As Received Doosan-EBPVD

SEM Images of the YSZ Surface

The ceramic top-coat is has typical uniform columnar grains with less inter-column spacing.

YSZ

YSZ

YSZ top-coat has tetragonal t’ phase and is textured along <200>.

XRD YSZ Top-Surface (As Received)

25 30 35 40 45 50 55 60 65 70 75 80 85 90

Diffraction Angle (2 theta)

Inte

nsi

ty (

a.u

.)

(111)

(200)

(220)(311)

(222)(400)

(004) (204)

(420)

ť ZrO2

50 um

20 um

50 um

Cross-sectional Back Scattered Electron Micrographs(As Received)

epoxy

YSZ

Bond coat

~ 151µm

~ 64µm

The bond-coat is rich in Co, hence it is CoCrAlY.

Failed Sample

25 30 35 40 45 50 55 60 65 70 75 80 85 90

Diffraction Angle(2 theta)

Inte

nsi

ty (

a.u

.)

ť ZrO2

Lifetime ~ 38251± cycles

YSZYSZ

After thermal cyclic oxidation the ceramic coating retains t’ phase and texture along <200>.

100 um

25 30 35 40 45 50 55 60 65 70 75 80 85 90

Diffraction Angle(2 theta)

Inte

nsity

(a.u

.) ť ZrO2

50 um

YSZ

TGO

100 umTGO

Bond Coat

Back-Scattered Microcraphs of Spalled YSZ Bottom Surface and Top-Surface of Bare Bond Coat

Spalled YSZ Bottom Surface

Top-Surface of Bare Bond Coat

The nature of spallation is mixed i.e. it occurred along YSZ/TGO, Bondcoat/TGO and within TGO.

m0.23μ3.9 ±

20 um

Cross-sectional Backscattered Electron Micrographs

TGO Thickness Tortuosity L/L0 0.41.39 ±

200 um

20 um

epoxyYSZ

Bond coat

YSZ

TGO

Bond coat

epoxy

Bond coat

YSZ

25 30 35 40 45 50 55 60 65 70 75 80 85 90

Diffraction Angle(2 theta)

Inte

nsi

ty (

a.u

.)

25 30 35 40 45 50 55 60 65 70 75 80 85 90

Diffraction Angle (2 theta)

Inte

ns

ity

(a

.u.)

27.5 28.5 29.5 30.5 31.5 32.5

Premature TBC Failure

Lifetime ~20 Cycles

Significant monoclinic ZrO2 was observed on the bottom surface of the spalled YSZ.

ť ZrO2

m ZrO2

F,T(111)

M ( )111 M(111)

Summary

•The microstructure of the as received has uniform YSZ columns with less column spacing.

•The EBPVD coated TBCs failed around 251 cycles which is lower than what is observed typical EBPVD TBCS.

•However, one of the five samples failed after ~20 cycles.•m-ZrO2 was observed on the bottom side of the spalled YSZ.

•The failure took place along the TGO-YSZ as well as TGO-Bond coat interface.

•Further study on the microstructural evolution with the cyclic oxidation at 11000C is in progress.