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Jaegu Choi,Sunguk Wee,Jae-Mean Koo,Eui-Suck Chung,권석환,Chang-Sung Seok 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.5
To increase efficiency and reduce greenhouse gas emissions, the operating temperatures of combined power plants have increased. As a result, high-pressure turbine (HPT) blades are subjected to increasingly harsh operating conditions, which cause thermomechanical fatigue (TMF) damage and reduce the lifetimes of the gas turbine blades. Therefore, accurate analysis of the TMF characteristics caused by various strain and temperature conditions is needed to ensure the integrity and provide accurate lifetime assessments of the components of gas turbines. However, there have been few studies on the TMF characteristics of single crystal Ni-based superalloys, particularly CMSX-4. In this study, the TMF characteristics of a <001> oriented single crystal Ni-based superalloy CMSX-4, which is used for HPT firststage rotor blades, were investigated via strain-controlled TMF tests and the fatigue fractography was observed using scanning electron microscopy. Additionally, the relationship between the fatigue lifetimes of CMSX-4 and IN738LC was evaluated, and the tensile properties and microstructures at different temperature were investigated. Such TMF test results can be useful for analyzing the thermo-mechanical behavior and predicting the lifetimes of blades.
Method for Predicting Thermal Fatigue Life of Thermal Barrier Coatings Using TGO Interface Stress
Junghan Yun,Sunguk Wee,Soo Park,Jeong-Min Lee,Hyunwoo Song,Chang-Sung Seok 한국정밀공학회 2020 International Journal of Precision Engineering and Vol.21 No.9
Thermal barrier coatings (TBCs) applied to high-temperature components of gas turbines consist of a ceramic top coat, a metallic bond coat, and thermally grown oxide (TGO) generated between the top coat and bond coat. Because TBCs are subjected to repeated thermal stress at the coating interface under thermal fatigue conditions and eventually breakage, it is crucial to evaluate the thermal fatigue durability of TBCs according to the stress. In this study, coin-type TBC specimens were prepared by depositing commercial coating powders on Ni-based super alloys via the air plasma spray method, and the thermal fatigue life of the TBCs was experimentally evaluated. According to the test results and references, a finite-element analysis was conducted. The maximum stress of the TGO interface was evaluated according to the thickness and equivalent elastic modulus, and simulating the microstructure including the pores of the top coat. Using these relationships, a thermal fatigue life prediction equation considering the coating thickness (t), equivalent elastic modulus (E), and operating temperature (T) was derived, and subsequently verified.
열차폐코팅의 미세구조가 TGO 계면 응력에 미치는 영향 평가를 통한 미세구조 형상 설계
김담현,박기범,위성욱,김기근,박수,석창성,Kim, Damhyun,Park, Kibum,Wee, SungUk,Kim, Keekeun,Park, Soo,Seok, Chang-Sung 한국군사과학기술학회 2020 한국군사과학기술학회지 Vol.23 No.5
Thermal barrier coating(TBC) applied to fighter and turbine engines is a technology that improves the durability of core parts by lowering the surface temperature of base material. The thermal stress caused by mis-match of the coefficient of thermal expansion between the top coating and the TGO interface is the main cause of TBC breakage. Since the thermal stress is dependent on the microstructure of the TBC, designing microstructure of TBC can improve the durability as well as lower the thermal stress. In this study, the effect of coating thickness, volume of porosity and vertical cracking on the thermal stress was analyzed through finite element analysis. Through the analysis results, a design range of a microstructure that can improve the durability of thermal barrier coating by lowering thermal stress is proposed.