Mechanical properties and ?/?? interfacial misfit network evolution: A study towards the creep behavior of Ni-based single crystal superalloys

The aim of this study is to investigate the role of the temperature, stress, and rhenium (Re) on the gamma/gamma' interfacial misfit dislocation network and mechanical response of Ni-based single crystal superalloys. After aging at elevated temperatures, mismatch between the two phases results in an interfacial dislocation network to relieve the coherency stress. Molecular dynamics (MD) simulations have been performed to study the properties of the (100), (110), and (111) phase interface crystallographic directions. Increasing temperature disperses the atomic potential energy at the interface diminishing the strength and stability of the networks. In the case of loading, when a constant strain rate of 2 x 108(s-1) is applied at 0 K, the (100) and (111) phase interface models lose their cocoordinating role of maintaining the dynamic equilibrium. Dislocation propagation in the gamma phase is the dominant deformation mechanism in these two interfacial models, resulting in dislocations pile-up in the damaged area, and the network is no longer able to fortify the interface. For the (110) phase interface model, the dominant deformational mechanism is precipitate shearing. As temperature increases, the elastic modulus, initial mismatch stress, and yield strength decrease. Also, the pinning effect of Re atoms is evaluated in the gamma phase at 1600 K. The dislocation hampering property of Re is more perceptible when enough dislocations in the gamma phase are moving at elevated temperatures. In addition, Re manages to relieve the interfacial stress field and does not affect the network morphology. Finally, an investigation of the creep behavior of the superalloy is provided. It is observed that the escalated damage to the interfacial network due to the increased temperature leads to the domination of the softening mechanisms (cross-slip and dislocation climb) on the deformation and shortens the steady-state creep. Moreover, Re atoms act as an extra hardening factor to improve the tertiary creep.