Surface Modification Of ZrO₂ Coating Irradiation By High Current Pulsed Electron Beam

In this thesis, the directionally solidified Ni-based superalloy DZ4 was used as the substrate. NiCrAlY bond coating was sprayed on the substrate by low-pressure plasma spraying (LPPS). Then 6%-8% Y2O3 partially stabilized ZrO2 (YSZ) ceramic top coating was deposition on the bond coating by electron beam physical vapor deposition (EB-PVD). The thicknesses of NiCrAlY and YSZ coatings were about 100μm and 110μm, respectively. To improve the oxidation resistance of the YSZ coating, the coating was irradiated by high current pulsed electron beam (HCPEB) with different energy density and pulse duration. The optimum ranges of HCPEB irradiation parameters were found according to the experimental results.The main results presented in the dissertation have been summarized as follows:The YSZ top coats with columnar crystals have been sealed successfully by HCPEB irradiation, and the oxidation resistance of the coating was improved. The surface of ceramic layer was melted completely when the energy density of HCPEB is greater than 8J/cm2. The thickness of the melting layer is about several micrometers, and the thickness increases with the increase of the energy density of HCPEB. When the energy density of HCPEB is greater than 20J/cm2, the thickness reduced because of ablation evaporation of the surface. Moreover, surface microcracks of the coating increase when the energy density of HCPEB reaches 20J/cm2. With the increase of energy density of HCPEB, the composition of tetragonal phase in t phase increase while the composition of cubic phase in t phase reduce, and no monoclinic phase structure is observed in the coating. The cyclic oxidation and static oxidation experiments in 1000℃show that the thickness of TGO of the coating irradiated by HCPEB with energy density 8-15J/cm2 decrease remarkably than the thickness of TGO of the coating without HCPEB irradiation. Thus, the oxidation resistance of the coating is greatly improved when the thickness of the melting layer is about several micrometers.The thickness of the melting layer of the coating irradiated by HCPEB with energy density15J/cm2 and different pulse duration is about 2-4μm. When the pulse duration of HCPEB irradiation is in range of 80-120μs, the thickness of the melting layer is about 4μm. After HCPEB irradiation, the composition of tetragonal phase in t phase of the coating increase while the grain size decrease, no monoclinic phase structure have observed in the coating. The 500 cyclic oxidation experiments in 1050℃indicate that the thickness of TGO of the coating without HCPEB irradiation is about 3μm, and the thickness of TGO of the coating irradiated by HCPEB with pulse duration of 80-120μs is about 2μm.It is therefore concluded that the oxidation resistance of the coating can be improved remarkably after HCPEB irradiation. The thermal diffusivity of the coating irradiated by HCPEB with energy density 12J/cm2 and pulse duration 120μs is lower than the coating without HCPEB irradiation. Hence, thermal resistance property of the coating is also improved by HCPEB irradiation.According to the investigations on the oxidation resistance of the coating, the optimum irradiation parameters of HCPEB have been found, as shown below:energy density of the HCPEB is in range of 8 to 20J/cm2; pulse duration is in range of 80 to 200μs.