Modeling of Deformation in Nanocrystalline Copper Using An Atomistic-Based Continuum Approach
- PDF / 2,099,104 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 15 Downloads / 175 Views
Q5.31.1
Modeling of Deformation in Nanocrystalline Copper Using An Atomistic-Based Continuum Approach D. H. Warner, F. Sansoz and J. F. Molinari Department of Mechanical Engineering, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 USA. ABSTRACT The deformation of copper with grain size less than 10 nm is investigated using a 2D continuum model incorporating atomistically-based constitutive relations. The local constitutive response of a series of symmetric and asymmetric tilt grain boundaries is obtained using an atomistic quasicontinuum method under tension and shear. The atomistic results show that it is possible to associate a constant maximum stress with each deformation mechanism triggered in the GB vicinity, i.e. GB sliding and decohesion, atom shuffling and partial dislocation emission. The GB strength is always found weaker in shear than in tension. This information is incorporated into a continuum polycrystalline model tested under compression. This model provides useful insights, in the absence of intragranular plasticity, into the onset of macroscopic quasi-plasticity, which results from GB sliding and collective grain rotation mechanisms.
INTRODUCTION The deformation mechanisms of nanocrystalline (nc) metals at room temperature can fall into 3 categories [1,2]. First, it is possible to identify intergranular mechanisms consisting of uncorrelated atom shuffling events at high-angle grain boundaries (GB), which results in GB sliding [3,4]. Second, intragranular mechanisms such as partial dislocation emission and twinning have been observed [5-7] in nc metals with grain size larger than 10 nm. Thirdly, it has been suggested [8] that cooperative grain behaviors, i.e. microshear banding or rotation of clusters of grains may operate at this scale. An attempt is made here to develop a continuum model for the deformation of nc copper. Special emphasis is placed on modeling intergranular and cooperative grain mechanisms, hence the bulk grain behavior being treated as anisotropic elastic. In contrast to a conventional polycrystalline model, two major difficulties must be overcome at the nanoscale. One of these is the lack of understanding in the local constitutive response of GB at the nanoscale. For instance, no systematic correlations have been conducted regarding the effects of GB structures on GB-related atomic shuffling processes in previous atomistic studies of bicrystal sliding [9-11]. The second difficulty arises from treating the contact/adhesion between grains in a polycrystalline continuum model. The local constitutive response of GB is addressed through atomistic calculations. These results are presented in the second section for 5 different GB structures tested under shear and tension. The last section presents the deformation of a polycrystalline model treated within a finite element (FEM) framework, which incorporates the atomistic-based constitutive relations obtained at GB’s and allows for sliding between the grains.
Q5.31.2
COMPUTATIONAL PROCEDURE The quasicontinuum
Data Loading...
