β-TCP coatings on zirconia bioceramics: The importance of heating temperature on the bond strength and the substrate/coating interface

• Published in: Journal of the European Ceramic Society 2018-12, Vol.38 (15), p.5264-5269
• Main Authors: Stefanic, Martin, Kosmač, Tomaž
• Format: Article
• Language: English
• Subjects: Bioactive coating; Bond strength; Interface; Tricalcium phosphate; Zirconia
• ISSN: 0955-2219; 1873-619X
• DOI: 10.1016/j.jeurceramsoc.2018.06.028

•Heating temperature has a strong influence on the bond strength of β-TCP coatings to zirconia ceramics and microstructure of the substrate/coating interface.•Heating at 800 °C and 900 °C results in the formation of defect-free β-TCP coatings with excellent bond strength (∼50 MPa) to zirconia substrate.•Heating at 1100 °C or higher results in the formation of β-TCP coatings with significantly reduced bond strength (∼30 MPa) as the result of substantial structural and microstructural changes at the interface: excessive microcracking of the coating, diffusion of Y3+ from the zirconia in the coating resulting in partial transformation of tetragonal zirconia into monoclinic form, surface roughening of the substrate (formation of surface uplifts) and generation of nanoporosity in the substrate.•Heating temperature does not have an effect on the flexural strength of the coated zirconia substrates under monotonic loading. β-tricalcium phosphate (β-TCP) coatings were synthesized on tetragonal zirconia (Y-TZP) discs by heating the apatite coating between 800 °C and 1200 °C. The study results suggest that heating temperature has a strong influence on the coating bond strength and microstructure of the substrate/coating interface. The β-TCP coatings fired at 800 °C and 900 °C exhibited excellent tensile bond strength (∼50 MPa) while heating at 1100 °C and 1200 °C led to decreased bond strength (∼30 MPa) as the result of substantial structural and microstructural changes: diffusion of Y3+ from the zirconia substrate in the coating resulting in partial crystal transformation (t-m) of zirconia, formation of surface uplifts and nanoporosity in zirconia, as well as generation of large residual thermal stresses leading to microcracking of the β-TCP coatings. However, these structural changes did not have any measurable effect on the flexural strength of the bulk zirconia substrates.