Different patterns of dislocation nucleation and propagation in heterogeneous HEA/Ni nanocomposites and its opposite mechanical response at the interface

Abstract

Heterogeneous high-entropy alloy (HEA) nanocomposites have garnered considerable scholarly attention due to their remarkable mechanical properties. However, their atomic deformation mechanisms during nanoindentation remain ambiguous. This study employs molecular dynamics simulation to perform indentation testing under three loading modes (Ni phase, Ni/HEA heterogeneous interface, and HEA phase). The results show that the indentation response is significantly influenced by the loading mode. The heterogeneous interface loading exhibits the most stable characteristics, whereas direct loading on the Ni phase induces significant force fluctuations and the highest hardness. These fluctuations arise from complex dislocation reactions, wherein dislocations generated in the Ni phase can traverse the heterogeneous interface and propagate throughout the whole nanocomposite. The HEA phase is essential for stabilizing the mechanical response. The Ni/HEA interface and HEA loading modes demonstrate significantly diminished force fluctuations and progressively declining hardness values. The surface roughness under HEA loading is the highest. The heterogeneous interface effectively blocks dislocation propagation from the HEA phase, confining dislocation activity to localized regions within the HEA. Sessile dislocations persist at the interface, impeding the propagation of dislocations. At a low temperature of 77 K, the nanocomposite demonstrates increased hardness and fewer variations in indentation force. The nanocomposite exhibits diminishing hardness values with increasing indenter size. Nonetheless, a larger indenter causes localized amorphization in the HEA region, hence increasing material hardness. The study thoroughly elucidates the mechanical property response to loading modes in heterogeneous HEA nanocomposites, providing guidance for the design of HEA nanocomposites with adjustable mechanical characteristics.