Molecular dynamics simulation of deformation mechanism and mechanical response of dual phase (FeCoNi)₈₆Al₇Ti₇ high-entropy alloy during nanoscratching

Deformation behavior and mechanical response of dual-phase (FeCoNi)₈₆Al₇Ti₇ high-entropy alloy (HEA) during the nanoscratching process were studied by molecular dynamics simulations. The nanoscratching force, friction coefficient and the morphology of scratched surface at different scratching depths were obtained firstly, and then the phase transition, evolution of stacking faults and dislocations caused by nanoscratching in dual-phase HEA were analyzed. Moreover, nanoscratching experiments were conducted to compare with the simulation results. Results show that nanoscratching force and friction coefficient change obviously during nanoscratching of the dual-phase HEA. The morphology of the scratched surface is attributed to combined effects of two-phase structure of the workpiece and the existence of grain boundaries. Shear slips are formed under effect of nanoscratching in the L1₂ phase grains in dual-phase (FeCoNi)₈₆Al₇Ti₇ HEA, while FCC phase grains in dual-phase HEA exhibit FCC-BCC phase transition. Plasticity of L1₂ grains is dominated by tacking faults and slip bands, while plasticity of FCC grains is dominated by the FCC-BCC phase transition. Dislocations are only formed in L1₂ grains rather than in FCC grains of dual-phase HEA. Shockley partial dislocation is the main dislocation type formed by nanoscratching. The results of TEM characterisation of the nanoscratching sub-surfaces proved the validity of the simulation. This work will provide further understanding of the friction and wear properties and deformation mechanism of HEAs, which maybe facilitate development of new HEAs with excellent tribological properties.