Cristina Zubizarreta

This work investigates the synergistic effect of femtosecond laser surface texturing (LST) and AlCrN coating on the wear performance of fine blanking tools. Dimple textures with 10, 15% and 20% surface coverage were fabricated on AISI M2 steel and coated with 1.5 µm AlCrN coating via HIPIMS. SEM and optical confocal microscopy confirmed the high geometrical accuracy of LST features and good coating adhesion at the coating-dimple interface. Contact angle measurements indicated that the as-coated surfaces were oleophilic, while increasing the textured area density led to a progressive shift toward higher contact angles, indicating a modification of lubricant spreading behavior. Ball-on-disk tests were performed under loads of 10, 30 and 50 N trying to simulate fine blanking contact conditions. An initial lubricant supply of 0.05 mL was sufficient to maintain a stable separation film, resulting in friction coefficients between 0.10 and 0.14 regardless of textured area density. In terms of wear, uncoated dimple-textured surfaces did not yield beneficial behaviour, showing higher wear rates than the untextured surface. In contrast, the application of the AlCrN coating on the untextured surface resulted in an approximately 90% reduction in the wear coefficient. A comparable wear reduction was observed for the sample textured at 10% dimple density; however, further increases in texture density led to an exponential increase in wear rate. SEM/EDX observations indicate that debris entrapment within the dimples promote third-body abrasion, contributing to the increased wear at higher texture densities.

This manuscript introduces and experimentally demonstrates a novel concept of selective metal ion irradiation by combining bipolar HIPIMS with conventional DC magnetron sputtering operation and simple DC biasing. The addition of the positive pulse to a conventional HIPIMS discharge accelerates the predominantly metal ions created during the negative HIPIMS phase with an energy proportional to the positive pulse amplitude and ionization state. Two distinct metal elements with large difference in atomic mass (Cr and Nb) are used on this work to irradiate a TiAlN matrix which is being deposited by conventional DCMS. The positive acceleration voltages used for both Cr and Nb discharges were varied between 0 to +200 V to analyze the influence of Nb and Cr metal ion irradiation on the mechanical and microstructural properties of TiAlN films. Even though the total metal ion incorporation into the TiAlN matrix for both Cr and Nb is less than 10% at%, strong effects are observed on the resulting film properties. It was observed that use of the lighter metal ion Cr is more beneficial than the heavier metal ion Nb. The Cr bombardment allows a hardness improvement from 7 to 22 GPa as well as a reduced film accumulated stress at the highest positive acceleration voltage. From the XRD measurements it is observed that the Cr atoms are inserted into the TiAlN cubic matrix maintaining its crystalline structure. However, the bombardment with the high-mass metal ion (Nb) promotes the deformation of the cubic TiAlN matrix, resulting in a spinodal decomposition and further degradation of the crystalline structure with the appearance of the hexagonal wurtzite-type Al-rich phase. This is also translated to the resulting film mechanical properties, as hardness rapidly decreases from 25 to 10 GPa and stress increases linearly with the positive voltage acceleration.

This paper focuses on the tribological behaviour of ZrN/ZrCN coating on bearing steel substrates DIN 17230, 100Cr6/1.3505. Coatings are applied at room temperature processes by means of Cathodic Arc Evaporation (CAE), a kind of Physical Vapor Deposition (PVD) technique. In order to achieve a satisfactory compromise between coating-substrate adhesion and the surface roughness requirement of the bearing rings, a polish post-processing is proposed. Different polish post-processing times and conditions are applied. The coated and polished bearing rings are tested under real friction torque test protocols. These tests show that the application of the coating does not entail a significant improvement in friction performance of the bearing. However, fatigue tests in real test bench are pending to evaluate the possible improvement in bearing life time.

This paper focuses on tribological behavior of ZrCN coating on bearing steel substrates DIN 17230, 100Cr6 / 1.3505, fulfilling also roughness and adherence requirements. Two strategies are followed to achieve a reduction of coefficient of friction. Initially, a low roughness coating by using Physical Vapour Deposition (PVD sputtering process) is developed. At this stage, PVD conditions guarantying adherence step and avoiding drops generated during that process are achieved. A second strategy consisting of application of several polish post-processes is proposed. These polish post-processes pretend to reduce roughness keeping, at the same time, a proper adherence. Different post-process durations and conditions are analysed to achieve positive adherence results. Coated bearing samples obtained from the application of these two strategies are tested in friction test rigs. These tests concluded that there is not a significant improvement of friction performance by applying ZrCN coatings compared to bearing baseline.