Deposition Of Chromium Nitride (CrN) By PVD Process and Assessment of Its Influence on Fatigue Performance of EN353 Grade Steel in Case Carburized Condition

Surface engineering has become an effective approach for improving the performance of fatigue-critical mechanical components such as gears, shafts, pinions, and transmission elements. EN353, a low-alloy nickel–chromium–molybdenum carburizing steel, is extensively used for these applications because of its excellent combination of surface hardness, wear resistance, and core toughness after case carburization. Among various surface modification techniques, Physical Vapour Deposition (PVD) of Chromium Nitride (CrN) coatings offers superior wear, corrosion, and oxidation resistance while employing relatively low deposition temperatures that minimize thermal distortion of heat-treated substrates. However, the influence of CrN coatings on the fatigue behaviour of case-carburized EN353 steel has not been comprehensively established. In the present investigation, a 2 μm thick CrN coating was deposited by ion-sputtering PVD on case-carburized EN353 specimens, and its influence on rotating bending fatigue performance was experimentally evaluated. Fatigue tests were conducted under four-point rotating bending conditions at a stress ratio of R = −1 in accordance with ASTM E739 (2015). Stress–life (S–N) behaviour was analysed using linear regression, while the endurance limit was determined using the Dixon–Mood staircase method. Fractographic examination of the fractured specimens was performed using scanning electron microscopy (SEM) to identify crack initiation and propagation characteristics. The experimental results showed that the CrN-coated specimens exhibited consistently shorter fatigue lives than the uncoated specimens throughout the investigated stress range. The endurance limit decreased from approximately 860 MPa to 807.5 MPa after CrN deposition, corresponding to a reduction of about 6%. SEM observations revealed that fatigue cracks initiated at the specimen surface in both material conditions; however, localized coating microcracks and coating/substrate interface stress concentrations promoted earlier crack nucleation in the coated specimens. Although the CrN coating significantly improves tribological performance, the present processing conditions produced a slight reduction in fatigue resistance, primarily because of partial relaxation of beneficial compressive residual stresses.