Nanoscale Structure and High Velocity Sliding at Cu/Ag Interfaces
- PDF / 600,057 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 49 Downloads / 207 Views
P6.5.1
Nanoscale Structure and High Velocity Sliding at Cu/Ag Interfaces James E. Hammerberg, Timothy C. Germann, Brad Lee Holian1, and Ramon Ravelo2 Applied Physics Division, Los Alamos National Laboratory, Los Alamos, NM 87545 1 Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545 2 Department of Physics and Materials Research Institute, University of Texas-El Paso, El Paso, TX 79968-0515 ABSTRACT We present the results of large-scale NonEquilibrium Molecular Dynamics (NEMD) simulations for Cu/Ag interfaces sliding in the velocity regime 0 ≤ v ≤ 1 km/sec. System sizes of 2.8 × 106 atoms are considered using Embedded Atom Method (EAM) potentials. Single crystals with (010) interfaces sliding along the 〈100〉 direction are considered. We discuss the observed velocity weakening in the tangential force at high velocities, and its connection with the observed dislocation structure and nanostructure that are nucleated during dry sliding. INTRODUCTION The frictional properties of smooth Cu/Ag interfaces are interesting from several points of view. Both materials are ductile fcc metals whose deformation properties are well known. They also represent a tribo-pair for which the plastic flow properties are substantially different, but not as dramatically different as for the Ta/Al tribo-pair. Consequently, they may provide a test of ideas inherent in subsurface plasticity theories of the frictional forces between ductile metals in dry sliding [1]. A further reason for studying this interface is that there are now Embedded Atom Method (EAM) atomic interaction potentials that credibly incorporate local defect properties such as defect, stacking fault, and surface energies, as well as thermodynamic properties such as compressibilities, elastic constants, and equations of state [2]. The focus of the present work is the behavior of the frictional force as a function of sliding velocity at fairly large compression. We discuss large-scale NEMD simulations of single crystal Cu and Ag interfaces sliding in the velocity range from 0 – 1 km/s at a pressure of 5.1 GPa, a pressure readily obtainable in impact experiments. The methods, potentials and results for (010) faces sliding along the 〈100〉 direction are discussed in the following sections. METHOD AND POTENTIALS Method For the three-dimensional dry sliding simulations we consider here, we use a constant velocity, constant temperature boundary condition for a large simulation cell. A two-dimensional section through the middle of this cell, normal to the Cu/Ag interface and along the 〈100〉 sliding direction, is shown schematically in figure 1. It consists of two material regions separated by an interface with an imposed initial roughness. There are also two reservoir regions that are shown as shaded regions. The reservoir regions consist of the same Cu (above) and Ag (below) atoms as
P6.5.2
y: 〈010〉 Cu x: 〈100〉
z: 〈001〉
Ag
Figure 1. Schematic drawing of the computational cell showing the reservoir regions shaded. Fnorm is a constant normal (y-direction) lo
Data Loading...
