Numerical Investigation of Multiphysics-Coupled Stress in MZO-YSZ Thermal Barrier-Coated Pistons

In internal combustion engines, pistons are subjected to coupled thermal and mechanical loading, which can induce temperature gradients, deformation and local stress concentration. In this study, a finite element thermomechanical model of a diesel engine piston with a MgZrO3/YSZ double-ceramic-layer thermal barrier coating was established to evaluate the effects of the outer-layer material and ceramic-layer thickness distribution. Perovskite ceramics, including MgZrO3, SrHfO3, SrZrO3 and BaTiO3, were first compared as outer ceramic layers. The MgZrO3/YSZ configuration showed the most evident thermal barrier response among the investigated materials. Under a constant total ceramic thickness of 0.30 mm, increasing the MgZrO3 outer layer from 0.10 mm to 0.20 mm increased the coating surface temperature while slightly reducing the maximum substrate temperature, coupled deformation and substrate fatigue rissk. The higher-stress regions of the coating system were mainly located near layer interfaces, whereas the high-stress region of the metallic substrate was concentrated near the pin boss and pin hole transition. The results indicate that outer-layer thickness optimization can improve substrate protection to a limited extent, but the associated increase in ceramic-layer stress should also be considered.