The variations of the maximum normal stress distributions with
the coating thickness on the TC, the BC and the SUBS surfaces are
shown in Fig. 12. The maximum value of the thermal stress is
observed on the BC surface and its value is 302.5 MPa for 0.2 mm
coating thickness. When the coating thickness increases gradually,
the maximum stress decreases by decreasing rate. The reason for
the decreasing thermal stress is that the ceramic material has low
thermal conductivity. As regards the coating surface, the maximum
normal stress is 174.8 MPa for the same coating thickness. When
the coating thickness increases gradually, the maximum normal
stress decreases at a decreasing rate on the top coating and bond
coat surface. Reduction of the thermal stress on the coating surface
is higher than that of the bond coat surface. In the substrate, the
maximum normal stress rises with coating thickness but at a
decreasing rate. Its value is 161.1 MPa for 1.6 mm coating thickness.
It is obvious that the maximum thermal stress is a function of
coating thickness. The reason for this is that SUBS material has high