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4851 |
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Thursday, May 12, 2016, Yellow River Hall 3:00 PM Power Generation IV |
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Comparative investigation of mechanical properties of thermal barrier coatings made by atmospheric plasma spaying and suspension plasma spraying |
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Maciej Gizynski * / National Institute for Materials Science, Japan Xiaolong Chen/ National Institute for Materials Science, Japan Makoto Watanabe/ National Institute for Materials Science, Japan Hiroshi Araki/ National Institute for Materials Science, Japan Seiji Kuroda/ National Institute for Materials Science, Japan Zbigniew Pakiela/ Warsaw University of Technology, Faculty of Materials Science and Engineering, Poland |
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Strong increasing trend in turbine efficiency and inlet gas temperature requires new solutions in TBC systems. One of such solutions is application of nano-sized yttria-stabilized zirconia (YSZ) powders deposited by Suspension Plasma Spray (SPS). Coatings made by SPS seem to merge benefits of both coatings deposited by Electron Beam Physical Vapor Deposition (EB-PVD) method, i.e., high compliance, and that of conventional Atmospheric Plasma Spray (APS), i.e., lower thermal conductivity with undemanding fabrication process and relatively low cost. Although fabrication process and related phenomena of SPS required further investigations and deeper understanding, mechanical properties of SPS coatings seem to have many advantages over ones made by APS. In the present work, fundamental mechanical properties of both SPS and APS coatings were investigated. Four point bending test of coated samples revealed lower values of Youngs modulus and larger values of strain to failure in compression for as-sprayed SPS than APS coatings. Measurements of interfacial toughness between ceramics and CoNiCrAlY-based bond coating showed higher values for SPS coatings. Fracture mechanics analysis shows that this combination of mechanical properties limits elastic energy stored in ceramic coating and, in turn, driving force of delamination, which is one of the dominant failure modes of TBC systems. Thus, SPS coatings might present longer lifetime under thermomechanical loads, e.g. thermal shocks. Performance of TBC systems is sensitive to evolution of mechanical properties while operated at elevated temperatures. Conventional APS coatings are known for sintering, which deteriorates their compliance. Youngs modulus measurements by indentation method revealed that heat treated SPS coatings are less prone to significant growth of stiffness due to complex porosity structure, which may contribute to the coatings durability. |