EVALUATING SERVICE TEMPERATURE FIELD OF HIGH PRESSURE TURBINE BLADES MADE OF DIRECTIONALLY SOLIDIFIED DZ125 SUPERALLOY BASED ON MICRO-STRUCTURAL EVOLUTION
Yadong CHEN1,Yunrong ZHENG1,Qiang FENG1,2()
1 State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China 2 Beijing Key Laboratory of Special Melting and Reparation of High-End Metal Materials, University of Science and Technology Beijing, Beijing 100083, China
Cite this article:
Yadong CHEN, Yunrong ZHENG, Qiang FENG. EVALUATING SERVICE TEMPERATURE FIELD OF HIGH PRESSURE TURBINE BLADES MADE OF DIRECTIONALLY SOLIDIFIED DZ125 SUPERALLOY BASED ON MICRO-STRUCTURAL EVOLUTION. Acta Metall Sin, 2016, 52(12): 1545-1556.
To get the actual service temperature distribution of turbine blades in aeroengines is very important for the design and maintenance. However, the acquisition of service temperature distribution has always been a challenge due to the complex and severe working condition of turbine blades. In this work, one turbine blade made of directionally solidified DZ125 superalloy was investigated after the service in air for 900 h. The microstructural evolution of DZ125 superalloy after thermal exposure at 900~1100 ℃ without the stress in different time period was also investigated, for comparison. According to microstructural degradation behaviors in the dendritic region, interdendritic region, carbides and grain boundary of DZ125 superalloy before and after service, the volume fraction of γ’ precipitates in the dendritic region was determined as the quantitative characterization parameter. A method to evaluate the service temperature of turbine blades was developed, based on the quantitative characterization of microstructural evolution, such as the relationship between the thermally exposured temperature and volume fraction of γ’ precipitates. The equivalent average service temperature (Tave) and the equivalent maximum service temperature (Tmax) were proposed based on the assumption of the constant temperature during service and the nearly service condition with variable temperature of blades, respectively. The results indicate that the service temperature was higher in the middle of the blade, and became lower at the locations closer to the tip or the root. For each cross-section, the service temperatures of the serviced blade in the descending order were leading edge, pressure side, trailing edge and suction side. The highest service temperature of 1050~1100 ℃ appeared at the leading edge in the middle of the blade. The distribution trend of Tave agreed well with that of Tmax, but Tmax was higher than Tave in some locations of the blade. This work suggests that the evaluation results of Tmax were more reasonable than those of Tave. This method would be helpful to establish the assessment method of the service-induced microstructural damage in turbine blades made of directionally solidified superalloys.
Fund: Supported by National High Technology Research and Development Program of China (No. 2012AA03A513) and Science Foundation of Ministry of Education of China (No. 625010337)
Fig.1 Illustration of cross sections along the blade airfoil (a) and four observed locations in each section (b) in a first stage blade made of DZ125 alloy after the service for 900 h
Fig.2 Typical microstructures of dendritic core (a), interdendritic region (b), grain boundary (c) and carbides (d) in the shank of the blade made of DZ125 alloy after the service for 900 h
Fig.3 Typical microstructures of dendritic core (a), interdendritic region (b), grain boundary (c) and carbides (d) in the pressure side of section A-3 in the blade made of DZ125 alloy after the service for 900 h
Fig.4 Typical microstructures in the dendritic core of leading edge in sections A-1 (a), A-2 (b), A-3 (c), A-4 (d) and A-5 (e) of the blade made of DZ125 alloy after the service for 900 h
Fig.5 Typical microstructures in the dendritic core of trailing edge (a) and suction side (b) in section A-3 of the blade made of DZ125 alloy after the service for 900 h
Fig.6 Volume fraction of γ’ precipitates in dendritic region at different locations of different sections in the blades made of DZ125 alloy after the service for 900 h
Fig.7 Typical microstructures in dendritic core of DZ125 alloy after thermal exposed at 900 ℃ (a) and 1050 ℃ (b) for 900 h, and at 1100 ℃ for 100 h (c) and 900 h (d)
Fig.8 Volume fraction of γ’precipitates in dendritic region of DZ125 alloy after thermal exposure at different temperatures for different times
Fig.9 Calculated phase equilibrium diagram of DZ125 alloy representing the amount of phases between 400 and 1400 ℃
Fig.10 Distribution of Tave of the blade made of DZ125 alloy after the service for 900 h
Location
Leading edge
Pressure side
Suction side
Trailing edge
Section A-1
950~1000
950~1000
≤900
≤900
Section A-2
1050~1100
950~1000
≤900
900~950
Section A-3
1050~1100
1000~1050
≤900
950~1000
Section A-4
1050~1100
950~1000
≤900
≤900
Section A-5
≤900
≤900
≤900
≤900
Table 1 Evaluation results for equivalent average service temperature (Tave) of the blade made of DZ125 alloy after the service for 900 h (℃)
Location
Leading edge
Pressure side
Suction side
Trailing edge
Section A-1
1000~1050
1000~1050
≤900
≤900
Section A-2
1050~1100
1000~1050
≤900
950~1000
Section A-3
1050~1100
1000~1050
≤900
1000~1050
Section A-4
1050~1100
950~1000
≤900
≤900
Section A-5
≤900
≤900
≤900
≤900
Table 2 Evaluation results for equivalent maximum service temperature (Tmax) of the blade made of DZ125 alloy after the service for 900 h (℃)
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