Influence of the alloying elements Re, Co and W on the propagation of the Ni/Ni₃Al interface crack

Abstract

The influence of the alloying elements Re, Co and W on the propagation of the (010) [101] Ni/Ni 3 Al interface crack has been investigated by molecular dynamics simulations and the discrete-variational method. The simulation results show that the interface crack propagates in a brittle manner at low temperature (5 K), but in ductile manner at high temperature (1273 K), both with and without the addition of alloying elements. Owing to the scientific and technological importance of superalloys, the effects of the chemical bonding behavior between the alloying element X (X = Re, Co, or W) and Ni atoms on the crack shape, crack propagation velocity, and dislocation emission were investigated. At low temperature, the alloying elements Re and W inhibit the propagation of the Ni/Ni 3 Al interface crack, while at high temperature Re, Co and W can improve the ductility of Ni-based single-crystal superalloys. Furthermore, the adhesion work of the interface, surface energy, and unstable stacking energy were calculated to understand the propagation mechanism of the Ni/Ni 3 Al interface crack because of alloying element addition. The results of this study may provide useful information for the design of Ni-based superalloys.

Effects of Re, W and Co on dislocation nucleation at the crack tip in the γ -phase of Ni-based single-crystal superalloys by atomistic simulation

“…E 0 is obtained by applying periodic boundary conditions in [1false¯ 1false¯ 2false¯], false[1 1 1¯false] and false[1 1¯ 0false] directions. The lattice parameters for all the systems are also calculated based on the models for calculating E 0 and the calculated lattice parameters are consistent with the previous result [24]. E surf is obtained by applying periodic boundary conditions in the [1false¯ 1false¯ 2false¯] and false[1 1¯ 0false] directions and free boundary condition in the false[1 1 1¯false] direction.…”

“…The unstable stacking fault energy ( γ us ) was first proposed by Rice [11], and this quantity can be used to approximately estimate the energy barrier of partial dislocation nucleation. The ratio of γ s and γ us can be used to evaluate the competition between brittle and ductile behaviour [11,24,33]. A larger value of γ s / γ us may result in easy dislocation emission relative to cleavage.…”

“…The discrete variational method (DVM) [48,49] is used to calculate the interatomic energy (IE) [50–52] between atoms. The IE is a quantity that can be used to evaluate the bonding and interaction between neighbouring atoms, and it had been used successfully in studying the electronic structure and properties in metals and alloys [23,24,53,54]. The IE is defined as Ellnormal′=∑n∑αα′Nnanα l∗anαnormal′lnormal′Hαnormal′lnormal′α l,where N n is the occupation number for the molecular orbital ψ n , a nαl given by a nαl = 〈 ϕ αl ( r )| ψ n ( r )〉, and Hαnormal′lnormal′α l is the interaction Hamiltonian matrix elements between atoms.…”

“…The IE is defined as Ellnormal′=∑n∑αα′Nnanα l∗anαnormal′lnormal′Hαnormal′lnormal′α l,where N n is the occupation number for the molecular orbital ψ n , a nαl given by a nαl = 〈 ϕ αl ( r )| ψ n ( r )〉, and Hαnormal′lnormal′α l is the interaction Hamiltonian matrix elements between atoms. A relatively larger absolute value of IE indicates a stronger interaction and bonding between neighbouring atoms [24,52,55]. More details of IE can be found in the literature [52].…”

“…They concluded that the effect of Re on decreasing the activation energy of dislocation nucleation may relate to the local atomic structure expansion around Re atoms when dislocation passes Re atoms and the ductility of the crack in Ni can be improved by Re addition. Liu et al [24] investigated the effects of Re, Co and W on the propagation of the γ / γ ′ interface crack. However, these works only considered Re effect or lack of emphasis and comparison of alloying effects on dislocation emission from the crack tip in the γ -phase of Ni-based superalloys.…”