Positron annihilation study of effects of Ti and plastic deformation on defect accumulation and annealing in electron-irradiated austenitic steels and alloys

Positron annihilation spectroscopy was used to study the formation and annealing of vacancy clusters in 16Cr15Ni3Mo austenitic steels and Fe-36%Ni model alloys and in the same compounds containing 1.02 and 2.5 wt% titanium respectively. Defects were induced by electron (5 MeV) irradiation at 270-573 K. How a developed initial dislocation structure influenced the accumulation and annealing of vacancy defects in these steels and alloys was analyzed. It was shown that vacancies interacted with titanium atoms. As a result, the Ti-containing steels and alloys exposed to radiation at temperatures from 270 to 423 K had an enhanced concentration of fine vacancy clusters decorated with titanium, which were thermally stable up to 450 K. A high initial dislocation density in the deformed steels and alloys led to a several-fold decrease in the concentration of vacancy clusters as compared to their concentration in the solution annealed state. The formation of fine TiC particles in Ti-modified deformed steel was monitored at the annealing temperatures from 850 to 1070 K.