Atomic simulations on the deformation mechanisms in nano-crystalline Ni–Al series Ni-based superalloy based on grain size, strain rate and temperature

Abstract

Molecular Dynamic (MD) simulations were used to investigate the tensile properties of nanocrystalline Ni–Al series Ni-based superalloy at different grain sizes (6.54–20 nm), strain rates (1 × 107–5 × 108 s−1) and temperatures (300–1000 K). Results indicate that plastic deformation of nanocrystalline Ni–Al series Ni-based superalloy was governed by stacking faults and FCC-to-HCP martensitic phase transformation, which was significantly different from twinning-dominated plastic deformation in nanocrystalline Ni. Nevertheless, the conventional Hall-Petch breakdown occurred at a critical grain size in both nanocrystalline Ni and Ni–Al series Ni-based superalloy. Moreover, the critical mean grain size was little influenced by the strain rate in the strain-rate range of 107 to 5 × 108 s−1. Strain rate sensitivity m was closely related to grain size and strain rate. Grains combination can be observed at lower strain rate, while at higher strain rate, GB diffusion was visible. Besides, flow stress and Young's modulus were both strongly affected by temperature, and an increase in temperature can accelerate GB diffusion and GB migration. The current study provides an atomic perspective on the deformation process and mechanisms in nanocrystalline Ni–Al series Ni-based superalloy, as well as new perspectives on designing novel superalloys with excellent mechanical properties.