Effects of microstructural factors on quasi-static and dynamic deformation behaviors of Ti-6Al-4V alloys with Widmanstatten structures

The effects of microstructural factors on the quasi-static tensile and dynamic torsional deformation behaviors in Ti-6Al-4V alloys with Widmanstatten structures were investigated in this study. Dynamic torsional tests were conducted using a torsional Kolsky bar for five Widmanstatten structures, in which iriicrostructural parameters such as colony size and a lamellar spacing were varied by heat treatments, and then the test data were analyzed in relation to microstructures, tensile properties, and fracture mode. Under dynamic torsional loading, maximum shear stress was largely dependent on colony size, whereas shear strain at the maximum shear stress point was on colony size as well as a lamellar spacing. Adiabatic shear bands were found in the deformed area of the fractured torsional specimens, and their width was smallest in the structure whose colony size and a lamellar spacing were both large. The possibility of the adiabatic shear band formation was quantitatively analyzed in relation to microstructural factors. It was the highest in the coarse Widmanstatten structure, which was confirmed by the theoretical critical shear strain (gamma(c)) condition for the adiabatic shear band formation.