Atomistic Simulation Of The Effect Of Heavy Element Re On The Crack Propagation In The Ni-based Single Crystal Model Superalloys

In the present work, the influences of Re on the crack propagation along the γ(Ni)/γ’(Ni3Al) interface and in the y phase (including on crack tip shape, crack propagation velocity, emission of dislocations, ductile-brittle characteristics, and lattice trapping and fracture stress) are investigated using the molecular dynamics (MD) method with a Ni-Al-Re embedded-atom-method (EAM) potential.This work consists of four parts:1. In the present work, the influences of Re on the propagation of a Ni/Ni3Al interface crack at low and high temperatures, including the shape of crack tip shape, dislocation emission, and crack velocity, are investigated. The MD simulations indicate:1) At high temperature, the crack tip becomes more blunt with Re addition due to the larger bond strength between Re and Ni atoms.2) With Re addition, the dislocations appear more readily and the cleavage becomes more difficult.3) The brittle crack propagation velocity at low temperature observably decreases with Re addition.2. In the present work, the effect of Re on the activation energy (△Edis) of the activation energy of SF nucleation and dislocation nucleation from a crack tip in Ni is investigated using the climbing image nudged elastic band (CI-NEB) method. The new parameter (△Ebsf), the activation energy of the SF nucleation under loading, is introduced to describe the effect of Re on SF and dislocation nucleation. The influence of Re on the dislocation nucleation frequency (v) and the ductility of crack at300and1500K are discussed. The MD simulations indicate:1) Both△Ebsf and△Edis decrease when Re concentration increases. The dislocation nucleation frequency exceeds the spontaneous nucleation threshold (v=106/(mm.s)) with Re addition. The ductility of the crack in Ni can be enhanced by Re. 2) The effect of Re on the SF nucleation was assessed by evaluating△Esfb△Edis is closely related to△Ebsf, and the effect of Re on the dislocation nucleation trends under the external loading is reflected by△Ebsf.3) The decrease of both△Ebsf and△Edis with the addition of Re is due to the expansion of the local structure around the Re atom (the average distance between the Re atom and the first nearest-neighbor atoms increases by0.035-0.052A) when the SF or dislocation goes through the Re atom. This expansion relaxes the volume mismatch between the Re and Ni atoms.3. The influence of Re on the lattice trapping and fracture stress of the five orientation cracks in Ni are investigated using the molecular dynamics (MD) method. The influence of temperature on the ductile-brittle characteristics of cracks in Ni is also investigated. The range (R) over which Re affects the jumps in bond lengths in neighbouring regions, the influence of Re on the range (S) of lattice trapping, the influence of Re on kinks and dislocations at crack tips, and the fracture stress are discussed. The MD simulations indicate:1) Without Re addition, the true Griffith load in the MD simulation is very close to the theoretical Griffith load.2) The lattice-trapping range for the five different crack orientations studied is small (S≈0.03), regardless of the single Re atom,3at%, and6at%Re addition. This implies that the Re-Ni interatomic interaction also has long-range characteristics.3) With the addition of3at%and6at%Re, both lower and upper trapping limits increase significantly, and the critical fracture stress usually increases by at least10%. Both the crack orientation and Re concentration can have a big effect on the critical fracture stress.4) R<5A in dilute Ni (Re) solid solutions with the single Re atom addition; R>17A in Ni (Re) solid solutions with3at%and6at%Re random addition.4. The influence of Re on the adhesion work of the Ni/Ni3Al interface, the interatomic energy of atoms in the crack tip of the Ni/Ni3Al interface, and the interatomic energy of atoms in Ni matrix, is calculated by ab initio methods. The calculations indicate:1) The order of the adhesion work induced by the alloying elements is: Re> W> Mo> Ta> Cr> Ru> Co>(Ni)2) The order of the interatomic energy of atoms in the crack tip of the Ni/Ni3Al interface induced by the alloying elements is: Ta> W> Mo> Re> Cr> Ru> Co>(Ni)3) The order of the interatomic energy of atoms in Ni matrix induced by the alloying elements is: Ta> W> Mo> Re> Cr> Ru>(Ni)> Co...