Crystal plasticity model for single crystal Ni-based superalloys: Capturing orientation and temperature dependence of flow stress

Abstract

We develop a dislocation density based crystal plasticity model to capture the micromechanical behavior of γ′ strengthening nickel-based superalloys. The elasto-viscoplastic model presented here accounts for hardening behavior of both γ and γ′ which are the two phases considered in the present work. The model includes multiple strengthening mechanisms such as Orowan stress, evolving slip resistance caused by dislocation interactions, and γ′ structural contribution to initial slip resistance. Interaction between γ and γ′, a key feature of these alloys has been modelled in terms of back stress induced by dislocation pileup or looping around the large γ′ precipitates. Furthermore, anti-phase boundary (APB) shearing is considered as the dominant deformation mechanism for shearable γ′ precipitates. In addition to octahedral {111}⟨110⟩ slip, the model also accounts for cube slip systems {100}⟨110⟩ which are known to be instrumental in γ′ shearing and introducing flow stress orientation dependence. Temperature dependence of the initial slip resistance is fitted against experimental observation of anomalous yielding for two different single crystal orientations. An optimization procedure based on the minimization of the error between simulated and experimental stress strain curves, is adopted to evaluate a selected group of material parameters. Subsequently, proper working of the model is tested against an independent set of single crystal experimental data available for CMSX-4 around service temperature and MD2 at room temperature. The model also represents a strong orientation dependence of yield stress anomaly (YSA), a salient feature of Ni-based superalloys.