Molecular Dynamics Simulation on Dislocation Nucleation and Motion at an Apex of Cuboidal .GAMMA.' Precipitate in Ni-Based Superalloy.

Abstract

The nucleation and motion of misfit dislocation at γ/γ' interface in Ni-based superalloy is studied by means of molecular dynamics simulations based on the Embedded Atom Method. In particular the dislocation nucleation at apices of cuboidal γ' precipitate surrounded by the other precipitates is discussed through the simulations of single crystalline γ/γ' microstructure in which eight cuboidal L12-Ni3A1 precipitates are aligned three dimensionally. First, the stability of the coherent interfaces of the microstructure is discussed in view of the residual stress at equilibrium state. Then the microstructure is subjected to uniaxial loading in the [001] direction up to the strain larger than 0.05 where dislocation nucleation is observed in it. Detail observation of the nucleation process reveals the new mechanism of dislocation nucleation and motion near apices of precipitates: (1) a closed loop of a partial dislocation nucleates at a γ/γ' interface on an apex of γ' precipitate and propagates in γ channel toward the other interface on the adjoining γ' precipitate, (2) the loop branches two partials bridging between two adjacent γ' precipitates when it reaches the interface, (3) dislocation pinning takes place at the edge of cuboidal precipitate since the end of dislocation line cannot continue to glide on the junction line between the slip plane and γ/γ' interface.