Improvement of Oxidation Resistance and Adhesion Strength of Thermal Barrier Coating by Grinding and Grit-Blasting Treat
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Improvement of Oxidation Resistance and Adhesion Strength of Thermal Barrier Coating by Grinding and Grit-Blasting Treatments Kiyohiro Ito1
•
Takashi Shima2 • Makoto Fujioka1 • Masayuki Arai1
Submitted: 10 December 2019 / in revised form: 20 May 2020 ASM International 2020
Abstract The formation of thermally grown oxide (TGO), which is composed of alumina and mixed oxides, leads to the delamination of thermal barrier coating (TBC). In this study, to improve the oxidation resistance and adhesion strength of TBCs, grinding and grit-blasting treatments with alumina grits were applied to the surface of the bondcoat (BC) before deposition of the top-coat (TC). These treatments are expected to pre-form an alumina layer as an oxidation barrier and also optimize the TC/BC interfacial roughness. A high-temperature exposure test of TBC specimens grit-blasted with alumina grits of different sizes (B-TBC) revealed the growth of a continuous alumina layer in the B-TBC specimens in contrast to the formation of a complex TGO with alumina and mixed oxides in nonblasted TBC (S-TBC). Moreover, the area and thickness of TGO in the B-TBC specimens were much lower than those in the S-TBC. An indentation test was conducted to evaluate the TC/BC interfacial fracture toughness KIFC which confirmed a significantly higher KIFC of the B-TBC
& Kiyohiro Ito [email protected] Takashi Shima [email protected] Makoto Fujioka [email protected] Masayuki Arai [email protected] 1
Department of Mechanical Engineering, Tokyo University of Science, 6-3-1, Niijuku, Katsushika-ku, Tokyo 125-8585, Japan
2
Graduate School of Mechanical Engineering, Tokyo University of Science, 6-3-1, Niijuku, Katsushika-ku, Tokyo 125-8585, Japan
specimens than that of the S-TBC specimen. These results demonstrated that the grinding and grit-blasting treatments are effective in improving the oxidation resistance and adhesion strength of the TBC system. Keywords gas turbine grit-blasting interfacial fracture toughness thermal barrier coating thermally grown oxide
Introduction Recently, gas turbine combined cycle systems have garnered intense interest due to their higher thermal efficiencies and lower emission of harmful gases such as CO2 and NOx as compared to those of conventional thermal power generation systems. The thermal efficiency can be further improved by increasing the turbine inlet temperature. However, the turbine inlet temperature of a gas turbine combined cycle system has already exceeded the metal temperature in a first-stage blade. Therefore, a technological breakthrough is required to decrease the metal temperature. Thermal barrier coating (TBC) is one of the effective technologies to increase turbine inlet temperature and is widely applied to the surfaces of metallic components. Usually, a TBC includes two coating layers: (1) a top-coat (TC) layer that consists of a ceramic material with a high thermal resistance and low thermal conductivity and (2) a bond-coat (BC) layer that consists of a metallic material w
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