Quantitative characterization of lamellar microstructure of plasma-sprayed ceramic coatings through visualization of void distribution

The visualization of the detailed microstructure of plasma-sprayed ceramic coating was realized through energy dispersed X-rays (EDX) line analysis of the distribution of an infiltrated element as a tracer. A method was proposed based on an idealized lamellar structure model that the coating consisted of a stacking of lamellae with an identical thickness and the EDX line distribution of a tracer in the coating to quantitatively characterize the microstructure of plasma-sprayed coatings. The characterization was performed using structural parameters including lamellar bonding ratio, mean lamellae thickness and interlamellar gap size distribution. The experiment was carried out using plasma-sprayed alumina coating with the infiltration of Cr2O3 as the tracer through chromic acid. The measurement yielded a mean bonding ratio of 32% between the lamellar interfaces, a mean lamellae thickness of 1.2 μm and a bimodal distribution for interlamellar gaps. The mean bonding ratio was defined as the ratio of the total bonded area to the total apparent interface area. These results agreed well with previously reported results obtained by copper plating technique. It was revealed that the proposed method could be applied to quantitatively characterize the lamellar structure of plasma-sprayed coatings.