Mechanical characterization of plasma sprayed ceramic coatings on metal substrates by contact testing

Hertzian indentation testing is used to generate contact damage in plasma sprayed ceramic coatings on metal substrates. Two basic ceramic/metal coating/substrate systems are examined: alumina on steel and zirconia on superalloy. Macroscopic mechanical responses are measured via indentation stress-strain curves, which quantify the relative role of the coating and substrate in the net deformation and facilitate evaluations of elastic moduli and yield stresses. Micromechanical damage processes within the coating and substrate subsurface layers are studied using a ''bonded-interface'' specimen. Degradation occurs primarily by delamination and other cracking at the coating/substrate interface or in the coating, but plastic deformation of the metal substrate contributes importantly to the crack driving force.