The results of the microhardness measurements are presented in Fig. 8. The hardness values quoted are an average of 30 measurements which were performed on the coating surface, and on five lines distributed along the cross-section. In order to measure the hardness of the diffusion layer formed inside the coating’s bottom layer a lower load of 100 g was used to allow indentation inside the layer. The micrograph presented in Fig. 9a shows the morphology of the new-formed diffusion layer in comparison to the substrate and the coating layers. Fig. 9b indicates the location of the indentation performed on the diffusion layer. Fig. 10 shows a decrease in the substrate microhardness approaching the coating/substrate interface. The results suggest that the treatment carried out at 1200 °C produced softening of the coating bottom layer in the vicinity of the interface (∼30 μm).