High-Temperature Cycling of Plasma Sprayed Multilayered NiCrAlY/YSZ/GZO/YAG Thermal Barrier Coatings Prepared from Liquid Feedstocks.

High-enthalpy hybrid water/argon-stabilized plasma (WSP-H) torch may be used for efficient deposition of coatings from dry powders, suspensions, and solutions. WSP-H torch was used to deposit two complete thermal barrier coatings (TBCs) with multilayered top-coat. NiCrAlY was used as bondcoat and deposited on nickel-based superalloy substrates. Top-coat consisted of up to three sublayers: (i) yttria-stabilized zirconia (ZrO-8 wt.%YO-YSZ) deposited from solution, (ii) gadolinium zirconate (GdZrO-GZO) deposited from suspension, and (iii) optional yttrium aluminum garnet (YAlO-YAG) overlayer deposited from suspension. Each of the sublayers was intended to provide different functionalities, namely improved fracture toughness, low thermal conductivity, and high erosion resistance, respectively. High-temperature performance and thermal shock resistance of the deposited coatings were tested by thermal cycling fatigue "TCF" test (maximum temperature 1100 °C, 1 h dwell per cycle) and "laser-rig" test (maximum temperature ~ 1530 °C, 5 min dwell per cycle) exposing samples to isothermal and gradient thermal conditions, respectively. In both tests, coatings endured around 800 test cycles which shows great potential for further development of these layers and their application in demanding thermal conditions. Analysis of the samples after the test showed microstructural changes and identified reason of ultimate coating failure.