Plastic deformation of hafnium under uniaxial compression

The plastic behavior of polycrystalline hafnium (Hf) was investigated over a range of strain rates under uniaxial compression. Hafnium exhibited considerable ductility and a moderately rate-sensitive plastic behavior. The stress-strain response consisted of initial yielding followed by parabolic hardening. Microstructural observations on quasistatically deformed specimens revealed that yielding occurred by dislocation activity and that hardening was dominated by twinning on {1012} planes and by slip/twin interactions. A considerable reduction in dislocation and twinning activity was observed in specimens deformed at high strain rates. Failure occurred by shear localization and void growth and coalescence within the shear bands. Measurement of the temperature rise during high strain rate deformation was also made. From these measurements, the fraction of work converted to heat as a function of strain was determined and found to decrease with increasing strain.