Modeling Of Thermal Barrier Coatings

Several ceramic thermal barrier coating systems for use in the turbocharged diesel engines were analyzed. The finite element method was used to perform a comparative numerical stress analysis of the different coating designs. A two dimensional axisymmetric finite element model was used for the stress analysis.

Several coating systems were considered: a layered system with a 2.5 mm thickness; a layered system with a 1.5 mm thickness; a variable thickness layered coating; and, various thicknesses of a single layer coating. These ceramic coatings were modeled in conjunction with three piston materials, or substrates: fiber reinforced aluminum, ductile iron, and a superalloy (nickel-based B1900). The resulting analysis matrix provided the opportunity to form conclusions concerning coating thickness, the layered coating design, and substrate material.

ni-ii

The layered coating design appears in Figure 1. This coating was designed and recommended by United Technologies Research Center (UTRC) of East Hartford, Connecticut. The operating concept of the layered coating design is to decrease coating stresses by more closely approximating the thermal behavior of the metal substrate.

Two types of loading were considered: thermal and pressure. A uniform gas temperature was applied as a boundary condition above the piston. Although the actual gas temperature varies as a function of many factors (turbomachinery configuration, engine load, position, and etc.), 850 deg C was felt to be representative of the combustion gas temperature. Ihe cylinder pressure was assumed to be 13.8 MPa (2000 psi) based on the previously described engine operating conditions (600 HP V903 operating at 2600 RPM).

To reduce the size of the analysis matrix, ductile iron was chosen as a suitable material to use in the investigation of stresses associated with the single layer coating. Coating thicknesses of 0.5, 1.0, 1.5, 2.0 and 2.5 mm were chosen. The coating material consisted of zirconia, Zr02- Figure 2 illustrates the dependence of maximum principal stresses on coating thickness. The nonlinearity resulted from changes in the maximum stress location.

The layered coating was also analyzed for a thickness of 1.5 mm on all three substrates. Coating thickness affected maximum stresses, but had only a small effect on the stress distribution. Table 1 offers a comparison of the stresses associated with the two layered coating thicknesses for each of the substrates.

Table 1. Variation of maximum stress thickness for the layered coating.

0 0

Post a comment