Abstract
In this investigation, submicron YSZ particles suspended in ethanol were sprayed on stainless steel substrates using a single-electrode cascaded arc-plasma torch. Various coating morphologies were produced by changing the input power, gas flow rate, and injection angle of the gun. Coating thicknesses between 500 and 600 μm were achieved for all experimental runs and stress evolution was monitored using an in situ coating property (ICP) sensor that measures changes in substrate curvature. Based on the stress-modulus relationship, there can be four microstructural zones in the coatings: a porous feathery zone, a dense columnar zone, a dense vertically cracked (DVC) zone, and a zone with cracked and defective columnar structures. From ICP curvatures, it was found that the porous columnar structures are highly compliant, the dense columnar structures are stiff, and the DVC structures are dense and compliant. The dense columnar and DVC microstructures displayed a twin stage curvature change which clearly indicated the stress build up, onset of cracking, and stress relief after axial crack propagation.
