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The modern turbines aimed to work at enhanced efficiencies demand the use of a novel high-performance thermal barrier coating (TBC) which may be susceptible to multiple failure modes. Specifically, ingestion of calcium–magnesium–alumino–silicate (CMAS) or volcanic ash (VA) at elevated temperatures induce accelerated deterioration of conventional yttria-stabilized zirconia (YSZ) TBCs. The ability to form an impervious and rapidly crystallizing rare earth-based apatite layer upon interaction with CMAS/VA salt favors the choice of rare earth zirconates (REZs) as novel TBCs. Among diverse REZs, Yb2Zr2O7 (YbZ) exhibits ideal TBC characteristics. A detailed insight into YbZ coating characteristics and performance is vitally needed to qualify these materials for TBC applications. Accordingly, in this study indigenously developed YbZ and commercial YSZ were deposited by air plasma spraying. Subsequently, the VA infiltration resistance of deposited coatings was comprehensively compared up to 1350 °C. The SEM analysis of VA-infiltrated YSZ and YbZ coatings revealed the thickness of the infiltration zone and the corresponding mechanism. YbZ coatings displayed significantly better VA infiltration resistance attributed to forming an impervious Yb-apatite-based arresting layer and pinning the further seepage of the VA salt front. Besides, VA rapidly infiltrated YSZ coatings, which failed to form an arresting layer. Overall, the study provides essential insights and thrust in developing next-generation TBCs. [ABSTRACT FROM AUTHOR]

The present study investigates the influence of substrate bias on edge-rounding of TiAlN-coated drill bits arising out of coating deposition and the resulting cutting performance while machining Inconel 718. Tungsten carbide (WC) drill bits were deposited with TiAlN coating through a cathodic arc physical vapor deposition (CAPVD) system. Five different substrate bias voltages varying from −20 V to −60 V were employed for the deposition. The hardness, adhesion strength, and residual stress were significantly influenced by substrate bias. The sharp edges of coated drill bits exhibited significant edge-rounding at relatively higher levels of substrate bias. The reason for such edge-rounding is the re-sputtering and residual stress-induced micro-chipping of the previously formed coating layer during the deposition. The edge-rounding of drill bits was in the order of: 20 V <30 V <40 V <50 V <60 V. The drill bits deposited at −50 V substrate bias exhibited the best tool life owing to optimum edge radius (resulting in better edge stability) and coating properties. The present study helps identify an optimum level of substrate bias, which results in a favorable edge radius and the best tool life of the coated drill bits. [ABSTRACT FROM AUTHOR]

Titanium chromium nitride (TiCrN) coatings with varying Cr content in two configurations, mono- and multilayer, were deposited on high speed steel substrates using a cylindrical cathodic arc physical vapor deposition technique. The physical, mechanical, and erosion behavior of the coatings were investigated. Among the monolayer coatings, the thicker Ti0.48Cr0.52N coatings yielded the best erosion resistance property. But with the increase in thickness, a considerable increase in residual stress is observed. Toward minimizing the stress accumulation, the effect of multilayering with periodic in situ heat treatment (after each 1μm film growth) was studied by growing films in Ti0.52Cr0.48N/Ti0.40Cr0.60N bilayer configuration. A new approach based on % area of erosion damage for measuring relative wear rate of thin films has been proposed and implemented. The multilayer coatings exhibited superior erosion performance compared to the well-known erosion resistant TiN coatings that are in use for compressor blades from past few decades. Further, the erosion failure mechanisms in TiCrN coatings were also studied and found to be clearly different for mono- and multilayer configurations. The results reveal that the thicker multilayer TiCrN coatings (20μm) exhibit promising choice for erosion resistance applications. [ABSTRACT FROM AUTHOR]

In the present study, the corrosion behavior of micro arc oxidation (MAO) coatings deposited at two current densities on 6061-Al alloy has been investigated. Corrosion in particular, simple immersion, and potentiodynamic polarization tests have been carried out in 3.5% NaCl in order to evaluate the corrosion resistance of MAO coatings. The long duration (up to 600 h) immersion tests of coated samples illustrated negligible change in weight as compared to uncoated alloy. The anodic polarization curves were found to exhibit substantially lower corrosion current and more positive corrosion potential for MAO-coated specimens as compared to the uncoated alloy. The electrochemical response was also compared with SS-316 and the hard anodized coatings. The results indicate that the overall corrosion resistance of the MAO coatings is significantly superior as compared to SS316 and comparable to hard anodized coating deposited on 6061 Al alloy. [ABSTRACT FROM AUTHOR]