Effect Of Softening And Dilatancy On Nanometric Cutting Mechanical Properties Of Amorphous Alloy

Amorphous alloys are new kinds of engineering materials which possess excellent mechanical properties and have wide application prospects in aerospace and military due to unique atomic clusters structure.Cutting is a high-efficiency machining method,therefore,deep understanding the cutting mechanism of amorphous alloy can help to improve its processing quality and reduce tool wear and processing costs.Experimental researches on cutting of amorphous alloys have observed an unusual phenomenon the normal force is substantially equal to the main cutting force.Because of the absence of crystal defects such as dislocations,the traditional cutting theory can not give reasonable explanation of the phenomenon.This research aims at investigating the physical mechanism behind this phenomenon based on microstructure characteristics of amorphous alloys.Due to the limitations of detection resolution on temporal and spatial scale,molecular dynamics simulation method was carried out to research nanometric cutting of amorphous alloys.Firstly,the effect of machining parameters on the cutting force and microstructure in nanometric cutting of Cu₅₀Zr₅₀ amorphous alloy was researched.Cu₅₀Zr₅₀ amorphous alloy was prepared by quick melt-quench way and the 2D orthogonal cutting model was established.The atoms structures were analyzed during cutting process.The cutting force was analyzed and compared with crystal Cu,which showed that there is no strain hardening phenomenon in the cutting process of amorphous alloy.The phenomenon that the normal force is substantially equal to the main cutting force is determined by varying cutting parameters.In addition,it was found that obvious elastic recovery of the machined surface during cutting process.Secondly,the elastic recovery of the machined surface during the nanometric cutting process of amorphous alloy was confirmed by quantitative analyzing atomic Y-direction displacement and machining surface volume calculation.It is considered that the elastic recovery of the machined surface is due to the tensile stress caused by the hydrostatic pressure after the shear deformation of the machined surface microcell Moreover,theshear simulation of the amorphous alloy unit was carried out,and normal stress was induce during the shear deformation process of the amorphous alloy.Confirmed the existence of dilatancy effect.By analyzing the normal stress on the rake and flank face of tool during the cutting process,it is found that the normal stress that is perpendicular to the shear plane acting on the cutting surface is induced during the shear deformation of the micro-element in the machining process.The tool flank face was affected by the normal stress,and the normal force become largerFree volume theory is an important method for the analysis of deformation mechanism of amorphous alloy.Based on the method,the free volume content with temperature is calculated.The changes of free volume,temperature,shear stress and hydrostatic stress are studied during cutting process.It is found that hydrostatic stress?compressive stress?suppresses the generation of free volume.Through the comparison of the chip layer and the machined surface layer,it was found that the hydrostatic stress of selected area in the chip layer was small,the temperature was high,and the free volume content is high during the shear deformation process.Therefore,softening effect is obvious and the chip layer materials yielded under smaller shear stress than machined surface layer,which leads to the reduced of main cutting force.