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Abstract The discrete-continue model (DCM) combining the three dimensional discrete dislocation dynamics (DDD) and finite element method (FEM) is employed to investigate the influence of interfacial dislocation networks (IDNs) and lattice mismatch on the dynamics evolution of dislocations in the matrix channel of the single crystalline Nickel-bases superalloys (SCNBSs). For a given slip plane, the matrix dislocations with all three possible Burgers vectors are considered. For comparison, the critical resolved shear stresses (CRSSs) for matrix dislocation entering and freely gliding in the channel are calculated for both cases with and without IDNs considered. It is found that the CRSS for free gliding is evidently larger than that for entering the matrix channel, although the latter only considering the Orowan mechanism is generally used to describe the hardening of SCNBSs in the literatures. More importantly, the IDNs not only increase the CRSS for free gliding evidently but also change the matrix dislocations dissociation to a certain extent. The IDNs and lattice mismatch can either promote the dislocation dissociation or has no evident influence on it. Which effect the IDNs take depends on the character of the matrix dislocation. By means of DDD simulations, new CRSS models considering the effects of IDNs, lattice mismatch, matrix dislocation character and dislocation dissociation are suggested. Further, a criterion is also developed to estimate whether the dislocation dissociation can happen or not in the matrix channel with or without IDNs. Highlights • The interfacial dislocation network (IDN) plays an important role in the dislocation evolution in Nickel-based superalloys. • The IDN increases the critical resolved shear stress (CRSS) for dislocation freely gliding in the channel evidently. • The IDN can change the dissociation of matrix dislocations. • New CRSS models including the influence of IDN, lattice mismatch, dislocation character and dissociation are developed. • A criterion for dislocation dissociation is suggested. [ABSTRACT FROM AUTHOR]

A new efficient framework coupling the two dimensional (2D) discrete dislocation dynamics (DDD) and the extended finite element method (XFEM) is developed for modeling the dynamic evolution of multiple dislocations in crystalline materials with abundant interfaces/surfaces. By a specially introduced stress calculation scheme with cut-off radius and virtual elements, the present algorithm can capture interaction between neighboring dislocations accurately although no time-consuming dislocation-core enrichment is employed. Since it is not sensitive to the FE mesh size and large XFEM time step can be used, its efficiency is evidently improved compared with other DDD frameworks. Due to the merits of XFEM itself, the present DDD-XFEM scheme can treat intractable surface/interface problems conveniently, with no additional image stress calculation as in the DDD-FEM superposition framework and special plastic-strain distribution near the surfaces/interfaces as in the discrete-continuous method (DCM) needed. For these, it can be used to model plastic behaviors of crystals with abundant interfaces/surfaces (i.e. grain/phase boundaries and crack/void surfaces). To show the ability of present DDD-XFEM scheme, it is used to simulate the mechanical responses of polycrystalline aluminum with assumed rigid and penetrable grain boundaries. A three-stage model for dislocation penetrating through grain boundary (DPTGB) is suggested. The results show that the present DDD-XFEM scheme can capture the formation of dislocation pile-ups and thus the Hall-Petch effect successfully. The DPTGB can decrease the flow stress and hardening rate evidently; moreover, it can weaken the grain size effect and may enhance the cyclic stress relaxation of polycrystals greatly. Image 1 • A more efficient and accurate XFEM-DDD framework for simulating the micro-plasticity of materials is developed. • The newly developed XFEM-DDD framework can well deal with various complex discontinuities in materials. • The present XFEM-DDD framework can simulate efficiently the problems on much longer/larger temporal/spatial scale. • A three-stage model for dislocation penetrating through GB (DPTGB) is suggested. • The grain size effect on strength and the cyclic stress relaxation are captured efficiently by the present scheme. [ABSTRACT FROM AUTHOR]