The microstructure characterization of adiabatic shearing band in Ti-17 alloy at high strain rates and elevated temperatures

摘要

The effect of process variables on flow response and microstructure evolution during high velocity deformation of Ti-17 with a colony alpha preformed microstructure was established using the Split Hop-kinson Pressure Bar (SHPB). The testing was conducted on samples with prior-beta grain sizes of 400 μm at strain rates of 2000-6000 s~(-1), test temperatures of 293-973 K. All flow curves exhibited a peak stress followed by a moderate flow softening which can be rationalized by the occurrence of the adiabatic shearing band (ASB) in this alloy. The ASBs could be divided into two types, "white" ASBs (deformation band) and "dark" ASBs (recrystallization band). In addition, the equiaxed beta grains with diameters of 3-5 μm in the "dark" ASBs could not be explained by the sub-grain rotation dynamic recrystallization (RDR) mechanism using the traditional calculation method of temperature rise. Therefore, a modified equation for calculating temperature rise was used to determine the temperature in the ASBs, and the recalculated results of RDR kinetics equations have the excellent agreement with the microstructure observations.