A micromechanical model of toughening behavior in the dual-phase composite

The fabrication of a special kind of dual-phase composite consisting of a hard matrix and ductile phase, such as metals with bimodal grain size distribution, is a promising strategy for improving the tensile ductility of nanocrystalline (nc)/ultrafine-grained (ufg) materials (Wang et al., 2002). This strategy is, however, challenged by the low reproducibility from low controllability of microstructural parameters and the existence of counterexamples (Prasad et al., 2009). The key to meet these challenges is to control the bimodal microstructural parameters to enable quantificational investigation of the relation between mechanical properties and microstructural parameters, and then set up a correlative quantitative model. In this paper, a new micromechanical model based on the propagation and multiplication of localized deformation bands is developed. To assess the model, a series of hypo-eutectoid Cu-Al alloys with controllable bimodal structures are prepared and their stress-strain curves in tension, together with those of bimodal copper (Wang et al., 2002) and bimodal Al-Mg alloys (Han et al., 2005) are predicted. Close agreement between the model-predicted and experimental results is obtained. The strength and uniform ductility of bimodal materials are observed in strong relation to the microstructural and constitutive parameters of volume fraction, strain hardening coefficient, and size of the coarse-grained ductile phase. Additionally, appropriate microstructural and constitutive parameters to achieve effective toughening can also be estimated according to the model. (C) 2010 Elsevier Ltd. All rights reserved.