不同组织状态TC4 ELI钛合金动态力学性能研究

利用分离式霍普金森压杆装置(SHPB)对低间隙Ti-6Al-4V(TC4 ELI)合金的等轴组织、双态组织和魏氏组织试样进行了动态压缩试验。应变率分别为ε=2000,3000,4000 s-1,得到了动态压缩真应力-应变(σ-ε)曲线,并对试验后发生剪切失效破坏的试样沿纵剖面切开,利用金相显微镜(OM)进行显微组织观察。结果表明:动态压缩条件下TC4 ELI合金3种组织试样的真应力-应变曲线大致分为弹性阶段和塑性阶段,没有明显的屈服平台,3种组织状态下的试样在高应变率下应变强化效应不明显,表现出一定的应变率强化效应;在4000 s-1应变率加载条件下,平均动态流变应力(σ)、均匀动态塑性应变(ε)以及冲击吸收功(E)按等轴组织、双态组织和魏氏组织顺序依次减小,等轴组织试样的σ,ε和E分别达到了1400 MPa,0.34%和470 kJ.m-3,具有较好的动态力学性能;在4000 s-1应变率加载条件下3种组织状态的试样均发生了剪切失效破坏,并在其纵剖面上都观察到了一条白亮的绝热剪切带(ASB),裂纹沿着绝热剪切带由圆柱试样的圆柱面向中心扩展,与ASB形成和扩展的方向一致,剪切带与导致断裂的裂纹密切相关。

Dynamic Mechanical Properties of TC4 ELI Titanium in Different Microstructure States

The dynamic mechanical properties of extra low interstitial Ti-6Al-4V(TC4 ELI) were studied with split hopkinson pressure bar device.The microstructures of TC4 ELI contained equiaxed,bimodal and widmanstatten.The dynamic stress-strain curves under different strain rates of 2000,3000 and 4000 s-1 were obtained.The microstructures of the cross-sectional area where adiabatic shear bands took place were examined using optical microscope(OM) technique.The results showed that the stress-strain curve of TC4 ELI in dynamic conditions was divided into elastic stage and plastic stage,without obvious yield platform.The strain hardening effect of the three microstructures were not obvious at high strain rate,but they showed some strain rate strengthening effect.At the strain rate of 4000 s-1,the average dynamic flow stress,dynamic plastic strain and impact absorbed energy reduced orderly according to the microstructures equiaxed,bimodal and widmanstatten.The σ,ε and E of equiaxed specimen were 1400 MPa,0.34% and 470 kJ · m-3 respectively,showing superior dynamic mechanical properties.The shear failure damage occurred in each of the three microstructures at the strain rate of 4000 s-1.A bright white adiabatic shear band(ASB) was also observed on the cross-sectional area.Crack extended along the adiabatic shear band from the cylindrical surface to inside.The adiabatic shear band was found to be closely related to the crack ignition,which led to the catastrophic fracture.