The effects of sealing on the mechanical properties of the plasma-sprayed alumina-titania coating

Mechanical properties of plasma-sprayed ceramic coatings were studied before and after sealing treatment. Plasma-sprayed Al2O3–13 wt.% TiO2 coating as the reference coating was sealed using three commercial sealants based on polymer. Penetration depth of the sealants to the ceramic coating was evaluated directly from the optical microscope using a fluorescent dye. It is estimated that the penetration depth of the sealants to the ceramic coating is from 0.2 to 0.5 mm depending on the sealants used. All of the microhardness, two-body abrasive wear resistance, bond strength and surface roughness of the ceramic coating after the sealing treatment are improved. The extent of improvement is different from the sealants used. However, three-point bending stress of the ceramic coating after the sealing treatment is decreased. This is attributed to the reduced microcrack toughening effect since the cracks propagate easily through the lamellar of the coating without crack deflection and/or branching after the sealing treatment.