TC4钛合金外物损伤下的显微组织及绝热剪切带

Microstructure and ASB of TC4 titanium alloy under foreign object damage

采用空气炮法以不同直径钢球和速度对TC4钛合金进行模拟外物冲击损伤试验,用超景深三维显微系统和扫描电镜分析了损伤凹坑直径、深度及形貌特征,着重分析了损伤凹坑显微组织及绝热剪切带(ASB)产生规律。结果表明:损伤凹坑直径D和深度H均随钢球直径和速度ν的增大而增大,当达到300 m/s速度,出现明显增大。损伤凹坑边缘宏观呈现材料隆起和挤出,微观为材料滑移、流变、微裂纹和流失的特征变化。冲击能量越大,边缘隆起、挤出越明显,损伤越严重。在微观组织尺度上损伤主要表现为绝热剪切带的产生,随着钢球直径和速度ν的增大,其产生倾向和数量均增加。尤其在凹坑边缘隆起处剪切带宽、分叉多,甚至并排、成群出现。当冲击凹坑深度H约大于180μm时,均会出现绝热剪切带。绝热剪切带的产生也是冲击导致材料的一种隐形损伤,往往成为疲劳裂纹萌生源,严重的直接产生微裂纹,将显著降低叶片的疲劳强度。

The foreign object damage simulation test on TC4 titanium alloy was carried out by means of air gun test system using steel balls with different diameter and speed.The diameter,depth and morphology features of the dents were investigated by means of digital microscopy and scanning electron microscopy.The microstructure of the dents and the generation of adiabatic shear band(ASB)were emphatically analyzed.The results indicate that both the diameter D and the depth H of the dents increases with the increase of the diameterand the velocityνof the steel ball.When the speed reaches 300 m/s,the increase is obvious.The edge of the dents exhibits material bulging and extrusion macroscopically,and the microscopic features are slippage,rheology,microcracks and material loss.The greater the impact energy,the more obvious the material bulging and extrusion presented,and the more serious the damage is.The damage in the microstructure is mainly characterized by the generation of ASB.As the diameterand the velocityνof the steel ball increase,the tendency and the quantity of ASBs increase.There are wider ASBs with more bifurcation in groups or side-by-side especially in the edge of the dents.When the depth H of the dents is greater than about 180μm,ASBs will occur.The generation of ASBs is an invisible damage caused by impact,which often becomes a source of fatigue crack initiation,and microcracks produced by huge impact will significantly reduce the fatigue strength of the blade.