Neutron diffraction study of stress and lattice mismatch induced by thermo-mechanical fatigue in single crystal superalloys

Abstract

The center points of the thermomechanical fatigued single crystal Nibased superalloys were measured by neutron diffraction and the results have been treated in two methods: two overlapped peaks and a single peak. The macroscopic equivalent stress, deviatoric stress components, γ/γ′ phase equivalent stress and lattice mismatch are determined according to the experimental results. The stress results show that the macroscopic equivalent stresses are basically consistent when using two analysis methods, the maximum of macroscopic equivalent stress and deviatoric stress components appeared at thermomechanical fatigue that of 100 cycles, and at this point, the microdefects， such as dislocations, are saturated and the stress of γ′ phase away from the center was reduced remarkably. The calculated results also indicate that the negative lattice mismatch is reduce markedly at the beginning of the thermomechanical fatigue. Subsequently, it increases linearly with the fatigue cycles at the speed 81×10-6 per cycle because of the accumulated plastic strain in the matrix.