Mechianical Behavior Of In-situ Ti-based Metallic Glass Matrix Composites Upon Dynamic Loading

Since firstly fabricated by accident,the bulk metallic glasses(BMGs)were developed quickly and attracted significant technological and scientific studies all over the world on account of a series of superior mechanical properties at ambient temperature,such as ultrahigh strength,high hardness,large elastic limits,and excellent wear and corrosion resistance.BMGs are esteemed as potential engineering structural materials.However,owing to highly localized shear deformation upon loading,BMGs exhibit limited plasticity at room temperature and have subsequent catastrophic failure without apparent macroscopic plasticity by shear softening in one band.In order to circumvent the poor plasticity,in-situ formed ductile secondary phases can be introduced into the glass matrix to form the metallic glasses matrix composites(MGMCs).The dendrites hinder the prompt propagation of shear bands and lead to multiplication of shear bands.Nevertheless,actual structural engineering materials are always performed superb ductility even upon dynamic compression.For example,the cars pass through a collision experiment before they go out and the mobile phones go through anti-throw experiment before manufacturing and so on.Thus,to expand the application of in-situ MGMCs,we must deeply understand its deformation behavior and microscopic deformation mechanism upon dynamic loading.In this study,two kinds of new in-situ MGMCs are fabricated and investigated the deformation mechanism by Split Hopkinson Pressure Bar(SHPB)upon dynamic loading.The main contents and conclusion are listed below:(1)By adjusting the ingredients,the in-situ Ti60Zr14V12Cu4Be10 composites which has single-phase dendrite are fabricated.Upon quasi-static compression,the ultimate strength of the composite is about 2600 MPa,and it exhibits obvious work-hardening capacity and the fracture strain is about 40 %.Under dynamic compression,the yielding strength and the plastic strain of the composites are 1290 MPa and 16 %,respectively.It can be found that the dynamic plasticity is significantly lower than that under quasi-static loading,which is mainly due to that there is no enough time to generate the multiple shear bands or dislocations and less dislocation clusters hinder the propagation of shear bands,which induces the decrease of resistance to fracture.(2)By adding Ta elements,the in-situ Ti50Zr18Ni5Ta15Be12 composites are fabricated and investigated.Under quasi-static compression,the yielding strength is about 1580 MPa and the plastic strain approaches about 20 %.In addition,it also has distinguished work-hardening behavior.On the other hand,the composite is nearly exhibiting brittle fracture after yielding.(3)The influence of strain rate on the deformation behavior of two kinds of composites are discussed.It can be found that upon dynamic loading,the strain rate sensitivity of Ti60Zr14V12Cu4Be10 is positive and Ti50Zr18Ni5Ta15Be12 is negative.Considering the influence of the temperature rise caused by adiabatic shearing,according to the critical shear theory,the constitutive equation between the yielding strength and the strain rate is established based on the CooperativeShear(C-S)model.(4)Based on the modified Johnson-Cook(J-C)plasticity model,the constitutive relationship of the composites is established upon the dynamic loading.And it can be used to effectively predict the plastic flows upon different strain rates for the present composites.