Project No: N R15 0007 06

Duration: September 1^st, 2009-August 30^th, 2012

Objective and methods:

The goal of the project was to produce Thermal Barrier Coatings (TBC/BC) on the aircraft engine turbine blades cast of Inconel 100 and Inconel 713C. The coatings were produced in the three stages:

a)            deposition of a diffusion layer which contains the AlNi intermetallic phase using AlCl₃ vapours in an atmosphere of hydrogen as the carrier gas (Chemical Vapour deposition – CVD);     

(b)          plasma spraying of the (ZrO₂+Y₂O₃) thermal barrier;

(c)          glow discharge-assisted annealing.

The thermal barriers thus produced were examined in NIKON EPIPHOT 200 and HITACHI SU70 electron scanning microscopes with a micro-area analyser (EDS-Energy Dispersive Spectroscopy), manufactured by the ThermoNoran Co. The phase composition was analyzed based on the X-ray diffraction patterns obtained using a Bruker D8 instrument with CuKα radiation. The heat resistance was examined in air at a temperature of 1100°C. Samples with and without the thermal barrier were subjected to 24h/1h and 24h/24h heating-cooling cycles which were highly dynamic since the samples were placed in a furnace heated to 1100°C and then cooled in air at ambient temperature. After each cycle, the samples were examined with the naked eye and in a microscope. In some selected samples, the chemical composition of the individual layers was analyzed. The chemical composition of a cross-section surface of the samples was examined by XPS (PHI 5000 VersaProbe).

Results

By combining (CVD) aluminizing deposition, plasma spraying, and final heat treatment realized by glow discharge annealing we can produce a (ZrO₂+Y₂O₃)+AlNi thermal barrier on the surface of turbine blades cast of the Inconel 100 and Inconel 713C nickel superalloy (Fig. 1). The AlNi intermetallic layer evidently reduces the diffusion of chromium into the outer (ZrO₂+Y₂O₃) thermal barrier. Due to its diffusive character, the thermal barrier coating adheres well to the substrate and shows exceptionally good corrosion resistance - especially at high temperatures.

Fig. 1. Microstructure of the TBC/BC thermal barrier formed on an INCONEL 713C nickel superalloy substrate

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1. Structure and properties of the multilayers produced on Inconel 600 by PACVD method with the participation of trimethylaluminum vapours