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

The initial gamma/gamma' microstructure (e.g. gamma' 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 gamma/gamma' 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 gamma/gamma' microstructure on creep of single crystal Nickel-based superalloys. The role of initial gamma' shape is studied by comparing simulations with different initial gamma' shapes but with the same gamma' size and volume fraction. The role of initial gamma' size and volume fraction are studied in the same methodology. Simulation results show that as the gamma/gamma' misfit magnitude increases, the gamma' shape transits from circular to cubic and the dislocation microstructure symmetry shifts. The cubic gamma' shape corresponding to gamma/gamma' misfit of -0.003 is the most beneficial for creep resistance, compare with gamma/gamma' misfit of -0.0015 and 0. Bigger gamma' size and higher gamma' volume fraction also result in better creep resistance, especially the benefit of high gamma' 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. (C) 2018 Elsevier B.V. All rights reserved.