Dynamic mechanical response and deformation mechanism of ultrafine-grained pure titanium
The dynamic impact experiments of ultrafine-grained(UFG)pure titanium were carried out with strain rate of 2000-3000 s-1 and temperature of 300-450℃by the split Hopkinson press bar(SHPB)technique to study dynamic mechanical response and deforma-tion mechanism.The microstructure after deformation was characterized using scanning electron microscopy(SEM)and transmission elec-tron microscopy(TEM).The results show that the true stress-true strain curves of UFG pure titanium show significant"double-stress peak"characteristic.The yield strength and flow stress of UFG pure titanium increase with the increase of the strain rate and the decrease of the temperature.UFG pure titanium exhibits positive strain rate sensitivity and negative temperature sensitivity.The strain rate sensitiv-ity index m of UFG pure titanium in the range of strain rate of 2000-3000 s-1 is 0.12-0.17.When the strain rate is larger than 2500 s-1,adiabatic shear bands(ASBs)appear in the UFG pure titanium and the critical strain for the appearance of ASBs is 0.316.Under dynam-ic impact load,the deformation mechanisms of UFG pure titanium transform from the increase of dislocation density and the formation of dislocation cell at low temperature to geometric dynamic recrystallization and grain coarsening at high temperature.
ultrafine-grained pure titaniumdynamic mechanical behaviordeformation mechanismmicrostructure evolutionadiabatic shear band
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