Fatigue crack growth in nickel-based superalloys at elevated temperatures

Research highlights: → Crack growth measurements are better estimated by the potential drop technique. → Crack propagation is faster at 550 than 450 oC for all the materials. → The crack propagates faster in the U720LC than in the U720PM mono-material. → The content of U720PM and U720LC mono-materials is very stochastic at the interface. → The heterogeneity at the interface affects the behaviour of the joint material. -- Abstract: In the present work, fatigue crack growth in two nickel-base mono-materials and one bi-material has been investigated at 450 and 550 oC. The electric potential drop technique was found to better estimate the crack length during cycling as compared to the compliance method. This finding is supported by microscopic observations of the fracture surface and also by the numerical simulation using finite element code Castem2000. The crack was found to grow faster in the coarse grained material than in the fine grained one. The fracture surface observation showed that the performance of the bi-material is linked to the mono-material content at the interface. In addition, the content of each mono-material at the interface was found to be very stochastic. This heterogeneity, due to the assembly process, strongly affects the behaviour of the biomaterial. Finite element computation showed a good agreement between numerical and experimental results in term of stress intensity factor.