Thermal and Elastic Anisotropy of Thermally Sprayed Coatings

The dependency of the physical property of thermally sprayed coatings on the microstructure which is characterized by a composite of lamellae was examined. The thermal and elastic properties determined parallel to the coating plane have been proved to be different from those determined perpendicularly to it, which indicates that the thermally sprayed coatings have an anisotropy. The thermal conductivities of copper, molybdenum, Type 316 austenitic stainless steel, alumina and WC-20 mass%Cr-7 mass%Ni cermet coatings are discussed. The values parallel to the coating plane were 1 to 2.27 times larger than those perpendicular to it. The behavior of anisotropy can be explained by the rule of mixture. Young’s moduli in the two directions of WC-12 mass%Co cermet coatings were measured and the value parallel to the coating plane was about twice as large as that perpendicular to it. The thermally sprayed coatings may be characterized by a composite of rapidly solidified lamellae between which there is only limited real contact and they also contain pores and oxides. It is clear that the directionality characteristic of the thermal barrier behavior or the less cohesion among the lamellae is dominant over the anisotropy of thermally sprayed coatings.