Impact response of cobalt over the 300-1400 K temperature range

The yield and tensile (spall) strengths and the dynamic viscosity of 99.95% pure cobalt were studied in a series of interferometer-instrumented planar impact experiments over the 300 to 1423 K temperature range. The spall strength of cobalt declines monotonously from 3.2 GPa at 300 K to 0.8 GPa at 1400 K. The dynamic yield strength grows linearly with temperature in both the hcp and fcc cobalt phases. The hcp to fcc transformation at 690 K is accompanied by an abrupt twofold drop of the yield strength. The similarity between the temperature dependence of the cobalt's dynamic viscosity and of the yield strength suggests that both properties are controlled by the interaction of the dislocations with the oncoming phonon flow (phonon drag).