Research On The Intervene And Control For Formation And Growth Of TGO In TBC

Thermal barrier coating (TBC) has been extensively employed to improve the efficiency of advanced gas turbines. Because of their low thermal conductivity and good chemical stability, TBC performs the important function of insulating nickel and cobalt base supperalloy components, allowing an increase in operating temperatures. A thermally grown oxide (TGO) layer between the top coat(TC) and bond coat(BC) layers in TBC has important effect on the TBC'life time.In this work, TBC which consisted of a NiCoCrAlY BC and a ZrO₂-8wt.%Y₂O₃ TC, was fabricated on the nickel-base superalloy. For researching on the intervene and control of the growth of TGO, several processes, including air plasma spray (APS),supersonic fine particle bombarding (SFPB),high velocity oxyfuel spray(HVOF) and vacuum heat treatment(VHT) technologies, were used to fabricate or treat the TBC. The properties of TBC were evaluated by high-temperature oxidation and thermal cycles tests. High-temperature anti-oxidation behavior,element diffusion,thermal cyclic failure and residual stress in TGO scale were studied by SEM with EDS and ruby fluorescence spectroscopy(RFS).BC was treated by SFPB, aiming to intervene the diffusion of Al and repair shape of TC/BC interface. The dislocation density may increase in surface of coat, which provide diffusion channels for Al atoms in BC. The enrichment of Al can extend the steady-state growth stage of TGO and promote the formation of a highly stable, protective aluminum oxide phase upon oxidation. At the same time, geometric shape of the TC/BC interface is also changed by SFPB technology. It can reduce the level of residual stress due to morphology fluctuation. The SFPB TBC was still remained well undergoing 350 thermal cycles. However, after same times thermal cycles, the separation of TC was observed in APS TBC. The residual stress of APS TBC reached a value of 650 MPa at 350 thermal cycles and that of SFPB TBC only reached 532 MPa at 400 thermal cycles.BC was fabricated by HVOF, HVOF can significantly improve interface rough,the interface of HVOF BC is regular. The grain was refined, which increased the spread channel of Al element in coat and helped to form Al2O3 layer. HVOF TBC only reached 571 MPa at 400 thermal cycles lower than that of APS TBC at 350.TBCs were heat treated in a vacuum furnace. Oxidation of the heat-treated samples resulted in a single layer oxide Al2O3. The formation of a thin Al2O3 layer during heat treatment appeared to prevent nucleation and growth of spinel oxides during subsequent oxidation.The curve equation of Al element under different spray technologies will be benefit for forecasting the growth mechanism of TGO.