Non-contact sensing of TBC/BC interface temperature in a thermal gradient M.M. Gentleman a, ⁎ , J.I. Eldridge b , D.M. Zhu b , K.S. Murphy c , D.R. Clarke a a Materials Department, University of California, Santa Barbara, CA 93106-5050, USA b NASA Glenn Research Center, Cleveland, OH 44135, USA c Howmet Research Center, Whitehall, MI 49461-1895, USA Available online 11 October 2006 Abstract Luminescence lifetimes of rare-earth ions in yttria-stabilized zirconia have been shown to exhibit temperature sensitivity from 500–1150 °C [Gentleman, M.M. and Clarke, D.R. (2005) Surface and Coatings Technology 200, 1264; Gentleman, M.M. and Clarke, D.R. (2004) Surface and Coatings Technology 188–189, 93.]. These doped zirconias can be deposited along with standard thermal barrier coatings to create thin temperature sensing layers within the coating. Of particular interest is the temperature at the coating/bond coat interface as the oxidation life of a TBC system is exponentially dependent on this temperature. In this study, thin (∼ 10 μm) layers of europia-doped yttria-stabilized zirconia were deposited by EB-PVD onto bond-coated CMSX-4 superalloy buttons to achieve sensor layers located next to the TBC/BC interface. These coatings were then used to measure the interface temperature in a thermal gradient. Combined with pyrometric measurements of the coating- surface temperature and metal-surface temperature, the thermal conductivity of the coating (1.5 W/mK) and heat flux (∼ 1 MW/m 2 ) in the tests were calculated. © 2006 Elsevier B.V. All rights reserved. Keywords: Thermal barrier coatings; Luminescence; Sensors; Thermal gradient 1. Introduction The continuing use of, and growing reliance on, ceramic coatings for thermal insulation of hot metallic components in power generation and aerospace turbines has led to the requirement that coatings must not fail during the scheduled lifetime of the component. As a result, a significant effort has been placed on the ability to assess the “health” of these parts during service. Of particular interest is the capability to monitor the temperature of the coating in contact with a blade or vane. This requires a non-contact technique that has the ability to see through the radiation emitted by engine surfaces and the hot gas as well as take a measurement on a moving engine part. Lumi- nescence decay lifetime of a phosphor embedded in the coating is one technique that shows promise to fulfill all these require- ments. The use of phosphors to measure temperatures dates back to the work of Bradley [3] and has been reviewed in detail by Allison et al. [4]. More recently the concept has been shown to be applicable to TBC materials and coatings [1,2,5,6]. A funda- mental requirement of any sensor is that the luminescent phosphor is thermodynamically stable as well as having tem- perature dependent luminescence lifetime decay. Thermodynamic compatibility poses a very severe constraint on the possible luminescent phosphors that can be used in thermal barrier coatings because the temperatures are so high and the service life is so long. The phosphor must not only be compatible with the coating material but also the materials in contact with the coating itself. For current coating materials, such as yttria-stabilized zirconia and the zirconates, phase compatibility precludes the use of many well known phosphor hosts such as Y 2 O 3 , the oxysulphides and Y 3 Al 5 O 12 in thermal barrier systems [2]. For this reason, the use of the coating material itself as the host material is the obvious choice for creating a durable coating that also has sensing capabilities. Crystal chemistry considerations dictate that the luminescent ions must be one or more of the lanthanide ions. The optical properties of these ions further narrows the choice for particular sensor applications. Previous work has illustrated the ability to measuring temperature using the 5 D 0 → 7 F 2 transition of Eu-doped thermal barrier materials for temperatures ranging from 500 to 1200 °C Surface & Coatings Technology 201 (2006) 3937 – 3941 www.elsevier.com/locate/surfcoat ⁎ Corresponding author. E-mail address: gentmol@engineering.ucsb.edu (M.M. Gentleman). 0257-8972/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2006.08.102