Characteristics Evaluation of Plasma Sprayed Ceramic Coatings by Nano/Micro-Indentation Test

The most controversial topics in plasma sprayed ceramic coating systems recently are mechanical properties such as bond strength, cohesive strength and toughness. In our research, critical fracture load (P _c) and interface toughness (K _c) of four-coating materials were computed from the applied load, crack length and Young's modulus data that were measured by micro-Vickers and a nano-indentation test. It is reasonable to consider the P _c value as comparison data of bond strength, and the K _c value, considering a trace of indent in the interface, was computed by a modified (E/H)_I ^1/2ratio. Also, we knew that P _c decreased as the hardness of the coating increased. In the case of the high load (9.8 and 19.6N) in the Al₂O₃+13%TiO₂ coating, the critical point (P _co) was found at which the coating was broken. Used by a XRD phase analysis, we checked changes of the coating's properties and predicted a possible change of the phases in plasma-sprayed coating.