Computational Micromechanics Modeling of Polycrystalline Superalloys: Application to Inconel 718
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abstract
A virtual testing methodology to obtain the mechanical response of a polycrystal as function of its microstructure is presented and applied to an Inconel 718 Ni-based superalloy. The mechanical behavior of the polycrystal for a given deformation history is obtained by the finite element simulation of the response of representative volume elements of the microstructure subjected to that particular deformation history. The microstructural information defining the representative volume elements (grain size distribution and texture) was obtained from standard metallographic characterization techniques. The behavior of the alloy crystals is given by a phenomenological crystal plasticity model, whose parameters were obtained using two different strategies, micropillar compression for the parameters defining the monotonic behavior and an inverse optimization strategy (using experimental macroscopic cyclic stress-strain curves) for the parameters controlling the cyclic deformation. From the macroscopic viewpoint, the material response under monotonic and cyclic deformation was in good agreement with the experimental data. At the micro level, the values of the local fields resolved throughout the volume elements were used to generate fatigue indicator parameters, which were able to determine the most critical points in the microstructure to initiate a fatigue crack. These fatigue indicator parameters were calibrated by comparison with a few experimental fatigue tests and then used to predict the effect of loading conditions (strain ranges and ratio) and microstructure (grain size) on the fatigue life of the superalloy. Overall, the strategy shows how a balanced combination of micromechanical and macromechanical tests together with the application of computational homogenization strategies can be used to predict the mechanical behavior of Ni-based superalloys taken into account the influence of the microstructure.
