Discrete Element Modeling of Fracture Behavior and Stress Analyses in Thermal Barrier Coatings During Wear Tests

Abstract

Thermal barrier coatings (TBCs) are extensively used in various industrial applications due to their high-temperature thermal insulation and environmental protection when applied to the surfaces of engine components. Wear and frictional behaviors are important when the TBCs are subject to foreign object contact. To characterize the wear performance of TBCs, this study presents an improved discrete element method (DEM)-based model to investigate the wear mechanisms induced by friction at the microscopic level. The studied TBCs consist of a ceramic top layer, a metallic bond coat, and a high-temperature nickel superalloy as the substrate, with the assumed thicknesses of 0.25 mm, 0.15 mm, and 0.8 mm, respectively. The simulation results indicate that the wear of the coating occurs in four stages: initial microcrack formation stage, particle detachment and small pit formation stage, extensive detachment and increased pit formation stage, and intensified extrusion and surface damage stage. The growth trend of crack and bonding failure energy resembles an “S” shape. The calculated coefficients of friction show a good agreement with experimental data in terms of normal force dependence. Using the Hertzian contact theory, the DEM shows that the maximum stress-induced crack formation was greatest at the contact edge. The maximum tensile stress, maximum compressive stress, and maximum shear stress increase with contact load. The shear stress distribution is entirely confined within the coating and did not significantly affect the coating substrate.