Investigation of reorganization of a nanocrystalline grain boundary network during biaxial creep deformation of nanocrystalline Ni using molecular dynamics simulation.

In this paper, simulated biaxial creep deformation behaviour for nanocrystalline (NC) nickel (Ni) has been performed at various applied load (i.e. 1 GPa, 1.4 GPa, 2 GPa, 2.5 GPa and 3 GPa) for a particular temperature (i.e. 1210 K) using molecular dynamics (MD) simulation to investigate underlying deformation mechanism based on the structural evolution during biaxial creep process. Primary, secondary and tertiary stages of creep are observed to be exhibited significantly only at 3 GPa applied stress. While, only primary and secondary stages of creep are exhibited at 1 GPa applied stress. Atomic structural evaluation, dislocation density, shear strains, atomic trajectory, inverse pole figures and grain orientation with texture distribution have been carried out to evaluate structural evolution. Stress exponent (m) for NC Ni is analysed for a particular creep temperature (i.e. 1210 K) and obtained m value is 1.30. According to shear strains counter plot, accumulation of higher shear strains are observed at grain boundary (GB) during biaxial creep deformation. It is found that dislocation density during biaxial creep is increased with the progress of creep process. Grain rotation and texture evaluation during biaxial creep process are studied using grain tracking algorithm (GTA). Grain rotation in ultrafine-grained NC Ni specimen during biaxial creep deformation is happened and exhibits almost distinct distribution, which is occurred due to the atomic shuffling within the GBs. Grain growth of ultrafine grained NC Ni is observed during biaxial creep deformation which is caused by mechanical stress.