Research On Preparation And Performance Of PS-PVD Ytterbium Oxide Doped Gadolinium Zirconate Thermal Barrier Coatings

Thermal barrier coating has been widely used in the field of aero-engine,and it was listed as one of the three key technologies of advanced aero-engine turbine blades,which showed excellent performance in protecting hot-end components.With the increasing thrust to weight ratio of aero-engines,the thermal barrier coatings prepared by traditional technology and traditional ceramic materials are difficult to meet the service requirements of high-performance aero-engines under ultra-high temperature conditions.Therefore,the development of advanced thermal barrier coating preparation technology and the research of new ultra-high temperature thermal barrier coating materials are urgent.At present,PS-PVD is the most advanced preparation technology of thermal barrier coating.By adjusting the process parameters,the quasi-columnar coatings with unique structure and excellent performance can be obtained,which have high deposition efficiency,low thermal conductivity and excellent thermal shock resistance.On the other hand,the new gadolinium zirconate thermal barrier coating material has the characteristics of low thermal conductivity,high phase transition temperature,good chemical stability,etc.After doping Yb element,its thermophysical properties will be further improved,and it has a promising application prospect.Thus,it is of great significance to study the preparation and properties of PS-PVD ytterbium oxide doped gadolinium zirconate ultra-high temperature thermal barrier coating.Major works are as follows:（1）This paper takes(Gd_0.9Yb_0.1)₂Zr₂O₇（GYb Z）/YSZ double ceramic layer（DCL）structure thermal barrier coating（TBC）as the research object.Firstly,in the simulation experiment,the influence of coating thickness on the residual stress in the coating during spraying then cooling to room temperature had been predicted.And the distribution of residual stress in the coating was analyzed.The simulation results show that the residual stress in the coating is mainly concentrated at the interface of each layer near the edge of the coating in the simulation experiment,and the maximum residual stress in the coating decreases with the increase of the total thickness of the coating or the thickness ratio of GYb Z:YSZ.（2）The GYb Z/YSZ DCL TBCs with different thickness of GYb Z layers were prepared by PS-PVD technology,and the effect of thickness on the structure and properties of coatings was studied.It is concluded that when the thickness of YSZ layer remains unchanged and the thickness of GYb Z layer is 40μm,the gaps between columnar crystals are not obvious,after 200cycles of water quenching,the failure area exceeds about 30%.When the thickness of GYb Z layer is 80μm,it shows a typical quasi-columnar structure,and there are no large area of failure occurred in the coatings after 200 cycles of water quenching.When the thickness of GYb Z layer increases to 160μm,it still shows the quasi-columnar structure,and the structure remains relatively complete after 200 cycles of water quenching.（3）The GYb Z/YSZ DCL TBCs were prepared by PS-PVD technology at different spraying distances,and the effects of spraying distances on the structure and properties of coatings were studied.The typical failure mechanisms of DCL structural coatings were summarized.It is concluded that the GYb Z coating prepared at a spray distance of 600 mm shows a tightly packed columnar structure,with has the highest Vickers hardness and Elastic modulus,and has a large area of failure after 200 cycles of water quenching.With the increase of spraying distances,the Vickers hardness and Elastic modulus of GYb Z coating has decreased.The GYb Z coatings prepared at 800 mm and 1000 mm spray distances show the typical quasi-columnar structures,among which the dendrites of columnar crystals have well developed and the gaps are most obvious at the spraying distances of 800 mm,and they also show the excellent thermal shock resistance in water quenching tests.In addition,for the GYb Z/YSZ DCL TBCs,the GYb Z layer is the most prone to crack and failure,because the fracture toughness of gadolinium zirconate is much lower than that of traditional YSZ.Besides this,the stress concentration effect in the edge of coating is most obvious.,because of the mismatch of thermal expansion coefficients between different layers,and finally formed the failure pattern of delamination cracks.（4）(Gd_1-xYb_x)₂Zr₂O₇（x=0,0.1,0.3,0.5,1）original powders were prepared by solid-state reaction method,and the change of mechanical properties with Yb doping ratios was studied.It is concluded that the Elastic modulus and Vickers hardness of(Gd_1-xYb_x)₂Zr₂O₇materials do not change obviously with the different doping ratios,but the fracture toughness increases with the increase of Yb doping ratios.In this paper,the GYb Z/YSZ DCL TBCs with a thickness of 80μm prepared at a spray distance of 800 mm as the top ceramic layer shows a typical quasi-columnar structure.This coating has the great comprehensive mechanical properties,and the structure remains intact after200 cycles of water quenching,which shows the excellent thermal shock resistance.Therefore,this study may helpful to promote the practical application of PS-PVD technology,and has the important reference value for the selection of process parameters when preparing gadolinium zirconate coating by PS-PVD technology and the application of gadolinium zirconate materials.