Articles written in Sadhana

    • Experimental investigations of sol-gel process parameters for wear reduction on thermal barrier coated AA2024 aluminum alloys with the use of Taguchi-based optimization


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      The present sol-gel processes present a surface modification technique for improving the sliding wear resistance characteristics of metallic materials of 2024-T351 aluminum alloy. With the help of dip-coating methods, seven weight% yttria stabilized zirconia (7YSZ) as a top-coat is applied over the air plasma sprayedbond-coated materials, CoNiCrAlY, on aluminum alloys. Thereafter, coating thickness is measured using an optical microscope. Further, sliding wear tests are performed on Pin-On-Disc Friction and Wear test rig as per L16 orthogonal arrays of Taguchi method. Investigations revealed temperature as the most influencing parameter for uncoated samples while temperature and applied load, both for coated samples. In comparison to base metallic alloys, sol-gel derived YSZ coating on the AA2024 surface exhibited better wear resistance, resultedinto the reduction of wear rate.

    • A comparative study of erosion wear rate of conventional and nonconventional thermal barrier coatings on IN800 superalloys


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      Air plasma sprayed (APS) 7weight percent yttria stabilized zirconia (7YSZ) typical thermal barrier coatings are commonly used in aero engine components to protect against thermal fatigue, corrosion, erosion, corrosion-erosion and oxidation phenomenon. In spite of extensive industrial application of 7YSZ coatings, very few works are there on erosion wear performance and its mechanisms on these coatings. In the present work, comparative inspection of the erosion wear behaviors of air plasma sprayed 7YSZ thermal barrier coatings and dip-coated sol-gel processed 7YSZ thermal barrier coatings are carried out. For the sake of comparison erosion of uncoated Inconel 800 superalloys substrate was also studied. Erosion tests were conducted on air jet erosionconditions with alumina erodent materials and process parameters determined as per Taguchi design of experiments at room and high temperature of 850˚C. Erosion wear resistance of non-conventional dip-coating of sol-gel derived 7YSZTBC was found better in comparison to conventional APS YSZ coatings.

    • Performance of 2024 aluminum alloy thermal barrier coating systems subjected to elevated temperature fluctuation as a fatigue


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      To improve the performance of thermal barrier coatings it is needed to characterize the top coat behavior on every aspect as a crucial factor. Understanding the microstructural behaviors of air plasma sprayed (APS) yttria-stabilized zirconia (YSZ) after experiencing the thermal cyclic test is practically significant for the coating in terms of structure and performance. The current study is initially fixated on the TBCs construction followed by thermal cyclic loading and then its fractography was studied through scanning electron microscopy (SEM). A fatigue fracture appearance is detected by scanning electron microscopy (SEM). Based on SEM images at 600°C, the mechanism of thermal fatigue behavior is revealed through Transmission Electron Microscopy (TEM) whether reasons of fracture due to applied thermal testing is thermal fatigue or any other. The results show that the extent of cracking in the coating, as observed on the sample surface, increased with an increase in temperature cyclically, confirmed by SEM and TEM analysis. In addition to this, under isothermal loading, the coating spallation was observed over the entire sample surface, which was unlike the localized spallation observed under thermal cycling. Results revealed that one dominant crack as a visible crack that isparallel to the interface consisting of YSZ and bonding layer happened at the localized regions, starting from edges/corners of the YSZ coating.

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