Abstract
Thermomechanical fatigue (TMF) crack growth testing has been performed on the polycrystalline superalloy IN792. All tests were conducted in mechanical strain control in the temperature range between 100 and 750 °C. The influence of in-phase (IP) and out-of-phase (OP) TMF cycles was investigated as well as the influence of applying extended dwell times (up to 6 hours) at the maximum temperature. The crack growth rates were also evaluated based on linear elastic fracture mechanics and described as a function of the stress intensity factor KI. Without dwell time at the maximum temperature, the crack growth rates are generally higher for the OP-TMF cycle compared to the IP-TMF cycle, when equivalent nominal strain ranges are compared. However, due to the fact that the tests were conducted in mechanical strain control, the stress response is very different for the IP and OP cycles. Also the crack closure level differs significantly between the cycle types. By taking the stress response into account and comparing the crack growth rates for equivalent effective stress intensity factor rages ΔKeff defined as Kmax − Kclosure, very similar crack growth rates were actually noticed independent of whether an IP or OP cycle were used. While the introduction of a 6 hour dwell time significantly increased the crack growth rates for the IP-TMF cycle, a decrease in crack growth rates versus ΔKeff were actually seen for the OP-TMF cycle. The fracture behaviour during the different test conditions has been investigated using scanning electron microscopy.
Highlights
The nickel-base superalloy IN792 is a cast polycrystalline material which is widely used in industrial and aircraft turbines due to its high strength and excellent hot corrosion resistance
As can be seen crack initiation occurred rather early in all tests and a significant amount of cycles were spent on crack propagation
For most tests the crack propagation rate decreased with increasing crack length, especially after that the crack reached a length of 2 mm
Summary
The nickel-base superalloy IN792 is a cast polycrystalline material which is widely used in industrial and aircraft turbines due to its high strength and excellent hot corrosion resistance. Often the material can be found in critical components such as turbine blades and vanes Even though such components sometimes are made in single crystalline form, polycrystalline materials are very common due to lower costs and easier production route. It is known from other alloys that the intergranular cracking behaviour in wrought fine grained. To what extent the coarse-grained cast material IN792 is sensitive to environmental assisted cracking during dwell times is to be determined in this study
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
