A molecular dynamic investigation of cyclic strengthening mechanism of Ni-based single crystal superalloy

Abstract

Ni-based single crystal superalloys, as crucial materials in the aviation and aerospace industry, frequently encounter fatigue failure induced by cyclic loading, which is one of the primary failure modes. In this study, molecular dynamics (MD) simulations are utilized to explore the cyclic strengthening mechanisms of Ni-based single crystal superalloys, with a focus on dislocation evolution under cyclic loading. Two typical feature atomistic models of the alloys are constructed and dislocations are introduced under cyclic loading, investigating the interactions between dislocations and the γ/γ′ interface. The results highlight the excellent capacity of the interfacial dislocation network for dislocation deposition, particularly for those attempting to penetrate the γ′ phase, and capture a transition in emission dislocations slip plane from the $\left\{111\right\}$ plane to the $\left\{100\right\}$ plane. The dislocation absorption is driven by two primary mechanisms: the formation of stable link points at the γ/γ′ interface and the obstructive effect of the γ′ phase. Additionally, a stress stratification phenomenon at the γ/γ′ interface is observed, hindering dislocation movement during loading and leading to dislocation trapping through cross-slip during unloading. Furthermore, the simulations reveal two distinct forms of dislocation barriers pile-up within the γ phase: one arising from the decomposition of the interfacial dislocation network, which leads to the emergence of stacking faults (SFs) bands and Lomer-Cottrell lock; the other stemming from the formation of SFs bands due to the decomposition of the emission dislocations within the γ phase channel. These findings provide meaningful insights into the cyclic hardening behavior of Ni-based superalloys.