Investigation of Pile-Up Behavior for Thermal Barrier Coatings Under Elevated-Temperature Indentation

Abstract

The elevated-temperature indentation has been utilized to measure the elevated-temperature mechanical properties of thermal barrier coatings (TBCs), which have a major influence on their thermomechanical characteristics and failures. In this paper, the pile-up phenomenon of TBCs under elevated-temperature indentation was investigated, and a characterization method for Young's modulus of TBCs was proposed. According to the dimensional analysis and finite-element method, a critical temperature-dependent factor was conducted as the criterion for pile-up behavior. Some experiment results agreed fairly well with the criterion. Then, the pile-up behavior of TBCs at elevated temperature was studied. It was found that the pile-up behavior depended on the temperature-dependent factor and got larger with increasing temperature. Finally, a characterization method was proposed to extract the Young's modulus of TBCs, which was found to be more suitable for elevated-temperature indentation.

Determining the layers’ Young’s moduli and thickness from the indentation of a bilayer structure

“…Because the layer elastic and plastic deformations can result in sink-in and pile-up, respectively, the contact depth (h c ) and measured indentation depth (h) are often different [24,35,39] In the sink-in scenario as shown in figure 1, h c < h; while, in the pile-up scenario, h c > h [34]. For simplicity, h = h c is assumed here, which can cause an error.…”

“…The ratio in Gao's indentation test [32] is 0.1/3 ≈ 3.33% and as shown later, the substrate effect stands out even more when the Young's modulus difference between the film and substrate is larger. Besides a 2D material on a substrate, the film/substrate model also applies to various coated materials with a bilayer structure [33,34].…”