Deformation and machining mechanism of nanocrystalline NiCoCrFe high entropy alloys

The effect of composition, grain sizes (GSs), and cutting depths on the deformation behaviors and subsurface damages of scratched NiCoCrFe high entropy alloys are investigated using molecular dynamics (MD) simulation. The ability to remove atoms during the cutting process depends on the alloy composition and GSs. When Ni, Co compositions are kept constant, the maximum tangential force-Fx and average friction coefficient-μ increase as decreasing Fe composition from 40% to 24%, then that inverse increase as continuous decrease Fe composition to 20%. Maximum normal force-Fz and average VMS increase with increasing percentage composition of Fe. Besides, the dislocation increases with the Co composition increase leading to a reduction in the efficiency of the cutting process or reducing the number of worn atoms. The reason is that the higher Co content results hinder dislocation movement and reduce the stacking fault energy of the material. The deformation mechanism presents that GBs keep a vital act in barring the propagation dislocation and the development of stacking fault. The GBs also act as an intermediary path to release thermal residual stresses to help reduce cutting force. Interestingly, the number of worn atoms clearly increases as increasing average GS to 81 Å, then decreases as continuously increasing GS to 108 Å.