Twin spacing and grain size dependent tensile deformation mechanism of a nano-ploycrystalline Ni-based alloy

It is easy to form twins in Ni-based wrought superalloys with low stacking fault energy, but the effect of grain size and twin spacing on mechanical properties in nano-ploycrystalline Ni-based alloys is rarely studied. Based on the composition of a novel Ni-based wrought superalloy, molecular dynamics simulations were used to study the effect of grain size and twin spacing on the deformation behavior of the Ni57Cr19Co19Al5 alloy. The results show that the elastic modulus and tensile strength of the nano-polycrystalline Ni57Cr19Co19Al5 alloy exhibit clear grain size dependence. As the grain size exceeded 16 nm, the elastic modulus remained unchanged. The tensile strength and grain size satisfy the Hall-Petch relationship, and the dislocation motion dominates the plastic deformation. For the grain size below 16 nm, the elastic modulus decreases as the grain size decreases. The tensile strength and the grain size exhibit an inverse Hall-Petch relationship. The grain boundary sliding and grain torsion mechanisms dominated plastic deformation in the nano-polycrystalline Ni57Cr19Co19Al5 alloy without twin. In the nano-polycrystalline Ni57Cr19Co19Al5 alloy containing twins, the twin boundaries inhibited the torsion of grains, and grain boundary sliding dominated plastic deformation.