Study on influence of porosity, pore size, spatial and topological distribution of pores on microhardness of as plasma sprayed ceramic coatings

Plasma sprayed ceramic coatings invariably form with at least 5–10% porosity due to inherent deficiency in the spray technology. On many occasions, the volume fraction, size and distribution of the pores alone do not suffice to predict properties such as microhardness. The spatial and topological arrangement of the pores in the precinct of intended hardness measurement area appears to be the most important parameters which could be directly correlated to hardness. In this paper an attempt was made to measure the topological and spatial distribution of the pores mathematically, respectively, with Voronoi cells and Euclidean distance mapping. The influence of pores on microhardness of the coatings was determined at loads of 2.97 N, 4.9 N and 9.8 N from 10 locations at every specified load. At intermediate and higher loads the influence of cluster and neighbor distance between pores could be easily elucidated. Hardness was found to be larger on occasions and for those locations which would result in large number of Voronoi cells corresponding to a cell area of 5000 pixels. Similarly, in terms of Euclidean distances, the hardness was found to be larger from areas which showed large number of widely separated pores.