Grain boundary segregation strengthening behavior caused by carbon chain network formation in nanocrystalline NiCoAl alloy

Abstract

Grain boundary movement is closely related to plastic deformation of materials. In our contribution, C atoms are introduced into the grain boundary and a highly stable C chain network is formed through structural optimization. The results show that the formation of C chains greatly enhances the stability of the grain boundaries and exhibits strong dislocation pinning capability. With the increase of C content, the generation of phase transformation and the nucleation of dislocations are inhibited. The yield strength and tensile strength first increase and then decrease, showing three different deformation mechanisms during tensile deformation. High-density dislocations and unstable grain boundaries jointly control the mechanical properties in the first stage. When the C content comes to 1%, the formation of C chain network greatly enhances the stability of the grain boundaries and effectively hinder and pin the dislocations, inducing a strengthening effect. In the third stage, the further increase of C content severely inhibits the nucleation of dislocations, and leads to a decline in the mechanical properties of alloy. This new strategy of modifying grain boundaries by introducing non-metallic atoms provides an interesting and positive idea for grain boundary engineering.