Depth profiles of defects in Ar-iondashirradiated steels determined by a least-squares fit of S parameters from variable-energy positron annihilation

Using a new method for reconstructing the depth profile of defects in an iondashirradiated sample by using slow positrons, the depth profiles of vacancy-type defects in 316 stainless steel samples, irradiated with 250 keV Ar ions to a dose of 7.5 × 1019 m−2 at room temperature, have been calculated from Doppler-broadening S parameters measured as a function of positron energies up to 16 keV. Without assuming any type of shape for the defect profiles, such as Gaussian, the defect profiling is done using a least-squares fitting method. The resulting profile suggests that in as-irradiated 316 stainless steel samples with lower carbon content, the defect distribution peaks at a depth four times larger than that of the ion range. After annealing at a high temperature of 1253 K for 0.5 h, the fitted profile shows that the peak around the average ion range is highly enhanced. While in the steel added with 0.3 wt% titanium, the profile exhibits almost no peak after annealing at 1073 K. The results indicate that the radiationdashproduced vacancy clusters are stabilized by the implanted Ar atoms more effectively in the Ti-free steel than in the Ti-added steel.