The numerical simulations clearly show that temperature and
thermal stress distribution are a function of coating thickness. For
all the coating thicknesses, the highest temperature appeared at
the crown center and on the edges of the bowl rim on the top
surface of the coating and on the piston surface. The temperature at
the surface of the coated region is significantly higher than that of
the uncoated piston surface. Increase in the maximum temperature
at the crown center, compared with the uncoated piston, is 32.7%,
55.8%, 72.5% and 84.8% for 0.4 mm, 0.8 mm, 1.2 mm and 1.6 mm
thick coating, respectively. It is clear that a higher combustion
chamber temperature is provided by means of TBC. As a result,
thermal efficiency of the engine increases. Moreover, reduction of
the piston (substrate) surface temperature has a positive effect on
engine performance.
It is quite obvious that the maximum thermal stress is a function
of coating thickness. The maximum normal and shear stress components
occur in the bond coat. The results indicate that thermal
stress is related to coating thickness. It increases with the coating
thickness on the SUBS. The greatest value of the normal stress
which produces spalling of the ceramic is produced on the bond
coat. It is nearly twice the value of the maximum normal stress on
the substrate. As seen here, thermal performance of the piston
increases with increased coating thickness. When stress values
obtained from FEA are compared with the mechanical properties of
the aluminum alloy and zirconia material, it can be seen that
calculated stress values are lower than the allowable stress values
of the materials, as shown in the figures.