Influence of plasma heat flux on segmentation cracking and permeability of thin suspension plasma sprayed coatings

Solid oxide fuel cell electrolytes with thicknesses of approximately 30 μm were deposited by suspension plasma spraying. The torch pass speed (the relative speed between torch and substrate) was adjusted to vary the amount of heat transferred from the plasma to the accumulating coating surface with each pass. With porous stainless steel substrates, no segmentation cracks were observed in electrolytes made with any spray conditions and torch pass speeds, and pass speed did not strongly affect electrolyte permeability. With substrates consisting of cathode or anode layers on porous steel supports, segmentation cracks were observed in most coatings, and the frequency of these cracks diminished with higher torch pass speeds. Electrolyte permeability with these substrates was also lower with higher pass speeds. ter understand the results, plasma-to-surface heat flux profiles were determined for a variety of spray conditions, and these data were used as boundary conditions to model coating and substrate temperatures during spraying. The model found that increasing the pass speed from 64 to 380 cm s− 1 should reduce the peak temperature difference between the electrolyte surface and the steel support by 35 to 40%. It is believed that a reduction in this temperature difference was the primary reason for the observed reduction in segmentation cracking with higher torch pass speeds.