Mechanical Behavior Of In-situ Ti-based Composites Upon Dynamic Loading At Room Temperature

Since the atomic arrangements of bulk metallic glasses?BMGs?are aperiodic,exhibiting long-range unordered and short-range ordered,BMGs possess many excellent mechanical properties,such as high strength,good wear resistance,corrosion resistance,and large elastic limit and so on,which makes them potential as structural materials.However,on account of the prompt propagation of highly localized shear bands,almost all the BMGs exert catastrophic failure upon tensile or compressive loading at room temperature,which has extremely confined widespread applications for BMGs in engineering application field.To improve macroscopic ductility,a series of in-situ dendrite reinforced metallic glass matrix composites?MGMCs?with high strength and ductility have been investigated thoroughly.The dendrites which are homogeneously distributed within the featureless and continuous glass matrix hinder the prompt propagation of shear bands and lead to multiplication of shear bands.The in-situ MGMCs customarily exhibit macroscopic ductility upon quasi-static loading at ambient temperature due to the interaction between the dendrites and the multiple shear bands.In terms of the actual engineering applications for in-situ MGMCs,many extremely complicated conditions such as high temperature and high speed dynamic loading.However,most studies have focused on the mechanical properties of MGMCs upon quasi-static loading rather than dynamic loading.Therefore,classifying the dynamic deformation behavior of MGMCs is becoming sufficiently necessary.In this study,by adjusting the component of the alloy,two kinds of new in-situTi-basedcompositearefabricated.Theyarein-situ Ti₅₈Zr₁₂Ni₆Ta₁₃Be₁₁(Ta₁₃)dendrite reinforced metallic glass matrix composites and Ti₅₈Zr₁₂Ni₆Nb₁₃Be₁₁(Nb₁₃)dendrite reinforced nanocrystalline composite,respectively.The deformations behaviors of two composites are investigated by Split Hopkinson Pressure Bar?SHPB?upon dynamic loading.The main contents and conclusions are listed below:The microstructures and mechanical properties of Ta₁₃3 Ti-based MGMCs were investigated upon quasi-static and dynamic loading room temperature,and plastic deformation mechanisms were explored in detail.It can be seen that the yielding strength is about 1235 MPa,and the ultimate strength approaches 1520MPa,together with the fracture strain of about 9.6%.After yielding,a distinguished work-hardening behavior prevails till the fracture takes place,which is attributed to the dendrites hinder the prompt propagation of shear bands and lead to multiplication of shear bands.Under dynamic compression,the yielding strength arranges between 1330-1440 MPa and the plastic strain of the composites is 10%.After yielding,a plastic flow behavior prevails till the fracture takes place and the ultimate strength approaches 1445 MPa,which is mainly due to the multiple shear bands,abundant dislocations in the dendrites,and hard and brittle?hindering the dislocation slips.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.By replacing Ta element with Nb element,the in-situ Nb₁₃ Ti-base nanostructure–dendrite composites are fabricated and investigated.Under quasi-static compression,the yielding strength is about 1100 MPa and the plastic strain approaches about 50%.There were interactional shear bands rather than obvious fracture on the material's surface.Wonderful plasticity occurs due to impediment of the dendrites to the propagation of shear bands and generating the new shear bands.Multiple dislocations can be found both in the dendrites and nanocrystalline.In addition,it also has distinguished work-hardening behavior.On the other hand,the composite is nearly exhibiting 15%plastic strain before fracture after plastic flow and the yielding strength increase100-200 MPa.Through micro characterization,the grain growth behavior of Ti-base nanostructure–dendrite composites occurs under quasi-static compression.It is mainly because the structure stability of nanocrystalline is decreased under stress field.However,the grain growth behavior can not be found under dynamic loading since there is not enough time to affect the the structure stability of nanocrystalline.