Microstructural observations of plasma sprayed thick films of nickel and laminated composites of Al2O3/MoSi2, have been made. It is shown that the lack of control of temperature gradients across the thickness of the deposit results in enormous microstructural gradients. Computational algorithms have been developed which trace the development of temperature gradients across the deposit thickness during rapid solidification by plasma processing. Based on reduced order models of heat transfer, a control problem is set up in order to minimize the temperature gradients across the deposit thickness, which consequently results in the desired microstructure and minimum residual stresses. The impact of the lack of such a temperature gradient control on microstructural evolution of the deposit is investigated, and the necessity of temperature gradient control is emphasized.