Effect of initial γ/γ^′ microstructure on creep of single crystal nickel-based superalloys: A phase-field simulation incorporating dislocation dynamics

The initial γ/γ^′ microstructure (e.g. γ^′ shape, size, volume fraction) may dramatically affect creep behaviour of single crystal Nickel-based superalloys. However, it is difficult to have accurate control on each of these initial aspects and to understand the role of each by experimental methods. In the present work, a novel coupled model of phase-field and continuum dislocation dynamics is developed for the co-evolution of γ/γ^′ and dislocation microstructures, such that the creep deformation of single crystal Nickel-based superalloys can be described in a physical way. The creep curve can be directly obtained by averaging dislocation activity, without any phenomenological effort that is needed for traditional constitutive models. With the coupled model, we study the effect of initial γ/γ^′ microstructure on creep of single crystal Nickel-based superalloys. The role of initial γ^′ shape is studied by comparing simulations with different initial γ^′ shapes but with the same γ^′ size and volume fraction. The role of initial γ^′ size and volume fraction are studied in the same methodology. Simulation results show that as the γ/γ^′ misfit magnitude increases, the γ^′ shape transits from circular to cubic and the dislocation microstructure symmetry shifts. The cubic γ^′ shape corresponding to γ/γ^′ misfit of −0.003 is the most beneficial for creep resistance, compare with γ/γ^′ misfit of −0.0015 and 0. Bigger γ^′ size and higher γ^′ volume fraction also result in better creep resistance, especially the benefit of high γ^′ volume fraction to creep resistance is dramatic. The simulation results may bring inspirations for design of new single crystal Nickel-based superalloys with excellent creep resistance.