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Depth-Resolved Phase Analysis of Expanded Austenite Formed in Austenitic Stainless Steel
Expanded austenite γN formed after nitrogen insertion into austenitic stainless steel and CoCr alloys is known as a hard and very wear resistant phase. Nevertheless, no single composition and lattice expansion can describe this phase with nitrogen in solid solution. Using in situ X-ray diffraction (XRD) during ion beam sputtering of expanded austenite allows a detailed depth-dependent phase analysis, correlated with the nitrogen depth profiles obtained by time-of-flight secondary ion mass spectrometry (ToF-SIMS) or glow discharge optical emission spectroscopy (GDOES). Additionally, in-plane XRD measurements at selected depths were performed for strain analysis. Surprisingly, an anomalous peak splitting for the (200) expanded peak was observed for some samples during nitriding and sputter etching, indicating a layered structure only for {200} oriented grains. The strain analysis as a function of depth and orientation of scattering vector (parallel/perpendicular to the surface) is inconclusive. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
Improved Adhesion of the DLC Coating Using HiPIMS with Positive Pulses and Plasma Immersion Pretreatment
Diamond-like carbon (DLC) coatings are used due to their extraordinary tribomechanical properties, great hardness, high elastic modulus, high wear resistance, low friction coefficient and chemical inertness, which provide them with biocompatibility. Compared to other physical vapor deposition (PVD) coatings of transition nitrides and carbonitrides, DLC has limited adhesion, so it is necessary to develop new techniques to overcome this limitation. This work reports the results of scratch testing for the measurement of adhesion and of tests for wear resistance and nanoindentation in AISI 316L stainless steel coated with a WC:C coating, produced using novel high-power impulse magnetron sputtering (HiPIMS) technology with positive pulses. In addition, the use of a preceding surface modification technique, specifically plasma immersion ion implantation (PIII), was studied with the aim of optimizing the adhesion of the coating. The results show how the coating improved the tribomechanical properties through the use of positive pulse HiPIMS compared to conventional HiPIMS, with an adhesion result that reached critical load values of 48.5 N and a wear coefficient of 3.96 × 10−7 mm3/nm