Feasibility of using graphene as a substitute to graphite in the laser surface hardening of ferritic stainless steel

Abstract

The broad potential applications of ferritic stainless steel in industry can be increased with the addition of protective elements such as carbon for surface hardening. Laser surface hardening (LSH) using carbon elements, such as graphite, has received widespread attention. However, to obtain high quality results, the use of graphite slurry, a specific environment, or remelting are required. To overcome this challenge, the LSH using graphene as an alternative to graphite was comparatively studied in this work. Accordingly, the stability of hardened layers, which depicts their sustainability in actual environmental conditions, was compared in graphene, graphite, and their slurries to improve the evaluation of graphene in the LSH process. The stability of hardened layers predominantly depends on the hardness, crack susceptibility, interfacial stress, hardness depth (or aspect ratio), and interfacial hardness. Under suitable process conditions, graphene exhibits good stability, with the highest hardness and low stress fluctuation without crack formation at the interface. Moreover, the powder layer thickness and laser power can be adjusted to achieve maximum improvements in the aspect ratio and microhardness in the area near the interface. Thus, high microhardness and a crack-free hardened layer without additional remelting or the use of a slurry were obtained.