Structural degradation of electric arc thermal-barrier coating on gas turbine engine blades after operation

Metallurgy and Material Science

Metal science and thermal processing of metals and alloys


Аuthors

Golovach A. M.*, Dmitrieva M. O.**, Bondareva O. S.***

Samara National Research University named after Academician S.P. Korolev, 34, Moskovskoye shosse, Samara, 443086, Russia

*e-mail: machete.ru2016@gmail.com
**e-mail: mdmitr1ewa@yandex.ru
***e-mail: osbond@yandex.ru

Abstract

Thermal protective coatings are the type of coatings employed to insulate components operating at elevated temperatures. Application area of such coatings is the gas turbine engine blades, combustion chamber, nozzle guide apparatus and pipelines. Thermal protective coatings allow increase gas turbines temperature, enhancing thereby the turbine efficiency.

In conditions of high-temperature operation, special requirements are imposed on components of gas turbine engines. In this regard, thermal barrier coatings (TBC) were developed to protect the gas turbine elements, representing a system of the two or more layers applied on a substrate in a special way.

Coatings, obtained by the electric arc technique of physical vapor deposition (EAPVD), were selected for studying in this work. Three types of alloys were employed for the TBS system, such as SDP-4, representing a coating of NiCoCrAlY alloy; VSDP-16, a diffusion coating of a AlNiY type; and, finally ceramic layer from Zirconium oxide, stabilized by the Yttrium oxide (ZrO2 + 8% Y2O3). Chemical composition of the thermal protective coating was determined by the X-ray micro-analyzer of the Inca Energy OXFORD instruments system. It was determined that after long-term operation the coating layer formed by the SDP-4 and VSDP-16 alloys had two clearly defined zones, such as β-NiAl phase and an inter-diffusion zone, while the NiCoCrAlY alloy did not exhibit phase separation, and the coating structure represents the β-NiAl and γ -phase mixture. It was established that oxygen diffusion occurs outside ceramic upper layer to its boundary with the heat-proof underlayer, which contributes to thermally grown oxide α-Al2O3 forming. It was noticed that the VSDP-16 alloy deposited on the SDP-4 layer increases the amount of aluminum in the binder coating layer, compensating its consumption for α-Al2O3 forming from the β-NiAl phase.

Keywords:

ceramic coating, heat proof underlayer, thermally grown oxide

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