Deformation Behavior of FCC Crystalline Metallic Nanowires Under High Strain Rates

Yue Qi,1 Hideyuki Ikeda,2 Tahir Çagin,1 Konrad Samwer,2 William L. Johnson,2 and William A. Goddard III1
1Materials and Process Simulation Center, California Institute of Technology, Pasadena, California 91125
2Keck Laboratory of Engineering Materials, California Institute of Technology, Pasadena, California 91125
We used molecular dynamics (MD) methods to study the deformation behavior of metallic alloy crystal nanowires of pure Cu, NiCu alloy and NiAu alloy, under high rates of uniaxial tensile strain, ranging from 5*108/s to 5*1010/s. These nanowires are just about 2 nm thick and hence cannot sustain dislocations, instead we find that deformation proceeds through twinning and coherent slipping mechanisms. NiAu has a 13% size mismatch whereas NiCu only 2.5%. As a result the critical strain rate at which the “nanowire crystals” flow like a “liquid” is 100 times smaller for NiAu. We also calculated the elastic constants at each strain state for all strain rates to identify the relation between mechanical “shear” instability and deformation process.