Development of Thermal Barrier Coating Systems from Al Microparticles—Part II: Characterisation of Mechanical and Thermal Transport Properties

Germain Boissonnet,Gilles Bonnet,Fernando Pedraza,Jean-Luc Grosseau-Poussard

doi:10.3390/coatings12020106

Abstract

In this study, the mechanical resistance and the thermal insulation potential of novel thermal barrier coatings (TBCs) made of a foam of hollow alumina particles are assessed through scratch testing, micro-indentation and thermal diffusivity measurements using laser-flash. The thermal diffusivity of the foam coatings ranges between 0.6 × 10−7 and 5 × 10−7 m2·s−1 and is thus comparable with the thermal insulation potential of the standard plasma-sprayed (PS) and electron beam–physical vapour-deposited (EB-PVD) TBCs made of yttria-stabilised zirconia (YSZ). The coatings annealed in more oxidative atmospheres exhibit greater mechanical resistance due to the thickening of the alumina shells and the increased sintering of the foam. However, when the oxidation is poorly tailored, the adhesion of the foam to the substrate decreases due to the presence of unwanted oxide that grows at the substrate/coating interface.

Highlights

The current demand for greater efficiency and a reduction in fuel consumption and greenhouse gas emissions requires higher-temperature operating conditions in gas turbines, including in the low-pressure turbine (LPT) section [1]
The mechanical resistance and the thermal insulation potential of novel thermal barrier coatings made of a foam of hollow alumina particles were assessed through scratch testing, micro-indentation and thermal diffusivity measurements
All the coatings showed great thermal insulation properties on a par with the ones of the state-of-the-art yttria-stabilised zirconia (YSZ) thermal barrier coatings (TBCs) made by plasma spraying or electron beam–physical vapour-deposited (EB-PVD)

Summary

Introduction

The current demand for greater efficiency and a reduction in fuel consumption and greenhouse gas emissions requires higher-temperature operating conditions in gas turbines, including in the low-pressure turbine (LPT) section [1]. The formation of a complete thermal barrier coating using the slurry technique appears to be attractive for the materials of the LPT section due to its relatively low cost and ease of application [2]. This technology often uses an aqueous slurry that contains Al microparticles, which forms a foam of hollow alumina microspheres on top of an aluminide coating after proper annealing [3,4].

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Discussion

Conclusion