Physical mechanisms of nanocrystallization of a novel Ni-based alloy under uniaxial compression at cryogenic temperature

Abstract

A novel Ni-based alloy, which possesses a nominal chemical composition of Ni52Cu20Cr15Mo5Ti2Al1Nb5 (wt.%), is designed and fabricated in order to be used for cryogenic environments. The Ni-based alloy exhibits high plasticity and high strength in the case of uniaxial compression at −150°C. Nanocrystalline phases, in particular, are observed in the matrix of Ni-based alloy subjected to plastic deformation at −150°C. Statistically stored dislocation (SSD) density and geometrically necessary dislocation (GND) density are found to play a significant role in nanocrystallization of Ni-based alloy. SSD density and GND density increase with the increase in the plastic strain. There appears a critical dislocation density above which the critical resolved shear stress (CRSS) for dislocation slip was greater than the CRSS for deformation twinning. Consequently, deformation twinning occurs instead of dislocation slip with increasing plastic strain. Under the simultaneous action of dislocation slip and deformation twinning, dislocation wall, dislocation cell, deformation twin, low angle grain boundary and high angle grain boundary occurs in such an alternative way that nanocrystalline grains are formed in the end.