PLASTIC-DEFORMATION OF HAFNIUM UNDER UNIAXIAL COMPRESSION

The plastic behavior of polycrystalline hafnium (Hf) was investigated over a range of sh-ain rates under uniaxial compression. Hafnium exhib ited considerable ductility and a moderately rate-sensitive plastic be havior. The stress-strain response consisted of initial yielding follo wed by parabolic hardening. Microstructural observations on quasistati cally deformed specimens revealed that yielding occurred by dislocatio n activity and that hardening was dominated by twinning on {<10(1)over bar2>} planes and by slip/twin interactions. A considerable reduction in dislocation and twinning activity was observed in specimens deform ed at high strain rates. Failure occurred by shear localization and vo id growth and coalescence within the shear bands. Measurement of the t emperature rise during high strain rate deformation was also made. Fro m these measurements, the fraction of work converted to heat as a func tion of strain was determined and found to decrease with increasing st rain.