IMPROVING THE IMPROVING THE CORROSIVE DURABILITY OF CORROSIVE - - PowerPoint PPT Presentation

IMPROVING THE IMPROVING THE CORROSIVE DURABILITY OF CORROSIVE DURABILITY OF THERMAL BARRIER COATINGS THERMAL BARRIER COATINGS

Presented by: Benson Gilbert Presented by: Benson Gilbert

Major: Mechanical Engineering/Material Science and Major: Mechanical Engineering/Material Science and Engineering Engineering College attended: Santa Rosa Junior College College attended: Santa Rosa Junior College Lab Mentor: Felicia Pitek Lab Mentor: Felicia Pitek Faculty Advisor: Carlos Levi Faculty Advisor: Carlos Levi Funded by: Funded by:

Overview of Thermal Barrier Coatings (TBCs)

• What are TBCs?
• Thermal and corrosion resistant ceramic shields to underlying

alloy components

• Conventional TBCs are made of yttria stabilized zirconia (7YSZ)
• Applications of TBCs
• Propulsion
• Power generation
• Failures of current TBCs
• Being corroded by dirty fuels and other contaminates such as

V, S, Na---reducing TBC life

• The need for improved TBCs

Heat Transfer

1. Production of 5 different yttria stabilized zirconia (YSZ) through reverse co-precipitation

• Doped with yttrium and/or tantalum

2. Producing Powders

• Pyrolization
• Grinding solid into powder form

3. Pressing the compositions into pellets 4. Analysis before corrosion testing using

• X-Ray Diffraction (XRD)

5. Corrosion Testing

• Putting vanadate/sulfate corrodant on pellets
• Heat Treatment of pellets

6. Analysis after corrosion testing looking for phase stability using

• X-Ray Diffraction (XRD)
• Transmission electron microscope (TEM)
• Scanning electron microscope (SEM) with

electron dispersive spectroscopy (EDS)

GOAL: Gain understanding of how to make a better TBC

Hot Corrosion Testing Device and Setup

Corrosion Environment 25-35mg/cm2 Na2SO4-30mole%NaVO3 900oC in air

Y2O3(in t-ZrO2) + V2O5(melt) = 2YVO4 + m-ZrO2

Phase Stability of Yttria Stabilized Zirconia (YSZ)

cubic (c) crystal structure tetragonal (t) crystal structure monoclinic (m) crystal structure fluorite (F) is a particular structure

• f cubic

mole fraction YO 1.5

Fabrichnaya, 2003

m+F m+δ

YO YO1.

1.5

Temperature (oC) te Fe

ZrO2-YO1.5-TaO2.5 Ternary Phase Diagram

• Sample A (a)---7.6mole% YO1.5
• Sample B (b)---15.2mole% YO1.5
• Sample C (c)---22.8mole% YO1.5
• Sample D (d)---15.2mole% YO1.5

+ 7.6mole%TaO2.5

• Sample E (e)---30.0mole% YO1.5

+ 7.6mole%TaO2.5

Sample Compositions

XRD and SEM Analysis of the Microstructure and Phase Changes

Exposure Time 2θ (degrees) 7.6YO1.5 Exposure Time 2θ (degrees) 15.2YO1.5 Spalled Area Spalled Area Crystal Product Formation

YVO4

2.0YO1.5 2.0YO1.5

400µm 2µm

22 26 30 34 38

YVO4 YVO4 m m m m t t t

0 hrs 100 hrs 200 hrs

22 26 30 34 38

0 hrs 100 hrs 200 hrs

YVO4 YVO4 m m m m c c c

YVO4

10µm

Exposure Time Exposure Time 2θ (degrees) 2θ (degrees) 22.8YO1.5 15.2YO1.5 + 7.6TaO2.5 Representative Surface Representative Surface

XRD and SEM Analysis of the Microstructure and Phase Changes

22 26 30 34 38

0 hrs 100 hrs 200 hrs

YVO4 YVO4 m m c c c

22 26 30 34 38

0 hrs 100 hrs 200 hrs

YVO4 t t t

YVO4 22.8YO1.5

5µm

15.2YO1.5 + 7.6TaO2.5 5.5Y 5.7Ta

4µm

Exposure Time 2θ (degrees) 30.0YO1.5 + 7.6TaO2.5 Representative Surface

22 26 30 34 38

0 hrs 100 hrs 200 hrs

XRD and SEM Analysis of the Microstructure and Phase Changes

c c c YVO4

30.0YO1.5 + 7.6TaO2.5

100µm

Summary of Analysis

• Hot corrosion tests on all 5 compositions for 200 hours
• 7.6YO1.5 and 15.2YO1.5 samples
• Formation of product YVO4 after 100 hours
• Phase Change from tetragonal to monoclinic after 100 hours
• Spalled areas (where product breaks away from sample)

found only on 7.6YO1.5 sample

• 22.8YO1.5 sample
• Formation of product YVO4 after 100 hours
• Phase Change (small amounts) from tetragonal to monoclinic

after 200 hours

• 15.2YO1.5 + 7.6TaO2.5 and 30.0YO1.5 + 7.6TaO2.5 samples
• Small amounts of product YVO4 formed after 200 hours
• Considerably less found on 30.0YO1.5 +7.6TaO2.5 than on

15.2YO1.5 + 7.6TaO2.5

• No phase change from tetragonal to monoclinic
• Best performance among samples

Future Plans

• Continue hot corrosion tests on all 5 compositions for up to

500 hours

• Conduct analysis on the phase changes and microstructure
• f the samples after each 100 hours of testing
• Comparison of compositions with baseline 7YSZ to

determine the effect of increasing yttria content and co-doping with TaO2.5

Acknowledgements Acknowledgements

Lab Mentor: Felicia Pitek Lab Mentor: Felicia Pitek Faculty Advisor: Carlos Levi Faculty Advisor: Carlos Levi Research Funded by: Research Funded by: Internship Funded by: Internship Funded by: