Search

Oxide thin films have been investigated as protection against corrosion of Fe-based materials in highly carburizing atmospheres at high temperature. The present study describes the structural evolution of an Al oxide/Cr thin film coating deposited on 304 L steel after 50 h of exposure to a CH 4 + H 2 + residual O 2 atmosphere at 1073 K. Comparisons are then made to the structural evolution observed after 20 h of exposure from a previous study [1]. The coatings were produced by reactive magnetron sputtering at low temperature. The resulting thin films had very fine columnar structure, good adhesion to the substrate, amorphous Al oxide and tensile residual stresses. The response of the films to the carburizing atmosphere was evaluated via thermogravimetric analysis (TGA). The exposed samples were analyzed by X-ray diffraction, scanning electron microscopy equipped with energy dispersive analysis, and optical microscopy. Both, the TGA and structural analyses indicate that the presence of the films prevents the massive formation of internal and external corrosion products observed in uncoated 304 L samples exposed in the same conditions. However, the films underwent some structural modifications, which resulted in abundant interdiffusion through the film changing its as-deposited characteristics. [ABSTRACT FROM AUTHOR]

Abstract: The evolution of the structure and properties of Cr/Cr oxide thin films deposited on HK40 steel substrates by reactive magnetron sputtering (RMS) was investigated and linked to their potential protective behavior against metal dusting. Deposition time, mode of oxygen feeding, and application of bias voltage were varied to assess their effect on the density, adhesion, and integrity of the films. All the films showed a very fine columnar microstructure and the presence of amorphous Cr oxide. Both, an increasing time and a constant oxygen flow during deposition led to the development of relatively low density films and mud-like cracking patterns. A graded oxygen flow resulted in films with fewer cracks, but a careful control of the oxygen flow is required to obtain films with a truly graded structure. The effect of the bias voltage was much more significant and beneficial. An increasing negative bias voltage resulted in the development of denser films with a transition to an almost crack-free structure and better adhesion. The amorphous oxide resulted in low values of hardness and Young''s modulus. [Copyright &y& Elsevier]

In this work, three plasma-enhanced techniques have been used to deposit Diamond-like Carbon coatings (DLCs), as follows: HiPIMS, PECVD, and PIID. The DLCs deposition was on nitrided and non-nitrided steel substrates. In the DLCs deposited by HiPIMS and by PECVD processes, an adhesion layer of Ti/TiN and Ti/TiN/TiC, respectively, was deposited using a W hot filament. In the PIID process, a SiCx interlayer was grown out of tetramethylsilane gas before DLC deposition. Subsequently, the DLCs coated systems were characterized by SEM/EDS, Raman Spectroscopy, instrumented hardness, adhesion, and tribological behavior. Raman characterization revealed that DLC deposited by PECVD presented the lowest ID/IG ratio, meaning the highest amount of sp3 bonding, consequently, was the hardest coating. Adhesion probed by a scratch test revealed that the DLC deposited by PECVD showed gross spallation, exposing the Ti/TiN/TiC adhesion layer. On the other hand, the DLCs deposited by HiPIMS and PIID showed wedging spallation, as the primary adhesive failure mode. The DLC that presented the best tribological behavior was the one deposited by PECVD due to its highest H/E ratio. • DLCs have been deposited by three techniques: PECVD, HiPIMS, PIID. • DLCs by HiPIMS and PIID show a higher gross spallation resistance. • H/E ratio is higher for the DLC by PECVD. • The most wear-resistant DLC is the one by PECVD. [ABSTRACT FROM AUTHOR]