issues related to visualization are also discussed.