Bradley AllisonAdvisor: Prof. Rodney Trice

Effects of Starting Powder Size on Sintering of YSZ Thermal Barrier Coatings

REU Presentation

August 5, 2004

What are TBCs?

• Ceramic Coating • Most commonly used in the gas turbine engines• Yttria Stabilized Zirconia (YSZ)

• ZrO2 - 7 wt% Y2O3

What makes TBCs Useful?• Improves fuel efficiency

– Allows for higher continuous service temperature – Low Thermal conductivity ( ~ 1 W/mK )

• Improves engine reliability – Increases lifetime of parts– Prevent corrosion

Processing• Plasma spray• Lamella formation

Lamella Formation

http://www.gordonengland.co.uk/tsc.htm

Research Investigation

• Varying starting powder will affect lamella microstructure

• 3 powder sizes separated from a single YSZ batch– 18-26 µm– 37-52 µm– 74-105 µm

Experimental Procedure• Sample Preparation

– Sprayed onto cylindrical and flat Copper substrates• Archimedes Density

– Total porosity is calculated from suspended, saturated, and dry mass

– Measurements taken in as-sprayed condition and after heat treatments of 5 hours and 50 hours at 1400°C

• Dilatometer– Quantifies sintering of coatings as heat treated for 5 hours at

1400°C• SEM

– Use SEM micrographs to quantify lamella thickness• XRD

– Quantify phases present at each step during heat treatment– Based on intensity of t-ZrO2 and c-ZrO2 peaks

Archimedes Density• Uniform decrease in

porosity• Large particle

coatings displayed most porosity before and after heat treatment

Dilatometer

• Medium powder exhibited most shrinkage

• Driving force for densification

SEM

Small

Medium Large

SEM

Measured Lamella Thickness (µm)

195-8 Small 1.34 ± 0.39

195-7 Medium 2.01± 0.72

195-6 Large 2.95 ± 0.97

X-ray Diffraction

•Super Saturated Solid Solution of Y2O3 in ZrO2

•As Y2O3 diffuses out of ZrO2 , c-ZrO2 is formed

X-ray Diffraction

Future Research to be Explored

• Study phase transformation during heat treatment with respect to varying lamella size

• Study thermal conductivity of coatings throughout heat treatment with respect to varying lamella size

Acknowledgments

• Prof. Trice and Prof. Kvam• Kei Yamamoto and Jan Eberle• Chris Petorak and Ben Iverson• REU and Surf Students