Conventionally used metallic materials do not often fully satisfy the desired properties related to their intended applications. Therefore, the modification of their surface properties is required aiming for reliable performance and a long lifetime of metallic components. Among different surface treatment techniques, plasma-assisted thermochemical diffusion treatments have drawn significant attention to modifying the surface properties due to the simple process implementation, low cost, and low environmental impact. Here, the enhanced surface properties gain due to the reactions between the generated gas species at the treatment environment and the metal surface.