| The development of aero-engines is important on the technology level of national defense.Thermal barrier coatings can effectively protect turbine blades of aero-engines due to their good thermal insulation performance,reduce the impact of heated airflow and improve the thermal efficiency of the engine.Classic yttria-stabilized zirconia?YSZ?thermal barrier coatings?TBCs?have been used in the aero engine industry since the 1970s.However,as operating temperatures continue to rise,TBCs are suffering from the erosion of molten extraneous deposition known as calcium-magnesium-alumino-silicates?CMAS?.The molten CMAS sinters the YSZ surface layer,resulting in volume change as a consequence of the phase change of YSZ and subsequently shortening the service life of the TBCs.Most researchers have focused on the effect of CMAS corrosion on the thermal barrier coatings prepared by atmospheric plasma spraying?APS?.Thermal barrier coatings prepared by electron beam physical vapor deposition?EB-PVD?,on the other hand,is actually more susceptible to be corroded by CMAS due to its columnar crystal structure.With respect to corrosion by CMAS,alumina materials have been widely studied for its ability to prevent or minimize the degradation impact of CMAS among advanced TBC technologies.The aim of this study is to develop and evaluate Al2O3 modified YSZ thermal barrier coating prepared by EB-PVD for possible mitigation of volcanic ash corrosion.By changing the alumina content in the EB-PVD ceramic ingot composition?i.e.0.5 wt.%,5 wt.%,20 wt.%,85 wt.%,100 wt.%Al2O3-7YSZ?,single layer coatings with each of the above composition as well as 0.5Al2O3 modified YSZ/YSZ and Al2O3/YSZ double layer coatings were prepared.Corrosion resistance of all alumina-doped coatings was investigated using real volcanic ash which has more complex component than CMAS,and the mitigation mechanism was studied.The main research contents are as follows:?1?The alumina modified YSZ ingot powder samples have higher peak melting temperature than YSZ ingot powder sample after the high temperature mixing reaction between the volcanic ash.Anorthite?CaAl2Si2O8?,magnetite?Fe3O4?and spinel(Al1.75Mg0.889Mn0.351O4)were formed as reaction products,and the melting temperatures of the three products were higher than the melting range of the volcanic ash studied?1071°C1251°C?.As a result,alumina can significantly inhibit the melt penetration of VA due to the new molten product temperature being higher than the typical surface operating temperature of the turbine components.?2?A variety of alumina-doped coatings were prepared by EB-PVD equipment,in the early stage of preparation the surface polishing and sand blasting of the substrate were confirmed and the preparation parameters such as substrate temperature and substrate rotation speed were explored.From these experiences,the double layer coatings of 0.5Al2O3 modified YSZ/YSZ and Al2O3/YSZ were prepared by EB-PVD,and were observed by scanning electron microscopy.The two coatings were structurally intact,and the interface between the two coatings was smooth,and the columnar crystal grain size was basically the same.?3?YSZ,0.5Al2O3 modified YSZ/YSZ double layer coating,Al2O3/YSZ double layer coating were simultaneously corroded by VA at 1150°C for 1 and 3 h,and the columnar crystal gaps of YSZ coating were filled with volcanic ash after 1 h,while 0.5Al2O3 modified YSZ/YSZ double layer coating was prevented VA enter into the YSZ layer after 1 or 3 h,and the Al2O3/YSZ double layer coating perfectly obstructed the volcanic ash and left VA on the alumina layer after 1 or 3 h.From the analysis of TGO thickness and Young's modulus,it can be telling that the 0.5Al2O3 modified YSZ/YSZ and Al2O3/YSZ double layer coatings well inhibited the penetration of volcanic ash,and the analysis of the XRD result showed that due to the reaction product between alumina and VA has high melting point prevented further penetration. |
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