Effect of Ta and Re on the fracture strength and creep strength of Ni/Ni₃Al interface

Abstract

The first principle method based on density functional theory and generalized gradient approximation is used to investigate the interaction of Ta and Re elements in Ni/Ni<sub>3</sub>Al interface and their influence on the interface strength. According to the calculation of the dissolution energy of these two alloying elements at 7 different positions, it can be concluded that in most of the stoichiometric ranges, Ta atoms preferentially occupy Ni site in the γ phase, while Re atoms occupy preferentially Al site in γ' phase. The doping positions do not change when these two atoms are co alloyed. The calculation of Griffith fracture work of Ni/Ni<sub>3</sub>Al interface system shows that the doping of Ta atoms can improve the interface fracture strength of the phase boundary region between the γ/γ' coherent atomic layer and γ atomic layer. The interface is easier to fracture at the phase boundary area between γ/γ' coherent atomic layer and γ' atomic layer after Ta atoms doped. Doping of Re atom can improve the interface fracture strength of the phase boundary region between γ/γ' coherent atomic layer and γ' atomic layer. The interface is easier to break at the phase boundary area between γ/γ' coherent atomic layer and γ atomic layer. The calculation results of the unstable stacking fault energy under the interface slip system before and after Ta and Re alloying show that the doping of these two types of atoms increases the value of the unstable stacking fault energy of the interface, and the slip system becomes difficult to start, which enhances the ability of the interface to block the movement of dislocations, thus enhances the creep strength of the nickel base superalloy. When doping Re atoms, the effect is greater, and the unstable stacking fault energy of the interface increases by 11.1%, which is better for improving the creep strength of the system. By studying the influence of alloying atoms on the path of vacancy migration and the energy barrier, it is concluded that the doping of Ta and Re atoms can increase the vacancy formation energy and the potential barrier of vacancy migration at the interface. The doping of Re atoms increases the migration energy barriers on both sides of the interface, and the doping of Ta atoms increases the migration energy barriers of γ phase. The increase of the migration barrier hinders the emission and absorption of vacancies, thereby improving the creep ability of the alloy.