Atomic-scale investigation on the mechanical behaviors of the γ ′ / γ " co-precipitates compounds in Ni-based superalloys

The gamma '/gamma '' co-precipitation strategy entails excellent mechanical properties for Ni-based superalloys, but the deformation mechanism of gamma '/gamma '' co-precipitates Ni-based superalloys at atomic-scale remains unclear. In this work, we studied the effect of loading rate, void size, and temperature on the mechanical behaviors of gamma '-Ni3Nb/gamma ''-Ni3Nb co-precipitates via molecular dynamic (MD) simulations. The simulation results show that the tensile load rate 1x10(9) s(-1) is critical for the free-void gamma '/gamma '' co-precipitates. When the loading rate exceeds 1x10(9) s(-1), a transition occurs in the deformation mechanism, leading to a rapid increase in tensile strength and a subsequent reduction in flow stress until it eventually vanishes (1.35 GPa -> 0.98 GPa -> 0 GPa). The presence of voids at the interphase boundary significantly reduces the material's strength, with this weakening effect becoming more pronounced as the void radius increases. Furthermore, the voids facilitate the easier penetration of dislocations into the gamma ' and gamma '' precipitated phases along the void peripheries through the interphase boundary. The study also reveals that the trends in Young's modulus and yield stress for both pre-void and void-free models are similar with increasing temperature, with Young's modulus decreasing as temperature rises. Notably, at elevated temperatures, gamma '' precipitated phase transitions occur within the gamma '/gamma '' co-precipitates, and the yield stress is maximum at 800 K. This study provides valuable insights into the mechanical behavior of gamma '/gamma '' co-precipitates and the weakening effects of atomic-scale voids in Ni-based superalloys.