Structural Chemistry & Crystallography Communication

Thermal cyclic life of glass-ceramic bonded thermal barrier coating system

Statement of the Problem: Gas turbines produce energy
at very high temperatures. Usually, creep, spallation and
delamination occur in the metallic parts of gas turbines
leading to deterioration of the turbine blades resulting
in decrease in gas turbine efficiency. Thermal barrier
coatings (TBCs) are provided to protect the metallic parts
of gas turbines from the high inlet temperature. During
thermal cycling at higher temperatures TBCs get damaged
due to spallation on account of hot corrosion and oxidation
of the metallic components of TBCs. In the present
study, two types of TBCs were investigated for their thermal
cyclic resistance at 1000â?? for 500 cycles: conventional
TBC having NiCoCrAlY bond coat and 8-YSZ top coat
and new TBC with glass-ceramic bond coat and 8-YSZ top
coat. Methodology: Assessment of weight change, X-ray
diffraction (XRD), scanning electron microscopy (SEM),
energy dispersive X-ray (EDX) analysis were performed
for both TBCs after thermal cyclic tests at 1000â?? for 500
cycles. Findings: Weight change measurement indicated
that formation of thermally grown oxide (TGO) dominated
over the coating spallation up to 300 cycles in case
of both TBCs. On the contrary, coating spallation was
much more than TGO formation beyond 300 cycles for
both TBCs. Further, TGO was not appeared at the bond
coat/top coat interface of glass-ceramic bond coated TBC
system whereas it was clearly observed in the interfacial
region of bond coat and top coat of conventional TBC
system after completion of 500 cycles at 1000oC. Conclusion
& Significance: Glass ceramics as a bond coat in
a TBC system can provide better heat resistance, oxidation
resistance and good stability towards thermal cycling
compared to conventional TBC system. Moreover, TGO
formation could be avoided by using this new TBC system,
which is the most significant controlling factor for
the TBC degradation.

Author(s):

Sumana Ghosh

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