Plastic deformation of titanium alloy Ti-6Al-4V in a complex stressed state under tension at high-strain rates

The article presents the results of a studies on mechanical behavior of titanium alloy Ti-6Al-4V (Ti Grade 5) in the range of strain rates from 0.1 to 103 s−1. Tensile tests were carried out on flat and notched specimens using the Instron VHS 40/50-20 servo-hydraulic testing machine. High-speed video recording was carried out with a Phantom 711 Camera. The strain fields in the measuring area of the sample were investigated by the Digital Image Correlation (DIC) method. Analysis of the deformation fields of Ti-6Al-4V specimens under uniaxial tension at high strain rates revealed the presence of stationary localized shear bands at the initial stages of strain hardening. The evolution of the deformation fields in the studied loading regime indicates that in the localization bands the plastic strain is significantly higher than the average values in the gage zone of the specimen. It was found that the value of strain before fracture of the Ti-6Al-4V alloy in the zone of strain localization increases with the tension strain rate. The fracture of the titanium alloy is a result of cracks formation in the zone of plastic strain localization bands oriented along the surface of the action of the maximum shear stresses. The results obtained confirm the ductile nature of fracture of Ti-6Al-4V at strain rates from 0.1 to 103 s−1, at the triaxiality stress parameter 0.33 < η < 0.44, and at an initial temperature of 295 K. At the same time, Ti-6Al-4V alloy demonstrates a tendency to embrittlement with an increase in the triaxiality stress parameter to 0.497 at the same loading condition.