Study of a Hardened Multilayer Coating Obtained by Cold Gas-Dynamic Spraying with Laser Intensification

When reconstructing products obtained using additive technologies based on layer-by-layer melting of metal powder by concentrated energy flows, it is advisable to use methods that minimize melting of the initial powder and reduce structural heterogeneity of the material. Cold gas-dynamic spraying with laser-induced intensification of the process (CGDSL) is one of them. The multilayer coatings obtained by the CGDSL method have a homogeneous metal structure, though a significant surface roughness attributed to the particle size of the original powder is observed. The goal of the study is to develop a new method of post-processing of multilayer coatings obtained by CGDSL which can provide a hardened layer on their surface. A hardened layer is formed through introduction of boron carbide powder particles into the laser-molten region formed on the surface of the coating based on 316L stainless steel. An acoustic wave triggered by a “microexplosion” induced by a laser pulse above the surface pushes carbide particles in different directions. Some of them are embedded into the melt pool on the surface of the coating. Thus, the laser microexplosion cartooning of the surface of the CGDSL coating is implemented. Study of the hardened layer revealed a high content of B, C, Cr, Fe, and Ni. Moreover, it is shown that solid carbides of rhombic form are formed in the hardened layer. Chemical and elemental analyses showed that diamond-shaped carbides—carbides of the type (Fe, Cr) x B y —contain a high concentration of Cr and Fe and a relatively small percentage of C. Most likely, the formation of diamond-shaped carbides occurs owing to interaction of chromium which is a part of the initial hardened coating with boron that is released from the surface of BC particles under laser impact. The developed method provides hardening of the surface layer of the coating previously obtained by CGDSL by embedding BC powder particles into the surface. The technology of hardening CGDSL coatings can be implemented using other powder materials.