Date of Award

2014-01-01

Degree Name

Doctor of Philosophy

Department

Environmental Science and Engineering

Advisor(s)

Ramana V. Chintalapalle

Abstract

Thermal efficiency of the gas turbines is influenced by the operating temperature of the hot gas path components. The material used for the hot gas path components can only withstand temperature up to a certain limit. Thermal barrier coatings (TBC) provide the additional thermal protection for these components and help the gas turbine achieve higher firing temperatures. Traditionally available yttria stabilized zirconia (YSZ) TBCs have a limitation up to 1200 C due to their phase transformation. The present work focuses on gadolinia based hafnia (GSH) TBCs to study their potential to replace the YSZ coatings. Different compositions of gadolinia doped hafnia coatings have been deposited using electron beam physical vapor deposition (EB-PVD) technique and characterized using x-ray diffraction (XRD) and scanning electron microscope (SEM). The crystal structure analysis performed using XRD confirmed the stabilization of the high temperature cubic phase of hafnia. Cross sectional analysis confirmed the presence of columnar structure in the coatings which is a signature of the EB-PVD coatings. Mechanical properties of the coatings were investigated using nanoindentation and nano impact testing at both room temperature and high temperature. Indentation tests indicate a reduction in hardness with an increase in temperature and gadolinia content in hafnia. Impact testing reveals the fracture resistance of the coatings as a function of stabilizer content and heat treatment. Thermal measurements and impedance testing was performed on the bulk material to study the effect of gadolinia content. Thermal cycling was performed to study the spallation behavior of the as deposited and aged samples. Finite element models were developed to study the interfacial stress development in the coatings subjected to thermal cycling.

Language

en

Provenance

Received from ProQuest

File Size

99 pages

File Format

application/pdf

Rights Holder

Satya Kiran Gullapalli

Download

Share

COinS