Transmission electron microscopy study of rapid solidification of plasma sprayed zirconia – part II. Interfaces and subsequent splat solidification

Transmission electron microscopy (TEM) is used to investigate the first two splat layers of a plasma sprayed yttria stabilized zirconia (YSZ). Sample preparation by modified wedge polishing technique and results for the first splat were presented in the first part of this paper. The second part focuses on two different interfaces present in the microstructure, rough substrate effects on first splat solidification, and finally on solidification of the second splat layer. The interface between plasma sprayed ceramic and metal substrate as well as the interface between two subsequent splats were examined by conventional and high resolution TEM. The presence of a thin layer of native oxide on polished and preheated stainless steel substrates was established. Such an interface appears to promote very good adhesion of YSZ. The effect of liquid flow on the solidified microstructure of the second and subsequent splats was clearly demonstrated. The top surface of the first solidified splat acts as an excellent nucleation site for a subsequent splat and causes epitaxial growth of columnar grains in subsequent splats.