Identification of lattice defects in laser powder bed fusion-fabricated 316L stainless steel by positron annihilation spectroscopy

The laser powder bed fusion (LPBF) process often introduces lattice defects, such as vacancies and dislocations, within the fabricated materials because of large thermal gradients and rapid cooling rates. In this study, lattice defects in LPBF-fabricated 316L stainless steel (SS) were quantitatively evaluated using positron annihilation spectroscopy, a sensitive technique for detecting and characterizing vacancies and dislocations. The number of lattice defects increased with the LPBF scan speed. Vacancy concentrations and dislocation densities were determined using component analysis of the positron lifetime spectra. The measured vacancy concentration was comparable to the thermal equilibrium concentration of vacancies at the melting point. Additionally, both vacancy concentration and dislocation density increased with scan speed. The increase in dislocation density in the fabricated 316L SS with increasing scan speed of the LPBF process was confirmed using transmission electron microscopy. This study enables the detection and identification of defects in 316L SS under various temperature conditions, offering insights into the performance of 316L SS across a wider range of operating temperatures. • Vacancies and dislocations were introduced in the LPBF-manufactured 316L Stainless Steel. • Both vacancy concentration and dislocation density increased with the LPBF scan speed. • Vacancy concentration was comparable to the thermal equilibrium concentration at the melting point. • Increase in dislocation density with increasing scan speed was confirmed using positron lifetime measurement and TEM.