Abstract: Zirconia based bioglass-hydroxylapatite coatings were prepared using slurry-dipping and sintering method. Mechanical and thermal properties of
the coatings were investigated. The results obtained in the experiment showed that the hydroxylapatite content in composite materials has great effect on
their thermal expansion properties. This is due to the main phase change from bioglass phase to hydroxylapatite phase in the microstructure. Thermal stress
in the graded coatings was theoretically calculated, which showed that the difference of thermal expansion properties between coating and substrate has
a greater effect on the thermal stress in the coating. Bonding strength between coating and substrate was tested according to
ASTM-C633, and the result is in accordance with the calculated thermal stress in the coating.

Key words: hydroxylapatite coating, graded material, thermal stress