Indentation responses of plasma sprayed ceramic coatings

This investigation aims at finding the Vickers and Knoop indentation responses of a few plasma sprayed ceramic coatings, namely Indian alumina, imported alumina, zircon, plasma dissociated zircon (PDZ) and zircon—20 wt% CaO. Some of the sprayed coatings under Vickers indentation show typical Indentation Size Effect (ISE) while others exhibit Reverse Indentation Size Effect (RISE). Such coating behaviour may be attributed to the heterogeneous phase composition and microstructure of the coatings. “True Hardness” and “Elastic Modulus” of the ceramic coatings have been calculated. Also the ISE phenomenon observed for all the coatings undergoing Knoop indentation are explained using models such as Meyer's law, Normalised Meyer's law, Hays' Kendall Approach and Proportional Resistance models. These models have so far been used for explaining the ISE behaviour of only the sintered crystalline ceramics. In this paper, it has been shown that these models hold good to an appreciable extent for plasma sprayed ceramic coatings as well.