Structural transformation and strain localization at twin boundaries in Al0.4CoCrFeNi high-entropy alloy

Surface nanotribological properties and subsurface damage of Al0.4CoCrFeNi high-entropy alloy during the nanoscratching processes are investigated using molecular dynamics. The results show that the surface wear characteristics and scratching-caused surface damage significantly depend on the crystallographic orientation, spacing and inclination angle of the twin boundary. For the variation of crystallographic orientation, the largest friction coefficient belongs to the crystallographic orientation [001], indicating that the movement of the indenter in this substrate is most restricted. The microstructure evolution reveals the formation of Lomer-Cottrell and Hirth dislocation locks because of the distinctness of angle between various slip systems. Both the Hall-Petch and inverse Hall-Petch relationships are observed for the difference of twin boundary spacing, and the maximum indentation force is achieved with a tilt angle of 0 degrees resulting from the various interactions among the dislocations and twin boundaries. The microstructure evolution and the atomic flow are greatly dependent on the spacing and the inclination angle of twin boundary, where the twin boundary migration is the significant factor. Furthermore, the surface morphology is distinct between workpieces due to the elastic recovery at the surface, nucleation and slipping of dislocation, which implies that the wear volume depends on the material microstructure.