Effect of Heat Treatment on Bonding Strength of Plasma Sprayed Al₂O₃-13%TiO₂ Coating

Plasma sprayed Al2O3-13% TiO2 coating with NiCrAl bond-coating was prepared on the Q235 steel substrate and then heat-treated at 300-900 ℃ in air, vacuum and Ar atmosphere, respectively. The influences of heating temperature, holding time and heat treatment atmosphere on the microstructure and bonding strength of the coating were investigated by means of optical microscope, SEM, XRD and electronic universal testing machine. The results show that the atmosphere had less effect on the bonding strength, the holding time had more, and the heating temperature had the most effect. Through a suitable heat treatment, the micro-crack size could be decreased and the bonding strength could be increased. Compared with the original coatings, the bonding strength of the coating was increased by 62.5%, up to 31.2 MPa after vacuum heat treated at 500 ℃ for 6 h.