Multiscale Modeling of Strengthening Mechanism in Aluminum-Based Amorphous Nanocomposites
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Multiscale Modeling of Strengthening Mechanism in Aluminum-Based Amorphous Nanocomposites H. T. Liu1 and L. Z. Sun2 1 Department of Civil and Environmental Engineering University of California, Los Angeles, CA 90095-1593, U.S.A. 2
Department of Civil and Environmental Engineering and Center for Computer-Aided Design The University of Iowa, Iowa City, IA 52242-1527, U.S.A. ([email protected]) ABSTRACT In this work we focus upon theoretical exploration of the mechanical constitutive behavior of amorphous nanocomposites in terms of a multi-scale approach starting from the nanostructure. Local heterogeneous stress field and deformation are calculated based on the concept of eigenstrain and equivalent inclusion method. The overall elastoplastic constitutive model for amorphous nanocomposites is developed through homogenization averaging procedures. Explicit expressions of the effective elastic stiffness and yield strength of amorphous nanocomposites in terms of the constituents’ properties and nanostructures are obtained. An interlayer phase between nanoparticles and the amorphous matrix is experimentally observed and incorporated in the proposed model. The interlayer thickness is treated as a characteristic length scale. Thus, the particle size effect on the nanocomposite properties is particularly investigated within continuum nanomechanics framework. It provides direct determination of the intrinsic mechanisms of the nanocomposite structure-property relationship at the nanoscale. INTRODUCTION Al-based amorphous nanocomposites exhibit exceptional mechanical properties while preserving reasonable ductility. It has been reported that the yield strength of the amorphous aluminum alloys is as high as 800 MPa in an amorphous state, and can be increased to 1,500 MPa by partial crystallization [1-3]. This extraordinarily high mechanical strength makes Albased amorphous nanocomposites a promising material for future industrial applications. The typical composition of Al-based amorphous nanocomposites is Al-TM-RE, where TM is a transition metal such as Ni, Fe, Co, Cr; and RE is a rare earth element such as Y, La, Ce, Nd [4]. The microstructure of amorphous nanocomposites constitutes nanometer-scale fcc α -Al particles dispersed in the amorphous aluminum matrix. The nanoparticle size and inter-particle distance are in the ranges of 5 to 50 nm and 7 to 100 nm, respectively [4, 5]. The total particle volume fraction is preferably in the range of 10% to 30% to preserve ductility. High-resolution electron microscopy examinations revealed that fcc α -Al nanoparticles exhibit a nearly spherical or an ellipsoidal morphology with no internal defects observed inside the nanoparticles [5]. Atomic probe field ion microscopy results of partially crystallized Al87Ni10Ce3 showed that Ce atoms are enriched within a distance of less than 3 nm at fcc α -Al particle interface and form a rare earth enriched interlayer between the nanoparticles and the amorphous matrix [4]. Although the extraordinarily high strength of nanocomposites ha
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