Strengthening of 304L Stainless Steel by Addition of Yttrium Oxide and Grain Refinement during Selective Laser Melting

This study investigates the role of submicron yttrium oxide on the microstructural evolution and mechanical properties of selective laser melted 304L oxide dispersion strengthening (ODS) nanocomposite. 304L SS powder and a mixture of 304L SS powder and yttria nanoparticles were used as two feedstocks for fabricating parts using selective laser melting (SLM) process. Scanning electron microscopy and energy-dispersive X-ray spectroscopy revealed a homogenous distribution of Si-Mn-O nanoparticles in the SLM 304L matrix and Y-Si-O nanoparticles in the SLM 304L ODS alloy. Electron backscatter diffraction images imply that the addition of yttria disrupts the formation of large columnar grains in SLM 304L, resulting in the formation of finer equiaxed grains. The average microhardness values increased from 240 HV in SLM 304L to 305 HV in SLM 304L ODS alloy, due to the combined effects of grain refinement and dispersion hardening.