Dynamic Homogenization of Internal Strain via High-concentration Doping of Oxygen with Large Mobility

Abstract Internal strain and its distribution in crystal lattice play important roles in tuning dislocation activities, which would affect the mechanical properties of materials consequently. Here, by combing integrated differential phase contrast, in situ transmission electron microscope characterizations and computer simulations, we revealed a way of homogenizing dislocation pinning by doping high concentration of oxygen atoms with high diffusion mobility into NiCoCr medium entropy alloy. The doping of massive oxygen atoms introduces high density of strong local pinning points for dislocation motion. Moreover, the oxygen interstitials can easily diffuse and move between different octahedral and tetrahedral sites in the distorted crystal lattice of NiCoCr alloy at even room temperature, based on which severe stress concentrations produced by dislocation tangling can be released and strong local dislocation pinning points can be re-built at other sites towards a uniform way, enabling the material with high strength and outstanding deformability. Our results indicate that the interstitial atoms may become highly mobile at even ambient temperature in complex multi-elements alloys with spreading lattice distortion, which may open a new branch of dislocation engineering.