Fabrication of thermal barrier coating using electrochemical methods

An electrochemical method of fabrication of (NiCoCrAlY)/MgO/Yttria stabilized zirconia (YSZ) multilayered coating was proposed. This multilayered coat is expected to work as a thermal barrier coating (TBC) for nickel superalloy substrates. The (NiCoCrAlY) layer was deposited using the electrophoretic deposition technique, the MgO layer was deposited by the electrolytic deposition technique and the YSZ layer was electrophoretically deposited.; In order to study the deposit morphology and to determine the appropriate processing parameters for the multilayered coat, one-layer coatings of (NiCoCrAlY), MgO and YSZ were deposited and characterized. At first, the process of depositing (NiCoCrAlY) alloy particles using an aqueous media with AlCl₃ or Al(NO₃)₃ as an electrolyte revealed that the alloy particles were deposited at the same time as aluminium oxide. The co-deposited aluminium oxide worked as a binder between the particles and the substrate.; In the electrolytic deposition process of the MgO coating, the layer deposited from Mg(NO₃)₂ solution was mainly magnesium hydroxide and it had to be calcinated to form a MgO coating. An optimization of the deposition process demonstrated that a crack free deposit of MgO could be obtained at low current density.; An optimum condition of the electrophoretic deposition process was established for YSZ; it was found that adding 5% water to the acetone bath increased the deposition rate of the YSZ particles, and had increased the porosity in the coat.; A composite coating of (NiCoCrAlY)/MgO was formed after heat treatment at 850°C for 1 hr. The electrochemically deposited MgO was easily sintered at 850°C, which resulted in a dense ceramic coating that protects the substrate and the (NiCoCrAlY) coating from oxidation during sintering of the electrophoretically deposited YSZ layer at 1100°C.