Effect Of Cutting Temperature On The Formation Mechanism Of Cu₅₀Zr₅₀ Shear Band In Metallic Glass

The microcosmic atomic arrangement of bulk metallic glasses is long range disordered,short range ordered structure,but macroscopically hard and brittle.The chip of bulk metallic glasses exhibits high frequency periodic shear band with thickness of 10nm-20 nm during cutting.Moreover,the structure of droplet and molten band is observed on the fracture surface of shear band,and the instantaneous high temperature of2400K-2700K is measured in cutting.In order to understand the effect of temperature on the formation of high frequency periodic shear band during cutting of metallic glasses,the following researches have been carried out.First of all,the metallic glass Cu₅₀Zr₅₀ fine partition model was set up by the molecular dynamics simulation platform,and a circular shaped radial distribution of temperature field was obtained in the cutting depth of 50?and the cutting speed of 50m/s.It reveals that uniform viscosity deformation occurs in the shear deformation zone for temperature reached the glass transition temperature of the material itself.Then,through two groups of orthogonal cutting experiments,the influence of cutting tool geometry parameters and cutting parameters on the temperature during shear deformation was investigated.The results show that the cutting speed has the greatest influence on the temperature of the first shear deformation zone and the machining surface region.As the cutting speed increases,the temperature of the two regions increases rapidly.When the cutting speed is less than 40m/s,the temperature of the shear deformation zone is lower than the glass transition temperature of the material itself.At this time,the shear deformation occurs non-uniform local shear deformation.Finally,by analyzing and comparing the temperature,stress and Voronoi volume of the first shear deformation zone and the machined surface area in the cutting process,it is found that the stress plays a decisive role in the change of Voronoi volume,and the temperature plays a secondary role.It is also found that the Voronoi volume in the first shear deformation region increases first and then decreases,which inevitably leads to the gradient distribution of viscosity between the continuous materials during the chip’s high speed flight out cooling process.The internal viscosity of the material varies periodically,which is probably the reason of the high frequency periodic shear band.Moreover,the cutting displacement length of Voronoi volume increases rapidly and decreases rapidly is17.5 nm,which is exactly between 10 nm and 20 nm and is consistent with the thickness of the high frequency periodic shear band.