The residual stress analysis is a well-established method for predicting fatigue failures of mechanical components. Within industrial constraints, the X-ray diffraction is a technique usually applied to measuring a small spot of the workpiece surface. This punctual and averaged outcome does not allow the proper representation of the residual stress. The objective of this study is to define a feasible method for assessing the heterogeneity of the surface residual stress state. The proposal is based on the theoretical relationship between the deviation of the residual macrostress and the intensity of the microstress. Steel shot peened gears were produced and their microstresses were assessed by means of the diffraction profiles broadening. The reference database was composed of topography measurements, metallographic analyses and residual macrostress maps. The stress heterogeneity was reasonably correlated to the intensity of the Gauss integral breadth. Applied to ground parts, the correlation’s parameter filled a comprehension gap between the measured residual stress intensity and observed contact fatigue failures. Using the same data from the macro residual stress measurement, the method proved to be feasibly applied. Moreover, by providing a deviation perspective to the residual stress state, the heterogeneity assessment enhances the analysis of a fatigue failure.

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.