Atomic insight into residual stress and microstructure evolution of amorphous carbon heterostructured films induced by multi-stage phase transformation of high-entropy alloys

Abstract

The residual stress has significant effects on the microstructure and service performance of films. With good toughness and low stacking fault energy, high-entropy alloy (HEA) can act as dopant to reduce the residual stress of films via self-plastic deformation. Nevertheless, the microscopic mechanism buried deep under the surface is difficult to study by experiments and the dynamic evolution cannot be observed, which the biggest obstacle to investigate the corresponding solutions is. In this paper, diamond-like carbon (DLC) models with different CoCrFeNi HEA doping ratios (1:2, 1:4, 1:6, and 1:8) were designed by molecular dynamics method. The effects of CoCrFeNi doping percentage on the structure and residual stress of this heterostructured films were investigated, and the mechanism of residual stress reduction was revealed. The results show that the phase transformation of HEA causes stress fluctuations in DLC films. The stress fluctuations at different orientations of the heterostructured films is gradually shifted to the right with the increase of HEA percentage, and the difference in stress level between the initial and final strain is significantly decreased. Meanwhile, when the doping ratio is 1:2, the compressive stresses inside the films is lower and the generation of stacking faults is later. With the increase of the HEA doping ratio, the proportion of C atoms with sp3 and sp2 hybridization structures is decreased significantly, and the percentages of the distorted C–C bond length and distorted C–C-C bond angle are also reduced. Therefore, HEA doping affects the number of hybrid atoms and the distribution of bond characteristics in DLC films, which leads to the decrease of the residual stress of the heterostructured films.Graphical