Structural investigation of austenitic stainless steel layers obtained by laser surface alloying

The goal of this study is to characterize the coatings obtained by laser surface alloying of low-alloy steel with 316L stainless steel powder. The laser surface alloying (LSA) process was carried out using a pulsed single-mode CO2 laser (600 W, 200 kHz operation frequency). In order to avoid the sample overheating during irradiation, the samples were cooled in liquid nitrogen. The alloyed layers were characterized by X-ray Diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, and microhardness testing. The layers were compact and homogeneous, with an uniform distribution of Cr, Ni and Mo elements, both at the surface and throughout their depth. EDX analysis revealed that the outer layer has a concentration of alloying elements (Cr, Ni, Mo) corresponding to a ferrito-austenitic stainless steel. These concentrations decreased to the substrate, as a result of the penetration process of the alloying elements from the surface towards the core. XRD analysis revealed nanostructured layers consisting of ferrito-austenite, regardless of the applied power density. Depending on the laser processing parameters, the surface layers exhibited higher hardness values than the untreated samples.