Study on the interface strength of zirconia coatings by a laser spallation technique

Tensile strength of interfaces between zirconia coatings and stainless steel substrates were measured using a laser spallation technique. In this technique, a laser-generated compression stress wave reflects into a tensile wave from the free surface of the coating and pries off its interface at a critical amplitude. Zirconia coatings were deposited using the gas tunnel-type plasma spraying process which was previously shown to result in denser and harder deposits compared with those produced by conventional spray methods. The interface strength was found to increase with a decrease in the spray distance and traverse speed, and with an increase in the traverse number, and coating and substrate thickness. The variation in the measured strength with these variables could be explained through their effect on controlling the temperature of the particles and that in the interfacial region. Higher temperature in the interfacial region during coating deposition is expected to increase adhesion by enhancing chemical and physical bonding mechanisms. Depending upon the processing conditions used, the tensile strength for the zirconia/steel interface system was found to vary anywhere between 206 and 501 MPa. (C) 2004 Elsevier Ltd. All rights reserved.