Mesoscale crystal plasticity modeling of nanoscale Al–Al2Cu eutectic alloy

Abstract

Nanolaminated composites composed of alternate metal and intermetallic or ceramic lamellae exhibit high strength, high strain hardening rate and measurable plasticity at ambient and elevated temperatures. Due to the difference in plastic deformation capability between the two phases, structural instability occurs in hard lamellae associated with buckling when a compression strain is applied parallel to the lamellae. Taking nanoscale Al–Al2Cu eutectic alloy as a model system, we develop a mesoscale crystal plasticity (CP) model based on the confined layer slip (CLS) mechanism (referred to as CLS-CP) to understand the buckling behavior of the nanolaminates. In the CLS-CP model, buckling in Al2Cu lamellae is constrained by the elastic-plastic deformation of Al lamellae. The critical resolved shear stress for dislocation slip in Al lamellae varies with layer thickness, estimated by the CLS mechanism. To capture the essential features of confined layer slip mechanism that dislocations propagate within the layer and are deposited at the interfaces, plastic deformation in each lamella is the same through the layer thickness. The variation of elastic deformation through the layer thickness is captured through dividing each Al lamella into three or more elements that have the same plastic deformation through the thickness. In comparison, we also conduct standard crystal plasticity modeling in which plastic deformation in the three elements through the layer thickness is calculated individually according to phenomenological power law. In these simulations, plasticity in Al2Cu lamellae is modeled with slips on {121} planes due to the slip continuity across the interface, which have been observed in our recent experiments. The CLS-CP model is able to predict mechanical properties of nano-scale lamellar materials. In contrast, the standard CP model is more suitable to study deformation behavior of sub-micro scale lamellar materials. The CLS-CP model calculations reveal that critical compression strain corresponding to buckling increases as layer thickness decreases, which agree with micro-pillar compression tests.