Effect Of Pre-existing Shear Bands On Mechanical Properties And Serrated Flow Behaviors In Bulk Metallic Glasses

Because of their great mechanical properties such as high strength and high hardness,bulk metallic glasses(BMGs)have attracted much attention.However,during deformation of BMGs,a limited plastic strain is usually highly localized within shear bands,resulting in their intrinsic brittleness at room temperature.Therefore,it becomes important to find a method to inhibit the rapid propagation of the dominant shear band and induce multiple shear bands in order to enhance their room-temperature plasticity.In this work,the pre-existing multiple shear bands were effectively introduced into BMGs by rapid defect-printing and cold-rolling methods,respectively,which can further enhance the compressive plasticity of BMGs.Besides,the corresponding plastic deformation mechanism and the serration events in the stress-strain curves were also analyzed.Firstly,Zr65Cu15Ni10Al10 BMG plates were prepared by copper-mold suction casting.The surface defects were introduced into BMG plates through a rapid defect-printing method and the pre-existing multiple shear band were introduced nearby the defects.The room-temperature compressive plasticity of Zr65Cu15Ni10Al10 BMGs enhanced from 6%to 8-10%.The main reasons can be summarized as:(1)It becomes easier for multiple shear bands to initiate during plastic deformation because of the existence of the pre-existing multiple shear band zones;the interaction of multiple shear bands also stabilize the propagation of the dominant shear band.(2)The defects is beneficial to the stress distribution on sample surfaces so that the multiple shear bands can propagate in a more stable way during plastic deformation.Secondly,Zr65Cu15Ni10Al10 and Zr56Co29Al16BMG rods were prepared by copper mold suction casting.Pre-existing multiple shear bands were introduced through the lateral-deformation into Zr56Co28Al16 and Zr65Cu15Ni10Al10 BMGs,respectively.The rapid propagation of the main shear band can be inhibited in the pre-deformed samples during plastic deformation due to the strong interaction between pre-existing multiple shear bands,resulting in the further enhancement of the room-temperature compressive plasticity of BMGs.The compressive plasticity enhanced from 6%to 12%for Zr56Co28Ali6 BMGs and from 11%to 30%for Zr6sCuisNiioAlio BMGs.According to the serration analysis on the plastic deformation behaviors of the as-cast and the pre-deformed samples,the serration events in the stress-strain curves during deformation of the pre-deformed samples display a more stable self-organized critical behavior.This should be due to the pronounced interactions of shear bands during plastic deformation for the pre-deformed BMGs,leading to a more stable shear banding process during deformation.Finally,the application possibility of pre-deformation was investigated in BMGs with different Poisson's ratio(such as Zr56Co28Ali6,Zr65Cu15Ni10Al10,Cu46Zr66Al8,and Fe48Cr15Mo14Y2C15B6).After pre-deformation,the pre-existing shear bands can be easily introduced into BMGs with a large Poisson's ratio such as Zr56Co28Ali6,Zr65CuisNiioAlio,and Cru46Zr46Als BMGs.Experimental results show that their corresponding room-temperature compressive plasticity can be effectively enhanced.However,it become easy to introduce cracks rather than pre-existing shear bands into BMGs with a low Poisson ratio(for example Fe48Cr15Mo14Y2C15B6).Besides,even for BMGs with a same high Poisson's ratio,the enhancement difference of the room-temperature compressive plasticity after pre-deformation is mainly due to their different shear modulus.During deformation,the pre-existing shear bands trend to form easily for the samples with a low shear modulus since the samples with a low shear modulus show a lower resistance for shear deformation,leading to the larger enhancement of plasticity for the pre-deformed samples with a lower shear modulus but a same Poisson's ratio.