Characterisation of thermal barrier sensor coatings synthesised by sol–gel route

Abstract

International audienceFurther improvements in the efficiency of gas turbines are recognised to come from increases in turbine entry temperatures. Accurate temperature measurements are crucial to achieve these increases whilst maintaining reliability and economic component life. The combination of phosphor thermometry and thermal barrier coating (TBC) technology has led to the development of functional temperature sensor coatings which have several advantages over conventional temperature measurement techniques. Developments in sol–gel processing indicate that this method could be used for the production, or particularly, the repair of TBCs in the future. This paper demonstrates, for the first time, that sol–gel processing can be used to make sensor TBCs. The optimum concentration of SmO1.5 was 2 wt.% in YSZ to achieve the brightest phosphorescence emission. Above this concentration the overall intensity of the emission reduces and the transitions from 4F3/2 were suppressed. Furthermore, a similar suppression of these transitions was observed when the product of the sol–gel was heat treated to 1100 ◦C. This was concluded to be due to a higher degree of crystallinity allowing a greater interaction between the dopant ions. The dependence of the phosphorescence spectrum on heat treatment temperature provides the first indication that YSZ produced through sol–gel could be used to detect historic temperatures. An evaluation of the subsurface measurement and temperature capabilities has shown that the phosphorescence can be detected from relatively thin layers, 20 µm, even under 50 µm of undoped YSZ coating. Although the temperature detection range, 400–700 ◦C, is too low for advanced TBCs the material could be used in low temperature regimes or for health monitoring purposes

Novel erbia-yttria co-doped zirconia fluorescent thermal history sensor

“…Preliminary investigations confirmed the potential of an intensity ratio approach, using a red emitting, temperature insensitive YSZ:Eu 3+ reference, as a robust method regarding small variations in experimental measurement conditions for future applications in off-line temperature mapping. Finally, the thermal stability of the YSZ:Er 3+ marker up to 973 K for a short period of time (2 h) is promising for its integration within coatings for practical thermal history sensing applications, such as sol-gel deposited YSZ-based coatings [20,21] that will be investigated in a future work.…”

“…Recently, the Institut Clement Ader, in collaboration with the CIRIMAT, has developed the synthesis by a sol-gel process of yttria-stabilized zirconia (YSZ) based phosphors functionalized with lanthanide ions such as Sm 3+ , Eu 3+ and Er 3+ for future applications in temperature sensing within thermal barrier coatings for gas turbines [20][21][22]. These phosphors, not fully crystallized in the initial state, exhibit irreversible changes in their fluorescence properties after annealing in the range 1173-1373 K, suggesting they could be potentially used to record thermal history [20,22].…”

Feasibility of luminescent multilayer sol-gel thermal barrier coating manufacturing for future applications in through-thickness temperature gradient sensing

“…x Y 0.0975-x Zr 1 -0.092-x O 1.951-2x (Ln ' = Eu, Er or Dy) with distinct emissions wavelengths were shaped by a dip-coating process previously developed [14,15].…”

“…This cost effective process allows one to deposit 9.75 mol% porous YSZ TBCs presenting the metastable t' phase with performance under cyclic oxidation comparable to that of EB-PVD coatings [13,14]. The easy composition control offered by the technique has already generated interest for manufacturing some high purity YSZ:Er and YSZ:Sm phosphor coatings and powders [15]. Therefore the effect of additions of several dopants including Sm, Eu, Dy, Er and Tm in 9,75 mol% YSZ was investigated, and a solution is proposed for the optimization of YSZ luminescence properties.…”

Remote temperature sensing on and beneath atmospheric plasma sprayed thermal barrier coatings using thermographic phosphors

“…Different degradation mechanisms of the ceramic coatings are directly related to the temperatures that the TBC system experience during operation, especially the temperature registered at the metallic substrate/TBC interface. An increase of temperature of 50°C at the substrate/TBC interface can lead to as much as six folds decrease in the lifespan of the TBC [1]. Thus, in situ monitoring of the temperature at the substrate/TBC interface is of high significance to evaluate the performance of the coatings and investigate the potential for further advancement in engine efficiency.…”