Molecular dynamics simulations of phase formation and stability in the Al(Ni) system under irradiation

Molecular dynamics simulations of displacement cascades in aluminium, aluminium-nickel solid solutions and inhomogeneous samples containing amorphous or crystalline Al3Ni precipitates are performed. It is shown that no segregation occurs inside the displacement cascade and that the nickel atoms are in an interstitial position after the thermal spike. The number of defects created by the cascade increases with the nickel initial composition until this concentration reaches 20 at% Ni, at which point a complete amorphization is observed. Furthermore, it is observed that precipitates are dissolved or remain stable under cascade conditions depending on their size

Stability of Al0.75Ni0.25 amorphous zones induced by Ni ion implantation into pure aluminium

Implantation of Ni ions into pure aluminium shows the formation of amorphous zones (AZ). Measurements by energy dispersive spectrometry attribute to the amorphous zones at Ni concentration of 25 at.%. These amorphous regions are relatively stable under heating and persist after post-implantation treatment. To understand microscopically this stability, molecular dynamic simulations (MD) are done. Using embedded atom method potentials, an amorphous Al3Ni is first obtained. The melting temperature determined for this sample from the calculations is in good agreement with the experimental data. A spherical amorphous zone is then introduced into a crystalline aluminium matrix. After relaxation to obtain the equilibrium at interface, the system is heated for hundreds of picosecond at various temperatures. The AZ remains after this treatment. One cascade of 5 keV is then simulated inside an AZ. A complete phase transition is not observed, but a partial recrystallization is present. (C) 1998 Elsevier Science B.V. All rights reserved

Structure analysis by diffraction of amorphous zones created by Ni ion implantation into pure Al

The implantation of Ni ions into pure Al leads to the formation of similar to 10 nm amorphous zones (AZ) which induce diffuse rings in the diffraction pattern in addition to the diffraction spots of the crystal. Measurements by energy dispersive spectrometry and electron energy loss spectrometry attributed to the amorphous zones an average Ni concentration of 25 at%. The exact structure of these AZ is still unknown. The structure is characterized here by both the total and partial radial distribution functions (RDF). Structure factor deduced from experiments is compared to calculated one. For this purpose, molecular dynamic (MD) simulations are used to model the AZ structure. The RDF are determined using this structure and analytical calculation of the diffraction pattern is achieved. Simulations of the diffraction pattern of the simulated MD sample using both a kinematic and a dynamic approach are achieved to refine the analytical procedure used on the experimental diffraction patterns. It appears that the amorphous structure is well reproduced by the MD simulations. Analytical calculation reveals the presence of a well-established chemical order in the amorphous material. (C) 2000 Elsevier Science B.V. All rights reserved