Xiaohu Li

The micro-elastic deformation behavior of dual-phase (y and y′) Mar-M247 Ni-based superalloy after long-term thermal exposure was investigated by means of in-situ tensile loading using time-of-flight neutron diffraction. The results showed that y′ phase undergoes coarsening when the superalloys is exposed to 850 °C for 1000 h. After thermal exposure at 1000 °C for 1000 h, the superalloy exhibits coarsening and coalescence of the y′ phase, as well as the formation of initial interface dislocation networks at the y/y′ phase interface. Compared to the Mar-M247 Ni-based superalloy after standard heat treatment, the elastic modulus of each (hkl) crystal plane gradually increases after the superalloy undergoes long-term thermal exposure. Among all the crystal planes considered, the (200) crystal plane has the lowest elastic modulus. The diffraction elastic constants (DECs) of the (311), (220), (200) and (111) reflections varied linearly according to the crystallographic anisotropy factor. Subsequently, the values of Single Crystal Elastic Constants can be obtained, which provide an alternative route to deduce DECs for any (hkl) orientation crystal planes. Compared to the y′ phase with cuboidal morphology, the elastic modulus of degraded y′ phase gradually increases. As the degree of degradation increases, the elastic modulus of y′ phase increases correspondingly. Although the thermal exposure process accelerates the stress redistribution, both the y′ phase and y phase maintain the elastic deformation behavior during the elastic stage.