Investigation into the evolution of interface fracture toughness of thermal barrier coatings with thermal exposure treat
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Investigation into the evolution of interface fracture toughness of thermal barrier coatings with thermal exposure treatment by wedge indentation Yue M. Wang1, Wei X. Weng1, Ming H. Chi1, Bai L. Liu1, Qiang Li1,a) 1
School of Materials Science and Engineering, Fuzhou University, Fuzhou 350116, China Address all correspondence to this author. e-mail: [email protected]
a)
Received: 19 November 2019; accepted: 18 March 2020
Thermal barrier coating is a high-temperature protective technology widely used in industrial gas turbines. However, the failure of coating peeling because of the generation of thermally grown oxide (TGO) at the interface during service hinders its further application. In this study, Raman spectroscopy and wedge indentation are used to determine the TGO residual stress and the interface energy release rate, respectively. The effect of TGO on the interfacial fracture toughness during the growth process was discussed. Raman spectroscopy test results show that the residual stress of TGO is about 0.5 GPa. Wedge indentation test results illustrate that high-temperature heat treatment could accelerate the interface degradation of thermal barrier coatings. Stress analysis and test research demonstrate that the microcracks induced by compressive stress of TGO will propagate with increasing heating time, ending with failure of barrier coatings.
Introduction A fundamental challenge in a gas turbine is that the inlet temperature has gradually increased with the rapid development of the modern industry. Specifically, the high-temperature structural materials can no longer meet the requirements of aerospace technology development [1–4]. In this regard, coating technology on the surface of the alloy has been developed in the field of engineering technology to improve the service life of alloys in high-temperature environment. As surface protection technology, the high-temperature resistance of thermal barrier coatings (TBCs) protects the turbine components from the influence of external conditions, significantly improving the thermal efficiency of the gas turbine. The TBCs are a composite structural system composed of top coat (TC) and bond coat (BC). TBCs are subjected to various adverse factors during its longtime service, such as mechanical load, thermal shock, and environmental corrosion, resulting in the accumulation of thermal or residual stresses to weaken the adhesion between coating and substrate [5–10]. Meanwhile, the effects of microcracks, pores, and other defects inside the TBCs make the interface become the most likely place to failure. Therefore, investigating the fracture mechanism of the TC–BC
ª Materials Research Society 2020
interface has become a hot topic in the realm of coating technology [11,12]. In brittle materials, such as ceramic coatings, fracture toughness expresses the ability to resist crack propagation and represents the energy required to promote crack propagation; the energy release rate refers to the energy provided by outside to generate a new surface. So far, various experime
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