Molecular dynamics simulation of structural evolution in crystalline and amorphous CuZr alloys upon ultrafast laser irradiation

Abstract

A promising route for manufacturing emergent metamaterials is the use of ultrafast laser pulses in complex alloy processing. Laser-induced structural transformations in Zr based alloys for crystalline and glassy states are investigated here. The ultrafast thermomechanical response is compared between relevant stable crystalline structures B2-Cu50Zr50, C11 b -Cu33.3Zr66.7 and the amorphous structures α-Cu50Zr50, α-Cu33.3Zr66.7. The subsurface modification resulting from ultrafast laser irradiation is investigated by a hybrid simulation to capture the phenomenon occurring at a picosecond time scale. This combines a two temperature model and molecular dynamics approaches to simulate laser matter interaction at the mesoscale. Our results indicate that the involved structural dynamics strongly depend on the initial atomic composition and phase structure. In particular, a martensite phase transition is unveiled for B2 crystalline alloy, and defects are induced in the irradiated C11 b phase, whereas the amorphous state of photoexcited metallic glasses remains remarkably preserved.I.

Molecular Dynamics Simulation of Femtosecond Laser Ablation of Cu50Zr50 Metallic Glass Based on Two-Temperature Model

“…The values of the parameters used in the TTM-MD method are shown in Table 1. The density of our prepared Cu 50 Zr 50 sample was 7.14 g/cm 3 , while that of the sample prepared by Iabbaden et al [19] was 7.18 g/cm 3 . This difference falls within an acceptable range.…”

“…T e and T ion are, respectively, the electronic and ionic temperature. For the Cu 50 Zr 50 metallic glass, a free electron model is used as C e (T e ) = γT e , where the electronic specific heat coefficient γ is available in [19]. When the simulation time t is shorter than the pulse duration τ, I(t) = I 0 and 0 otherwise.…”

“…To avoid reflection of the pressure wave at the bottom of the target, we define non-reflecting boundary conditions composed of a viscous damping region [31-33] with a 100 nm in the x direction. A damping factor γ damp = 0.0025 eV•ps•Å −2 [19] is used in this work in all simulations. The simulation is a regular MD run in the NVE ensemble after the laser pulse irradiation is completed.…”

“…For metallic glasses, Marinier et al [18] studied the ablation dynamics of CuZr metallic glass and crystal structure materials using a MD simulation combined with the TTM under femtosecond laser irradiation. Iabbaden et al [19] also employed a hybrid TTM-MD model to investigate the structural evolution of crystalline CuZr alloys and amorphous alloys of the same compositions under ultrashort laser irradiation. However, they overlooked the structural evolution of metallic glasses under different femtosecond laser irradiation conditions, which could significantly guide practical processing.…”

Dynamics of Cu–Zr metallic glass devitrification under ultrafast laser excitation revealed by atomistic modeling

“…Each 3D-periodic 8.13 × 8.13 × 8.13 nm 3 simulation cell is filled with 31250 atoms and is subjected to a classical amorphization cycle using MD as described in Ref. [83]. First, the system is heated up to 2000 K in the liquid state at a rate of 10 13 K.s −1 and then it is quenched down to 300 K using a rate of 10 11 K.s −1 where another equilibration run is performed during 100 ps in the NPT ensemble (isothermal-isobaric) using the Nosé-Hoover thermostat and barostat [84].…”