Impact response of titanium from the ambient temperature to 1000 °c

The yield and spall strengths of polycrystalline high purity (99.99%) and commercial (grade 2) titanium were studied in a series of planar impact experiments with the initial sample temperature ranging from 20 to 1000 °C. In a separate series of impact experiments, the temperature dependence of the longitudinal speed of sound in pure Ti was measured making use of the reverberation of the stress pulse generated in the 3 mm Ti sample by an aluminum impactor. In all the experiments, the velocity of the sample free surface was continuously monitored by VISAR. The stress-strain diagrams of the two kinds of samples were derived from the free surface velocity profiles using the simple wave approximation. Analysis of these diagrams made allowed revealing the sequence of the dislocation-based processes governing the plastic flow in the two materials, from the ambient to some 100 °C above the hcp-bcc transformation temperature. On the basis of the spall data obtained from impact experiments with pure titanium, the limits of existence of nonequilibrium titanium phases were outlined.