Low Cycle Fatigue Behaviour of a Turbine Blade Made of Nickel Base Wrought Alloy

2014 ◽  
Vol 891-892 ◽  
pp. 506-511 ◽  
Author(s):  
Benudhar Sahoo ◽  
Sashi Kanta Panigrahi
Keyword(s):  
Turbine Blade ◽  
Strain Amplitude ◽  
Low Cycle Fatigue ◽  
Fatigue Behaviour ◽  
Dynamic Strain ◽  
Transgranular Fracture ◽  
Cycle Fatigue ◽  
Aero Engine ◽  
Nickel Base ◽  
Super Alloy

Life of an aero-engine is limited by the life of the turbine blade in particular and that of hot end components in general. Design of aero-engine is always conservative in nature considering the flight safety as paramount important. Earlier engines have been assigned life in hours but the life of the component is limited by LCF cycles particularly during the start-stop cycles. In this paper LCF behaviour of a typical Russian origin nickel base wrought super alloy AP220BD used for turbine blade has been studied at room temperature (RT), 400 °C and 700 °C that corresponds to idle rating and cruise rating of a typical aero-engine. Low cycle fatigue (LCF) tests have been carried out at RT, 400°C and 700 °C at three strain amplitudes of ±0.3%, ±0.5% and ±0.8%. Hysteresis loop have been developed at each strain and temperature. It has been observed that LCF life of the nickel base wrought alloy AP220BD is not influenced significantly at strain amplitude of ±0.3% till it reaches 400° C. Reduction in LCF life with increase in strain amplitude from ±0.3% to ±0.8% is much significant compared to that of increase in temperature up to 700°c.The higher life at intermediate strain of ±0.5% may be due to DSA(dynamic strain aging) of the material. Transgranular fracture has been observed at RT & 400° C while intergranular fracture at 700° C.

High Temperature Low-Cycle Fatigue, Deformation Microstructure and Final Fracture Behavior of a Nickel-Base Superalloy

2008 ◽  
Vol 378-379 ◽  
pp. 249-270 ◽  
Author(s):  
Du Yi Ye ◽  
Jin Yang Zheng
Keyword(s):  
Plastic Strain ◽  
Crack Propagation ◽  
Strain Amplitude ◽  
Low Cycle Fatigue ◽  
Cyclic Stress ◽  
Cycle Fatigue ◽  
Final Fracture ◽  
High Plastic Strain ◽  
Nickel Base ◽  
High Plastic

The low-cycle fatigue (LCF) properties of a nickel-base precipitation-strengthened superalloy (GH4145/SQ), obtained at a temperature of 538 o C, were reported and discussed in this paper. The properties investigated include cyclic stress response, fatigue life, deformation microstructure and final fracture features as a function of applied strain amplitude. It was shown that the alloy exhibited a pronounced initial hardening followed by continuous softening to failure at high plastic strain amplitudes ( > 0.2% ap ε ), while at low plastic strain amplitudes ( < 0.2% ap ε ) the initial hardening was followed by a well-defined saturation stage. Bilinear behavior with a change of slope at a plastic strain amplitude of about 0.2% was observed in the cyclic stress-strain (CSS) and Coffin-Manson (C-M) plots. TEM observations revealed that slip band density increased with increasing total strain amplitude and precipitate degradation resulting from dislocation-precipitate interactions took place with continuous cyclic straining. The change in the microstructure during cycling is thus responsible for the fatigue hardening / softening behavior of the alloy. SEM examinations indicated that at low plastic strain amplitudes ( < 0.2% ap ε ) crack propagation was basically transgranular, while at high plastic strain amplitudes ( > 0.2% ap ε ) crack propagation exhibited intergranular features, as a whole. The variation in both the number of operating slip systems and the fracture modes with the strain amplitude employed was used to explain the observed two-stage LCF behavior of the present investigated superalloy.

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