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UCSB - Materials for Cleaner Engines Thermal Barrier Coatings

Thermal Properties of Novel Thermal Barrier Coatings (TBCs)

Professor David Clarke, Mentor Mike Winter Materials Department University of California, Santa Barbara Funded by Office of Naval Research Marcos Garcia, INSET Summer Research Program Ventura Community College, Ventura CA Mechanical Engineer at UCSB Fall 2003

UCSB - Materials for Cleaner Engines Thermal Barrier Coatings

What is a TBC?

Thermal Barrier Coatings (TBCs)

Are a system of oxides grown atop a super alloy bond coat

providing a protective layer.

TBCs increase the efficiency and life of the components of

gas powered turbine engines.

UCSB - Materials for Cleaner Engines Thermal Barrier Coatings

Why is 7YSZ unsuitable for the next generation of gas turbine engines?

• The components of a gas turbine engine begin

to deform at high temperatures. By selecting a coating with lower thermal conductivity, the engine can run hotter without damaging the components

• The focus of the research is to select oxides with

lower thermal conductivity than 7YSZ

UCSB - Materials for Cleaner Engines Thermal Barrier Coatings

A look at thermal conductivity

Minimal thermal conductivity can be approximated using known constants in the following expression:

2/3 2/3

M m * 87 .

2 / 1 6 / 1 3 / 2 min

E N k

A B

ρ κ → 

Clarke, David R. Materials selection guidelines for low thermal conductivity thermal barrier

• coatings. [Conference Paper] Elsevier. Surface & Coatings Technology, vol.163-164, 30

January, 2003, pp.67-74

UCSB - Materials for Cleaner Engines Thermal Barrier Coatings

Minimum thermal conductivity approximation

By adding hafnia in with the zirconia, the effect of raising the mean atomic mass will be explored.

) / ( 1

min

M m Mass Atomic Mean to al proportion is κ

How can thermal conductivity be minimized?

Based upon the minimum thermal conductivity approximation:

UCSB - Materials for Cleaner Engines Thermal Barrier Coatings

Determining thermal conductivity

• Flash Lamp 3000

measures infrared intensity

• Device measures

diffusivity (α) used in thermal conductivity equation

Indium IR detector Convex lens Sample holder Convex lens Tungsten flash lamp

UCSB - Materials for Cleaner Engines Thermal Barrier Coatings

Flashline 3000 data to solve for κ

(100) Single Crystal YSZ at 100°C

2.5 3 3.5 4 4.5 5 5.5 0.1 0.2 0.3 0.4 0.5

Time (s) Voltage (V)

t 0 t 1 t 1/2

Thermal Conductivity:

κ =α ρ Cp

ρ = Density of sample Cp = Heat capacity

Flash Method of Determining Thermal Diffusivity, Heat Capacity, and Thermal Conductivity, WJ Parker et al. Journal of Applied Physics, Volume 32, Number 9, September 1961

2 1

2 2

48 . t L π α =

UCSB - Materials for Cleaner Engines Thermal Barrier Coatings

Current project YSZr/Hf mixed at two levels

7 mole percent Y2O3 14 mole percent Y2O3

90/10 C10 90/10 C5 80/20 C9 80/20 C4 50/50 C8 50/50 C3 20/80 C7 20/80 C2 10/90 C6 10/90 C1

Mix Percent Hf/Zr Composition Mix Percent Hf/Zr Composition

UCSB - Materials for Cleaner Engines Thermal Barrier Coatings

7YSZ vs. 7YSZr/HF C1

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 100 200 300 400 500 600 700 800 900

Thermal Diffusivity (cm2/s) 7YSZ 7YSZr/Hf C1 Temperature (C)

Comparison of values

YSZ vs YSZr/Hf (Composition 1)