Nano Composite Thermal Barrier Coatings Fabricated on Gh3128Supperalloy
|Course||Materials Processing Engineering|
|Keywords||Thermal barrier coatings Magnetron sputtering Electrophoreticdeposition Microstructure High temperature oxidation High temperature corrosion|
The typical double-layer nano composite thermal barrier coatings were investigated concerning the preparation technology, microstructure and high temperature performances. GH3128superalloy was used as the substrate material. Two techniques were employed. The first is composite technology of sputtering and electrophoresis which prepare the metallic bond coat and the ceramic coat by magnetron sputtering and electrophoretic deposition respectively. The second is composite technology of electrophoresis which prepare both the metallic bond coat and the ceramic coat by electrophoretic deposition.Evenly dense nanocrystalline NiCoCrAlY bond coat can be obtained by magnetron sputtering and it possesses a polycrystalline austenitic structure (FCC). NiCoCrAlY bond coat can effectively protect the superalloy from oxidation at high temperature. With the reduce of substrate surface roughness, the surface roughness of NiCoCrAlY bond coat is also dropped, the adhesion is strengthened, and the high temperature oxidation resistance is increased. NiCoCrAlY/YSZ thermal barrier coating can be obtained by composite technology of sputtering and electrophoresis. After high vacuum heat treatment, the YSZ ceramic coat maintains a stable tetragonal phase. The YSZ ceramic coat is macroscopically compact and uniform, but there are some nano-scale pores on microscopic level. The high temperature performances of samples are significantly affected by the applied voltage, deposition time, suspension solid content, additive content and heat treatment temperature in the process of ceramic coat. Sputtering time and pressure of metallic bond coat are also having impacts on the high temperature performances of samples. Nano La2O3, CeO2and Nd2O3can be effectively doped in the ceramic coat by electrophoretic deposition. After high vacuum heat treatment, a small amount of perovskites (La.Nd)2(Zr,Ce)2O7was formed in the doped ceramic coat, and the coat is more compact and uniform than non-doped YSZ ceramic coat under the same process conditions, so as to effectively improve the high temperature performance of NiCoCrAlY/YSZ TBC system.NiCoCrAlY metallic bond coat can be successfully prepared by electrophoretic deposition. After high vacuum heat treatment at1200℃, the main phases in the coating are y-Ni and y’-Ni3Al, also a very small amount of α-Al2O3. A certain composition fluctuations observed in the coating. The adhesion of electrophoretic deposited NiCoCrAlY coating on the superalloy substrate is excellent, and the coating can effectively protect the superalloy from oxidation. The Ti diffused from superalloy substrate to the coating surface during vacuum heat treatment and high temperature oxidation testing would accelerate the flaking of the scale, so as to adverse to the high temperature oxidation resistance of the coating. It is difficult to avoid the existence of small amounts cracks and pores on the surface of NiCoCrAlY/YSZ TBC system deposited by composite technology of electrophoresis. The high temperature performances of samples are significantly affected by the applied voltage, deposition time and suspension solid content in the process of metallic bond coat. Nano Gd2O3, Sm2O3and YbO3can be effectively doped in the ceramic coat by electrophoretic deposition. After high vacuum heat treatment, the coat is compact and uniform, avoiding the problems of cracks in undoped YSZ coating. Nano Gd2O3, Sm2O3and Yb2O3play a role similar to Y2O3to stabilize the ZrO2, so as to effectively improve the high temperature performance of NiCoCrAlY/YSZ TBC system.