| During the past decades, TBCs had got more than ever employed in the hot section of gas turbine engines for protection against extreme service conditions. The current state-of-art material for TBCs was6-8wt%YSZ and it was well-established the microstructure and properties of TBCs could vary enormously depending on their manufacturing method. TBCs prepared by plasma spray took on a layered structure with general adhesion but very low thermal conductivity. TBCs produced by EB-PVD presented columnar microstructure with superior adhesion and excellent strain tolerance which qualified its application on high-stress hot section such as the turbine blades, however, the thermal conductivity is high. How to effectively reduce the thermal conductivity of the EB-PVD TBCs has been focus within related research. Recently, considering the lamilar structure within sprayed TBCs can favour reduction of the heat transfer into the coatings for reference, layering of the EB-PVD TBCs is an emerging direction. In the present strudy, the two kinds of layered TBCs were designed within the top coat and successfully prepared using ion beam assisted deposition, low substrate rotation speed as well as the high-low deposition temperature staggered, etc. Then, microstructure and performance was investigated after the introduction of layered structure.On the basis of research of assisted ion source, the microlaminar TBCs was fabricated by pulse ion beam bombardment with current density in the range0-0.094mA/cm2; while the other methods can develop the multilayered TBCs with the interfaces across the coating and resulted in a flat ribbon pores. The microlaminar TBCs were accompanied with greatdeal of interfaces and the density modulation variation between adjacent micro-laminates. The microlaminates and grain refinement can be more distinguished with increasing level of ion assistance, however, the substrate temperature is still dominant factor in the control of the atomic mobility and surface morphology. Ion assistance had little influence on the composition of layered TBCs, the introduced Ti content was very little and ignorable. In addition, there was no densification was presented.The two kinds of layered TBCs were still showing the dominant non-transformation tetragonal (t’) structural features. The dominant crystallographic orientation can be induced gradually from (100) to (111) by ion assistance, and then there was coexistence of{111} and {100} type texture. The mechanism resultd from the combined action between the adjustment of net growth and direction of columnar grains with orientations with respect to the ion beam and the growth instability induced by surface roughness. Compared with the conventional TBCs, the thermal diffusivity and thermal conductivity of the two kinds of layered TBCs was both reduced at the same temperature, in which the microlaminar TBCs by ion assistance show a more significant reduction up to35%. The mechanism was attributed to a large interfacial thermal resistance after the introduction of interfaces which was perpendicular to the heat conduction gradient. In addition, refined grains and more boundaries and density modulation between adjacent micro-layer contributed together.The oxidation rate of the bond coat was both reduced by the two kinds of layered structure. The low rotation specimens exhibited better performance of oxidation resistance, but worse coating life; the ion-assisted specimens shown slightly lower weight gain rate than that of the conventional TBCs, but better coatings duration lifetime. The mechanism lies in the difference of layered structure itself, the location of such two kinds of interface and whether these interfaces reduced the excellent strain tolerance of YSZ column when they restrain the heat transfer and improve the oxidation resistance within the coatings. Overall, ion beam assisted EB-PVD can be a novel method for the preparation of TBCs. |
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