AISI 5160 steel has high toughness and ductility. However, in specific applications, better tribological performance is required. In this sense, the study's objective was to perform plasma nitriding with Hastelloy's cathodic cage followed by the conventional plasma nitriding in AISI 5160 steel to produce high hardness and wear resistance. The results showed that the samples and cutting tools subjected to this process showed higher wear resistance than untreated samples and high-speed steel tools. The sample submitted to treatments with 450°C and 3 h showed greater surface hardness and less volume loss in the mechanical and machining tests. Therefore, the duplex treatment presented in this work with posterior plasma nitriding proved efficient with the low processing time.

Molybdenum disulfide is a 2D material with excellent lubricant properties, resulting from weak van der Waals forces between lattice layers and shear-induced crystal orientation. The low forces needed to shear the MoS₂ crystal layers grant the tribological system low coefficients of friction (COF). However, film oxidation harms its efficacy in humid atmospheres, leading to an increased COF and poor surface adhesion, making its use preferable in dry or vacuum conditions. To overcome these challenges, doping MoS₂ with elements such as Nb, Ti, C, and N emerges as a promising solution. Nevertheless, the adhesion of these coatings to a steel substrate presents challenges and strategies involving the reduction in residual stresses and increased chemical affinity to the substrate by using niobium-based materials as interlayers. In this study, Nb-doped MoS₂ films were deposited on H13 steel and silicon wafers using the pulsed direct current balanced magnetron sputtering technique. Different niobium-based interlayers (pure Nb and NbN) were deposited to evaluate the adhesion properties of Nb-doped MoS₂ coatings. Unlubricated scratch tests, conducted at room temperature and relative humidity under a progressive load, were performed to analyze the COF and adhesion of the coating. Instrumented indentation tests were conducted to assess the hardness and elastic modulus of the coatings. The microstructure of the coatings was obtained by Scanning Electron Microscopy (SEM), Scanning Transmission Electron Microscopy (STEM), and Transmission Electron Microscopy (TEM), with Energy-Dispersive X-Ray Spectroscopy (EDS). Results indicated that niobium doping on MoS₂ coatings changes the structure from crystalline to amorphous. Additionally, the Nb concentration of the Nb:MoS₂ coating changed the mechanical properties, leading to different cohesive failures by different loads during the scratch tests. Results have also indicated that an NbN interlayer optimally promoted the adhesion of the film. This result is justified by the increase in hardness led by higher Nb concentrations, enhancing the load-bearing capacity of the coating. It is concluded that niobium-based materials can be used to enhance the adhesion properties of Nb-doped MoS₂ films and improve their tribological performance.

Diamond-like Carbon (DLC) films demonstrate substantial hardness, minimal friction, and exceptional wear resistance when applied to metal substrates; however, they face challenges related to inadequate adhesion. Furthermore, concerns about thermal stability are prevalent in DLC films, particularly concerning cutting tools, where processing temperatures may reach significant levels. To mitigate these issues, incorporating various dopants and applying multilayer treatments may enhance adhesion, thermal stability, and wear resistance while simultaneously decreasing the coefficient of friction. This study systematically examines the effects of nitrogen and silicon doping on DLC films applied to M2 steel. It employs multilayer treatments to evaluate their influence on wear resistance, employing a fixed ball wear test that monitors wear progression by interrupting the test at various intervals. Plasma treatments, including nitriding, nitrocarburizing, and DLC coatings, were evaluated independently and in combination. A combination of DLC coatings with nitrocarburizing proved to be better for wear resistance when both the coating and the compound layer present a controlled thickness and high hardness, promoting low friction and avoiding debris formation. The findings reveal that Si-doped DLC combined with nitrocarburized layers significantly improves wear resistance and adhesion, highlighting the benefits of integrating duplex treatments with DLC doping to enhance coating performance.