Positron annihilation study on hafnium specimens given various treatments

Abstract

Positron annihilation measurements for annealed, cold-worked, annealedquenched, and cold-worked and hydrogen-charged hafnium specimens were made to investigate kinds of defects existing in the specimens, interaction between defects and hydrogen atoms and behavior of defects on isochronal annealing. Lifetime and Doppler broadening lineshape measurements for cold-worked and hydrogen-charged specimens indicated that a new kind of positron traps as well as dislocations are produced during hydrogen charging. It was inferred that the new positron traps formed are hydrogen bubbles or voids. Doppler broadening lineshape parameter P/W for cold-worked hafnium specimens increased first and then decreased due to the proton screeing of some defects, and this sequence was repeated when their hydrogen-charging was continued. Positron annihilation characteristics and microhardness of cold-worked, and cold-worked and hydrogen-charged hafnium specimens isochronally annealed were compared to study recovery and recrystallization stages of hafnium specimens. The general trend observed was an increase of the positron lifetime after hydrogenation. It was inferred that this increase in lifetime is attributed to the covalent nature of the Hf-H bond of hafnium hydride.